CN113266373A

CN113266373A - Freezing wall and cement reinforcement combined enclosure system in large-section tunnel construction and excavation method thereof

Info

Publication number: CN113266373A
Application number: CN202110702666.1A
Authority: CN
Inventors: 黄宝龙; 高伟; 韩玉福; 张松; 温汉宏; 许舒荣; 李宁; 杨志刚; 陈红蕾; 孔令辉; 叶玉西; 郑新赟; 董世卓; 崔兵兵; 丁航; 申鹏举; 魏可东; 郭鹏; 刘冰; 李孔刚
Original assignee: Beijing China Coal Mine Engineering Co ltd
Current assignee: Beijing China Coal Mine Engineering Co ltd
Priority date: 2021-06-24
Filing date: 2021-06-24
Publication date: 2021-08-17
Anticipated expiration: 2041-06-24
Also published as: CN113266373B

Abstract

The invention discloses a frozen wall and cement reinforcement combined enclosure system in large-section tunnel construction and an excavation method thereof, wherein the enclosure system comprises a frozen soil curtain and a cement reinforcement; the frozen soil curtain is a cylindrical freezing wall, the cylindrical freezing wall forms a strong freezing area, and an area to be excavated, which is surrounded by the cylindrical freezing wall, is a weak freezing area; the cement reinforcing body is located in surrounding rocks of the tunnel face of the large-section tunnel to be excavated along the excavation direction. The excavation method comprises the following steps: drilling according to the planning design of the cylindrical freezing wall, and installing a freezing system; after the active freezing is finished, grouting is carried out at a position 10m away from the excavation face. The invention is different from the traditional cup-shaped freezing mode, but adopts the barrel-shaped freezing wall, does not need to drill freezing holes on the face to be excavated, and uses horizontal grouting reinforcement to replace the traditional full-scale end freezing, thereby saving a large amount of drilling time and materials, and greatly reducing the excavation difficulty because the excavation area is a weak freezing area.

Description

Freezing wall and cement reinforcement combined enclosure system in large-section tunnel construction and excavation method thereof

Technical Field

The invention relates to the technical field of tunnel construction. In particular to a freezing wall and cement reinforcement combined enclosure system in large-section tunnel construction and an excavation method thereof.

Background

Compared with other small-section and short-distance tunnel projects, the large-section long-distance tunnel project has the advantages that the construction risks are more, the construction difficulty is higher, the structure, the construction environment and the construction organization of the tunnel are more complicated, and a large number of project technical problems exist. How to select a reasonable and optimal construction method to safely pass through a bad section of engineering geology and reduce the damage to the surrounding environment to the maximum extent is a problem which is very concerned by engineering construction owners, designers, constructors and managers.

In order to build a tunnel in an unstable stratum, a plurality of stratum pre-consolidation technical measures are provided at home and abroad, and the technologies such as grouting, small pipes, pipe sheds and the like are generally applied to a soil tunnel. The manual freezing method is widely applied to mine construction and municipal engineering as a temporary reinforcing technology, but the application experience in large-section long-distance tunnel engineering is still insufficient, and a mature construction method is lacked particularly when a large-section long-distance tunnel needs to be built in an unstable stratum. In the construction engineering, when the soil mass at the periphery of the tunnel is reinforced by using an artificial freezing method, a traditional cup-shaped freezing wall reinforcing mode is usually adopted. The reinforcing mode needs to be full-scale freezing, the number of drilled holes is large, a strong freezing area is formed in an excavation area, the excavation difficulty is increased, and the engineering quantity of pulling out the freezing pipe in the later period is large.

Disclosure of Invention

Therefore, the technical problem to be solved by the invention is to provide a freezing wall and cement reinforcement combined enclosure system in large-section tunnel construction and an excavation method thereof, so as to solve the problems of large quantity of drilled holes, large excavation difficulty and the like when a freezing method is adopted to reinforce peripheral soil bodies in the large-section tunnel construction process with large stratum water inflow, large soil layer sand content and no open excavation condition.

In order to solve the technical problems, the invention provides the following technical scheme:

a frozen wall and cement reinforcement combined enclosure system in large-section tunnel construction is characterized by comprising a frozen soil curtain and a cement reinforcement; the frozen soil curtain is a cylindrical frozen wall, the cylindrical frozen wall forms a strong freezing area, and an area to be excavated, which is surrounded by the cylindrical frozen wall, is a weak freezing area; the cement reinforcing body is located in a non-excavation area of the face of the large-section tunnel to be excavated along the excavation direction.

An excavation method for a freezing wall and cement reinforcement combined enclosure system in large-section tunnel construction comprises the following steps:

step A: drilling according to a design scheme of a cylindrical freezing wall, installing a freezing system, and actively freezing to form a frozen soil curtain, wherein the frozen soil curtain is the cylindrical freezing wall, the cylindrical freezing wall forms a strong freezing area, and an area to be excavated, which is surrounded by the cylindrical freezing wall, is a weak freezing area;

and B: after the active freezing is finished, performing first horizontal grouting in surrounding rocks 10m away from the small-section face to be excavated to form the cement reinforced body;

and C: after the excavation acceptance is passed, carrying out sectional horizontal excavation until the primary support of the excavated part is completed, and then carrying out the next section of grouting and excavation; excavating after horizontal grouting is finished once every 10m in sequence until the primary support of the section to be excavated is completely finished; grouting reinforcement is carried out after the end head is excavated to complete the reinforcement of the tail end;

step D: and (4) after the water is prevented, performing secondary lining construction, stopping freezing, plugging all the freezing holes inside and outside, and filling, melting, settling and grouting.

In the step B, according to the arrangement rule of freezing holes, a construction area of a large section to be excavated is sequentially divided into 4 excavation areas of a first step, a second step, a third step and a fourth step from top to bottom, wherein each excavation area is excavated horizontally; dividing the active freezing into a first stage freezing and a second stage freezing; the first-stage freezing comprises freezing two excavation areas of the first step and the second step; the second-stage freezing comprises freezing two excavation areas of the third step and the fourth step; the second-stage freezing is construction after the excavation of the second step excavation area is finished; step C can be divided into the following steps:

step (C-11) excavation of a first step: sequentially carrying out sectional horizontal excavation after grouting once every 10m horizontally, and supporting along with excavation until the primary support of the first step is completely finished; then, carrying out horizontal grouting reinforcement after the first step is excavated to the end head so as to finish the reinforcement of the tail end of the first step; after the excavation of the first step is completely finished: a first middle partition plate is installed in the first step in a construction mode, and a vertical grouting hole is constructed in the excavation space of the first step to perform grouting, end sealing and reinforcing on a region to be excavated of the second step;

and (C-12) excavating a second step: excavating a second step by adopting the excavation method of the first step; after the end head is excavated, horizontal grouting reinforcement is carried out to complete the reinforcement of the tail end of the second step; after the excavation of the second step is completely finished, a first bottom middle partition plate is installed on the second step in a construction mode, and a vertical grouting hole is constructed in the excavation space of the second step to perform grouting, end sealing and reinforcement on a region to be excavated of the third step;

step (C-13) excavating a third step: after the second step is excavated, performing second-stage freezing, and excavating the third step according to the excavation construction method of the first step after the second-stage freezing is finished; after the end head is excavated, horizontal grouting reinforcement is carried out to finish the reinforcement of the tail end of the third step; after the excavation of the third step is completely finished, a second middle partition plate is installed in the third step in a construction mode, and a vertical grouting hole is constructed in the excavation space of the third step to perform grouting, end sealing and reinforcement on a region to be excavated of the fourth step;

and (C-14) excavating a fourth step: excavating a fourth step by adopting the excavation method of the first step; and (5) carrying out horizontal grouting reinforcement after the end head is excavated to complete the reinforcement of the tail end of the fourth step.

In the step B, according to the arrangement rule of freezing holes, a construction area of a large section to be excavated is sequentially divided into 3 excavation areas of a first step, a second step and a third step from top to bottom, and each excavation area is excavated horizontally; step C can be divided into the following steps:

step (C-21) excavation of a first step: sequentially carrying out sectional horizontal excavation after grouting once every 10m horizontally, and supporting along with excavation until the primary support of the first step is completely finished; then, carrying out horizontal grouting reinforcement after the first step is excavated to the end head so as to finish the reinforcement of the tail end of the first step; after the excavation of the first step is completely finished: a third middle partition plate A is installed in the first step in the construction process, and a vertical grouting hole is constructed in the excavation space of the first step to perform grouting, end sealing and reinforcement on the to-be-excavated area of the second step;

and (C-22) excavating a second step: excavating a second step by adopting the excavation method of the first step; after the end head is excavated, horizontal grouting reinforcement is carried out to complete the reinforcement of the tail end of the second step; after the excavation of the second step is completely finished, a third middle partition plate B is installed on the second step in a construction mode, and a vertical grouting hole is constructed in the excavation space of the second step to perform grouting, end sealing and reinforcement on a region to be excavated of the third step;

and (C-23) excavating a third step: excavating a third step by adopting the excavation method of the first step; and (5) carrying out horizontal grouting reinforcement after the end head is excavated to complete the reinforcement of the tail end of the third step.

The technical scheme of the invention achieves the following beneficial technical effects:

(1) the invention adopts a cylindrical frozen wall form to freeze and reinforce the soil body at the periphery of the tunnel to be built, a frozen soil curtain with high strength and good sealing performance can be formed, and the excavation area forms a weak freezing area, so that the excavation difficulty of the excavation area is reduced; and then, horizontally and pre-grouting and reinforcing the tunnel face of the tunnel to form a frozen wall and cement reinforcement combined enclosure system, wherein the enclosure system can meet the construction requirements of large-section tunnels in unstable strata.

(2) According to the invention, because the section of the large-section tunnel is larger and the stratum structure is unstable, the frozen soil curtain is divided into two freezing and reinforcing areas, the strength of the enclosing system in the soil body around the section and the excavation process can be ensured, and the construction safety risk caused by insufficient reinforcing strength is avoided; in addition, the invention adopts the form of a cylindrical frozen wall for reinforcement, does not need to increase frozen holes on the tunnel face, and adopts horizontal grouting for replacement, thereby saving a large amount of drilling time and materials and improving the construction efficiency. Before excavation, horizontal advanced grouting reinforcement is carried out on the tunnel face of the large-section tunnel, and a complete enclosure system can be formed in a region to be excavated, so that the stability and the water resistance of surrounding rocks in construction are ensured, and the smooth construction is ensured. In the excavation process, the whole construction process is monitored in real time, the stratum deformation condition is observed in time, and the whole construction process can be carried out smoothly.

(3) The excavation construction method is different from the traditional cup-shaped freezing mode, adopts the barrel-shaped freezing wall, does not need to drill freezing holes on the tunnel face, and replaces the traditional full-space end freezing by horizontal grouting reinforcement, thereby saving a large amount of drilling time and materials, and the excavation difficulty is reduced because the excavation area is a weak freezing area. Dividing a construction area with a large section to be excavated into 3 or 4 excavation areas, sequentially and horizontally excavating from top to bottom in a layered mode, separating a partition plate in each layer of excavation construction, and performing grouting, end sealing and reinforcement on the next step by using the excavation space of the previous step in the construction process, so that the problems of water burst, sand burst and the like which possibly occur due to unreinforced bottom of a shaft type frozen wall when the next step is excavated in construction can be avoided; the ring is closed in time along with excavation and support in the excavation process so as to reduce the time of the hollow upper, thereby ensuring that the construction problem caused by unstable stratum in the construction process can not occur.

Drawings

FIG. 1 is a schematic view of a cross channel 1 in example 2 of the present invention;

FIG. 2 is a sectional view of a 1# transverse channel A-A in example 2 of the present invention;

FIG. 3 is a sectional view of a 1# cross passage B-B in example 2 of the present invention;

FIG. 4a is a longitudinal section of the frozen wall of the 1# cross channel in the first stage of the embodiment 2 of the present invention;

FIG. 4b is a cross-sectional view of the first stage frozen wall 1-1 of the 1# cross channel in example 2 of the present invention;

FIG. 4c is a cross-sectional view of the first stage frozen wall of the 1# cross channel of example 2 of the present invention 2-2;

FIG. 5a is a longitudinal section of the frozen wall of the second stage of the No. 1 cross channel in the embodiment 2 of the present invention;

FIG. 5b is a cross-sectional view of the second stage frozen wall 1-1 of the 1# cross channel in example 2 of the present invention;

FIG. 5c is a cross-sectional view of the second stage frozen wall of the 1# cross channel in example 2 of the present invention;

FIG. 6a is a layout diagram of freezing holes in the outer ring of the 1# cross passage in embodiment 2 of the present invention;

FIG. 6b is a layout view of the inner ring and bottom freeze holes of the No. 1 cross passage in the embodiment 2 of the present invention;

FIG. 7 is a view showing the position of the opening of the freezing hole of the 1# cross passage in the embodiment 2 of the present invention;

FIG. 8 is a schematic view of step 1 of excavating a No. 1 cross tunnel in example 2 of the present invention;

fig. 9 is a schematic view of step 2 of excavating a # 1 transverse channel in embodiment 2 of the present invention;

fig. 10 is a schematic view of step 3 of excavating a 1# cross tunnel in embodiment 2 of the present invention;

fig. 11 is a schematic view of step 4 of excavating a 1# cross tunnel in embodiment 2 of the present invention;

fig. 12 is a schematic view of the step 5 of excavating the 1# cross passage in embodiment 2 of the present invention;

fig. 13 is a schematic view of the step 6 of excavating the 1# cross passage in the embodiment 2 of the present invention;

fig. 14 is a schematic view of the step 7 of excavating the 1# cross passage in the embodiment 2 of the present invention;

FIG. 15 is a schematic view showing completion of drilling of a 1# cross passage in embodiment 2 of the present invention;

FIG. 16 is a schematic view of the active freezing of the 1# cross passage in embodiment 2 of the present invention;

fig. 17 is a schematic view of the first step excavation of the 1# cross passage in embodiment 2 of the present invention;

fig. 18 is a schematic view showing completion of excavation of the # 1 lateral passage in embodiment 2 of the present invention;

FIG. 19 is a longitudinal sectional view of a first-stage freezing and reinforcing area of a combined enclosure system of a freezing wall and a cement reinforcing body in construction of a large-section tunnel according to embodiment 1 of the present invention;

FIG. 20 is a longitudinal sectional view of a second-stage freezing and reinforcing area of a combined enclosure system of a freezing wall and a cement reinforcing body in construction of a large-section tunnel according to embodiment 1 of the present invention;

FIG. 21 is a cross-sectional view of a first-stage freezing and reinforcing area of a combined enclosure system of a freezing wall and a cement reinforcing body in the construction of a large-section tunnel according to embodiment 1 of the present invention;

FIG. 22 is a cross-sectional view of a second-stage freezing and reinforcing area of a combined enclosure system of a freezing wall and a cement reinforcing body in the construction of a large-section tunnel according to embodiment 1 of the present invention;

FIG. 23 is a schematic view of a 2# horizontal channel structure according to example 4 of the present invention;

FIG. 24 is a schematic diagram showing the structure of a longitudinal section of a frozen wall of a No. 2 cross passage in example 4 of the present invention;

FIG. 25a is a schematic cross-sectional view of a frozen wall 1-1 of the 2# cross channel in example 4 of the present invention;

FIG. 25b is a schematic cross-sectional view of the 2-2 cross-sectional structure of the frozen wall of the 2# cross channel in example 4 of the present invention;

FIG. 26a is a layout view of freezing holes in the outer ring of the No. 2 cross passage in embodiment 4 of the present invention;

FIG. 26b is the layout of the inner ring and bottom freeze holes of the No. 2 cross passage in embodiment 4 of the present invention;

FIG. 27 is a view showing the position of the opening of the freezing hole of the No. 2 cross passage in embodiment 4 of the present invention;

fig. 28 is a schematic view of the 2# cross tunnel excavation step 1 in embodiment 4 of the present invention;

fig. 29 is a schematic view of the 2# cross tunnel excavation step 2 in embodiment 4 of the present invention;

fig. 30 is a schematic view of # 2 cross tunnel excavation step 3 in embodiment 4 of the present invention;

fig. 31 is a schematic view of the 2# cross tunnel excavation step 4 in embodiment 4 of the present invention;

fig. 32 is a schematic view of the 2# cross tunnel excavation step 5 in embodiment 4 of the present invention;

fig. 33 is a schematic view of the 2# cross tunnel excavation step 6 according to embodiment 4 of the present invention;

FIG. 34 is a schematic view showing the completion of drilling of the 2# cross passage in embodiment 4 of the present invention;

FIG. 35 is a schematic view of active freezing of the No. 2 cross passage in embodiment 4 of the present invention;

fig. 36 is a schematic view showing completion of excavation of # 2 lateral passage in embodiment 4 of the present invention;

FIG. 37 is a schematic structural view of a third freezing and consolidation zone of a No. 2 cross passage in example 3 of the present invention;

FIG. 38 is a view showing the arrangement of No. 1 cross-channel grouting holes in example 2 of the present invention.

The reference numbers in the figures denote: 1-first stage freezing consolidation zone; 11-first upper frozen wall; 12-first bottom middle partition frozen wall; 13-first sidewall frozen wall; 14-the first middle clapboard freezes the wall; 2-second stage freezing and reinforcing area; 21-second upper frozen wall; 22-second bottom frozen wall; 23-second side wall frozen wall; 24-freezing the wall of the middle clapboard in the second middle part; 3, excavating a tunnel face of the large-section tunnel to be excavated; 30-a third freeze-hardened zone; 301-third upper frozen wall; 302-third bottom frozen wall; 303-third side wall freezing wall; 304-a third middle clapboard freezing wall A; 305-a third middle clapboard freezing wall B; 4-a cement grouting area; 5-excavating a small-section tunnel face; 6-pressure relief hole group X; 61-a first pressure relief hole group X; 62-a second pressure relief hole group X; 63-a third pressure relief hole group X; 64-a fourth pressure relief vent group X; 7-heating hole group DJ; 81-outer ring freezing hole group D; 82-a first row of outer ring freezing hole groups FB; 83-second row outer ring freezing hole group D; 84-the first row of outer ring freezing hole groups DB; 85-second row outer ring freezing hole group DB; 86-third row outer ring freezing hole group DB; 87-fourth row outer ring freezing hole group DB; 88-the fifth row outer ring freezing hole group DB; 89-sixth row outer ring freezing hole group DB; 91-outer ring auxiliary freezing hole group DN; 92-a first row of outer ring auxiliary freezing hole groups DN; 101-a first interface enhancing freeze hole group G; 102-a second interface enhanced freeze hole group G; 103-third interface enhanced freeze hole group G; 104-fourth interface enhanced freeze hole group G; 105-fifth interface strengthen the freeze hole population G.

Detailed Description

Example 1

As shown in fig. 19 and 20, a frozen wall and cement reinforcement combined enclosure system in large-section tunnel construction comprises a frozen soil curtain and a cement reinforcement; the frozen soil curtain is a cylindrical freezing wall, the cylindrical freezing wall forms a strong freezing area, and an area to be excavated, which is surrounded by the cylindrical freezing wall, is a weak freezing area; the frozen soil curtain comprises a first-stage freezing and reinforcing area 1 and a second-stage freezing and reinforcing area 2; the cement reinforcing body is located in a non-excavation area of the tunnel face 3 of the large-section tunnel to be excavated along the excavation direction. In the embodiment, the soil body at the periphery of the tunnel to be built is frozen and reinforced in a cylindrical frozen wall form, a frozen soil curtain with high strength and good sealing performance can be formed, and the excavation area forms a weak freezing area, so that the excavation difficulty of the excavation area is reduced; and then, horizontally and pre-grouting and reinforcing the tunnel face of the tunnel to form a frozen wall and cement reinforcement combined enclosure system, wherein the enclosure system can meet the construction requirements of large-section tunnels in unstable strata.

As shown in fig. 21, the first-stage freezing and reinforcing area 1 is a straight wall circular arc top-bottom type freezing wall in a shape like a Chinese character ri; the first-stage freezing and reinforcing region 1 comprises a first upper freezing wall 11, a first bottom middle clapboard freezing wall 12, a first side wall freezing wall 13 and a first middle clapboard freezing wall 14; the thickness of the first upper freezing wall 11 is 3.0m, the thickness of the first bottom middle clapboard freezing wall 12 is 3.5m, and the thicknesses of the first side wall freezing wall 13 and the first middle clapboard freezing wall 14 are both 2.5 m; the first upper freezing wall 11, the first bottom middle partition freezing wall 12, the first side wall freezing wall 13 and the first middle partition freezing wall 14 all extend to the trenchless area by 8.0m along the front end face 3;

as shown in fig. 22, the second-stage freezing and reinforcing area 2 is a frozen wall with a rectangular-shaped straight wall and an arc bottom; the second-stage freezing and reinforcing area 2 comprises a second upper freezing wall 21, a second bottom freezing wall 22, a second side wall freezing wall 23 and a second middle clapboard freezing wall 24; the second upper frozen wall 21 is connected to the first bottom intermediate diaphragm frozen wall 12 of the first stage frozen consolidation zone 1; the thickness of the second side wall frozen wall 23 and the second middle clapboard frozen wall 24 is 2.5m, the thickness of the second bottom frozen wall 22 is 3.5m, and the second upper frozen wall 21, the second bottom frozen wall 22, the second side wall frozen wall 23 and the second middle clapboard frozen wall 24 all extend to the non-excavation area along the front end face 3 by 8.0 m. Because the section of the large-section tunnel is large and the stratum structure is unstable, the frozen soil curtain is divided into two freezing and reinforcing areas, so that the strength of a containment system in the soil body around the section and the excavation and construction process can be ensured, and the construction safety risk caused by insufficient reinforcing strength is avoided; in addition, the embodiment adopts the cylindrical frozen wall form to reinforce, does not need to increase frozen holes on the tunnel face, and adopts horizontal grouting to replace, thereby saving a large amount of drilling time and materials and improving the construction efficiency.

The cement reinforcing body is a cement grouting area 4, the tunnel face 3 of the large-section tunnel to be excavated consists of four small-section tunnel faces 5 to be excavated which are sequentially arranged from top to bottom, and the cement grouting area 4 is positioned in front of the small-section tunnel faces 5 to be excavated; and the cement grouting area 4 is arranged at intervals of 10m along the excavation direction of the small-section tunnel face 5 to be excavated in the excavation process. Before excavation, horizontal advanced grouting reinforcement is carried out on the tunnel face of the large-section tunnel, and a complete enclosure system can be formed in a region to be excavated, so that the stability of the stratum in construction is ensured, and the smooth construction is ensured.

As shown in fig. 7, the freezing holes of the frozen soil curtain are laid out on the longitudinal section of the area to be excavated as follows:

above the area to be excavated: a pressure relief hole group X6 consisting of 7 pressure relief holes, a heating hole group DJ7 consisting of 9 heating holes, an outer ring freezing hole group D81 consisting of 19 outer ring freezing holes and an outer ring auxiliary freezing hole group DN91 consisting of 10 outer ring auxiliary freezing holes are sequentially distributed from top to bottom; pressure relief holes in the pressure relief hole group X6 are distributed at equal intervals along the horizontal direction, the hole distance between every two adjacent pressure relief holes is 1500mm, and the vertical distance L1 between each pressure relief hole and the arc top of the area to be excavated is 6800 mm; heating holes in the heating hole group DJ7 are distributed at equal intervals along the same heating hole group arc, the hole distance between two adjacent heating holes is 1500mm, the arc top of the heating hole group arc and the arc top of the area to be excavated are on the same vertical line, the distance between the two arc tops is 5460mm, and the longitudinal distances L2 from any point on the heating hole group arc to the arc on which the upper edge of the area to be excavated is located are equal; 15 outer ring freezing holes in the outer ring freezing hole group D81 are distributed along the arc of the same outer ring freezing hole group, the hole distance between two adjacent outer ring freezing holes is 800mm, 1 outer ring freezing hole is distributed on the arc top of the outer ring freezing hole group arc, 6 outer ring freezing holes with equal distance are respectively distributed from the arc top of the outer ring freezing hole group arc to two sides, an outer ring freezing hole is respectively arranged at the end point of the outer ring freezing hole group arc, and two outer ring freezing holes respectively positioned at two sides of the outer ring freezing hole group arc are distributed on a horizontal line between the last outer ring freezing hole and the last second outer ring freezing hole at the end point of the outer ring freezing hole group arc; the arc top of the outer ring freezing hole group arc and the arc top of the area to be excavated are on the same vertical line, the distance between the arc top and the area to be excavated is 4660mm, and the longitudinal distance L3 from any point on the outer ring freezing hole group arc to the arc on which the upper edge of the area to be excavated is located is equal; 8 outer ring auxiliary freezing holes in the outer ring auxiliary freezing hole group DN91 are distributed on the same outer ring auxiliary freezing hole group arc at equal intervals, and the hole interval between two adjacent outer ring auxiliary freezing holes is 1200 mm; in addition, 2 outer ring auxiliary freezing holes are respectively distributed near the tail ends of the outer ring auxiliary freezing hole group arcs and are positioned between the outer ring auxiliary freezing hole group arcs and the outer ring freezing hole group arcs, the arc tops of the outer ring auxiliary freezing hole group arcs and the arc tops of the to-be-excavated area are on the same vertical line, the distance between the arc tops and the arc tops of the to-be-excavated area is 3160mm, and the longitudinal distances L4 from any point on the outer ring auxiliary freezing hole group arcs to the arcs of the upper edge of the to-be-excavated area are equal;

a first temperature measuring hole, a second temperature measuring hole and a third temperature measuring hole are further distributed above the area to be excavated, the first temperature measuring hole is distributed on the circular arcs of the heating hole group and is positioned on the left side of the arc tops of the circular arcs of the heating hole group, and the second temperature measuring hole and the first temperature measuring hole are in the same horizontal line and are positioned between the circular arcs of the heating hole group and the circular arcs of the outer ring freezing hole group; the third temperature measuring hole is positioned right below the arc top of the outer ring auxiliary freezing hole group;

on the left side of the area to be excavated: a first row of outer ring freezing hole group FB82 and a second row of outer ring freezing hole group D83 are longitudinally distributed, and the distance from the first row of outer ring freezing hole group FB82 to the area to be excavated is greater than the distance from the second row of outer ring freezing hole group D83 to the area to be excavated; an auxiliary freezing hole and a temperature measuring hole are further formed in a longitudinal straight line where the first row outer ring freezing hole group FB82 is located, an auxiliary freezing hole is further formed in a longitudinal straight line where the second row outer ring freezing hole group D83 is located, and an auxiliary freezing hole and a temperature measuring hole are distributed in a region between the second row outer ring freezing hole group D83 and a region to be excavated;

the method comprises the following steps that hole groups which are symmetrical to the left side of a region to be excavated about a longitudinal central line of the region to be excavated are distributed on the right side of the region to be excavated;

in the area to be excavated: a first pressure relief hole group X61 consisting of 2 pressure relief holes, a first interface strengthening freezing hole group G101 consisting of 7 interface strengthening freezing holes, a second interface strengthening freezing hole group G102 consisting of 4 interface strengthening freezing holes, a second pressure relief hole group X62 consisting of 2 pressure relief holes, a third interface strengthening freezing hole group G103 consisting of 7 interface strengthening freezing holes, a fourth interface strengthening freezing hole group G104 consisting of 8 interface strengthening freezing holes, a third pressure relief hole group X63 consisting of 2 pressure relief holes, a fifth interface strengthening freezing hole group G105 consisting of 7 interface strengthening freezing holes and a fourth pressure relief hole group X64 consisting of 2 pressure relief holes are sequentially distributed from top to bottom; 2 pressure relief holes in the first pressure relief hole group X61 are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, the vertical distance L5 between the pressure relief holes and an arc top of the area to be excavated is 782mm, and the hole distance between the 2 pressure relief holes is 3000 mm; 7 interface strengthening freezing holes in the first interface strengthening freezing hole group G101 are distributed at equal intervals along the horizontal direction, and one interface strengthening freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L51 between a straight line formed by the first interface strengthening freezing hole group G101 and the arc top of the area to be excavated is 5300mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1230 mm; the 4 interface reinforcing freezing holes in the second interface reinforcing freezing hole group G102 are formed and are distributed on two sides of the longitudinal central axis of the region to be excavated at equal intervals along the horizontal direction; the vertical distance L6 between a straight line formed by the second interface strengthening freezing hole group G102 and the arc top of the area to be excavated is 6103mm, and the hole distance between two adjacent interface strengthening freezing holes is 2000 mm; 2 pressure relief holes in the second pressure relief hole group X62 are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, and the vertical distance L7 between the pressure relief holes and the arc top of the area to be excavated is 7384 mm; the hole spacing between the 2 pressure relief holes is 3000 mm; 7 interface strengthening freezing holes in the third interface strengthening freezing hole group G103 are distributed at equal intervals along the horizontal direction, and one interface strengthening freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L8 between a straight line formed by the third interface strengthening freezing hole group G103 and the arc top of the area to be excavated is 10303mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1230 mm; 8 interface reinforcing freezing holes in the fourth interface reinforcing freezing hole group G104 are formed and are distributed on two sides of the longitudinal central axis of the area to be excavated at equal intervals along the horizontal direction; the vertical distance L9 between a straight line formed by the second interface strengthening freezing hole group G104 and the arc top of the region to be excavated is 11000mm, and the hole distance between two adjacent interface strengthening freezing holes is 1200 mm; 2 pressure relief holes in the third pressure relief hole group X63 are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, and the vertical distance L10 between the pressure relief holes and the arc top of the area to be excavated is 11172 mm; the hole spacing between the 2 pressure relief holes is 3000 mm; 7 interface strengthening freezing holes in the fifth interface strengthening freezing hole group G105 are distributed at equal intervals along the horizontal direction, and one interface strengthening freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L11 between a straight line formed by the third interface strengthening freezing hole group G105 and the arc top of the area to be excavated is 11853mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1230 mm; 2 pressure relief holes in the fourth pressure relief hole group X64 are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, and the vertical distance L12 between the pressure relief holes and the arc top of the area to be excavated is 12262 mm; the hole spacing between the 2 pressure relief holes is 3000 mm;

a fourth temperature measuring hole, a fifth temperature measuring hole, a sixth temperature measuring hole and a seventh temperature measuring hole are further formed in the area to be excavated, 4 temperature measuring holes are formed in the longitudinal central axis of the area to be excavated, and the fourth temperature measuring hole is located between the first interface strengthening freezing hole group G101 and the second interface strengthening freezing hole group G102; the fifth temperature measuring hole is positioned on a straight line formed by connecting the second interface strengthening freezing hole group G104; the sixth temperature measuring hole is positioned between the third pressure relief hole group X63 and the fifth interface strengthening freezing hole group G105; the seventh temperature measuring hole is positioned below the fourth pressure relief hole group X64;

a first column of outer ring auxiliary freezing hole groups DN92 consisting of 4 outer ring auxiliary freezing holes are distributed at the edges of the two sides of the area to be excavated along the longitudinal direction;

below the area to be excavated: a first row of outer ring freezing hole group DB84 consisting of 11 outer ring freezing holes, a second row of outer ring freezing hole group DB85 consisting of 10 outer ring freezing holes, a third row of outer ring freezing hole group DB86 consisting of 11 outer ring freezing holes, a fourth row of outer ring freezing hole group DB87 consisting of 10 outer ring freezing holes and a fifth row of outer ring freezing hole group DB88 consisting of 11 outer ring freezing holes are sequentially distributed from top to bottom; 11 outer ring freezing holes in the first row of outer ring freezing hole group DB84 are distributed at equal intervals in the horizontal direction, and one outer ring freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L13 between a straight line formed by connecting the first row of outer ring freezing hole groups DB84 and the arc bottom of the area to be excavated is 13133mm, and the hole distance between every two adjacent outer ring freezing holes is 1200 mm; 10 outer ring freezing holes in the second row of outer ring freezing hole groups DB85 are distributed at equal intervals in the horizontal direction; the vertical distance L14 between a straight line formed by connecting the second row of outer ring freezing hole groups DB85 and the arc bottom of the area to be excavated is 13463mm, and the hole distance between every two adjacent outer ring freezing holes is 1200 mm; 11 outer ring freezing holes in the third row of outer ring freezing hole groups DB86 are distributed at equal intervals in the horizontal direction, and one outer ring freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L15 between a straight line formed by connecting the third row of outer ring freezing hole groups DB86 and the arc bottom of the area to be excavated is 13760mm, and the hole distance between every two adjacent outer ring freezing holes is 1200 mm; 10 outer ring freezing holes in the fourth row outer ring freezing hole group DB87 are distributed at equal intervals in the horizontal direction; the vertical distance L16 between a straight line formed by connecting the fourth row of outer ring freezing hole groups DB87 and the arc bottom of the area to be excavated is 14163mm, and the hole distance between every two adjacent outer ring freezing holes is 1200 mm; 11 outer ring freezing holes in the fifth row outer ring freezing hole group DB88 are distributed at equal intervals in the horizontal direction, and one outer ring freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L17 between a straight line formed by connecting the freezing hole groups DB88 on the outer ring of the fifth row and the arc bottom of the area to be excavated is 14463mm, and the hole distance between every two adjacent freezing holes on the outer ring is 1200 mm.

Example 2

By adopting the excavation construction method of the freezing wall and cement reinforced body combined enclosure system in the large-section tunnel construction in the embodiment 1, taking the 1# transverse channel freezing project of the large-section tunnel between the XXX station and the XXX station of the XXX subway XXX line as an example, excavation construction tests are carried out.

1 general overview of the engineering

1.1 engineering Contents

A shield method is mainly adopted for construction of a large-section tunnel between XXX stations and XXX stations of XXX subway XXX lines, and a mine method is adopted as an auxiliary method. The XXX interval adopts a three-line shield, a local turnout transition section is constructed by an underground excavation method, the underground excavation part mainly comprises a No. 1 transverse passage, a No. 2 transverse passage, a wiring extension section, a turnout transition section and a station underground excavation section, the total length is about 265m, and the maximum excavation section width is 17.6 m. After going out of the XXX station, the golf course is worn by people with XXX, and most of the interval is positioned below the golf course and laid along the south of the XXX.

The 1# working well is constructed, and because the stratum nearby the 1# working well has large water inflow, large sand content in the soil layer, poor self-stability and no open excavation condition, the 1# cross passage in the XXX interval adopts a construction method of freezing method reinforcement and mining method underground excavation.

1.2 engineering geology and hydrogeology

1.2.1 landform

XXX is located in the middle of the notch (tertiary unit) in Guangdong, and the Guangdong, lean dog ridge and Guangdong three fractures are basic skeletons of the structure of the region, and are divided into four structural regions by mainly taking the Guangdong fracture and the lean dog ridge fracture as boundary lines: zengcheng convex, Guang Hua concave, Dongguan basin, and Sanshui sinking basin. The circuit in this section is located in the Dongguan basin.

The interval is located in XXX area in XXX city, and the landform units are landform units of alluvial plain zone transited to pre-mountain alluvial basin zone, inter-mountain alluvial zone, denudation residual dune and micro-dune terrace.

1.2.2 engineering geology

The No. 1 transverse channel mainly passes through a plastic sandy cohesive soil layer <5Z-1>, a hard plastic sandy cohesive soil layer <5Z-2>, and a fully weathered mixed granite <6Z >; the No. 2 transverse passage mainly passes through a hard plastic sandy cohesive soil layer <5Z-2> and sandy cohesive soil <7Z-B >; the top soil covering thickness of the transverse channel is 7 m.

The geological conditions in the area are complex, and the underlying bedrock mainly comprises clastic rock, carbonaceous shale, carbonaceous limestone, mixed granite and other rocks. In this embodiment, the mixed granite residual soil can be divided into plastic sandy cohesive soil (5Z-1) and hard plastic sandy cohesive soil (5Z-2).

The 1# cross channel crosses the unfavorable geological zone mainly comprises: residual soil formations, sandy soil liquefaction, and the like.

(1) Ground settlement: the earth fill (1) and the mucky soil (4-2 b) are distributed on the ground surface, and the divot damage in the golf course of the foot lake can be caused if the transverse channel is excessively frozen.

(2) Ground collapse: the bottom of the 1# cross passage passes through a mixed granite residual soil stratum which is mainly sandy cohesive soil in a shape of hard plastic, is mostly in a shape of hard soil when completely weathered, is easy to disintegrate when meeting water, has poor engineering water physical properties and poor surrounding rock stability, and can cause collapse accidents when a combined system deforms seriously if a frozen wall and a supporting structure are not proper.

(3) And (3) disturbance of the stratum: the artificial filling, sandy clay, residual soil, fully and strongly weathered mixed granite mainly exists in the range of the No. 1 transverse channel, the total mechanical property is poor, and the granite is easy to soften and disintegrate when meeting water.

1.2.3 hydrogeology

The groundwater level disclosed by investigation in the range of No. 1 transverse channel is shallow, the water level burial depth is 1.80-18.10 m, the change of groundwater level is closely related to occurrence, supply and drainage of groundwater level, and is influenced by seasonal changes, 4-9 months per year is the supply period of groundwater, the water level can obviously rise, 10-3 months per year are the groundwater consumption period and the drainage period, the groundwater level falls along with the groundwater level, and the annual change range is 2.5-3.0 m. The underground water is divided into fourth series soil layer pore water, layered bedrock fracture water, blocky bedrock fracture water and carbonate rock fracture karst cave water according to occurrence modes. Because the fluctuation of the topography of the work site is large, the topography cutting is deep, the groundwater is mainly vertical circulation, the groundwater runoff path is short, the runoff direction is generally consistent with the slope direction, the groundwater is mostly discharged to nearby valleys in a scattered flow mode, and in addition, the groundwater is also discharged in modes of surface evaporation, vegetation surface transpiration and the like.

1.31 # transverse channel structure

The size of the No. 1 working well is 12m multiplied by 9.5m (length multiplied by width), the height of the tunnel bottom is 7.790m, and the height of the ground is 34.000 m. The maintenance structure of the No. 1 working well is an underground continuous wall with the thickness of 800mm, and 4 annular frame beams with the width of 1.8m multiplied by 1.5m (width multiplied by height) are arranged inside the maintenance structure. The length of the 1# transverse channel is 31.00m, the 1# transverse channel is of variable cross section, the cross section width of the B-B cross section of the inlet channel is 9.1m, the height of the inlet channel is 13.00m, the cross section width of the D-D cross section of the end head of the inlet channel is 9.1m, and the height of the D-D cross section of the inlet channel is 18.25 m. The structure of the 1# transverse channel is shown in fig. 1-3.

Four steps are excavated in the No. 1 cross passage, and the middle partition plate is I25a section steel and C25 sprayed concrete with the thickness of 320 mm. The 1# transverse channel primary support is C25P6 shotcrete + grid steel frame with thickness of 350mm, and the secondary lining structure is C35P6 impervious concrete with thickness of 700 mm.

2 freezing design

Freezing wall and cement reinforced body combined enclosure system

For a large-section tunnel with large stratum water inflow, large soil layer sand content and no open excavation condition, a 'frozen wall + cement reinforcement' combined enclosure system and mine excavation construction method can be adopted.

The overall construction scheme is as follows: the method comprises the steps of freezing and reinforcing soil mass on the periphery of a tunnel to be built in a cylindrical frozen wall mode to form a frozen soil curtain with high strength and good sealing performance, forming a weak freezing area in an excavation area, then carrying out horizontal advanced grouting reinforcement on the tunnel face of the tunnel to form a combined enclosure system of the frozen wall and a cement reinforcement body, and carrying out tunnel excavation supporting construction by adopting a mining method after the enclosure system is qualified in quality detection.

The combined enclosure system has the advantages that: the traditional freezing wall is a cup-shaped freezing wall, full freezing needs to be adopted, the number of drilled holes is large, a strong freezing area is formed in an excavation area, the excavation difficulty is high, an end freezing hole is removed from a 'freezing wall and cement reinforced body' combined enclosure system, namely the traditional end freezing is replaced by horizontal grouting reinforcement, a large amount of drilling time and materials are saved, the excavation area is a weak freezing area, and the excavation difficulty is reduced.

The freeze method for reinforcing the stratum has the following outstanding advantages: the frozen soil curtain has good uniformity, tight combination with the maintenance structure wall, good reinforcing effect and safe and reliable construction. The general scheme of the freezing construction of the No. 1 transverse passage comprises the following steps: by adopting a freezing and reinforcing scheme and an outer ring cylindrical freezing wall form, a soil body in the range of the freezing wall at the periphery of the planned transverse channel is frozen and reinforced to form a frozen soil curtain with high strength, and an excavated area forms a weak freezing area. In order to control the formation deformation caused by freezing and thawing of the soil layer, follow-up grouting is needed during the thawing process of the freezing and consolidating area. The monitoring of deformation and freezing system parameters is enhanced in the whole construction process.

2.1 freezing plan

According to the design, the No. 1 transverse channel is frozen in two stages, the first stage of freezing adopts a straight wall circular arc top-bottom type frozen wall, the thickness of the upper frozen wall is 3.0m, the thicknesses of the frozen walls of the side wall and the middle clapboard are 2.5m, the thickness of the frozen wall of the middle clapboard at the bottom is 3.5m on average, and the frozen wall at the front end excavation tunnel face extends for 8.0 m. The 1# cross channel first stage freeze wall is shown in fig. 4a, 4b and 4 c.

According to the design, the second-stage freezing of the No. 1 transverse channel adopts a straight-wall arc bottom freezing wall, the upper part of the straight-wall arc bottom freezing wall is connected with the bottom freezing wall frozen in the first stage, the thickness of the freezing wall of the side wall is 2.5m, the thickness of the freezing wall of the bottom plate is 3.5m on average, and the freezing wall at the front end excavation tunnel face extends for 8.0 m. The second phase frozen wall of the 1# cross channel is shown in fig. 5a, 5b and 5 c.

The construction freezing holes are divided into outer ring freezing holes D, DB and FB, outer ring auxiliary freezing holes DN, DNB and F, and interface reinforcing freezing holes G; temperature measuring hole C, pressure relief hole X and heating hole DJ. The 1# cross passage freeze hole arrangement is shown in fig. 6a and 6b, and the open hole position is shown in fig. 7.

2.2 freezing design parameters

The freezing design main parameters are shown in table 1:

TABLE 1

2.3 construction emphasis and difficulty

(1) Engineering geological risk

The No. 1 transverse channel is mainly located in a mixed granite residual soil stratum, and is difficult in engineering construction of the embodiment, rocks are broken and easily softened when meeting water, and the transverse channel belongs to V-level surrounding rocks and is poor in geological conditions. The upper part of the No. 1 transverse channel is positioned in a plastic sandy cohesive soil layer <5Z-1> and a hard plastic sandy cohesive soil layer <5Z-2>, the soil layers are disintegrated by entering water, the sand content is large, and the phenomena of sand gushing, mud bleeding and the like are easy to occur in drilling; the bottom is positioned at the 6Z of the strongly weathered mixed granite, the drilling construction of part of the freezing holes needs to pass through soft and hard stratums, and the drilling construction difficulty is higher.

(2) Difficulty in drilling

The number of the freezing pore-forming holes of the No. 1 cross passage is up to 266 (including 225 freezing holes, 17 temperature measuring holes, 15 pressure relief holes and 9 heating holes).

The construction working face of the working well is narrow, the open holes are densely distributed on the maintenance structure of the main face of the working well, and structures such as ring frame beams need to be avoided, so that hole repairing conditions are basically not met. The horizontal drilling construction distance is as long as 40m, the freezing holes are divergently arranged, the construction precision control difficulty is high, and the requirement on the quality of formed holes is high.

(3) Large cross section of transverse passage

The width of the standard section of the No. 1 transverse channel is 9.1m, the section form is that the height of the gradual section is from 13.0m to 18.25m, and the maximum section is 166m 2. Considering that the frozen wall and the primary support are jointly supported, timely supporting is needed, the primary support and the frozen wall are guaranteed to be tightly attached, the stress is coordinated, meanwhile, the excavation time is long, and considering the creep deformation of the frozen wall and the exposure and temperature rise influence of an excavation surface, the frozen wall must be timely supported during excavation, and the deformation of the frozen wall is strictly monitored and controlled.

(4) Long construction period of frozen excavation and great difficulty in controlling frozen expansion and thawing settlement

The freezing volume of the No. 1 cross passage reaches 8405.76m³The freezing time can reach more than 12 months. The freezing volume is large, the freezing time is long, and the control difficulty of frost heaving and thaw collapse is large.

(5) The shield crossing area freezing pipe cleaning workload is large

Nearly 70 freezing holes in the construction of the No. 1 transverse channel have influence on subsequent wiring and positive line shield crossing, and the freezing pipe cleaning work needs to be carried out after the construction of the transverse channel is finished. The cleaning workload of the freezing pipe is large, and the pipe breakage and other adverse effects can occur in the cleaning process.

(6) Extended end 8m frozen wall quality control

Because the end part ground of the 1# transverse channel cannot be occupied, the end of the 1# transverse channel is extended to 8m to freeze the wall, the development condition of the frozen wall is matched, and advanced reinforcement is adopted before excavation of the end part tunnel face.

3 excavation construction scheme

3.1 construction method

The 1# transverse passage is excavated and supported by a mining method, advanced horizontal grouting reinforcement is carried out in the construction process, and the later shield tunnel range freezing pipe is pulled out to ensure later shield tunneling.

The engineering of the embodiment mainly comprises main processes of freezing pore-forming construction in a No. 1 working well, installation of a freezing system of a ground freezing station, freezing and reinforcing of a stratum around a structure, excavation and construction of a No. 1 transverse channel, pulling out of a freezing pipe, filling and melting and precipitating grouting, cutting of the pipe, sealing of the hole and the like.

3.2 excavation procedure

The No. 1 transverse passage is reinforced by outer ring support in a freezing method and is reinforced by forward grouting of a tunnel face sleeve valve pipe. The construction is carried out by adopting a step method, 4 steps are divided totally, a working platform is erected in the No. 1 vertical shaft, the vertical shaft is excavated from top to bottom in sequence, after the previous chamber is communicated, the construction of the next chamber is carried out, two steps are excavated in each chamber, and the circulating footage is 0.5 m. And (5) performing primary support in time after excavation. The arch frame and the reinforcing mesh are installed manually, and the sprayed concrete is operated by a wet spraying machine. And after the whole tunnel is through, performing secondary lining construction from bottom to top. Specifically, according to design planning, construction is performed by two times of freezing, namely, the first stage of freezing freezes the first step and the second step, and the second stage of freezing freezes the third step and the fourth step. The partition boards in each layer of excavation construction are cut and supported along with excavation in the excavation process, and are closed to form a ring in time, so that the time of the hollow side is shortened.

And dividing the 1# transverse channel into 4 excavation areas according to the freezing hole layout rule, and horizontally excavating from top to bottom in sequence. The excavation steps are as follows:

step 1: drilling according to the planning design of the cylindrical frozen wall, completing drilling construction, installing a freezing system, completing pressure leakage test after all freezers are installed, completing heat preservation construction, completing salt melting, and starting up for freezing, wherein the figure is 8;

step 2: finishing the first-stage active freezing, performing first horizontal grouting in an unearthed area 10m away from the front-end excavation face, enabling the thickness of the frozen wall and the average temperature to meet design requirements, completely preparing materials required for excavation, completely putting emergency rescue materials in place, passing excavation acceptance, and preparing for tunnel excavation construction, wherein the figure is 9;

and step 3: and excavating after horizontal grouting is completed once every 10m in sequence, excavating to an end, and grouting and reinforcing the next step of excavating a step area by utilizing the upper space construction vertical grouting hole after primary supporting is completed. Excavating a first step, excavating a supporting-following step, wherein the time for excavating an exposed surface is required to be not more than 24 hours, and supporting operation is required to be carried out in time, so that the primary support is closely attached to the frozen soil, the cooperative stress condition is met, and the tunnel convergence deformation monitoring is carried out along with the excavation process, which is shown in figure 10;

and 4, step 4: and (2) excavating the second step, wherein the technical requirement is consistent with that of the first step, the exposed surface excavating time is required to be not more than 24 hours along with excavation, supporting operation is required to be carried out in time, the primary support is ensured to be closely attached to the frozen soil, the cooperative stress condition is met, and the tunnel convergence deformation monitoring is carried out along with the excavation process. And (5) after the end is excavated, horizontal grouting reinforcement is carried out, and the end reinforcement is completed. After the excavation is finished, the end sealing and reinforcing of the next step are carried out, and the figure 11 is shown;

and 5: and (3) actively freezing and finishing the second stage, excavating a third step, excavating along with the excavation, requiring that the time for excavating the exposed surface is not more than 24h, and carrying out support operation in time to ensure that the primary support is closely attached to the frozen soil, so that the cooperative stress condition is met, and monitoring the convergence deformation of the tunnel along with the excavation process. And (5) after the end is excavated, horizontal grouting reinforcement is carried out, and the end reinforcement is completed. After the excavation is finished, the end sealing and reinforcing of the next step are carried out, and the figure 12 is shown;

step 6: and (4) carrying out subsequent whole excavation, wherein the excavation time of the exposed surface is required to be not more than 24h along with excavation and supporting, and the supporting operation is required to be carried out in time, so that the close fitting of the primary support and the frozen soil is ensured, and the cooperative stress condition is met. The excavation process is accompanied with the monitoring of the convergence deformation of the tunnel. After the end is excavated, horizontal grouting reinforcement is carried out to finish the reinforcement of the tail end, which is shown in figure 13;

and 7: after the water resistance is finished, secondary lining construction is carried out, freezing is stopped, all freezing holes inside and outside are plugged, and filling and fused deposition grouting are carried out, as shown in figure 14; namely, after the tunnel is integrally communicated, a support method is adopted, 4 layers are divided from bottom to top, and each layer is divided into 3 sections, so that secondary lining construction is carried out.

3.3 horizontal grouting scheme for Cross channel

3.3.1 hole site layout

The length of a No. 1 transverse channel grouting subsection is 10m, the lap joint is 2.5m, and a grouting hole @1400mmx1400mm is arranged in a quincunx manner. The grouting sequence is carried out from bottom to top and from outside to inside in sequence. The grouting hole site is shown in detail in fig. 38.

3.3.2 grouting sequence

And 2 sets of grouting equipment are adopted for grouting simultaneously in each cycle, the grouting sequence is sequentially carried out from bottom to top and from outside to inside, two grouting machines are used for grouting on the same horizontal plane, and the distance between grouting holes is larger than 2.5 m. When grouting, the grouting spray heads cannot be positioned at the same cross section, and the longitudinal staggered distance of the two grouting spray heads is not less than 8 m.

3.3.3 grouting pressure

The grouting pressure of the test section is 0.5-1.5 MPa, and the grouting pressure is adjusted in later construction according to the analysis of data such as the diffusion radius, the grouting pressure, the ground surface settlement, the ground surface uplift and the like of the test section.

3.3.4 slip casting mixing ratio

P042.5 ordinary portland cement is selected, and the slurry is selected from the following components: water: 1, cement: 1.

3.3.5 grouting construction preparation

(1) Grout stop wall and tunnel face seal

The step construction step is staggered by 5m to construct the grout stopping wall. The tunnel face is sealed by binding steel bar meshes, arranging anchor pipes and spraying concrete. The steel bar meshes are double-layer meshes, the diameter of the steel bar meshes is phi 25mm, the mesh spacing is 250mm multiplied by 250mm, and the steel bar meshes are welded with the grid arch frame and the temporary inverted arch section steel support. The anchor pipe is a common seamless steel pipe with the diameter of 42mm, the driving length is 3.5m, and the transverse and vertical spacing is 1200mm multiplied by 1500 mm. The sprayed concrete thickness is 500 mm.

(2) Scaffold platform erection

The scaffold is erected firmly and reliably, the working platform is fully paved with scaffold boards, the scaffold is erected and accepted, and the scaffold can be used after the operation personnel are subjected to bottom-delivery training. The scaffold is multirow scaffold, and level and vertical all set up the bridging, and the bridging is all connected the fastening with the fastener in response to the scaffold pole setting.

3.3.6 grouting construction process

(1) Hole positioning: and fixing the hole position guider according to the set extrapolation angle, wherein the deviation of the hole position is required to be not more than 3 cm.

(2) Positioning a drilling machine: the first grouting hole is a No. 1 hole above, a drilling machine must be placed on a built temporary scaffold which passes the acceptance check, and after the verticality of a drill rod is adjusted to be aligned with the hole position, the drilling machine cannot be shifted and fixed firmly and cannot be lifted and lowered randomly.

(3) Drilling to form a hole: during the first hole construction, the operation is slow. And (3) grasping the influence of the stratum on the drilling machine to determine the drilling parameters under the stratum condition. Closely paying attention to the overflow water outlet condition, when a large amount of overflow water is discharged, immediately stopping drilling, analyzing reasons and then conducting construction. And checking one section of the drill hole after drilling one section of the drill hole, and correcting the deviation in time, wherein the deviation of the position of the hole bottom is not more than 30cm finally. And drilling and grouting are sequentially carried out from bottom to top and from outside to inside.

(4) Drawing back the drill rod: and strictly controlling the lifting amplitude, wherein each step is not more than 20cm, performing constant-speed pumping back, and paying attention to the change of grouting parameters.

(5) Proportioning the slurry: and carrying out mix proportion operation according to the set mix proportion parameters, and carrying out mix proportion configuration by adopting a calibrated accurate metering tool, so that the matching of the slurry setting time and the mix proportion parameters is ensured, and the grouting parameters are ensured to effectively control the grouting radius to meet the reinforcement requirement.

(6) Grouting: the diameter of the opening of the grouting hole is not less than 45mm, grouting pressure is strictly controlled, the grouting amount is closely concerned, grouting is stopped immediately when pressure suddenly rises or the surrounding rock of the hole wall and the section overflows, and grouting is performed again by adopting measures such as adjusting grouting parameters or shifting after reasons are found.

(7) When the grouting is about to finish the sealing, the grouting pressure at the tunnel face position is controlled to be 0.4-0.8 MPa, and the grouting flow is controlled, and 1 grade of grouting is required. Avoid damaging the closed tunnel face due to overlarge grouting pressure. And (3) adjusting grouting parameters during sealing to ensure that no slurry overflows and runs.

(8) The overall grouting process should be enhanced for construction inspection and monitoring measurements.

(9) The special person is responsible for the operation record of each procedure.

4 course of construction and results

In the 1# transverse passage freezing and reinforcing engineering of the XXX section of the XXX line XXX of the rail transit in XXX city, drilling is started from XX day of XXX year XX month XX, the drilling process is completed on XXXXXX month XX day of XXXXXXX year, the freezing holes and the temperature measuring holes are accumulated to be 246, the heating holes are accumulated to be 9, and the supplementary holes are accumulated to be 9, as shown in FIG. 15;

and in XXXX, XX month XX day in XXXXXX year, the freezing system is completely installed, and then the whole pipeline system is tested for water, and the sealing property is qualified. Positive freezing started on XX month XX day XXXX of XXXX, see fig. 16;

the first step of the 1# transverse channel is excavated in XX month XX day of XXXXXX (see figure 17), and the excavation of the four steps of the 1# transverse channel is successfully completed in XXXX month XX day of XXXXXX year, as shown in figure 18.

5 conclusion

A construction method of freezing reinforcement and mining excavation is adopted in the section 1# transverse channel freezing reinforcement project of XX line XX of rail transit in XX city, the excavation test is completed safely and smoothly after XXX days, and the conclusion obtained in the embodiment mainly includes:

(1) the artificial freezing method can effectively enhance the self-bearing capacity of the surrounding rock, isolate the relation of underground water, and can safely and smoothly pass through the section with severe engineering geological conditions by matching with the mining method excavation mode.

(2) Parameters of a freezing system must be strictly monitored in the freezing and excavation construction processes, if abnormal parameters such as temperature and the like are found, the system must respond immediately, the cause of the problem is searched, and effective measures are taken to solve the problem.

(3) In the excavation construction process of the large-section channel by adopting the artificial freezing method, the monitoring on the sinking deformation of surrounding rocks of the vault of the channel and the deformation of the side wall is enhanced, and when abnormal changes occur, the deformation of the vault and the side wall is immediately controlled.

Example 3

As shown in fig. 19, a frozen wall and cement reinforcement combined enclosure system in large-section tunnel construction comprises a frozen soil curtain and a cement reinforcement; the frozen soil curtain is a cylindrical freezing wall, the cylindrical freezing wall forms a strong freezing area, and an area to be excavated, which is surrounded by the cylindrical freezing wall, is a weak freezing area.

As shown in fig. 37, the frozen soil curtain is a third freezing and reinforcing area 30 consisting of a mesh-shaped circular arc top-bottom freezing wall; the third freeze reinforcement zone 30 comprises a third upper freeze wall 301, a third bottom freeze wall 302, a third side freeze wall 303, a third middle diaphragm freeze wall a304, and a third middle diaphragm freeze wall B305; the thickness of the third upper frozen wall 301 is 3m, the thickness of the third bottom frozen wall 302 is 3.5m, the thickness of the third side frozen wall 303 is 2.5m, and the thickness of the third middle diaphragm frozen wall a304 and the third middle diaphragm frozen wall B305 are both 2.5 m;

the third upper freezing wall 301, the third bottom freezing wall 302, the third side wall freezing wall 303, the third middle clapboard freezing wall A304 and the third middle clapboard freezing wall B305 all extend to the non-excavation area by 8.0m along the front end face 5 of the small section to be excavated.

The cement reinforcing body is a cement grouting area 4, the tunnel face 3 of the large-section tunnel to be excavated consists of three small-section tunnel faces 5 to be excavated which are sequentially arranged from top to bottom, and the cement grouting area 4 is positioned in front of the small-section tunnel faces 5 to be excavated; and the cement grouting area 4 is arranged at intervals of 10m along the excavation direction of the small-section tunnel face 5 to be excavated in the excavation process.

As shown in fig. 27, the freezing holes of the frozen soil curtain are laid out on the longitudinal section of the area to be excavated as follows:

above the area to be excavated: a pressure relief hole group X6 consisting of 7 pressure relief holes, a heating hole group DJ7 consisting of 9 heating holes, an outer ring freezing hole group D81 consisting of 19 outer ring freezing holes and an outer ring auxiliary freezing hole group DN91 consisting of 10 outer ring auxiliary freezing holes are sequentially distributed from top to bottom; pressure relief holes in the pressure relief hole group X6 are distributed at equal intervals along the horizontal direction, the hole distance between every two adjacent pressure relief holes is 1500mm, and the vertical distance L1 between each pressure relief hole and the arc top of the to-be-excavated area is 4540 mm; heating holes in the heating hole group DJ7 are distributed at equal intervals along the arc of the same heating hole group, the hole distance between two adjacent heating holes is 1500mm, the arc top of the arc of the heating hole group and the arc top of the area to be excavated are on the same vertical line, the distance between the arc top and the area to be excavated is 3500mm, and the longitudinal distances L2 from any point on the arc of the heating hole group to the arc on which the upper edge of the area to be excavated is located are equal; 15 outer ring freezing holes in the outer ring freezing hole group D81 are distributed along the arc of the same outer ring freezing hole group, the hole distance between two adjacent outer ring freezing holes is 800mm, 1 outer ring freezing hole is distributed on the arc top of the outer ring freezing hole group arc, 6 outer ring freezing holes with equal distance are respectively distributed from the arc top of the outer ring freezing hole group arc to two sides, an outer ring freezing hole is respectively arranged at the end point of the outer ring freezing hole group arc, and two outer ring freezing holes respectively positioned at two sides of the outer ring freezing hole group arc are distributed on a horizontal line between the last outer ring freezing hole and the last second outer ring freezing hole at the end point of the outer ring freezing hole group arc; the arc top of the outer ring freezing hole group arc and the arc top of the area to be excavated are on the same vertical line, the distance between the arc top and the area to be excavated is 2400mm, and the longitudinal distance L3 from any point on the outer ring freezing hole group arc to the arc on which the upper edge of the area to be excavated is located is equal; 8 outer ring auxiliary freezing holes in the outer ring auxiliary freezing hole group DN91 are distributed on the same outer ring auxiliary freezing hole group arc at equal intervals, and the hole interval between two adjacent outer ring auxiliary freezing holes is 1200 mm; in addition, 2 outer ring auxiliary freezing holes are respectively distributed near the tail ends of the outer ring auxiliary freezing hole group arcs and are positioned between the outer ring auxiliary freezing hole group arcs and the outer ring freezing hole group arcs, the arc tops of the outer ring auxiliary freezing hole group arcs and the arc tops of the to-be-excavated area are on the same vertical line, the distance between the arc tops and the arc tops of the to-be-excavated area is 877mm, and the longitudinal distances L4 from any point on the outer ring auxiliary freezing hole group arcs to the arcs of the upper edge of the to-be-excavated area are equal;

in the area to be excavated: a first pressure relief hole group X61 consisting of 2 pressure relief holes, a first interface strengthening freezing hole group G101 consisting of 9 interface strengthening freezing holes, a second pressure relief hole group X62 consisting of 2 pressure relief holes, a second interface strengthening freezing hole group G102 consisting of 5 interface strengthening freezing holes, a third interface strengthening freezing hole group G103 consisting of 9 interface strengthening freezing holes, a fourth interface strengthening freezing hole group G104 consisting of 5 interface strengthening freezing holes and a third pressure relief hole group X63 consisting of 2 pressure relief holes are sequentially distributed from top to bottom;

2 pressure relief holes in the first pressure relief hole group X61 are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, the vertical distance L5 between the pressure relief holes and an arc top of the area to be excavated is 3924mm, and the hole distance between the 2 pressure relief holes is 3000 mm; 9 interface strengthening freezing holes in the first interface strengthening freezing hole group G101 are distributed at equal intervals along the horizontal direction, and one interface strengthening freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L51 between a straight line formed by connecting the first interface strengthening freezing hole groups G101 and the arc top of the area to be excavated is 7742mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1230 mm; 2 pressure relief holes in the second pressure relief hole group X62 are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, the vertical distance L7 between the pressure relief holes and an arc top of the area to be excavated is 9522mm, and the hole distance between the 2 pressure relief holes is 3000 mm; 5 interface reinforcing freezing holes in the second interface reinforcing freezing hole group G102 are formed and are distributed on two sides of a longitudinal central axis of the region to be excavated at equal intervals along the horizontal direction; the vertical distance L6 between a straight line formed by the second interface strengthening freezing hole group G102 and the arc top of the area to be excavated is 9742mm, and the hole distance between every two adjacent interface strengthening freezing holes is 2000 mm; 9 interface strengthening freezing holes in the third interface strengthening freezing hole group G103 are distributed at equal intervals along the horizontal direction, and one interface strengthening freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L8 between a straight line formed by the third interface strengthening freezing hole group G103 and the arc top of the region to be excavated is 12742mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1230 mm; the 5 interface reinforcing freezing holes in the fourth interface reinforcing freezing hole group G104 are formed and are distributed on two sides of the longitudinal central axis of the region to be excavated at equal intervals along the horizontal direction; the vertical distance L9 between a straight line formed by the fourth interface strengthening freezing hole group G104 and the arc top of the area to be excavated is 13342mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1700 mm;

2 pressure relief holes in the third pressure relief hole group X63 are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, and the vertical distance L10 between the pressure relief holes and the arc top of the area to be excavated is 13501 mm; the hole spacing between the 2 pressure relief holes is 3000 mm;

a first column of outer ring auxiliary freezing hole groups DN92 consisting of 9 outer ring auxiliary freezing holes are distributed on the edge lines on the two sides of the area to be excavated along the longitudinal direction;

below the area to be excavated: a third row of outer ring freezing hole group DB86 consisting of 11 outer ring freezing holes, a fourth row of outer ring freezing hole group DB87 consisting of 10 outer ring freezing holes, a fifth row of outer ring freezing hole group DB88 consisting of 11 outer ring freezing holes and a sixth row of outer ring freezing hole group DB89 consisting of 10 outer ring freezing holes are sequentially distributed from top to bottom; 11 outer ring freezing holes in the third row of outer ring freezing hole groups DB86 are distributed at equal intervals in the horizontal direction, and one outer ring freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L15 between a straight line formed by connecting the freezing hole groups DB86 of the third row of outer rings and the arc bottom of the area to be excavated is 14908mm, and the hole distance between every two adjacent outer ring freezing holes is 1197 mm; 10 outer ring freezing holes in the fourth row outer ring freezing hole group DB87 are distributed at equal intervals in the horizontal direction; the vertical distance L16 between a straight line formed by connecting the fourth row of outer ring freezing hole groups DB87 and the arc bottom of the area to be excavated is 15308mm, and the hole distance between every two adjacent outer ring freezing holes is 1189 mm; 11 outer ring freezing holes in the fifth row outer ring freezing hole group DB88 are distributed at equal intervals in the horizontal direction, and one outer ring freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L17 between a straight line formed by connecting the freezing hole groups DB88 of the outer ring of the fifth row and the arc bottom of the area to be excavated is 15608mm, and the hole distance between two adjacent freezing holes of the outer ring is 1197 mm; 10 outer ring freezing holes in the outer ring freezing hole group DB89 in the sixth row are distributed at equal intervals in the horizontal direction; the vertical distance L18 between a straight line formed by connecting the outer ring freezing hole groups DB89 in the sixth row and the arc bottom of the area to be excavated is 15911mm, and the hole distance between every two adjacent outer ring freezing holes is 1189 mm;

a first row of outer ring freezing hole groups DB84 formed by 8 outer ring freezing holes and a second row of outer ring freezing hole groups DB85 formed by 10 outer ring freezing holes are distributed on the bottom edge line of the region to be excavated from top to bottom; outer ring freezing holes in the first row of outer ring freezing hole groups DB84 are distributed at equal intervals along the horizontal direction, and the vertical distance from a straight line formed by connecting the first row of outer ring freezing hole groups DB84 to a straight line formed by connecting the third row of outer ring freezing hole groups DB86 is L11; outer ring freezing holes in the second row outer ring freezing hole group DB85 are distributed at equal intervals in the horizontal direction, and the vertical distance from the straight line connecting the second row outer ring freezing hole group DB85 to the straight line connecting the third row outer ring freezing hole group DB86 is L12.

Example 4

Compared with other small-section tunnel projects, the extra-large-section tunnel project has the advantages of higher construction difficulty, more construction risks and a large number of project technical problems. Among them, how to select a reasonable and safe construction method to pass through a stratum under complex conditions is a problem of particular concern to all parties of engineering construction. Meanwhile, the problem is also one of the hot spots of the research in the academic world. In order to build a tunnel in a weak stratum, scientific researchers at home and abroad propose a plurality of stratum reinforcing methods, and technologies such as grouting, small pipes, pipe sheds and the like are generally applied to a soil tunnel. As a temporary reinforcing technology, the manual freezing method is widely applied to mine construction and municipal engineering, but the application experience of tunnel engineering with extra-large sections is still insufficient.

In this embodiment, a freezing method and a grouting method are combined, a combined enclosure system method of 'freezing wall + cement reinforcement' in embodiment 3 is adopted, and a construction test is performed on the combined enclosure system by taking a # 2 transverse passage freezing project of a tunnel between XXX station and XXX station of a subway XXX number line XXX in XXX city as an example in embodiment 2.

The 2# working well is constructed, and the 2# cross passage in the XXX interval is reinforced by a freezing method and is constructed by a mining method and an underground excavation method because the stratum nearby the 2# working well has large water inflow, large sand content in the soil layer, poor self-stability and no open excavation condition.

6 general description of the engineering

6.1 the engineering contents are the same as in example 2.

6.2 engineering geology and hydrogeology

6.2.1 topographic features similar to example 2.

6.2.2 engineering geology

The No. 2 transverse passage mainly passes through a hard plastic sandy cohesive soil layer <5Z-2> and a sandy cohesive soil layer <7Z-B >. The top soil covering thickness of the transverse channel is 7 m. The geological conditions in the area are complex, and the underlying bedrock mainly comprises clastic rock, carbonaceous shale, carbonaceous limestone, mixed granite and other rocks. The mixed granite residual soil in the embodiment can be divided into plastic sandy cohesive soil (5Z-1) and hard plastic sandy cohesive soil (5Z-2).

The 2# cross channel crossing unfavorable geological zones mainly have: residual soil formations, sandy soil liquefaction, and the like.

(2) Ground collapse: the bottom of the 2# cross passage passes through a mixed granite residual soil stratum which is mainly sand cohesive soil in a shape of hard plastic, is mostly in a hard soil shape after being completely weathered, is easy to disintegrate in water, has poor engineering water physical properties and poor surrounding rock stability, and can cause collapse accidents if a frozen wall and a supporting structure are improper, and a combined system deforms seriously.

(3) And (3) disturbance of the stratum: the artificial filling, sandy clay, residual soil, fully and strongly weathered mixed granite mainly exists in the range of the No. 2 transverse channel, the total mechanical property is poor, and the granite is easy to soften and disintegrate when meeting water.

6.2.3 hydrogeology

The groundwater level disclosed by investigation in the range of No. 2 transverse channel is shallow, the water level burial depth is 1.80-18.10 m, the change of groundwater level is closely related to occurrence, supply and drainage of groundwater level, and is influenced by seasonal changes, 4-9 months per year is the supply period of groundwater, the water level can obviously rise, 10-3 months in the next year are the groundwater consumption period and the drainage period, the groundwater level falls along with the groundwater level, and the annual change range is 2.5-3.0 m. The underground water is divided into fourth series soil layer pore water, layered bedrock fracture water, blocky bedrock fracture water and carbonate rock fracture karst cave water according to occurrence modes.

6.32 # transverse channel structure

The size of the No. 2 working well is 12m multiplied by 11.1m in length multiplied by width, the bottom hole elevation 7.431m and the ground elevation 34.000 m. The 2# working well maintenance structure is an underground continuous wall with the thickness of 800mm, and 4 ring frame beams with the width multiplied by the height 1.8m multiplied by 1.5m are arranged inside the underground continuous wall. And (3) constructing freezing holes of the No. 2 cross passage on the main surface of the maintenance structure of the working well, wherein the ring frame beam is avoided in the drilling construction. The length of the No. 2 transverse channel is 30.00m, the No. 2 transverse channel is of variable cross section, as shown in figure 23, the cross section of the inlet channel B-B is 9.7m wide and 12.75m high, and the cross section of the channel end D-D is 9.7m wide and 17.00m high.

The 2# cross passage is excavated into three steps, and each layer of excavation construction partition plate is I25a section steel and C25 sprayed concrete with the thickness of 320 mm. The 2# transverse channel primary support is C25P6 shotcrete + grid steel frame with thickness of 350mm, and the secondary lining structure is C35P6 impervious concrete with thickness of 700 mm.

7 'frozen wall + cement reinforced body' combined enclosure system and excavation method

The freeze method for reinforcing the stratum has the following outstanding advantages: the frozen soil curtain has good uniformity, tight combination with the maintenance structure wall, good reinforcing effect and safe and reliable construction. However, the sealing end is reinforced in a full space, the number of freezing holes is large, the excavation difficulty is high, and the engineering cost is high. The grouting method is an effective technical means for preventing and treating water damage of underground engineering and reinforcing soft stratum, but has large risk when being used alone.

The 'frozen wall and cement reinforced body' combined enclosure system of the embodiment combines a freezing method and a grouting method, gives full play to the advantages of the two methods, and abandons the disadvantages of the two methods; the outer ring of the tunnel is frozen and reinforced by adopting a freezing and reinforcing method, namely the outer ring is in a cylindrical frozen wall form, so that the soil body in the range of the peripheral frozen wall of the proposed tunnel is frozen and reinforced to form a frozen soil curtain with high strength, and the excavated area forms a weak freezing area. The end is reinforced by adopting horizontal grouting, the underground water of the end can be sealed, the freezing and reinforcing effect is ensured, the number of drilled holes is greatly reduced, and the excavation difficulty is obviously reduced. In order to control the formation deformation caused by freezing and thawing of the soil layer, follow-up grouting is needed during the thawing process of the freezing and consolidating area. The monitoring of deformation and freezing system parameters is enhanced in the whole construction process.

7.1 frozen wall Structure

The No. 2 transverse channel adopts a straight wall circular arc top-bottom type frozen wall, the thickness of the frozen wall at the upper part is 3m, the thickness of the frozen wall at the side wall is 2.5m, the thickness of the frozen wall at the bottom plate is 3.5m, and the frozen wall at the front end excavation tunnel face extends for 8 m. See fig. 24, 25a and 25b for # 2 transverse passage frozen walls.

The construction freezing holes are divided into outer ring freezing holes D, DB and FB, an outer ring auxiliary freezing hole DN and an interface strengthening freezing hole G; temperature measuring hole C, pressure relief hole X and heating hole DJ. The 2# cross passage freeze hole arrangement is shown in fig. 26a and 26b, and the open hole position is shown in fig. 27.

7.2 freezing design parameters

The freeze design main parameters are shown in table 2:

TABLE 2

7.3 construction emphasis and difficulty

(1) Engineering geological risk

The No. 2 transverse passage is positioned in the hard plastic sandy cohesive soil layers <5Z-2>, <7Z-B > sandy cohesive soil, and the vast majority of the transverse passage is positioned in the hard plastic sandy cohesive soil layers <5Z-2>, <7Z-B > sandy cohesive soil, the soil layers are disintegrated by water, the sand content is large, and the phenomena of sand gushing and mud bleeding are easy to occur in drilling holes; the bottom is located on the weathered rock, few parts of the freezing holes in the bottom are embedded in the hard rock, and the drilling construction difficulty is high.

(2) Difficulty in drilling

The number of frozen holes of the No. 2 transverse channel is as high as 251 (including 213 freezing holes, 16 temperature measuring holes, 13 pressure releasing holes and 9 heating holes).

The construction working face of the working well is narrow, the open holes are densely distributed on the maintenance structure of the main face of the working well, and structures such as ring frame beams need to be avoided, so that hole repairing conditions are basically not met. The horizontal drilling construction distance is as long as 38.8m, the freezing holes are divergently arranged, the construction precision control difficulty is high, and the requirement on the quality of formed holes is high.

(3) Large cross section of transverse passage

The width of the standard section of the No. 2 transverse channel is 9.7m, the section form is that the height of the gradual section is from 12.75m to 17.00m, and the maximum section is 166m 2. In the engineering of the embodiment, the combined bearing of the frozen wall and the primary support is considered, the primary support and the frozen wall need to be supported in time, the close fitting of the primary support and the frozen wall is guaranteed, the stress is coordinated, the excavation time is long, the creep deformation of the frozen wall and the exposure and temperature rise influence of an excavation surface are considered, and therefore the frozen wall needs to be supported in time during excavation, and the deformation of the frozen wall is strictly monitored and controlled.

The freezing volume of the No. 2 cross passage reaches 6346.76m³The freezing time can reach more than 12 months. The freezing volume is large, the freezing time is long, and the control difficulty of frost heaving and thaw collapse is large.

(5) The shield crossing area freezing pipe cleaning workload is large

Nearly 70 freezing holes in the No. 2 transverse channel construction have influence on subsequent wiring and positive line shield crossing, and the freezing pipe cleaning work needs to be carried out after the transverse channel construction is finished. The cleaning workload of the freezing pipe is large, and the pipe breakage and other adverse effects can occur in the cleaning process.

(6) The quality control difficulty of the frozen wall with 8m of the extending end part is large

Because the ground at the end part of the 2# transverse channel cannot be occupied, the end part of the 2# transverse channel extends to form a 8m frozen wall, the development condition of the frozen wall is matched, and advanced reinforcement is adopted before excavation of the tunnel face at the end part.

8 excavation construction scheme

8.1 construction method

And 2, excavating and supporting construction of the 2# transverse channel by steps by adopting a mining method, erecting a construction platform in the vertical shaft, performing full-face advanced grouting reinforcement on each step on the platform, and breaking excavation construction of the underground diaphragm wall after grouting and freezing reinforcement effects meet design requirements through inspection. Namely: and (5) adopting a freezing method to support and reinforce the outer ring. The construction is carried out by adopting a step method, 3 steps are divided, a working platform is erected in the No. 2 vertical shaft, the excavation is carried out in sequence from top to bottom, after the previous chamber is communicated, the construction of the next chamber is carried out, the excavation is carried out by dividing the steps in each chamber, and the circulating footage is 0.5 m. And after excavation, performing primary support and primary spraying in time. The sprayed concrete is operated by a wet spraying machine, and the anchor rod, the arch frame and the reinforcing mesh are manually installed. And after the whole tunnel is through, performing secondary lining construction from bottom to top, and after the shield is lifted out of the influence part to support the reserved steel bars.

8.2 excavation procedure

And 2# transverse channel excavation construction divides excavation into 3 areas according to the arrangement rule of freezing holes, and horizontal excavation is sequentially carried out from top to bottom. The partition boards in each layer of excavation construction are cut and supported along with excavation in the excavation process, and are closed to form a ring in time, so that the time of the hollow side is shortened. The excavation steps are as follows:

step 1: and (4) finishing the drilling construction, finishing the pressure leakage test after all the freezers are installed, and finishing the heat insulation construction. Starting the machine for freezing after salt dissolving is finished; see fig. 28.

Step 2: actively freezing, enabling the thickness of the frozen wall and the average temperature to meet design requirements, grouting and reinforcing, completely preparing materials required for excavation, completely putting emergency materials in place, and performing tunnel excavation construction through preparation for excavation acceptance; see fig. 29.

And step 3: and excavating the first subarea until primary support is finished. And grouting reinforcement is carried out on the next step area by utilizing the vertical grouting hole for upper space construction. Excavating a first step, excavating a supporting-following step, wherein the time for excavating an exposed surface is required to be not more than 24 hours, supporting operation needs to be carried out in time, the primary support is ensured to be closely attached to frozen soil, a cooperative stress condition is met, and the excavation process is accompanied with tunnel convergence deformation monitoring; see fig. 30.

And 4, step 4: horizontally grouting to reinforce the second step, excavating after reinforcement is completed, wherein the technical requirement is consistent with that of the first step, excavating exposure surface time is required to be not more than 24 hours along with excavation and support, timely supporting operation is required, the primary support is ensured to be closely attached to frozen soil, a cooperative stress condition is met, monitoring of tunnel convergence deformation is carried out along with the excavation process, and the lower third step is reinforced after excavation is carried out to the end head; see fig. 31.

And 5: carrying out horizontal grouting reinforcement and excavation by adopting the same technical requirements, excavating a third step, excavating a following support, wherein the exposed surface excavation time is not more than 24 hours, timely supporting operation is required, the primary support is closely attached to the frozen soil, the cooperative stress condition is met, and the tunnel convergence deformation monitoring is carried out along with the excavation process; see fig. 32.

Step 6: after the water resistance is finished, performing secondary lining construction, stopping freezing, plugging all freezing holes inside and outside, and filling, melting, sinking and grouting; see fig. 33.

Secondary lining construction: after the tunnel is integrally communicated, a lining wall is constructed in a layered mode from bottom to top by adopting a support method, and negative two-layer medium plate lap steel bars are reserved; constructing the inner lining wall to 0.2m below the bottom surface of the temporary opposite support, erecting a second lining temporary support, dismantling the I-shaped steel concrete-sprayed temporary opposite support, and constructing a negative layer of middle plate; constructing residual lining walls and vault, and sealing the two linings into a ring; disassembling and hoisting the shield machine, and sequentially disassembling the temporary supports; and after the shield machine is hoisted out, recovering the middle plate and the partition wall of the second layer.

9 working procedure and results

In the 2# cross passage freezing and reinforcing engineering of the XXX section of the XXX line XXX of the rail transit in XXX city, drilling is started from XX day of XXX year XX month XX, the drilling process is completed on XXXXXX month XX day of XXXXXXX year, 248 freezing holes and temperature measuring holes are cumulatively completed, 9 heating holes are formed, and 15 supplementary holes are formed, as shown in FIG. 34.

And in 12 and 30 months in 2019, the freezing system is installed completely, then the whole pipeline system is tested for water, and the sealing performance is qualified. The positive freezing starts at 1/10 of 2020, see fig. 35.

The first step of the 2# cross passage is excavated in 5-month and 1-day 2020, and the excavation of the three steps of the 2# cross passage is successfully completed in 10-month and 18-day 2020, as shown in fig. 36.

Conclusion 10

A frozen wall and cement reinforced body combined enclosure system and an excavation method are adopted in a frozen reinforcement project of a 2# transverse channel between XX section lines XX of track traffic XXX in XXX city, excavation is safely and smoothly completed, and the conclusion obtained in the embodiment mainly comprises the following steps:

(1) the combined enclosure system of the frozen wall and the cement reinforcement body effectively enhances the bearing capacity of the enclosure rock and isolates the connection of underground water, and the combined enclosure system is matched with a mining method stepped excavation mode and can safely and smoothly pass through a section with complex stratum conditions.

(2) The horizontal end grouting technology can effectively solve the water sealing problem of the end area, cut off the connection between the end area and underground water, and ensure the safety during excavation and structure pouring.

(3) The freezing system and the freezing wall parameters must be strictly monitored in the whole construction process, and if the freezing system parameters such as temperature and the like are found to be abnormal, the cause of the problem must be immediately searched and effective measures are taken to solve the problem.

(4) A 'frozen wall and cement reinforced body' combined enclosure system is adopted in an extra-large section channel, the monitoring on the deformation of surrounding rocks and side walls of the vault of the channel is enhanced, and when abnormal changes occur, corresponding measures are immediately taken to control the deformation of the vault and the side walls.

Claims

1. A frozen wall and cement reinforcement combined enclosure system in large-section tunnel construction is characterized by comprising a frozen soil curtain and a cement reinforcement; the frozen soil curtain is a cylindrical frozen wall, the cylindrical frozen wall forms a strong freezing area, and an area to be excavated, which is surrounded by the cylindrical frozen wall, is a weak freezing area; the cement reinforcing body is located in surrounding rocks of a tunnel face (3) of the large-section tunnel to be excavated along the excavation direction.

2. The system of claim 1, wherein the frozen soil curtain comprises a first stage freezing and reinforcing area (1) and a second stage freezing and reinforcing area (2); the first-stage freezing and reinforcing area (1) is a reversed-Y-shaped straight-wall arc top-bottom freezing wall; the first-stage freezing and reinforcing area (1) comprises a first upper freezing wall (11), a first bottom middle clapboard freezing wall (12), a first side wall freezing wall (13) and a first middle clapboard freezing wall (14); the first upper freezing wall (11), the first bottom middle partition freezing wall (12), the first side wall freezing wall (13) and the first middle partition freezing wall (14) extend towards a non-excavation region along a small-section tunnel face (5) to be excavated;

the second-stage freezing and reinforcing area (2) is a vertical-wall arc bottom type freezing wall in a shape like the Chinese character 'ri'; the second-stage freezing and reinforcing area (2) comprises a second upper freezing wall (21), a second bottom freezing wall (22), a second side wall freezing wall (23) and a second middle clapboard freezing wall (24); the second upper freezing wall (21) is connected to the first bottom intermediate diaphragm freezing wall (12) of the first stage freezing consolidation zone (1); the second upper freezing wall (21), the second bottom freezing wall (22), the second side wall freezing wall (23) and the second middle partition plate freezing wall (24) extend towards the non-excavation area along the small-section tunnel face (5) to be excavated.

3. The combined freezing wall and cement reinforcement enclosure system for the construction of the large-section tunnel according to claim 1, wherein the frozen soil curtain is a third freezing and reinforcing area (30) consisting of a circular arc top-bottom freezing wall in a shape like a Chinese character mu; the third freeze reinforcement zone (30) comprises a third upper freeze wall (301), a third bottom freeze wall (302), a third side freeze wall (303), a third middle diaphragm freeze wall a (304), and a third middle diaphragm freeze wall B (305); the third upper freezing wall (301), the third bottom freezing wall (302), the third side wall freezing wall (303), the third middle partition plate freezing wall A (304) and the third middle partition plate freezing wall B (305) extend towards a non-excavation area along a small-section tunnel face (5) to be excavated.

4. The system of claim 2, wherein the freezing holes of the frozen soil curtain are arranged on the longitudinal section of the area to be excavated as follows:

above the area to be excavated: a pressure relief hole group X (6) consisting of 7 pressure relief holes, a heating hole group DJ (7) consisting of 9 heating holes, an outer ring freezing hole group D (81) consisting of 19 outer ring freezing holes and an outer ring auxiliary freezing hole group DN (91) consisting of 10 outer ring auxiliary freezing holes are sequentially distributed from top to bottom;

the pressure relief holes in the pressure relief hole group X (6) are distributed at equal intervals along the horizontal direction, the hole distance between every two adjacent pressure relief holes is 1500mm, and the vertical distance L1 between each pressure relief hole and the arc top of the area to be excavated is 6800 mm;

the heating holes in the heating hole group DJ (7) are distributed at equal intervals along the arc of the same heating hole group, the hole interval between every two adjacent heating holes is 1500mm, the arc top of the arc of the heating hole group and the arc top of the area to be excavated are on the same vertical line, the distance between the arc top and the area to be excavated is 5460mm, and the longitudinal distances L2 from any point on the arc of the heating hole group to the arc on which the upper edge of the area to be excavated is located are equal;

15 outer ring freezing holes in the outer ring freezing hole group D (81) are distributed along the same outer ring freezing hole group arc, the hole distance between every two adjacent outer ring freezing holes is 800mm, 1 outer ring freezing hole is distributed at the arc top of the outer ring freezing hole group arc, 6 outer ring freezing holes with equal intervals are respectively distributed from the arc top of the outer ring freezing hole group arc to two sides, one outer ring freezing hole is respectively arranged at the end point of the outer ring freezing hole group arc, and two outer ring freezing holes respectively positioned at two sides of the outer ring freezing hole group arc are distributed on a horizontal line between the last outer ring freezing hole and the last but one outer ring freezing hole at the tail end of the outer ring freezing hole group arc; the arc top of the outer ring freezing hole group arc and the arc top of the area to be excavated are on the same vertical line, the distance between the arc top and the area to be excavated is 4660mm, and the longitudinal distance L3 from any point on the outer ring freezing hole group arc to the arc on which the upper edge of the area to be excavated is located is equal;

8 outer ring auxiliary freezing holes in the outer ring auxiliary freezing hole group DN (91) are distributed on the same outer ring auxiliary freezing hole group arc at equal intervals, and the hole interval between every two adjacent outer ring auxiliary freezing holes is 1200 mm; the other 2 outer ring auxiliary freezing holes are respectively distributed near the tail ends of the outer ring auxiliary freezing hole group arcs and located between the outer ring auxiliary freezing hole group arcs and the outer ring freezing hole group arcs, the arc tops of the outer ring auxiliary freezing hole group arcs and the arc tops of the to-be-excavated area are on the same vertical line, the distance between the arc tops and the arc tops of the to-be-excavated area is 3160mm, and the longitudinal distances L4 from any point on the outer ring auxiliary freezing hole group arcs to the arcs where the upper edges of the to-be-excavated area are located are equal;

a first temperature measuring hole, a second temperature measuring hole and a third temperature measuring hole are further distributed above the area to be excavated, the first temperature measuring hole is distributed on the arc of the heating hole group and is positioned on the left side of the arc top of the arc of the heating hole group, and the second temperature measuring hole and the first temperature measuring hole are in the same horizontal line and are positioned between the arc of the heating hole group and the arc of the outer ring freezing hole group; the third temperature measuring hole is positioned right below the arc top of the outer ring auxiliary freezing hole group;

on the left side of the area to be excavated: a first row of outer ring freezing hole groups FB (82) and a second row of outer ring freezing hole groups D (83) are longitudinally distributed, and the distance from the first row of outer ring freezing hole groups FB (82) to the area to be excavated is greater than the distance from the second row of outer ring freezing hole groups D (83) to the area to be excavated; an auxiliary freezing hole and a temperature measuring hole are further formed in a longitudinal straight line where the first row outer ring freezing hole group FB (82) is located, an auxiliary freezing hole is further formed in a longitudinal straight line where the second row outer ring freezing hole group D (83) is located, and an auxiliary freezing hole and a temperature measuring hole are distributed in a region between the second row outer ring freezing hole group D (83) and the region to be excavated;

in the area to be excavated: a first pressure relief hole group X (61) consisting of 2 pressure relief holes, a first interface strengthening freezing hole group G (101) consisting of 7 interface strengthening freezing holes, a second interface strengthening freezing hole group G (102) consisting of 4 interface strengthening freezing holes, a second pressure relief hole group X (62) consisting of 2 pressure relief holes, a third interface strengthening freezing hole group G (103) consisting of 7 interface strengthening freezing holes, a fourth interface strengthening freezing hole group G (104) consisting of 8 interface strengthening freezing holes, a third pressure relief hole group X (63) consisting of 2 pressure relief holes, a fifth interface strengthening freezing hole group G (105) consisting of 7 interface strengthening freezing holes and a fourth pressure relief hole group X (64) consisting of 2 pressure relief holes are sequentially distributed from top to bottom;

2 pressure relief holes in the first pressure relief hole group X (61) are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, the vertical distance L5 between each pressure relief hole and an arc top of the area to be excavated is 782mm, and the hole distance between every two 2 pressure relief holes is 3000 mm;

7 interface strengthening freezing holes in the first interface strengthening freezing hole group G (101) are distributed at equal intervals along the horizontal direction, and one interface strengthening freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L51 between a straight line formed by the first interface strengthening freezing hole group G (101) and the arc top of the area to be excavated is 5300mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1230 mm;

4 interface reinforcing freezing holes in the second interface reinforcing freezing hole group G (102) are formed and are distributed on two sides of the longitudinal central axis of the area to be excavated at equal intervals along the horizontal direction; the vertical distance L6 between a straight line formed by connecting the second interface strengthening freezing hole groups G (102) and the arc top of the area to be excavated is 6103mm, and the hole distance between two adjacent interface strengthening freezing holes is 2000 mm;

2 pressure relief holes in the second pressure relief hole group X (62) are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, and the vertical distance L7 between the pressure relief holes and the arc top of the area to be excavated is 7384 mm; the hole spacing between 2 pressure relief holes is 3000 mm;

7 interface strengthening freezing holes in the third interface strengthening freezing hole group G (103) are distributed at equal intervals along the horizontal direction, and one interface strengthening freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L8 between a straight line formed by connecting the third interface strengthening freezing hole group G (103) and the arc top of the area to be excavated is 10303mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1230 mm;

8 interface reinforcing freezing holes in the fourth interface reinforcing freezing hole group G (104) are formed and are distributed on two sides of the longitudinal central axis of the area to be excavated at equal intervals along the horizontal direction; the vertical distance L9 between a straight line formed by the second interface strengthening freezing hole group G (104) and the arc top of the area to be excavated is 11000mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1200 mm;

2 pressure relief holes in the third pressure relief hole group X (63) are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, and the vertical distance L10 between each pressure relief hole and the arc top of the area to be excavated is 11172 mm; the hole spacing between 2 pressure relief holes is 3000 mm;

7 interface strengthening freezing holes in the fifth interface strengthening freezing hole group G (105) are distributed at equal intervals along the horizontal direction, and one interface strengthening freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L11 between a straight line formed by connecting the third interface strengthening freezing hole group G (105) and the arc top of the area to be excavated is 11853mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1230 mm;

2 pressure relief holes in the fourth pressure relief hole group X (64) are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, and the vertical distance L12 between each pressure relief hole and the arc top of the area to be excavated is 12262 mm; the hole spacing between 2 pressure relief holes is 3000 mm;

a fourth temperature measuring hole, a fifth temperature measuring hole, a sixth temperature measuring hole and a seventh temperature measuring hole are further formed in the area to be excavated, 4 temperature measuring holes are formed in the longitudinal central axis of the area to be excavated, and the fourth temperature measuring hole is located between the first interface strengthening freezing hole group G (101) and the second interface strengthening freezing hole group G (102); the fifth temperature measuring hole is positioned on a straight line formed by connecting the second interface strengthening freezing hole group G (104); the sixth temperature measuring hole is positioned between the third pressure relief hole group X (63) and the fifth interface strengthening freezing hole group G (105); the seventh temperature measuring hole is positioned below the fourth pressure relief hole group X (64);

a first row of outer ring auxiliary freezing hole groups DN (92) consisting of 4 outer ring auxiliary freezing holes are longitudinally and uniformly distributed at the edges of the two sides of the area to be excavated;

below the area to be excavated: a first row of outer ring freezing hole group DB (84) consisting of 11 outer ring freezing holes, a second row of outer ring freezing hole group DB (85) consisting of 10 outer ring freezing holes, a third row of outer ring freezing hole group DB (86) consisting of 11 outer ring freezing holes, a fourth row of outer ring freezing hole group DB (87) consisting of 10 outer ring freezing holes and a fifth row of outer ring freezing hole group DB (88) consisting of 11 outer ring freezing holes are sequentially distributed from top to bottom;

11 outer ring freezing holes in the first row of outer ring freezing hole groups DB (84) are distributed at equal intervals in the horizontal direction, and one outer ring freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L13 between a straight line formed by connecting the first row of outer ring freezing hole groups DB (84) and the arc bottom of the area to be excavated is 13133mm, and the hole distance between every two adjacent outer ring freezing holes is 1200 mm;

10 outer ring freezing holes in the second row of outer ring freezing hole groups DB (85) are distributed at equal intervals in the horizontal direction; the vertical distance L14 between a straight line formed by connecting the second row of outer ring freezing hole groups DB (85) and the arc bottom of the area to be excavated is 13463mm, and the hole distance between every two adjacent outer ring freezing holes is 1200 mm;

11 outer ring freezing holes in the third row of outer ring freezing hole group DB (86) are distributed at equal intervals in the horizontal direction, and one outer ring freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L15 between a straight line formed by connecting the freezing hole groups DB (86) of the third row of outer ring and the arc bottom of the area to be excavated is 13760mm, and the hole distance between every two adjacent outer ring freezing holes is 1200 mm;

10 outer ring freezing holes in the fourth row of outer ring freezing hole groups DB (87) are distributed at equal intervals in the horizontal direction; the vertical distance L16 between a straight line formed by connecting the fourth row of outer ring freezing hole groups DB (87) and the arc bottom of the area to be excavated is 14163mm, and the hole distance between every two adjacent outer ring freezing holes is 1200 mm;

11 outer ring freezing holes in the fifth row outer ring freezing hole group DB (88) are distributed at equal intervals in the horizontal direction, and one outer ring freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L17 between a straight line formed by connecting the freezing hole groups DB (88) of the outer ring of the fifth row and the arc bottom of the area to be excavated is 14463mm, and the hole distance between every two adjacent freezing holes of the outer ring is 1200 mm.

5. The system of claim 3, wherein the freezing holes of the frozen soil curtain are arranged on the longitudinal section of the area to be excavated as follows:

the pressure relief holes in the pressure relief hole group X (6) are distributed at equal intervals in the horizontal direction, the hole distance between every two adjacent pressure relief holes is 1500mm, and the vertical distance L1 between each pressure relief hole and the arc top of the area to be excavated is 4540 mm;

the heating holes in the heating hole group DJ (7) are distributed at equal intervals along the arc of the same heating hole group, the hole interval between every two adjacent heating holes is 1500mm, the arc top of the arc of the heating hole group and the arc top of the area to be excavated are on the same vertical line, the distance between the arc top and the area to be excavated is 3500mm, and the longitudinal distances L2 from any point on the arc of the heating hole group to the arc on which the upper edge of the area to be excavated is located are equal;

15 outer ring freezing holes in the outer ring freezing hole group D (81) are distributed along the same outer ring freezing hole group arc, the hole distance between every two adjacent outer ring freezing holes is 800mm, 1 outer ring freezing hole is distributed at the arc top of the outer ring freezing hole group arc, 6 outer ring freezing holes with equal intervals are respectively distributed from the arc top of the outer ring freezing hole group arc to two sides, one outer ring freezing hole is respectively arranged at the end point of the outer ring freezing hole group arc, and two outer ring freezing holes respectively positioned at two sides of the outer ring freezing hole group arc are distributed on a horizontal line between the last outer ring freezing hole and the last but one outer ring freezing hole at the tail end of the outer ring freezing hole group arc; the arc top of the outer ring freezing hole group arc and the arc top of the area to be excavated are on the same vertical line, the distance between the arc top and the area to be excavated is 2400mm, and the longitudinal distance L3 from any point on the outer ring freezing hole group arc to the arc on which the upper edge of the area to be excavated is located is equal;

8 outer ring auxiliary freezing holes in the outer ring auxiliary freezing hole group DN (91) are distributed on the same outer ring auxiliary freezing hole group arc at equal intervals, and the hole interval between every two adjacent outer ring auxiliary freezing holes is 1200 mm; the other 2 outer ring auxiliary freezing holes are respectively distributed near the tail ends of the outer ring auxiliary freezing hole group arcs and located between the outer ring auxiliary freezing hole group arcs and the outer ring freezing hole group arcs, the arc tops of the outer ring auxiliary freezing hole group arcs and the arc tops of the to-be-excavated area are on the same vertical line, the distance between the arc tops and the arc tops of the to-be-excavated area is 877mm, and the longitudinal distances L4 from any point on the outer ring auxiliary freezing hole group arcs to the arcs where the upper edges of the to-be-excavated area are located are equal;

in the area to be excavated: a first pressure relief hole group X (61) consisting of 2 pressure relief holes, a first interface strengthening freezing hole group G (101) consisting of 9 interface strengthening freezing holes, a second pressure relief hole group X (62) consisting of 2 pressure relief holes, a second interface strengthening freezing hole group G (102) consisting of 5 interface strengthening freezing holes, a third interface strengthening freezing hole group G (103) consisting of 9 interface strengthening freezing holes, a fourth interface strengthening freezing hole group G (104) consisting of 5 interface strengthening freezing holes and a third pressure relief hole group X (63) consisting of 2 pressure relief holes are sequentially distributed from top to bottom;

2 pressure relief holes in the first pressure relief hole group X (61) are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, the vertical distance L5 between each pressure relief hole and an arc top of the area to be excavated is 3924mm, and the hole distance between every two 2 pressure relief holes is 3000 mm;

9 interface strengthening freezing holes in the first interface strengthening freezing hole group G (101) are distributed at equal intervals along the horizontal direction, and one interface strengthening freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L51 between a straight line formed by the first interface strengthening freezing hole group G (101) and the arc top of the area to be excavated is 7742mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1230 mm;

2 pressure relief holes in the second pressure relief hole group X (62) are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, the vertical distance L7 between each pressure relief hole and an arc top of the area to be excavated is 9522mm, and the hole distance between every two 2 pressure relief holes is 3000 mm;

5 interface reinforcing freezing holes in the second interface reinforcing freezing hole group G (102) are formed and are distributed on two sides of the longitudinal central axis of the area to be excavated at equal intervals along the horizontal direction; the vertical distance L6 between a straight line formed by connecting the second interface strengthening freezing hole groups G (102) and the arc top of the area to be excavated is 9742mm, and the hole distance between every two adjacent interface strengthening freezing holes is 2000 mm;

9 interface strengthening freezing holes in the third interface strengthening freezing hole group G (103) are distributed at equal intervals along the horizontal direction, and one interface strengthening freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L8 between a straight line formed by connecting the third interface strengthening freezing hole group G (103) and the arc top of the area to be excavated is 12742mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1230 mm;

5 interface reinforcing freezing holes in the fourth interface reinforcing freezing hole group G (104) are formed and are distributed on two sides of the longitudinal central axis of the area to be excavated at equal intervals along the horizontal direction; the vertical distance L9 between a straight line formed by the fourth interface strengthening freezing hole group G (104) and the arc top of the area to be excavated is 13342mm, and the hole distance between every two adjacent interface strengthening freezing holes is 1700 mm;

2 pressure relief holes in the third pressure relief hole group X (63) are symmetrically distributed on two sides of a longitudinal central axis of the area to be excavated along the horizontal direction, and the vertical distance L10 between each pressure relief hole and the arc top of the area to be excavated is 13501 mm; the hole spacing between 2 pressure relief holes is 3000 mm; a first column of outer ring auxiliary freezing hole groups DN (92) consisting of 9 outer ring auxiliary freezing holes are distributed on the edge lines on the two sides of the area to be excavated along the longitudinal direction;

below the area to be excavated: a third row of outer ring freezing hole group DB (86) consisting of 11 outer ring freezing holes, a fourth row of outer ring freezing hole group DB (87) consisting of 10 outer ring freezing holes, a fifth row of outer ring freezing hole group DB (88) consisting of 11 outer ring freezing holes and a sixth row of outer ring freezing hole group DB (89) consisting of 10 outer ring freezing holes are sequentially distributed from top to bottom;

11 outer ring freezing holes in the third row of outer ring freezing hole group DB (86) are distributed at equal intervals in the horizontal direction, and one outer ring freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L15 between a straight line formed by connecting the third row of outer ring freezing hole groups DB (86) and the arc bottom of the area to be excavated is 14908mm, and the hole distance between every two adjacent outer ring freezing holes is 1197 mm;

10 outer ring freezing holes in the fourth row of outer ring freezing hole groups DB (87) are distributed at equal intervals in the horizontal direction; the vertical distance L16 between a straight line formed by connecting the fourth row of outer ring freezing hole groups DB (87) and the arc bottom of the area to be excavated is 15308mm, and the hole distance between every two adjacent outer ring freezing holes is 1189 mm;

11 outer ring freezing holes in the fifth row outer ring freezing hole group DB (88) are distributed at equal intervals in the horizontal direction, and one outer ring freezing hole is positioned on the longitudinal central axis of the area to be excavated; the vertical distance L17 between a straight line formed by connecting the freezing hole groups DB (88) of the outer ring of the fifth row and the arc bottom of the area to be excavated is 15608mm, and the hole distance between every two adjacent freezing holes of the outer ring is 1197 mm;

10 outer ring freezing holes in the sixth row of outer ring freezing hole groups DB (89) are distributed at equal intervals in the horizontal direction; the vertical distance L18 between a straight line formed by connecting the outer ring freezing hole groups DB (89) in the sixth row and the arc bottom of the area to be excavated is 15911mm, and the hole distance between every two adjacent outer ring freezing holes is 1189 mm;

a first row of outer ring freezing hole group DB (84) consisting of 8 outer ring freezing holes and a second row of outer ring freezing hole group DB (85) consisting of 10 outer ring freezing holes are distributed on the bottom edge line of the region to be excavated from top to bottom; the outer ring freezing holes in the first row of outer ring freezing hole groups DB (84) are distributed at equal intervals in the horizontal direction, and the vertical distance from a straight line formed by connecting the first row of outer ring freezing hole groups DB (84) to a straight line formed by connecting the third row of outer ring freezing hole groups DB (86) is L11; the outer ring freezing holes in the second row outer ring freezing hole group DB (85) are distributed at equal intervals in the horizontal direction, and the vertical distance from a straight line formed by connecting the second row outer ring freezing hole group DB (85) to a straight line formed by connecting the third row outer ring freezing hole group DB (86) is L12.

6. The combined enclosing system of the frozen wall and the cement reinforcement body in the large-section tunnel construction is characterized in that the cement reinforcement body is a cement grouting area (4), the tunnel face (3) of the large-section tunnel to be excavated consists of two or more small-section tunnel faces (5) to be excavated which are sequentially arranged from top to bottom, and the cement grouting area (4) is positioned in front of the small-section tunnel faces (5) to be excavated; and in the excavation process of the cement grouting area (4), one part is arranged every 10m along the excavation direction of the small-section tunnel face (5) to be excavated.

7. An excavation method for a freezing wall and cement reinforcement combined enclosure system in large-section tunnel construction is characterized by comprising the following steps:

and B: after the active freezing is finished, performing primary horizontal grouting in the surrounding rock 10m away from the small-section face (5) to be excavated to form the cement reinforced body;

8. The excavation method for the building envelope system combining the frozen wall and the cement reinforcement body in the large-section tunnel construction according to claim 7, wherein in the step B, the construction area to be excavated into the large section is sequentially divided into 4 excavation areas of a first step, a second step, a third step and a fourth step from top to bottom according to the arrangement rule of the frozen holes, and each excavation area is excavated horizontally;

dividing the active freezing into a first stage freezing and a second stage freezing; the first-stage freezing comprises freezing two excavation areas of the first step and the second step; the second-stage freezing comprises freezing two excavation areas of the third step and the fourth step; the second-stage freezing is construction after the excavation of the second step excavation area is finished;

the first-stage freezing adopts a cylindrical freezing mode of a reversed Y-shaped straight wall arc top bottom, and the frozen first-stage freezing and reinforcing area (1) comprises a first upper freezing wall (11), a first bottom middle clapboard freezing wall (12), a first side wall freezing wall (13) and a first middle clapboard freezing wall (14); the first upper freezing wall (11), the first bottom middle partition freezing wall (12), the first side wall freezing wall (13) and the first middle partition freezing wall (14) extend towards a non-excavation region along a small-section tunnel face (5) to be excavated; the second-stage freezing adopts a cylindrical freezing mode with a right-angled straight wall and an arc bottom, and the frozen second-stage freezing and reinforcing area (2) comprises a second upper freezing wall (21), a second bottom freezing wall (22), a second side wall freezing wall (23) and a second middle clapboard freezing wall (24); the second upper freezing wall (21) is connected to the first bottom intermediate diaphragm freezing wall (12) of the first stage freezing consolidation zone (1); the second upper freezing wall (21), the second bottom freezing wall (22), the second side wall freezing wall (23) and the second middle partition plate freezing wall (24) extend towards the non-excavation area along the small-section tunnel face (5) to be excavated.

9. The excavation method for the building envelope system combining the frozen wall and the cement reinforced body in the large-section tunnel construction according to claim 8, wherein the step C comprises the following steps:

step (C-11) excavation of a first step: carrying out sectional horizontal excavation after horizontal grouting is carried out every 10m in sequence, and supporting along with excavation until the primary support of the first step is completely finished; then, carrying out horizontal grouting reinforcement after the first step is excavated to the end head so as to finish the reinforcement of the tail end of the first step; after the excavation of the first step is completely finished: a first middle partition plate is installed in the first step in a construction mode, and a vertical grouting hole is constructed in the excavation space of the first step to perform grouting, end sealing and reinforcing on a region to be excavated of the second step;

10. The excavation method for the building envelope system combining the frozen wall and the cement reinforcement body in the large-section tunnel construction according to claim 7, wherein in the step B, the construction area to be excavated into the large section is sequentially divided into 3 excavation areas of a first step, a second step and a third step from top to bottom according to the arrangement rule of the frozen holes, and each excavation area is excavated horizontally;

after the positive freezing is finished, the formed frozen soil curtain is a mesh-shaped circular arc top-bottom frozen wall, and a third freezing and reinforcing area (30) is enclosed by the circular arc top-bottom frozen wall; the third freeze reinforcement zone (30) comprises a third upper freeze wall (301), a third bottom freeze wall (302), a third side freeze wall (303), a third middle diaphragm freeze wall a (304), and a third middle diaphragm freeze wall B (305); the third upper frozen wall (301), the third bottom frozen wall (302), the third side frozen wall (303), the third middle clapboard frozen wall A (304) and the third middle clapboard frozen wall B (305) extend to a non-excavation region along a small-section tunnel face (5) to be excavated;

step C can be divided into the following steps:

step (C-21) excavation of a first step: carrying out sectional horizontal excavation after horizontal grouting is carried out every 10m in sequence, and supporting along with excavation until the primary support of the first step is completely finished; then, carrying out horizontal grouting reinforcement after the first step is excavated to the end head so as to finish the reinforcement of the tail end of the first step; after the excavation of the first step is completely finished: a third middle partition plate A is installed in the first step in the construction process, and a vertical grouting hole is constructed in the excavation space of the first step to perform grouting, end sealing and reinforcement on the to-be-excavated area of the second step;