CN113202106B

CN113202106B - Deep foundation pit excavation method

Info

Publication number: CN113202106B
Application number: CN202110412852.1A
Authority: CN
Inventors: 夏瑞萌; 娄海成; 郑杰; 代永双; 张小伟; 王力勇; 李星烨; 张一川; 李俊峰; 刘东天
Original assignee: Beijing Urban Construction Design and Development Group Co Ltd
Current assignee: Beijing Urban Construction Design and Development Group Co Ltd
Priority date: 2021-04-16
Filing date: 2021-04-16
Publication date: 2022-03-29
Anticipated expiration: 2041-04-16
Also published as: CN113202106A

Abstract

A deep foundation pit excavation method comprises the following steps: step one, constructing a foundation pit locking collar beam structure system, and step two: and (3) excavating by the blocking and dividing method to form a single-time footage excavation finished surface, and the third step: constructing a first horizontal annular supporting structure, and performing the fourth step: constructing a subsequent horizontal annular supporting structure, and performing the following steps: forming a vertical supporting structure, and a sixth step: utilizing the non-stressed vertical gap between the two annular horizontal supporting structures adjacent to each other up and down to punch an advance supporting structure, and realizing hole entering under the supporting condition, and the seventh step: based on a vertical supporting system consisting of a reinforcement cage and a square steel concrete structure, the conversion from a horizontal annular supporting bearing mode in a foundation pit excavation stage to a vertical supporting bearing mode in a secondary lining pouring stage is realized, and the return construction of a permanent secondary lining structure is facilitated; therefore, the invention can improve the defects that the supporting and retaining type supporting structure is difficult to realize the hidden excavation and hole entering of the foundation pit in the supporting and retaining state, is not favorable for advanced supporting construction, is not favorable for the control of hidden excavation section risks and is difficult to construct adjacent underground sensitive facilities, and also carries out better innovation aiming at the unsafe state that the foundation pit is not supported in the construction stage of the permanently stressed secondary lining structure of the method for inversely hanging the well wall or the difficult guarantee of multiple durability of secondary lining pouring construction joints.

Description

Deep foundation pit excavation method

Technical Field

The invention relates to the technical field of underground space construction, in particular to a deep foundation pit excavation method.

Background

With the enhancement of comprehensive national force of China, underground spaces of large and medium-sized cities in China are developed and utilized in a large range, so that a large number of excavation methods are developed in the process of constructing the underground spaces. The open cut method is most widely used in the construction of underground spaces because of its safety, economical efficiency of construction costs, and wide application range. In the construction process of basic facilities such as basement excavation of civil buildings, rail transit stations, comprehensive pipe galleries and the like, the figure of the basic facilities can be seen everywhere. The open cut method has various excavation modes, wherein the research on the excavation method of the deep foundation pit is always a hotspot of the industry.

According to the requirements of the construction quality of the Ministry of construction [ 2018 ] 31 document, namely the notice of the related problems about the implementation of the safety management rule of the project of the high-risk subsection of the Ministry of urban and rural construction of housing in the office of the Ministry of construction: the general deep foundation pit refers to a project with the excavation depth of more than 5 meters (including 5 meters), more than three layers (including three layers) of a basement, or the excavation depth of less than 5 meters, but the geological conditions, the surrounding environment and underground pipelines are particularly complex.

When foundation pit engineering is constructed in urban environment, because a large number of underground important facilities such as water pressure pipelines, rail transit and the like are distributed in an excavation influence area of the foundation pit, a foundation pit supporting structure can only be constructed by adopting a supporting and retaining type supporting structure. The commonly adopted supporting mode comprises a pile (wall) + anchor cable structure, a pile (wall) + inner supporting structure (steel structure support or concrete structure support), a cantilever type supporting structure and a reverse construction method structure. The specific method comprises the following steps:

pile (wall) and anchor cable structure

The method can be suitable for deep foundation pits with any depth, and is usually adopted under the condition that the width of the foundation pit is large and the inner support is inconvenient to construct. The construction step sequence is as follows: the construction method comprises the steps of leveling a site → constructing piles (walls) on large-scale machinery (rotary drilling rigs, trenching machines and the like), constructing a crown beam → excavating to 500mm below the crown beam, constructing a first anchor cable → excavating to 500mm below a second anchor cable, constructing a waist beam, constructing a second anchor cable → excavating sequentially until the bottom of a pit → constructing a cushion layer and preventing water, building bricks and backfilling fertilizer grooves, and sequentially constructing pouring → earthing, backfilling the upper part and recovering the pavement. The construction method is widely applied to wide and large urban foundation pits, such as deep and large foundation pits of high-rise buildings and deep and large foundation pits of subways. The main stress structure is a vertical (vertical natural terrace direction) pile (wall), and the anchor cable in the horizontal direction and the waist beam form a constraint structure of the vertical pile (wall), so that the stress span of the pile (wall) is reduced, and the purposes of reducing the thickness of the pile (wall) and saving the engineering investment are achieved.

Pile (wall) and inner supporting structure

The method can be suitable for deep foundation pits with any depth, and is usually adopted when the requirement on foundation pit deformation control is high. The application method comprises the following steps: leveling a field → driving piles (walls) by large-scale machinery (rotary drilling rigs, trenching machines and the like), constructing a crown beam → excavating first-layer soil, erecting a first support on the crown beam → excavating second-layer soil, constructing a waist beam, erecting a second support → excavating sequentially until the bottom of a pit → constructing a cushion layer and preventing water, pouring a bottom plate → dismantling supports from bottom to top, constructing each layer of floor slabs and side walls → sealing the top of a structure, and covering soil and backfilling the top. The construction method is widely applied to wide and large urban foundation pits, such as deep and large high-rise building foundation pits close to pipelines and deep and large subway foundation pits close to pipelines. The main stress structure is a vertical pile (wall) perpendicular to the natural terrace direction, and the horizontal inner support and the waist beam (sometimes no waist beam) form a constraint structure of the vertical pile (wall), so that the stress span of the pile (wall) is reduced, and the purposes of reducing the thickness of the pile (wall) and saving the engineering investment are achieved.

Cantilever type supporting structure

The method is mainly suitable for deep foundation pits with small depth, and is usually adopted when the foundation pits are limited by the environment and cannot be used for slope releasing. Leveling a field → piling piles (walls) of large-scale machinery (rotary drilling rigs, trenching machines and the like) → excavating to the bottom of a pit once → constructing a cushion layer, pouring a structure from bottom to top → capping → backfilling soil above. The construction method is applied to a certain extent in wide and large foundation pits in cities, but the deformation control capability of the construction method is relatively poor, and when deformation sensitive facilities exist at the periphery, the construction method can be generally used for converting anchor cables or inner support structures into pile (wall) + inner support structures or pile (wall) + anchor cable structures. The main stress structure is a vertical pile (wall) perpendicular to the natural terrace.

Structure of four, reverse construction method

When the geological environment of the excavation position of the foundation pit is poor, the depth of the foundation pit is deep, and deformation sensitive facilities such as rail transit exist, the reverse construction method is generally adopted. The construction steps are as follows: the method comprises the steps of field leveling → large machinery (rotary drilling rigs, trenching machines and the like) driving side piles (walls), middle columns and temporary pile foundations under the columns → excavating soil to 500mm below a structural top plate, constructing the top plate, backfilling and covering soil and recovering ground roads → excavating to 500mm below an underground first-layer bottom plate under the support of the top plate, constructing the underground first-layer bottom plate and side walls → excavating to 500mm below an underground second-layer bottom plate, constructing the underground second-layer bottom plate and side walls → excavating to the bottom of a pit in sequence → constructing a cushion layer, and pouring the bottom plate and the side walls to connect with an upper structure to form a complete structure. The construction method has certain application in wide and large foundation pits in cities, has the best deformation control capability, but has higher construction cost, and is generally used in complicated foundation pit engineering. The stress form is complex compared with the structure, a composite stress system is formed by a temporary structure and a permanent structure, and the main stress structure is a vertical temporary pile (temporary wall) perpendicular to the natural terrace direction, a permanent structure wall and a horizontal permanent plate structure plate.

In recent years, the following new problems appear in underground engineering construction of China:

1. in the first-line cities of Beijing and the like, problems of broken circuit construction, traffic, pipeline guide and modification and the like caused by underground space construction are increasingly not accepted by the modern large-scale cities, and the adaptability of the open cut method is gradually reduced. The construction of underground space in four rings by taking Beijing as an example has already entered the era of 'energy in light and dark'. The underground excavation engineering needs to carry out underground excavation construction by means of a small open excavation foundation pit, the open excavation foundation pit is usually arranged at a position which does not affect underground facilities such as traffic, pipelines and the like, and the open excavation foundation pit is used as an unearthed feeding channel for underground excavation. In the design and use of the foundation pit, in order to facilitate the hidden excavation, the hole entering, the safety improvement of the hidden excavation section and the engineering investment saving, the foundation pit is usually designed into an annular (parallel to the natural terrace direction) stressed inverted well wall structure. The construction steps are generally as follows: leveling the field → constructing a collar tie beam and a retaining wall → excavating downwards for 0.5m (generally manually), annularly laying grids and utilizing vertical tie bars to tie with the crown beam, spraying concrete → -continuing excavating downwards for 0.5m, annularly laying grids and utilizing vertical tie bars to tie with the crown beam → repeatedly excavating downwards and supporting layer by layer until bottom sealing → excavating the ingate to enter the hole and excavating underground. Because the annular stress structure is adopted, the construction of advanced support measures such as advanced small guide pipes, large pipe sheds, pipe curtains and the like is facilitated, and the safety of construction of the underground excavation section can be greatly improved. Particularly, under the condition of constructing large-scale advance supports (large pipe sheds and pipe curtains), the construction method has the advantages that the former four support structure forms can not be replaced (other four structures have vertical main stress components, and the construction of the horizontal advance supports can cause the truncation of a vertical main stress system, so that the overall safety of foundation pit engineering is influenced).

Years of engineering construction practice proves that the safety of entering the hole is far higher than that of the first four supporting structure forms under the supporting state of the foundation pit due to the characteristic of annular stress of the inverted well wall structure. Particularly, in the case of entering a large hole, the four supporting structures are difficult to complete. And the entering of the hole under the foundation pit supporting state can save the construction period of the project (the entering of the hole under the foundation pit supporting state reduces the working procedure of the two-lining construction and the time for occupying the total construction period), is convenient for the construction and the quality of the two-lining structure, and has great advantages and irreplaceability under the condition of short construction period of the project. Moreover, the underground sensitive facilities can be better protected. The traditional support piles and underground continuous walls are all constructed by large-scale machinery, non-excavation construction is carried out on the ground by the large-scale machinery, construction errors are difficult to avoid, and the cutting force of the large-scale machinery is large, so that the safety of sensitive facilities such as underground pipelines can be ensured by a certain safety distance from the sensitive facilities such as pipelines. Along with the urbanization construction of China, the urban underground space environment is increasingly complex, cases of small-clear-distance and ultra-small-clear-distance construction in large cities such as Beijing and the like are increased, and in order to ensure the safety of sensitive facilities such as adjacent underground pipelines and the like in construction, a large number of foundation pits are constructed by adopting an inverted well wall method. The underground pipeline underground mining artificial excavation method has the advantages that the artificial excavation can be adopted near the sensitive facilities, the disturbance to the soil body and the sensitive facilities is small, the positions of the sensitive facilities such as the adjacent underground pipelines can be clearly distinguished, the effective protection can be realized, and the problem of mistaken collision caused by unclear reconnaissance can be avoided.

However, with the large number of applications of the inverted well wall method, the disadvantages become more and more prominent. When a permanent two-lining stress structure is applied in the foundation pit of the inverted well wall, the horizontal ring of the inverted well wall structure is stressed and each ring forms a stress system, and the structural (stress) conversion of the two-lining and the primary support is difficult to complete. The vertical interval of selecting for use 0.5m ~0.75m usually of hanging wall of a well structure upside down, the level is usually not more than 4.0m ~4.5m to the span, if need the safety guarantee to return the safety of building the stage, has following three kinds of modes in the reality application:

(1) the permanently stressed secondary lining structure is vertically constructed by 0.5-0.75 m each time, so that the durability of a plurality of construction joints of the secondary lining structure is difficult to guarantee, and the engineering construction period is multiplied.

(2) And (3) completing the structure (horizontally 4.0-4.5 m) in each small partition, and then removing the supporting structure to complete the connection of the permanent structure. This also results in the difficulty in ensuring the durability of the multiple construction joints of the two-lining structure, and the horizontally completed two-lining structure usually has no self-supporting property, so that the structural safety can be ensured by arranging a large number of temporary support structures.

(3) To reduce a large number of construction joints, to ensure durability and to improve construction speed. And (4) the construction unit automatically removes the supporting structure in a certain area, and a secondary lining structure is constructed under the condition. The durability and convenience of the second lining construction are greatly improved, but the foundation pit supporting structure can be in an unsafe state in a state that the supporting structure is dismantled, and great potential safety hazards exist.

Therefore, in view of the above-mentioned drawbacks, the present inventors have conducted extensive research and design to overcome the above-mentioned drawbacks by developing and designing a deep excavation method based on the experience and results of the related industries for many years.

Disclosure of Invention

The invention aims to provide a deep foundation pit excavation method which can be improved aiming at the defects that a retaining type supporting structure is difficult to realize the hidden excavation and hole entry of a foundation pit in a supporting state, is not favorable for advanced supporting construction, is not favorable for controlling the risk of a hidden excavation section and is difficult to construct adjacent underground sensitive facilities, and is also better innovated aiming at the defects that the multiple durability of construction joints in the construction stage of a permanently stressed secondary lining structure of an inverted well wall method is difficult to ensure or the supporting state of the foundation pit is unsafe.

In order to achieve the aim, the invention discloses a deep foundation pit excavation method which is characterized by comprising the following steps:

constructing a foundation pit fore shaft ring beam structure system, constructing an fore shaft ring beam and a retaining wall on the ground to serve as a foundation before the foundation pit is not closed, reserving a first square steel structure in the fore shaft ring beam, and erecting a first channel of section steel inner support structure at the fore shaft ring beam to ensure the horizontal stability of the foundation pit;

step two: determining a foundation pit excavation footage and excavating to an excavation completion surface, determining the excavation footage of the foundation pit according to stratum conditions and conditions of sensitive facilities needing to be protected underground at the periphery of the foundation pit, excavating a planar central soil body of the foundation pit firstly, excavating after approaching a side wall soil body of the foundation pit, adopting mechanical excavation or manual excavation for the planar central soil body, and adopting manual excavation for the side wall soil body so as to form an excavation working surface;

step three: constructing a first horizontal circumferential supporting structure, erecting and sealing the first horizontal circumferential supporting structure below the fore shaft ring beam after excavating to a single-layer footage excavation completion surface, wherein the first horizontal circumferential supporting structure consists of a first soil facing supporting structure and a profile steel inner supporting structure, the first soil facing supporting structure is connected in a horizontal circumferential direction of a first square steel structure, and the first profile steel inner supporting structure is erected to form the first horizontal circumferential supporting structure;

step four: constructing a subsequent horizontal supporting structure, wherein after the first horizontal supporting structure in the third step is closed, soil is continuously excavated according to the mode in the second step, after the soil is excavated to the surface where the single excavation footage is finished, a second horizontal circumferential supporting structure is erected, the second square steel structure is longitudinally spliced with the first square steel structure in the third step, a second soil-facing supporting structure of the second horizontal circumferential supporting structure is constructed in the horizontal direction of the second square steel structure, and the second horizontal circumferential supporting structure is constructed according to the mode in the third step, so that a second horizontal circumferential supporting structure similar to the first horizontal circumferential supporting structure is formed, construction is continuously carried out, the 3 rd, 4 th, 5 th, 6 th to nth horizontal circumferential supporting structures are sequentially completed until the bottom of the pit is closed;

step five: placing a small reinforcement cage in a first square steel structure reserved on the fore shaft ring beam, and pouring concrete in a vertical space formed by sections of the first square steel structure and a second square steel structure to form a vertical supporting structure;

step six: the method has the advantages that the prestressed vertical gap between the two annular horizontal supporting structures which are adjacent up and down is utilized to drive the advanced supporting structure, the safety of underground excavation of the tunnel under the protection of the underground excavation tunnel supporting structure is better guaranteed, and the tunnel is entered under the supporting condition;

step seven: and the permanent secondary lining structure is built again based on a vertical supporting system formed by the steel reinforcement cage and the square steel concrete structure.

Wherein: in the first step, the first square steel structures are arranged in the peripheral locking collar beams at intervals, and the first channel section steel inner supporting structure comprises a plurality of straight supports arranged in the middle and inclined supports positioned at the corners.

Wherein: the tip welding of directly propping is to first party steel construction, the tip welding of bracing is to first party steel construction or face native supporting construction to form holistic firm support.

Wherein: the side of the first party steel structure is fixed through a plurality of studs, the end part of the first channel of steel support is welded and fixed to the first party steel structure through a welding steel plate, and the lower end of the fore shaft ring beam is provided with a cushion layer.

Wherein: the length of the first square steel structure and the length of the second square steel structure in the direction perpendicular to the ground are taken as the length of an excavation step pitch plus the length of a two-way lap joint, and the first square steel structure and the second square steel structure adopt different model sizes to play the role of longitudinal splicing and positioning.

Wherein: the first square steel structure and the second square steel structure are correspondingly provided with bolt holes so as to be fastened and connected with the first square steel structure and the second square steel structure through fastening bolts, and built-in transverse clapboards are arranged in the first square steel structure and the second square steel structure.

Wherein: the first concrete facing supporting structure is of a steel structure or a steel bar grating structure, concrete or an exposed steel structure is sprayed when the steel structure is adopted, and concrete is sprayed when the steel bar grating structure is adopted.

Wherein: the second road faces the soil supporting construction and adopts steel construction or steel bar grating structure, sprays concrete or naked steel construction when adopting the steel construction, sprays concrete when adopting steel bar grating structure.

Wherein: and erecting the profile steel inner supporting structure after the second soil supporting structure is completed.

Wherein: removing the inner support interfering with the second lining structure, pouring second lining concrete, removing the section steel inner support interfering with the underground first-layer structure, pouring the second lining concrete until the top is closed, removing the rest support above the top plate, chiseling off the crown beam and the like, backfilling and covering soil, and recovering the ground.

According to the above contents, compared with the traditional open-cut deep foundation pit, the deep foundation pit excavation method provided by the invention has the following effects:

1. the deep foundation pit excavation method provided by the invention adopts manual excavation of the soil body on the side wall, the horizontal annular supporting structure of the adjacent soil on the basis adopts manual construction, and compared with the traditional supporting and retaining type supporting structure which adopts large-scale mechanical construction, the method has high construction precision and small influence on the surrounding environment, thereby realizing small-clear-distance construction of underground sensitive facilities such as pipelines and the like, effectively utilizing underground space resources and avoiding the migration and the change of the sensitive facilities such as the existing pipelines and the like.

2. The deep foundation pit excavation method provided by the invention adopts manual excavation of soil bodies on the soil facing side, and the soil facing supporting structure is manually constructed on the basis, compared with the large-scale mechanized construction of the traditional supporting and retaining type supporting structure, the deep foundation pit excavation method can accurately detect the underground environment in the excavation process, and avoids the damage to sensitive facilities such as pipelines when large-scale machinery is vertically operated on the ground under the condition that the sensitive facilities such as pipelines are not clearly surveyed.

3. Based on the characteristics of circumferential arrangement and circumferential bearing of the main stress structure, compared with the characteristics of vertical arrangement and vertical bearing of the main stress structure of the traditional retaining type supporting structure, the invention utilizes the non-stressed vertical gap between two horizontal circumferential supporting structures which are adjacent up and down, and is more beneficial to the construction of underground excavation advanced supporting measures, in particular to the construction of large-scale underground excavation advanced supporting measures. Compared with open excavation foundation pits constructed by a traditional supporting and retaining type supporting structure, the safety degree of the underground excavation part can be greatly improved.

4. The foundation pit constructed by the method is based on a vertical support system consisting of the reinforcement cage and the square steel concrete structure, the conversion from a horizontal annular support bearing mode in the excavation stage of the foundation pit to a vertical support bearing mode in the secondary lining pouring stage is realized, and compared with an inverted well wall method, the occurrence of an unsupported state of an adjacent soil support structure after the horizontal annular support is removed in the traditional secondary lining construction is effectively avoided, so that the safety of the foundation pit in the secondary lining pouring is greatly improved; meanwhile, the two-lining structure can be poured in one step, the number of construction joints is greatly reduced, and the durability and safety of the project are improved.

In conclusion, the foundation pit construction method provided by the invention absorbs the advantages of the traditional retaining type supporting structure and the inverted well wall structure. Compare its underground space resource of more practicing thrift of traditional fender formula supporting construction, be favorable to the safety protection of sensitive facilities such as underground pipeline, can avoid the migration of sensitive facilities such as underground pipeline to change simultaneously, can greatly promote the safety of undercut engineering in addition. Compare the wall of a well structure of hanging upside down, its degree of safety that can show the promotion foundation ditch effectively reduces the construction joint, very big promotion engineering's security and durability.

The details of the present invention can be obtained from the following description and the attached drawings.

Drawings

Figure 1 shows a cross-sectional view of the foundation pit support of the present invention.

Figure 2 shows a plan view of the foundation pit support of the present invention.

Figure 3A shows a plan view of a first square steel structure and a fore-and-aft collar beam in an excavation support.

FIG. 3B shows a cross-sectional view taken along line 1-1 of FIG. 3A.

Figure 4 shows a schematic view of an excavation face of the present invention.

Fig. 5 shows a schematic view of the present invention applied as a first horizontal soil-adjacent supporting structure.

Fig. 6 shows the connection scheme of fig. 5.

Figure 7 shows a schematic view of the construction of a second horizontal circumferential support structure.

Fig. 8 shows a schematic view of the construction of a subsequent horizontal supporting structure.

Figure 9 shows a schematic view of the excavation to the bottom.

Fig. 10 shows a schematic view of the reinforcement cage.

Figure 11 shows a schematic drawing of the undermining of the hole in support.

Fig. 12 shows an enlarged schematic view of point a in fig. 11.

Fig. 13 shows a schematic view of removing the inner support interfering with the secondary lining structure and casting the secondary lining concrete.

Fig. 14 shows a schematic view of removing the support structure in section steel interfering with the underground one-storey structure and pouring secondary lining concrete to the capping.

Figure 15 shows a schematic view of removing the remaining supports above the roof, chiseling off the crown beams etc, backfilling the earth and restoring the ground.

Reference numerals:

10. a ground surface; 11. a fore shaft collar beam; 111. a cushion layer; 12. retaining walls; 13. a first square steel structure; 131. a stud; 14. a first channel of section steel inner support structure; 141. welding a steel plate; 15. single excavation footage; 16. a planar central earth mass; 17. a sidewall soil mass; 18. excavating a finished surface; 19. a first soil-facing supporting structure; 20. a second square steel structure; 21. a second soil-facing supporting structure; 22. bolt holes; 23. fastening a bolt; 24. a diaphragm plate is arranged in the inner cavity; 25. a second channel of section steel inner support structure; 26. supporting an anchor rod; 27. a longitudinal connecting structure; 28. a pit bottom sealing structure; 29. a small reinforcement cage; 30. concrete; 31. a forepoling structure; 32. a supporting structure of the underground excavation tunnel; 33. entering a hole and excavating; 34. an unstressed vertical gap.

Detailed Description

Referring to the drawings, the deep foundation pit excavation method of the present invention is shown.

The deep foundation pit excavation method comprises the following steps:

step one, constructing a foundation pit fore shaft ring beam structure system, which specifically comprises the following steps: construct fore shaft collar tie beam 11 and barricade 12 on ground 10 to as the foundation basis before the foundation ditch is not sealed, guarantee the vertical stability of foundation ditch, reserve first party steel construction 13 (or similar shaped steel structure) in fore shaft collar tie beam 11 simultaneously, erect fore shaft inner bearing structure 14 of fore shaft collar tie beam department, guarantee foundation ditch horizontal stability, wherein, see fig. 1 and fig. 2, first party steel construction 13 sets up in the fore shaft collar tie beam for a plurality of and interval, fore shaft inner bearing structure 14 contains a plurality of stull that the middle part set up and is located the bracing in bight, the tip welding of stull is to first party steel construction 13, the tip welding of bracing is to first party steel construction or faces native supporting construction (steel bar grating) to form holistic firm support.

Referring to fig. 3A and 3B, the side surface of the first square steel structure 13 is fixed by a plurality of studs 131, the end of the first channel steel inner support structure 14 can be welded and fixed to the first square steel structure 13 by a welding steel plate 141, and the lower end of the fore shaft collar beam 11 is provided with a cushion layer 111.

Step two: determining the excavation footage of the foundation pit and excavating to form an excavation working surface, referring to fig. 4, determining the excavation footage 15 of the foundation pit according to the stratum condition and the condition of the sensitive facilities needing to be protected underground at the periphery of the foundation pit, wherein the preferable excavation footage can be 0.5-0.75 m, and a support anchor rod can be arranged before excavation when the peripheral soil layer is weak.

The planar central soil body 16 of the foundation pit is excavated firstly, and the sidewall soil body 17 close to the foundation pit is excavated later, wherein the planar central soil body 16 is excavated mechanically, and the sidewall soil body 17 needs to be excavated manually, so that an excavation completion surface 18 is formed.

Step three: and constructing a first horizontal supporting structure, and immediately erecting and sealing a first horizontal annular supporting structure below the locking collar beam by using a space-time effect after the foundation pit is excavated to the excavation finished surface 18 of the foundation pit, wherein the first horizontal annular supporting structure consists of a first soil facing supporting structure 19 and a profile steel inner supporting structure 25, and forms a supporting effect after the sealing is finished.

Referring to fig. 5 and 6, a first soil facing supporting structure 19 is connected to two horizontal circumferential sides of the first square steel structure 13, and a section steel inner supporting structure is erected to form a first horizontal circumferential supporting structure.

Step four: constructing a subsequent horizontal supporting structure, wherein after the first horizontal supporting structure in the third step is closed and reaches the design strength, soil is excavated continuously according to the second step, after the soil is excavated to the finished surface of the single excavation footage, a second horizontal circumferential supporting structure is erected, namely, the second square steel structure and the first square steel structure in the third step are longitudinally spliced (connected through fastening bolts), wherein the second square steel structure 20 (or similar steel structure) can be connected below the first square steel structure 13, a second soil-facing supporting structure 21 of the second horizontal circumferential supporting structure is constructed in the horizontal direction of the second square steel structure 20, the lengths of the first square steel structure 13 and the second square steel structure 20 in the vertical ground direction are the excavation step length + the two-way lap joint length (about 0.5 m), the first square steel structure 13 and the second square steel structure 20 adopt different models, so as to play a role in longitudinal splicing and positioning. The size of the square steel structure 13 and the square steel structure 20 is controlled to be convenient for assembling and not to form too large gaps, bolt holes 22 are correspondingly formed in the first square steel structure 13 and the second square steel structure 20, so that the first square steel structure 13 and the second square steel structure 20 are fastened and connected up and down through fastening bolts 23, built-in transverse partition plates 24 are arranged in the first square steel structure 13 and the second square steel structure 20, the second soil facing supporting structure 21 and the section steel inner supports 25 are constructed according to the third step, a second horizontal annular supporting structure similar to the first horizontal annular supporting structure is formed, construction is continued, the 3 rd, 4 th, 5 th, 6 th to nth horizontal annular supporting structures shown in the figure 8 are sequentially completed, and the construction is continued until the pit bottom and the pit bottom sealing structure 28 is completed, wherein the construction is shown in the figure 9.

Wherein, first road and second are faced native supporting construction and need satisfy following requirement: the first and second horizontal soil-facing supporting structures are of steel structures or steel bar grating structures. When the steel structure is adopted, concrete can be sprayed, and a bare steel structure can also be directly adopted (in this case, a necessary soil retaining structure is arranged outside the main stress structure, and the soil retaining structure can adopt a thin steel plate or a reinforcing mesh). When using a steel grid construction it is necessary to spray concrete.

Referring to fig. 7, after the second soil supporting structure 21 is completed, a section steel inner supporting structure 25 is erected in time, and the second soil supporting structure 21 may further be provided with supporting anchor rods 26 according to the stratum conditions.

Step five: referring to fig. 10, a small reinforcement cage 29 is placed in a first square steel structure 13 reserved on a fore shaft collar beam 11, and concrete 30 is poured in a vertical space formed by sections of the first square steel structure and a second square steel structure to form a vertical supporting structure 27. Vertical support should fully consider to the influence that closes on the pipeline, exists the condition with pipeline local conflict when the support, can adopt the mode of local shrink, on the basis of first square steel structure and second square steel structure, sets up other square steel structures.

Step six: referring to fig. 11 and 12, the advance supporting structure 31 is arranged by utilizing the unstressed vertical gap 34 between the upper and lower adjacent two ring supporting structures, the safety of the underground excavation 33 of the tunnel is better ensured under the protection of the underground excavation tunnel supporting structure 32, the tunnel is entered under the supporting condition, and the situation that two linings in the pit are poured is not needed to be waited, so that the construction period can be more effectively saved.

Step seven: based on a vertical supporting system consisting of a steel reinforcement cage and a square steel concrete structure, an interfered profile steel inner supporting structure is dismantled and built with a second lining in one step, in a stable supporting structure formed by a horizontal supporting structure and the vertical supporting system, the building of a permanent second lining structure is completed, namely, an inner support interfered with the second lining structure is dismantled, second lining concrete (see figure 13) is poured, the profile steel inner supporting structure interfered with an underground first-layer structure is dismantled, second lining concrete is poured to a top sealing (see figure 14), the rest supports above a top plate are dismantled, a crown beam is chiseled, earth covering is backfilled, and the ground is restored (see figure 15).

Therefore, the invention can effectively avoid the occurrence of the unsupported state of the adjacent soil supporting structure after the horizontal annular support is removed in the traditional inverted well wall method secondary lining construction, and greatly improves the safety of the foundation pit during secondary lining pouring; meanwhile, the two-lining structure can be poured in one step, and the number of construction joints is greatly reduced.

It should be apparent that the foregoing description and illustrations are by way of example only and are not intended to limit the present disclosure, application or uses. While embodiments have been described in the embodiments and depicted in the drawings, the present invention is not limited to the particular examples illustrated by the drawings and described in the embodiments as the best mode presently contemplated for carrying out the teachings of the present invention, and the scope of the present invention will include any embodiments falling within the foregoing description and the appended claims.

Claims

1. A deep foundation pit excavation method is characterized by comprising the following steps:

step four: constructing a subsequent horizontal supporting structure, wherein after the first horizontal supporting structure in the third step is closed, soil is continuously excavated according to the mode in the second step, after the soil is excavated to the surface where the single excavation footage is finished, a second horizontal circumferential supporting structure is erected, the second square steel structure is longitudinally spliced with the first square steel structure in the third step, a second soil-facing supporting structure of the second horizontal circumferential supporting structure is constructed in the horizontal direction of the second square steel structure, and the second horizontal circumferential supporting structure is constructed according to the mode in the third step, so that a second horizontal circumferential supporting structure which is the same as the first horizontal circumferential supporting structure is formed, construction is continuously carried out, the 3 rd, 4 th, 5 th, 6 th to nth horizontal circumferential supporting structures are sequentially completed until the pit bottom and the pit bottom closed structure is completed;

step seven: finishing the back construction of a permanent two-lining structure based on a vertical supporting system consisting of a steel reinforcement cage and a square steel concrete structure;

wherein, first party steel construction and second square steel structure are got for excavation step length + two-way overlap joint length at the length of perpendicular ground direction, and first party steel construction and second square steel structure adopt different model sizes in order to play the effect of vertical concatenation location, correspond on first party steel construction and the second square steel structure to be equipped with the bolt hole in order to carry out the upper and lower fastening connection of first party steel construction and second square steel structure through fastening bolt, and be equipped with built-in cross slab in first party steel construction and the second square steel structure.

2. The method of excavating a deep foundation pit according to claim 1, wherein: in the first step, the first square steel structures are arranged in the peripheral locking collar beams at intervals, and the first channel section steel inner supporting structure comprises a plurality of straight supports arranged in the middle and inclined supports positioned at the corners.

3. The method of excavating a deep foundation pit according to claim 2, wherein: the tip welding of directly propping is to first party steel construction, the tip welding of bracing is to first party steel construction or face native supporting construction to form holistic firm support.

4. The method of excavating a deep foundation pit according to claim 3, wherein: the side of the first party steel structure is fixed through a plurality of studs, the end part of the first channel of steel support is welded and fixed to the first party steel structure through a welding steel plate, and the lower end of the fore shaft ring beam is provided with a cushion layer.

5. The method of excavating a deep foundation pit according to claim 1, wherein: the first concrete facing supporting structure is of a steel structure or a steel bar grating structure, concrete or an exposed steel structure is sprayed when the steel structure is adopted, and concrete is sprayed when the steel bar grating structure is adopted.

6. The method of excavating a deep foundation pit according to claim 1, wherein: the second road faces the soil supporting construction and adopts steel construction or steel bar grating structure, sprays concrete or naked steel construction when adopting the steel construction, sprays concrete when adopting steel bar grating structure.

7. The method of excavating a deep foundation pit according to claim 1, wherein: and erecting the profile steel inner supporting structure after the second soil supporting structure is completed.

8. The method of excavating a deep foundation pit according to claim 1, wherein: removing the inner support interfering with the second lining structure, pouring second lining concrete, removing the section steel inner support interfering with the underground first-layer structure, pouring the second lining concrete until the top is closed, removing the rest support above the top plate, chiseling off the crown beam, backfilling and covering soil, and recovering the ground.