CN115710916A - Loose stratum tunnel portal slope protection structure and design method - Google Patents
Loose stratum tunnel portal slope protection structure and design method Download PDFInfo
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Abstract
The invention relates to a slope protection structure of a tunnel portal in a unconsolidated formation and a design method thereof, wherein the structure comprises vertical pre-reinforcing piles which are arranged at two sides of a tunnel portal and extend into a stable mountain; the ring beam is arranged at the top of the tunnel portal and is rigidly connected to the vertical pre-reinforcing pile; the horizontal reinforcing piles are arranged at the top of the tunnel, and horizontally extend into the stable mountain from the slope surface of the unconsolidated formation; the plurality of groups of prestressed anchor cables are arranged on the horizontal reinforcing pile, each group of prestressed anchor cables comprises a plurality of prestressed anchor cables, and two adjacent groups of prestressed anchor cables are arranged vertically at intervals; and the minimum distance D between the end part of the anchoring section of the bottom row of anchor cables in the lowest group of prestressed anchor cables and the boundary of the top of the tunnel is not less than the tunnel diameter. The method solves the problem of integral stability of the slope, solves the problem of a reinforcing blind area of a traditional reinforcing measure in a shallow buried area at the top of the tunnel, and avoids top collapse and collapse during construction and operation of the shallow buried section at the tunnel opening.
Description
Technical Field
The invention relates to the field of tunnel engineering, in particular to a slope protection structure of a tunnel portal of a unconsolidated formation and a design method.
Background
In the railway and highway engineering in mountain areas, a tunnel inevitably enters a hole from a slope of a loose stratum, the slope stability of the hole slope of the loose stratum is poor, a plurality of sliding surface shear outlets are formed, when the tunnel enters the hole and is excavated, top edge slope collapse and top collapse accidents of the tunnel easily occur due to unloading loosening effect.
Disclosure of Invention
The invention aims to: the slope protection of the tunnel portal of the unconsolidated formation existing in the prior art is characterized in that a full slope surface is adopted to set an anchor rope to be combined with a tunnel advance support for reinforcement protection, certain included angles generally exist between the anchor rope and a tunnel portal body, the anchor rope anchoring section is too close to the tunnel, the anchor rope is loosened due to unloading loosening after tunnel excavation and even fails, the anchoring section is too far away from the tunnel, and the reinforcement reliability is poor.
In order to achieve the purpose, the invention adopts the technical scheme that:
a unconsolidated formation tunnel portal slope protective structure, comprising:
the vertical pre-reinforcing piles are arranged on two sides of the tunnel portal and extend into the stable mountain body;
the ring beam is arranged at the top of the tunnel portal and is rigidly connected to the vertical pre-reinforcing pile;
the horizontal reinforcing piles are arranged at the top of the tunnel, and horizontally extend into the stable mountain from the slope surface of the unconsolidated layer;
the plurality of groups of prestressed anchor cables are arranged on the horizontal reinforcing pile, each group of prestressed anchor cables comprises a plurality of prestressed anchor cables, and two adjacent groups of prestressed anchor cables are arranged at intervals in the vertical direction;
and the minimum distance D between the end part of the anchoring section of the bottom row of anchor cables in the lowest group of prestressed anchor cables and the boundary of the top of the tunnel is not less than the tunnel hole diameter.
By adopting the slope protection structure for the tunnel portal of the unconsolidated formation, the slope at the top of the tunnel portal is integrally stabilized by arranging the prestressed anchor cables, and the prestressed anchor cables adopt a graded reinforcement method, so that the problem that the sliding surface of the slope of the unconsolidated formation is more in shearing and more in outlet is solved, meanwhile, the protection project can be saved, and the damage to ecology is reduced; the vertical pre-reinforcing piles simultaneously stabilize the longitudinal and transverse sliding surfaces at the bottom of the tunnel portal, and the crown-shaped body formed by the horizontal reinforcing piles and the ring beam is connected with the vertical pre-reinforcing piles at two sides to jointly resist the downward sliding force at the top of the tunnel, so that the reinforcing reliability is greatly improved; the end part of the anchoring section of the prestressed anchor cable arranged at the bottom has a safe distance D from the top of the tunnel, the stratum is reinforced by the horizontal reinforcing pile in the period, and the ring beam and the vertical pre-reinforcing pile are combined to support the horizontal reinforcing pile area, so that the anchoring force is not influenced during tunnel excavation, the integral stability of a slope is solved, the problem of a reinforcing blind area of a shallow buried area at the top of the tunnel in the traditional reinforcing measure is solved, and top collapse and collapse of the shallow buried section at the tunnel opening in the construction and operation periods are avoided.
Preferably, each group of the prestressed anchor cables is arranged in a rectangular array, and the horizontal reinforcing piles are arranged in a rectangular array.
Preferably, the vertical pre-reinforcing piles and the ring beams are reinforced concrete members.
Preferably, the ring beam is semi-arch shaped.
Preferably, the horizontal reinforcing pile is a steel pipe pile.
Further preferably, a tendon reinforcement and a cement grout are arranged in the steel pipe pile.
Preferably, an included angle α is formed between a connecting line of the arrangement boundary line of the lowest group of prestressed anchor cables and two sides of the horizontal reinforcing piles and the tunnel excavation bottom and the horizontal direction, and α is not greater than a fracture angle of rock-soil bodies on two sides of the tunnel portal.
The invention also provides a design method of the slope protection structure of the tunnel portal of the unconsolidated formation, which is used for designing the slope protection structure of the tunnel portal of the unconsolidated formation, and comprises the following steps:
s1, determining arrangement of slope prestressed anchor cables;
according to the calculation and analysis of the stability of the slope, the slope is graded from top to bottom, so that the 1 st-level gliding force N 1 Can be borne by a first group of pre-stressed anchor cables, and then a second group of pre-stressed anchor cables are arranged at intervals S, so that the second group of pre-stressed anchor cables can bear the sliding force N 2 -N 1 And repeating the steps until the lowest group of prestressed anchor cables on the top of the tunnel can bear the downward sliding force N i -N i-1 The minimum distance D between the end part of the anchoring section of the bottom row of anchor cables in the lowest group of prestressed anchor cables and the boundary of the tunnel is not less than the tunnel diameter;
s2, determining the stress and the size of the vertical pre-reinforcing pile;
determining the transverse spacing L of the vertical pre-reinforcing piles according to the size of the tunnel portal, wherein the thrust of a single vertical pre-reinforcing pile is N = L x (N) i+1 -N i ) 2, then determining the pile section and the anchoring length of the vertical pre-reinforced pile;
s3, determining the stress and the size of the ring beam;
the ring beam transmits the gliding force among the vertical pre-reinforcing piles to the vertical pre-reinforcing piles, and the force borne by the ring beam is uniformly loaded by q = Lx (N) i -N i-1 ) Calculating h, wherein h is the calculated height of the ring beam, and the ring beam is designed and calculated according to the beam with fixed constraints at two ends, namely the maximum bending moment M = (q multiplied by L) = 2 ) 12, maximum shear force Q = (Q × L)/2;
s4, determining the stress and distribution of the horizontal reinforcing piles;
the residual glide at the landslide outlet of the ith sliding surface is N i -N i-1 Decomposed into horizontal pulling forces N ix And vertical force N iy In which N is ix ＝(N i -N i-1 )cosβ，N iy ＝(N i -N i-1 ) sin beta and beta are included angles between the downward sliding force of the ith sliding surface and the horizontal direction, and the tension force P of the horizontal reinforcing pile is single x ＝N ix X a/b, shear force under vertical direction is P y ＝N iy And (b) calculating the anchoring length of the horizontal reinforcing piles, wherein a is the horizontal distance of the horizontal reinforcing piles, b is the longitudinal row number of the horizontal reinforcing piles, and if the required anchoring length is calculated to be too long or the single uplift resistance is not satisfactory, reducing the horizontal distance a of the horizontal reinforcing piles and/or increasing the longitudinal row number b of the horizontal reinforcing piles.
By adopting the design method of the slope protection structure of the tunnel portal in the unconsolidated formation, accurate anchoring measures can be made for a plurality of sliding surfaces and corresponding sliding forces of the slope, the horizontal reinforcing piles, the vertical pre-reinforcing piles and the ring beams arranged at the tunnel portal resist the sliding force of the top of the tunnel together, and the reinforcing reliability is greatly improved; and determining that the safe distance D is reserved between the end part of the anchoring section of the prestressed anchor cable and the top of the tunnel, reinforcing the stratum by the horizontal reinforcing pile in the period, and providing a basis for design and construction by combining the ring beam and the vertical pre-reinforcing pile to support the area of the horizontal reinforcing pile.
Preferably, in the step S1, the axial tension, the anchoring length, and the distance of the prestressed anchor cables are calculated according to "design specifications of a railway roadbed retaining structure".
Preferably, in the step S1, each set of the prestressed anchor cables includes 3 to 5 rows.
Preferably, in the step S2, the net distance from the inner side of the vertical pre-reinforcing pile to the tunnel edge is determined according to the size of the tunnel portal.
Preferably, in the step S2, a pile section and an anchoring length of the vertical pre-reinforcing pile are calculated according to "design specification of a supporting structure of a railroad bed".
Preferably, in the step S2, the vertical pre-reinforced piles are reinforced concrete pre-reinforced piles, and reinforcing bars are arranged according to the concrete structure design specification.
Preferably, in the step S3, the ring beam is a reinforced concrete ring beam, and reinforcement is performed according to "concrete structure design specifications".
Preferably, in the step S4, the anchoring length of the horizontal reinforcing pile is calculated by referring to anchor rods and anti-slide piles in the design specification of the railway roadbed retaining structure.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. according to the slope protection structure for the tunnel portal of the unconsolidated formation, the slope of the tunnel portal top is integrally stabilized by arranging the prestressed anchor cables, and the prestressed anchor cables are reinforced in a grading manner, so that the problem that the slope of the unconsolidated formation has more sliding surfaces and more shearing outlets is solved, meanwhile, protection engineering can be saved, and damage to ecology is reduced; the vertical pre-reinforcing piles simultaneously and integrally stabilize the longitudinal and transverse sliding surfaces at the bottom of the tunnel portal, and the crown-shaped body formed by the horizontal reinforcing piles and the ring beam is connected with the vertical pre-reinforcing piles at two sides to jointly resist the downward sliding force at the top of the tunnel, so that the reinforcing reliability is greatly improved; the end part of the anchoring section of the prestressed anchor cable has a safe distance D from the top of the tunnel, the stratum is reinforced by the horizontal reinforcing pile in the period, and the ring beam and the vertical pre-reinforcing pile are combined to support the horizontal reinforcing pile area, so that the anchoring force is not influenced during tunnel excavation, the integral stability of a slope is solved, the problem of a reinforcing blind area of a traditional reinforcing measure in a shallow buried area at the top of the tunnel is solved, and the collapse and collapse of the shallow buried section at the tunnel entrance during construction and operation are avoided;
2. according to the design method of the slope protection structure of the tunnel portal in the unconsolidated formation, accurate anchoring measures can be made aiming at a plurality of sliding surfaces and corresponding sliding forces of the slope, the horizontal reinforcing piles, the vertical pre-reinforcing piles and the ring beams arranged at the tunnel portal resist the sliding force of the top of the tunnel together, and the reinforcing reliability is greatly improved; and determining that the safe distance D is between the end part of the anchoring section of the prestressed anchor cable and the top of the tunnel, and reinforcing the stratum by the horizontal reinforcing pile in the period, and providing a basis for design and construction by combining the ring beam and the vertical pre-reinforcing pile to support the horizontal reinforcing pile area.
Drawings
FIG. 1 is a schematic longitudinal section view of a slope protection structure of a tunnel portal in unconsolidated formation;
fig. 2 is a front schematic view of a slope protection structure of a tunnel portal of a unconsolidated formation.
The labels in the figure are: 1-prestressed anchor cable, 2-horizontal reinforcing pile, 3-vertical pre-reinforcing pile, 4-ring beam and 5-tunnel.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
As shown in fig. 1 and 2, the slope protection structure for the tunnel portal in unconsolidated formation comprises a prestressed anchor cable 1, horizontal reinforcing piles 2, vertical reinforcing piles 3 and ring beams 4.
The vertical pre-reinforcing piles 3 are arranged on two sides of a tunnel 5-hole door, the vertical pre-reinforcing piles 3 extend into a stable mountain, and the vertical pre-reinforcing piles 3 are reinforced concrete pre-reinforcing piles.
The ring beam 4 is arranged at the top of the tunnel 5 portal, the ring beam 4 is semi-arch and is rigidly connected to the vertical pre-reinforcing pile 3, and the ring beam 4 is a reinforced concrete ring beam.
The horizontal reinforcing piles 2 comprise a plurality of piles and are arranged at the tops of the 5 holes of the tunnel, the horizontal reinforcing piles 2 horizontally extend into a stable mountain from a loose layer slope surface, the horizontal reinforcing piles 2 are steel pipe piles and are made of stainless steel pipes with the diameter of 159mm, reinforcing bar reinforcement bodies and cement grouting bodies are arranged in the horizontal reinforcing piles, and the horizontal reinforcing piles 2 are arranged in a rectangular array.
The prestressed anchor cables 1 comprise a plurality of groups and are arranged on the horizontal reinforcing piles 2, each group of prestressed anchor cables 1 comprises a plurality of prestressed anchor cables, every two groups of prestressed anchor cables 1 are arranged at vertical intervals S, each group of prestressed anchor cables 1 are arranged in a rectangular array, and the minimum distance D from the end part of the anchoring section of the bottom row of anchor cables in the lowermost group of prestressed anchor cables 1 to the top boundary of the tunnel 5 is not smaller than the hole diameter of the tunnel 5.
And an included angle alpha is formed between the connecting line of the arrangement boundary line of the lowest group of prestressed anchor cables 1 and the two sides of the horizontal reinforcing pile 2 and the excavated bottom of the tunnel 5 and the horizontal direction, and the alpha is not greater than the fracture angle of rock and soil masses on the two sides of the tunnel 5.
According to the slope protection structure for the tunnel portal of the unconsolidated formation, the prestressed anchor cable 1 is arranged to integrally stabilize the slope at the tunnel top 5, the prestressed anchor cable 1 adopts a graded reinforcement method, the problem that the sliding surface of the slope of the unconsolidated formation is multiple in shearing and multiple in outlet is solved, meanwhile, protection engineering can be saved, and damage to ecology is reduced; the vertical pre-reinforcing piles 3 simultaneously stabilize the longitudinal and transverse sliding surfaces at the bottom of the tunnel 5, the crown-shaped body formed by the horizontal reinforcing piles 2 and the ring beam 4 is connected with the vertical pre-reinforcing piles 3 at two sides, so that the downward sliding force at the top of the tunnel 5 is resisted together, and the reinforcing reliability is greatly improved; the end part of the anchoring section of the prestressed anchor cable 1 arranged at the bottom has a safe distance D from the top of the tunnel 5, the stratum is reinforced by the horizontal reinforcing pile 2 in the period, and the ring beam 4 and the vertical pre-reinforcing pile 3 are combined to support the horizontal reinforcing pile 2 area, so that the anchoring force is not influenced when the tunnel 5 is excavated, the integral stability of a slope is solved, the problem of a reinforcing blind area of a shallow buried area at the top of the tunnel 5 by a traditional reinforcing measure is solved, and the top collapse and the collapse in the construction and operation periods of a shallow buried section at the tunnel entrance are avoided.
Example 2
As shown in fig. 1 and fig. 2, the method for designing a slope protection structure of a tunnel entrance of a unconsolidated formation according to the present invention is used for designing the slope protection structure of the tunnel entrance of the unconsolidated formation according to embodiment 1, and the method includes the following steps:
s1, determining arrangement of slope prestressed anchor cables;
as shown in FIG. 1, according to the slope stability calculation analysis, the slope can be graded from top to bottom, so that the glide force N of the 1 st grade 1 Can be grouped into a first group (each group 3)About 5 rows) the prestressed anchor cable 1 bears, the axial tension, the anchoring length, the distance and the like of the prestressed anchor cable 1 can be calculated according to the design specification of a railway roadbed retaining structure, then the interval S is provided with a second group of the prestressed anchor cables 1, so that the prestressed anchor cables 1 of the second group can bear the sliding force N 2 -N 1 And repeating the steps until the lowest group of prestressed anchor cables 1 at the top of the tunnel 5 can bear the downward sliding force N i -N i-1 And the minimum distance D between the end part of the anchoring section of the bottom row of anchor cables in the lowest group of prestressed anchor cables 1 and the boundary of the tunnel is not less than the diameter of the tunnel 5.
S2, determining the stress and the size of the vertical pre-reinforcing pile 3;
as shown in fig. 2, the vertical pre-reinforcing piles 3 are reinforced concrete pre-reinforcing piles, the clear distance between the inner side of each vertical pre-reinforcing pile 3 and the edge of the tunnel 5 is 0.5m according to the size of the tunnel 5, the transverse distance L between the inner side of each vertical pre-reinforcing pile 3 and the edge of the tunnel 5 is determined, and the thrust of each single vertical pre-reinforcing pile 3 is N = L × (N) i+1 -N i ) And 2, calculating the section and anchoring length of the pile according to the design specification of the railway subgrade retaining structure, and reinforcing the steel bars according to the design specification of the concrete structure.
S3, determining the stress and the size of the ring beam 4;
as shown in fig. 2, the ring beam 4 is a reinforced concrete ring beam, and the ring beam 4 mainly transfers the downward sliding force between the vertical pre-reinforcing piles 3 to the vertical pre-reinforcing piles 3, so that the force applied to the ring beam 4 can be uniformly loaded by q = L × (N) i -N i-1 ) H, wherein h is the height of the ring beam 4, the ring beam 4 can be designed and calculated according to the beam with fixed constraints at two ends, namely the maximum bending moment M = (q multiplied by L) 2 ) And/12, the maximum shearing force Q = (Q multiplied by L)/2, and reinforcing bars are arranged according to concrete structure design specifications.
S4, determining the stress and distribution of the horizontal reinforcing piles 2;
as shown in figure 1, the horizontal reinforcing pile 2 is a horizontal miniature steel pipe pile, and the residual downward sliding of the landslide outlet of the ith sliding surface is N i -N i-1 Can be decomposed intoHorizontal tension N ix And a vertical force N iy In which N is ix ＝(N i -N i-1 )cosβ，N iy ＝(N i -N i-1 ) sin beta and beta are included angles between the downward sliding force of the ith sliding surface and the horizontal direction, and the tension force P of the single horizontal reinforcing pile 2 x ＝N ix X a/b, shear force under vertical direction is P y ＝N iy And x a/b, wherein a is the horizontal distance between the horizontal reinforcing piles 2, and b is the longitudinal row number of the horizontal reinforcing piles 2, the anchoring length of the horizontal reinforcing piles 2 can be calculated by referring to anchor rods and anti-slide piles in the design specification of the railway roadbed retaining structure, and if the required anchoring length is calculated to be too long or the single uplift resistance is not satisfactory, the horizontal distance a between the horizontal reinforcing piles 2 is reduced and/or the longitudinal row number b of the horizontal reinforcing piles 2 is increased.
And an included angle alpha is formed between the connecting line of the arrangement boundary line of the lowest group of prestressed anchor cables 1 and the two sides of the horizontal reinforcing pile 2 and the excavated bottom of the tunnel 5 and the horizontal direction, and the alpha is not greater than the fracture angle of rock and soil masses on the two sides of the tunnel 5.
According to the design method of the slope protection structure of the tunnel portal in the unconsolidated formation, accurate anchoring measures can be made for a plurality of sliding surfaces and corresponding sliding forces of the slope, the horizontal reinforcing piles 2, the vertical pre-reinforcing piles 3 and the ring beams 4 arranged at the tunnel 5 portal resist the sliding forces at the top of the tunnel 5 together, and the reinforcing reliability is greatly improved; the safe distance D between the end part of the anchoring section of the prestressed anchor cable 1 and the top of the tunnel 5 is determined, and the stratum is reinforced by the horizontal reinforcing piles 2 in the period, and the ring beam 4 and the vertical pre-reinforcing piles 3 are combined to support the area of the horizontal reinforcing piles 2, so that the design and construction are provided.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A unconsolidated formation tunnel portal slope protective structure is characterized by comprising:
the vertical pre-reinforcing piles (3) are arranged on two sides of a tunnel door of the tunnel (5), and the vertical pre-reinforcing piles (3) extend into the stable mountain body;
the ring beam (4) is arranged at the top of the tunnel door of the tunnel (5) and is rigidly connected to the vertical pre-reinforcing pile (3);
the horizontal reinforcing piles (2) are arranged at the top of the tunnel (5), and the horizontal reinforcing piles (2) horizontally extend into the stable mountain from the loose layer slope;
the prestressed anchor cables (1) are arranged on the horizontal reinforcing piles (2), each prestressed anchor cable (1) comprises a plurality of prestressed anchor cables, and two adjacent prestressed anchor cables (1) are arranged vertically at intervals;
and the minimum distance D between the end part of the anchoring section of the bottom row of anchor cables in the lowest group of prestressed anchor cables (1) and the top boundary of the tunnel (5) is not less than the tunnel diameter of the tunnel (5).
2. The unconsolidated formation tunnel portal slope protection structure according to claim 1, wherein each set of the prestressed anchor cables (1) is arranged in a rectangular array, and the horizontal reinforcing piles (2) are arranged in a rectangular array.
3. Unconsolidated formation tunnel portal slope safeguard structure according to claim 1, characterized in that the vertical pre-reinforcing piles (3) and the ring beams (4) are both reinforced concrete members.
4. Unconsolidated formation tunnel portal slope protection structure according to claim 1, characterized in that the ring beam (4) is semi-arched.
5. The unconsolidated formation tunnel portal slope protection structure of claim 1, wherein the horizontal reinforcement piles (2) are steel pipe piles.
6. The unconsolidated formation tunnel portal slope protection structure according to any one of claims 1 to 5, wherein a connecting line between a boundary line of arrangement of the prestressed anchor cables (1) and the two sides of the horizontal reinforcing pile (2) in the lowest group and the excavated bottom of the tunnel (5) forms an included angle α with the horizontal direction, and α is not greater than a fracture angle of rock and soil bodies on two sides of the tunnel portal of the tunnel (5).
7. A design method of a slope protection structure of a tunnel portal in unconsolidated formation, which is used for designing the slope protection structure of the tunnel portal in unconsolidated formation according to any one of claims 1 to 6, and comprises the following steps:
s1, determining arrangement of slope prestressed anchor cables;
according to the calculation and analysis of the stability of the slope, the slope is graded from top to bottom, so that the 1 st-level gliding force N 1 Can be borne by a first set of pre-stressed anchor cables (1), and then a second set of pre-stressed anchor cables (1) are arranged at intervals S, so that the second set of pre-stressed anchor cables (1) can bear a downward sliding force N 2 -N 1 And the rest is repeated until the lowest group of the prestressed anchor cables (1) on the tunnel top of the tunnel (5) can bear the downward sliding force N i -N i-1 The minimum distance D between the end part of the anchoring section of the bottom row of anchor cables in the lowest group of prestressed anchor cables (1) and the boundary of the tunnel is not less than the hole diameter of the tunnel (5);
s2, determining the stress and the size of the vertical pre-reinforcing pile (3);
determining the transverse spacing L of the vertical pre-reinforcing piles (3) according to the tunnel door size of the tunnel (5), wherein the thrust of a single vertical pre-reinforcing pile (3) is N = L x (N) i+1 -N i ) 2, and then determining the pile section and the anchoring length of the vertical pre-reinforcing pile (3);
s3, determining the stress and the size of the ring beam (4);
the ring beam (4) transmits the gliding force between the vertical pre-reinforcing piles (3) to the vertical pre-reinforcing piles (3), and the force borne by the ring beam (4) is q = Lx (N) according to uniform load i -N i-1 ) Calculating h, wherein h is the calculated height of the ring beam (4), and the ring beam (4) is designed and calculated according to the beam with fixed constraints at two ends, namely the maximum bending moment M = (q multiplied by L) 2 ) 12, maximum shear force Q = (Q × L)/2;
s4, determining the stress and distribution of the horizontal reinforcing piles (2);
the residual glide at the landslide outlet of the ith sliding surface is N i -N i-1 Decomposed into horizontal pulling forces N ix And a vertical force N iy In which N is ix ＝(N i -N i-1 )cosβ，N iy ＝(N i -N i-1 ) sin beta and beta are included angles between the downward sliding force of the ith sliding surface and the horizontal direction, and the tension force P of the single horizontal reinforcing pile (2) x ＝N ix X a/b, shear force under vertical direction is P y ＝N iy And x a/b, wherein a is the horizontal spacing of the horizontal reinforcing piles (2), b is the number of longitudinal rows of the horizontal reinforcing piles (2), the anchoring length of the horizontal reinforcing piles (2) is calculated, and if the required anchoring length is calculated to be too long or the single uplift resistance is not met, the horizontal spacing a of the horizontal reinforcing piles (2) is reduced and/or the number of longitudinal rows b of the horizontal reinforcing piles (2) is increased.
8. The design method of the slope protection structure of the unconsolidated formation tunnel portal according to claim 7, wherein in the step S1, the axial tension, the anchoring length and the distance of the prestressed anchor cables (1) are calculated according to the design specifications of the railway subgrade retaining structure.
9. The method for designing the slope protection structure of the unconsolidated formation tunnel portal according to claim 7, wherein in the step S2, the pile section and the anchoring length of the vertical pre-reinforcing pile (3) are calculated according to the design specifications of the supporting structure of the railway roadbed.
10. The method for designing a slope protection structure of a tunnel portal in unconsolidated strata according to any one of claims 7 to 9, wherein in the step S4, the anchoring length of the horizontal reinforcing piles (2) is calculated by referring to anchor rods and slide-resistant piles in the design specifications of supporting structures of railway beds.
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