Long and short pile combined supporting structure in soil and rock composite stratum and design method thereof

Abstract

The present application belongs to the technical field of urban rail design structure, and provides a long-short pile combined supporting structure and design method in soil-rock composite stratum. The long-short pile combined supporting structure in soil-rock composite stratum comprises a corbel, a steel surrounding purlin, a support piece, a long pile piece and a short pile piece. The structure and method of the present application optimize the pile length of the retaining pile, reduce the redundant length of the long pile in the rock stratum, save the engineering investment, reduce the rock penetration depth of the retaining pile, improve the construction efficiency of the foundation pit retaining structure in the rock stratum, optimize the pile diameter and reinforcement of the retaining pile, fully exert the bending resistance of the retaining pile, and reduce the engineering cost. The calculation theory of the long-short pile combined supporting system is proposed, which makes up for the lack of the theoretical part of the long-short pile combined supporting system.

Description

Technical Field

[0001] This invention belongs to the field of urban rail design and structural technology, specifically relating to a long and short pile combination support structure and design method for soil-rock composite strata. Background Technology

[0002] The construction of urban rail transit has driven the development and utilization of underground space, promoting the rapid development of foundation pit engineering theory and technology. The design of foundation pit support needs to consider the stability of the foundation pit itself, while also taking into account the impact on the surrounding environment. Since subway projects are usually located in city centers, the surrounding environment and underground pipelines are complex, and many foundation pit support methods cannot be adopted due to external environmental constraints. The pile-supported internal bracing system is usually the first choice for subway foundation pit support due to its mature technology, small footprint, and reasonable cost. For pile support, the pile length needs to simultaneously meet requirements for overall stability, heave resistance, and deformation control. However, research data shows that the bending moment below the bottom of the foundation pit decreases rapidly with increasing depth, and under normal circumstances, the bending resistance of the support piles below the bottom of the pit cannot be fully utilized. Especially in soil-rock composite strata, the deformation of the foundation pit is mainly concentrated in the soil layer, while the lateral deformation of the rock layer is very small. Designing equal pile lengths will inevitably lead to excessive redundancy in the safety factor.

[0003] In soil-rock composite strata, the traditional equal-length pile support method has the following problems:

[0004] (1) In the soil-rock composite strata, the lateral pressure in the rock layer is almost negligible, and the lateral earth pressure of the foundation pit is mainly concentrated in the soil layer of the foundation pit; all the retaining piles are inserted below the bottom of the pit, and the retaining piles in the rock layer cannot fully exert their bending resistance, resulting in material waste.

[0005] (2) When the depth of the subway foundation pit is relatively deep and the rock surface is relatively high, it is difficult to drill holes in the rock layer for the retaining piles, resulting in low construction efficiency and affecting the progress of the project. Summary of the Invention

[0006] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of this invention is to provide a combined long and short pile support structure for soil-rock composite strata, which aims to solve the problems existing in the prior art.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A combined long and short pile support structure for soil-rock composite strata includes:

[0009] Crown beams, steel walers, supporting components, long piles, and short piles;

[0010] The long piles and short piles are arranged side by side at intervals and in a continuous manner along the first end face of the cap beam and in the extension direction of the cap beam;

[0011] The second end face of the crown beam is provided with a support member, and the crown beam is arranged continuously side by side in the extension direction;

[0012] The first end face of the crown beam is perpendicular to the second end face of the crown beam;

[0013] The steel walers are arranged parallel to the capping beam, and the steel walers are arranged continuously side by side along the extension direction of the long pile;

[0014] Support members are continuously arranged side by side on the steel waler along its extension direction;

[0015] The length of the long pile extends through the soil and rock layers to below the bottom of the foundation pit, while the length of the short pile extends through the soil layer to the surface of the rock layer.

[0016] Preferably, the number of short piles is two or more.

[0017] Preferably, the steel walers are respectively installed at the interface between the soil layer and the rock layer and at the rock layer.

[0018] Preferably, the support includes a concrete support and a steel support, the concrete support is located on the second end face of the cap beam, and the steel support is located on the steel waler, with the concrete support and the steel support arranged in parallel.

[0019] Preferably, the positions of the steel support and the steel waler correspond to the connection positions of the steel waler and the long pile.

[0020] This invention also includes a design method for a combined long and short pile support structure in soil-rock composite strata, applied to the aforementioned combined long and short pile support structure in soil-rock composite strata, comprising the following steps:

[0021] S1. Short pile design: The short pile is equivalent to a rod. The concrete support and steel support are set as elastic supports. The interface between the soil layer and the rock layer and the bottom of the short pile are set as hinged supports. The stress model of the short pile is established, and the stress calculation of the short pile is performed to determine the reinforcement of the short pile.

[0022] S2. Long Pile Design: In rock foundation pits, the rock mass within the sliding tendency range of the rock foundation pit is regularized into a slider. Static equilibrium equations are established through the equilibrium conditions of the slider. The force exerted on the long pile by the slope slider is determined according to the limit equilibrium method. Furthermore, a force model of the long pile is established, and the force calculation of the long pile is performed to determine the reinforcement of the long pile and the ratio design of long pile and short pile.

[0023] Preferably, in S1:

[0024] Set the spacing of the elastic supports to The distance from the elastic support to the top surface of the rock stratum is set as The depth to which the short pile is embedded into the rock strata is set as ;

[0025] The lateral earth pressures on the short pile members at both ends of the soil layer are respectively set as follows: , ,

[0026] in, , , In the above formula: Overload (kPa) at the top of the slope; The distance between long and short piles (m); The cohesion of the soil layer (kPa); The friction angle of the soil layer; is the unit weight of the soil layer (kN / m3); ka is the active earth pressure coefficient.

[0027] Preferably, in S2:

[0028] The long pile is equivalent to a rod, the rock crest and the point of action of the support are equivalent to elastic supports capable of withstanding bending moments, the remaining supports of the rock stratum are equivalent to elastic supports, the interface between the soil layer and the rock stratum and the bottom of the long pile are designated as hinged supports, and the spacing of the elastic supports is set as... The distance from the elastic support to the bottom of the pit is set as ;

[0029] The lateral rock and soil pressures on the long pile at both ends of the rock stratum are respectively set as follows: , .

[0030] Preferably, in S2:

[0031] When the rock mass is a rock slope without outward-dipping structural planes, the lateral rock pressure should be calculated using the lateral earth pressure method based on the equivalent internal friction angle of the rock mass; the stress analysis of the landslide body is as follows:

[0032] Based on the principle of similar triangles, the following system of equations can be established:

[0033] ;

[0034] ;

[0035] ;

[0036] In the above formula:

[0037] : Active earth pressure (kN) exerted by the slider on the long pile; : Sliding body fracture angle; Equivalent internal friction angle of rock mass;

[0038] : Self-weight of rock mass slider (kN); : Overload at the top of the rock slope (kN); : Spacing between long piles (m);

[0039] A stress analysis is performed on the overlying soil column acting on the sliding block of a rock slope in a soil foundation pit. Assuming that the friction angle between the soil column and the back of the wall is the same as the friction angle of the soil, the circular sliding surface is simplified to a straight sliding surface. The static equilibrium equations are then established to obtain the load acting on the top of the rock slope.

[0040] ;

[0041] ;

[0042] ;

[0043] ;

[0044] ;

[0045] ;

[0046] ;

[0047] ;

[0048] ;

[0049] In the above formula:

[0050] : Self-weight of the overlying soil column (kN); Frictional force between the soil column and the pile (kN); (Frictional force between soil column and soil mass, kN)

[0051] : Active earth pressure (kN / m) exerted by the soil column on the pile body; Active earth pressure (kN / m) exerted by the soil column on the sliding surface.

[0052] : The angle of fracture of the soil column; : Length of sliding surface (m).

[0053] Preferably, in S2:

[0054] When a weak, outward-dipping structural plane exists, the force model of the sliding body is shown below, and the calculation method for the overlying soil column is as follows:

[0055] First, it is necessary to determine whether the slope is self-stabilizing. For the slope safety factor,

[0056] ;

[0057] when When the slope is self-stabilizing, the force exerted by the slider on the long pile is zero. At that time, the following system of equations is established:

[0058] ;

[0059] ;

[0060] ;

[0061] In the above formula:

[0062] : Length of the smooth surface (m); Friction angle of weak structural surfaces; : Cohesion of weak structural surfaces (kPa); (Friction between the slider and the rock surface, kN) : The pressure exerted by the slider on the sliding surface (kN / m);

[0063] Further conversion allows us to calculate the line load acting on the long pile:

[0064] ;

[0065] ;

[0066] ;

[0067] According to the above formula, we can obtain:

[0068] ;

[0069] By establishing the static equilibrium equations, the line load acting on the long pile can be calculated.

[0070] Compared with the prior art, the beneficial effects of the present invention include:

[0071] The structure and method of this invention optimize the pile length of the retaining piles, reducing the redundant length of long piles in the rock strata and saving engineering investment; reduce the rock penetration depth of the retaining piles, improving the construction efficiency of the foundation pit retaining structure in the rock strata; optimize the pile diameter and reinforcement of the retaining piles, giving full play to the bending resistance of the retaining piles and further reducing the engineering cost; and propose a calculation theory for the long and short pile combined support system, making up for the lack of theoretical part of the long and short pile combined support system. Attached Figure Description

[0072] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0073] Figure 1 This is a plan view of the combined long and short pile support structure for soil-rock composite strata according to the present invention.

[0074] Figure 2 This is a cross-sectional view of the combined long and short pile support structure for soil-rock composite strata of the present invention.

[0075] Figure 3 This is a longitudinal cross-sectional view of the combined long and short pile support structure for soil-rock composite strata of the present invention.

[0076] Figure 4 This is a schematic diagram of the stress on the short pile component of the present invention.

[0077] Figure 5 This is a schematic diagram of the stress on the long pile component in the rock strata according to the present invention.

[0078] Figure 6 The first illustration shows the force diagram of the sliding body according to the present invention.

[0079] Figure 7 Figure 2 shows a schematic diagram of the forces acting on the sliding body according to the present invention.

[0080] Figure 8 This is a schematic diagram of the stress on the soil column on the rock slope slider of the present invention.

[0081] Figure 9 Figure 2 shows a schematic diagram of the stress on the soil column on the rock slope slider of the present invention.

[0082] Figure 10 Figure 3 shows a schematic diagram of the forces acting on the sliding body according to the present invention.

[0083] in:

[0084] 1-Cover beam, 2-Steel waler, 3-Long pile, 4-Short pile, 5-Concrete support, 6-Steel support. Detailed Implementation

[0085] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0086] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0087] Example:

[0088] like Figure 1-10 As shown, this embodiment provides a combined long and short pile support structure for soil-rock composite strata, including:

[0089] 1. Crown beam; 2. Steel waler; 3. Supporting components; 4. Long piles; 5. Short piles.

[0090] Long pile 3 and short pile 4 are arranged side by side at intervals and in a continuous manner along the extension direction of the capping beam 1 on the first end face of the capping beam 1.

[0091] A support member is provided on the second end face of the cap beam 1, and the support members are arranged continuously side by side in the extension direction of the cap beam 1;

[0092] The first end face of the capping beam 1 and the second end face of the capping beam 1 are set perpendicular to each other;

[0093] The steel walers 2 are set parallel to the capping beam 1, and the steel walers 2 are set continuously side by side along the extension direction of the long pile 3;

[0094] Support members are continuously arranged side by side on the steel waler 2 and along the extension direction of the steel waler 2;

[0095] The length of the long pile 3 extends through the soil and rock layers to below the bottom of the foundation pit, while the length of the short pile 4 extends through the soil layer to the surface of the rock layer.

[0096] Specifically, the number of short piles 4 is two or more.

[0097] Specifically, the steel walers 2 are respectively set at the interface between the soil layer and the rock layer and at the rock layer.

[0098] Specifically, the supporting components include concrete support 5 and steel support 6. Concrete support 5 is located on the second end face of cap beam 1, and steel support 6 is located on steel waler 2. Concrete support 5 and steel support 6 are arranged in parallel.

[0099] Specifically, the positions of the steel support 6 and the steel waler 2 correspond to the connection positions of the steel waler 2 and the long pile 3.

[0100] The structure of this scheme is optimized in the following aspects based on the traditional pile support scheme:

[0101] (1) Reduce the number of retaining piles that extend below the bottom of the pit. Long piles (i.e. retaining piles that extend below the bottom of the pit) should be extended below the bottom of the pit to meet the stability requirements of the foundation pit.

[0102] (2) Short piles are installed in the middle of long piles, and the short piles penetrate below the rock surface to meet the stress and stability requirements of the soil foundation pit. Internal supports are installed at the soil interface, which function similarly to the anchor bolts. The specific location of the supports is adjusted appropriately based on the location of the station structure slab.

[0103] (3) Optimize the pile diameter and spacing of short piles, and ensure that the specific parameters meet the stress requirements of the retaining structure.

[0104] The present invention also includes a design method for a combined long and short pile support structure in soil-rock composite strata, applied to the aforementioned combined long and short pile support structure in soil-rock composite strata, comprising the following steps:

[0105] S1. Design of short pile 4: Short pile 4 is equivalent to a rod. The concrete support 5 and the steel support 6 are set as elastic supports. The interface between the soil layer and the rock layer and the bottom of the short pile 4 are set as hinge supports. The stress model of short pile 4 is established, and the stress calculation of short pile 4 is performed to determine the reinforcement of short pile 4.

[0106] Specifically, in S1:

[0107] like Figure 4 Set the spacing of the elastic supports to The distance from the elastic support to the top surface of the rock stratum is set as The depth to which short pile 4 is embedded into the rock stratum is set as ;

[0108] The lateral earth pressures on both ends of the short pile 4 are respectively set as follows: , ,

[0109] in, , , In the above formula: Overload (kPa) at the top of the slope; The distance between the long pile 3 and the short pile 4 is (m). The cohesion of the soil layer (kPa); The friction angle of the soil layer; is the unit weight of the soil layer (kN / m3); ka is the active earth pressure coefficient.

[0110] When the earth pressure generated by the weight of the soil and the resistance generated by cohesion manifest as negative earth pressure, i.e., tensile stress, the pile and soil have no actual tensile strength. The presence of tensile stress will cause the backfill to separate from the pile, resulting in cracks of a certain depth. At this point, the earth pressure above the crack can be considered zero.

[0111] S2, Long Pile Component 3 Design: The portion below the rock surface in the soil-composite strata can be considered a slope problem. When the potential sliding block of the slope can stabilize itself, the long pile component only serves as a safety reserve. When the slope slides and becomes unstable, the long pile component needs to play a supporting role.

[0112] In the rock foundation pit, the rock mass within the sliding tendency range of the rock foundation pit is regularized into a slider. The static equilibrium equation is established through the equilibrium conditions of the slider. The force of the slope slider acting on the long pile 3 is determined according to the limit equilibrium method. Furthermore, the force model of the long pile 3 is established, and the force calculation of the long pile 3 is performed to determine the reinforcement of the long pile 3 and the ratio design of the long pile 3 and the short pile 4.

[0113] Specifically, in S2:

[0114] like Figure 5 The long pile 3 is equivalent to a rod, the top of the rock stratum and the position of the supporting member are equivalent to elastic supports capable of withstanding bending moments, the remaining supports of the rock stratum are equivalent to elastic supports, the interface between the soil layer and the rock stratum and the bottom of the long pile 3 are set as hinged supports, and the spacing of the elastic supports is set as... The distance from the elastic support to the bottom of the pit is set as ;

[0115] The lateral rock and soil pressures on both ends of the long pile 3 are respectively set as follows: , .

[0116] Specifically, in S2:

[0117] When the rock mass is a rock slope without outward-dipping structural planes, the lateral rock pressure should be calculated using the lateral earth pressure method based on the equivalent internal friction angle of the rock mass; the stress analysis of the landslide body is as follows:

[0118] like Figures 6 to 7 Based on the principle of similar triangles, the following system of equations can be established:

[0119] ;

[0120] ;

[0121] ;

[0122] In the above formula:

[0123] : Active earth pressure (kN) exerted by the slider on the long pile; : Sliding body fracture angle; Equivalent internal friction angle of rock mass;

[0124] : Self-weight of rock mass slider (kN); : Overload at the top of the rock slope (kN); : Spacing between long piles (m);

[0125] like Figures 8 to 9 A stress analysis is performed on the overlying soil column acting on the sliding block of a rock slope in a soil foundation pit. Assuming that the friction angle between the soil column and the back of the wall is the same as the friction angle of the soil, the circular sliding surface is simplified to a straight sliding surface. The static equilibrium equation can be established to obtain the load acting on the top of the rock slope.

[0126] ;

[0127] ;

[0128] ;

[0129] ;

[0130] ;

[0131] ;

[0132] ;

[0133] ;

[0134] ;

[0135] In the above formula:

[0136] : Self-weight of the overlying soil column (kN); Frictional force between the soil column and the pile (kN); (Frictional force between soil column and soil mass, kN)

[0137] : Active earth pressure (kN / m) exerted by the soil column on the pile body; Active earth pressure (kN / m) exerted by the soil column on the sliding surface.

[0138] : The angle of fracture of the soil column; : Length of sliding surface (m).

[0139] Specifically, in S2:

[0140] like Figure 10 When a weak, outward-dipping structural plane exists, the force model of the sliding body is shown below, and the calculation method for the overlying soil column is as follows:

[0141] First, it is necessary to determine whether the slope is self-stabilizing. For the slope safety factor,

[0142] ;

[0143] when When the slope is self-stabilizing, the force exerted by the slider on the long pile 3 is zero. At that time, the following system of equations is established:

[0144] ;

[0145] ;

[0146] ;

[0147] In the above formula:

[0148] : Length of the smooth surface (m); Friction angle of weak structural surfaces; : Cohesion of weak structural surfaces (kPa); (Friction between the slider and the rock surface, kN) : The pressure exerted by the slider on the sliding surface (kN / m);

[0149] Further conversion allows us to calculate the line load acting on long pile 3:

[0150] ;

[0151] ;

[0152] ;

[0153] According to the above formula, we can obtain:

[0154] ;

[0155] By establishing the static equilibrium equations, the line load acting on the long pile can be calculated.

[0156] By simplifying the stress as described above, the stress on long and short piles in soil-rock composite strata can be simplified into a continuous beam model. By solving the continuous beam, the deformation, bending moment, and shear force of the pile body can be calculated separately, thereby guiding the design of the reinforcement of the retaining piles and solving the calculation problem of the long and short pile support structure.

[0157] The advantages of this solution are as follows:

[0158] (1) Optimizing the pile length of the retaining piles reduces the redundant length of long piles in the rock strata and saves project investment;

[0159] (2) The depth of the retaining piles into the rock is reduced, which improves the construction efficiency of the foundation pit retaining structure in the rock strata;

[0160] (3) Optimize the pile diameter and reinforcement of the retaining piles to give full play to the bending resistance of the retaining piles and further reduce the project cost;

[0161] (4) The calculation theory of the long and short pile combined support system is proposed, which makes up for the lack of theoretical part of the long and short pile combined support system.

[0162] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A design method for a combined long and short pile support structure in soil-rock composite strata, characterized in that, A combined long and short pile support structure is applied to a soil-rock composite stratum, the combined long and short pile support structure comprising: Crown beams, steel walers, supporting components, long piles, and short piles; The long piles and short piles are arranged side by side at intervals and in a continuous manner along the first end face of the cap beam and in the extension direction of the cap beam; The second end face of the crown beam is provided with a support member, which is arranged continuously side by side along the extension direction of the crown beam; The first end face of the crown beam is perpendicular to the second end face of the crown beam; The steel walers are arranged parallel to the capping beam, and the steel walers are arranged continuously side by side along the extension direction of the long pile; Support members are continuously arranged side by side on the steel waler along its extension direction; The length of the long pile extends through the soil and rock layers to below the bottom of the foundation pit, and the length of the short pile extends through the soil to the surface of the rock layer. The design method includes the following steps: S1. Short pile design: The short pile is equivalent to a rod. The concrete support and steel support are set as elastic supports. The interface between the soil layer and the rock layer and the bottom of the short pile are set as hinged supports. The stress model of the short pile is established, and the stress calculation of the short pile is performed to determine the reinforcement of the short pile. Set the spacing of the elastic supports to The distance from the elastic support to the top surface of the rock stratum is set as The depth to which the short pile is embedded into the rock strata is set as ; The lateral earth pressures on the short pile members at both ends of the soil layer are respectively set as follows: , , in, , , In the above formula: Overload (kPa) at the top of the slope; The distance between long and short piles (m); The cohesion of the soil layer (kPa); The friction angle of the soil layer; is the unit weight of the soil layer (kN / m3); ka is the active earth pressure coefficient. S2. Long pile design: In rock foundation pits, the rock mass within the sliding tendency range of the rock foundation pit is regularized into a slider. Static equilibrium equations are established through the equilibrium conditions of the slider. The force of the slider on the long pile is determined according to the limit equilibrium method. The force model of the long pile is further established, and the force calculation of the long pile is performed to determine the reinforcement of the long pile and the ratio design of long pile and short pile. The long pile is equivalent to a rod, the rock crest and the point of action of the support are equivalent to elastic supports capable of withstanding bending moments, the remaining supports of the rock stratum are equivalent to elastic supports, the interface between the soil layer and the rock stratum and the bottom of the long pile are designated as hinged supports, and the spacing of the elastic supports is set as... The distance from the elastic support to the bottom of the pit is set as ; The lateral rock and soil pressures on the long pile at both ends of the rock stratum are respectively set as follows: , .

2. The design method for the combined long and short pile support structure in soil-rock composite strata according to claim 1, characterized in that, The number of short piles is two or more.

3. The design method for the combined long and short pile support structure in soil-rock composite strata according to claim 1, characterized in that, The steel walers are respectively installed at the interface between the soil layer and the rock layer and at the rock layer.

4. The design method for the combined long and short pile support structure in soil-rock composite strata according to claim 1, characterized in that, The supporting components include concrete supports and steel supports. The concrete supports are located on the second end face of the cap beam, and the steel supports are located on the steel waler. The concrete supports and steel supports are arranged in parallel.

5. The design method for the combined long and short pile support structure in soil-rock composite strata according to claim 4, characterized in that, The positions of the steel support and the steel waler correspond to the connection positions of the steel waler and the long pile.

6. The design method for the combined long and short pile support structure in soil-rock composite strata according to claim 1, characterized in that, In S2: When the rock mass is a rock slope without outward-dipping structural planes, the lateral rock pressure should be calculated using the lateral earth pressure method based on the equivalent internal friction angle of the rock mass; the stress analysis of the landslide body is as follows: Based on the principle of similar triangles, the following system of equations can be established: ； ； ； In the above formula: : Active earth pressure (kN) exerted by the slider on the long pile; : Sliding body fracture angle; Equivalent internal friction angle of rock mass; : Self-weight of rock mass slider (kN); : Overload at the top of the rock slope (kN); : Spacing between long piles (m); A stress analysis is performed on the overlying soil column acting on the sliding block of a rock slope in a soil foundation pit. Assuming that the friction angle between the soil column and the back of the wall is the same as the friction angle of the soil, the circular sliding surface is simplified to a straight sliding surface. The static equilibrium equations are then established to obtain the load acting on the top of the rock slope. ； ； ； ； ； ； ； ； ； In the above formula: : Self-weight of the overlying soil column (kN); Frictional force between the soil column and the pile (kN); (Frictional force between soil column and soil mass, kN) : Active earth pressure (kN / m) exerted by the soil column on the pile body; Active earth pressure (kN / m) exerted by the soil column on the sliding surface. : The angle of fracture of the soil column; : Length of sliding surface (m).

7. The design method for the combined long and short pile support structure in soil-rock composite strata according to claim 6, characterized in that, In S2: When a weak, outward-dipping structural plane exists, the force model of the sliding body is shown below, and the calculation method for the overlying soil column is as follows: First, it is necessary to determine whether the slope is self-stabilizing. For the slope safety factor, ； when When the slope is self-stabilizing, the force exerted by the slider on the long pile is zero. At that time, the following system of equations is established: ； ； ； In the above formula: : Length of the smooth surface (m); Friction angle of weak structural surfaces; : Cohesion of weak structural surfaces (kPa); (Friction between the slider and the rock surface, kN) : The pressure exerted by the slider on the sliding surface (kN / m); Further conversion allows us to calculate the line load acting on the long pile: ； ； ； According to the above formula, we can obtain: ； By establishing the static equilibrium equations, the line load acting on the long pile can be calculated.

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