Design method of soil-rock combined foundation pit cantilever pile supporting structure

Abstract

The application provides a design method of a soil-rock combined foundation pit hanging foot pile supporting structure, the hanging foot pile supporting structure comprises a supporting pile and a reserved rock shoulder in a pit, and the design method comprises the following steps: a semi-infinite rock mass and an actual finite rock mass model are established by means of finite element software, a uniform load is applied to the rock mass model, the horizontal resistance coefficient of the rock mass is calculated and the reduction coefficient of the finite rock mass is obtained by comparison, and the reduction coefficient is substituted into a specification method to calculate the horizontal resistance coefficient of the finite rock mass in design; the supporting pile displacement, passive resistance safety factor, anti-overturning and anti-sliding checking are completed by using Lizheng deep foundation pit software, the suitable rock-embedded depth is determined, the pile reinforcement is determined according to the shear force and the bending moment calculated by the software; and the shear resistance and tensile resistance bearing capacity of the reserved rock shoulder in front of the pile are checked, and the rock shoulder width is determined. The passive resistance effect of the reserved rock shoulder in front of the pile is fully considered, the rock-embedded depth of the supporting pile can be effectively shortened, the supporting cost is saved, and certain economic benefits are obtained.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, specifically to a design method for a soil-rock combined foundation pit suspended pile support structure. Background Technology

[0002] With the continuous advancement of urbanization, infrastructure construction is booming. Underground space development projects are increasingly common, including real estate basements, subway, intercity railway and high-speed rail underground stations, municipal underground passages, and civil defense underground spaces. Underground space construction generally requires the excavation of foundation pits. To save surface space, the excavation depth of foundation pits is increasing, with many deep foundation pits reaching or nearing the bedrock surface, especially in soil-rock strata. Since urban building deep foundation pits generally lack the conditions for slope excavation, the foundation pit support system typically consists of lateral retaining structures (such as diaphragm walls or piles) and horizontal supports (such as internal supports like steel supports, reinforced concrete supports, or prestressed anchor cable supports). Constructing retaining structures in hard rock strata is difficult and time-consuming, significantly impacting the foundation pit construction schedule. Furthermore, the noise from the support structure construction has a significant impact on the surrounding environment. To mitigate these adverse effects, suspended piles have been developed.

[0003] Traditional suspended pile foundations typically employ a combination of suspended piles, trapezoidal rock shoulder protection, and anchor bolts for anchoring. The suspended piles are secured by the rock shoulder, requiring the pile bottom to be embedded a certain depth into the rock shoulder. Current design specifications for suspended pile foundation support in foundation pits simply treat the rock as a soil layer, using soil layer models to calculate the pile embedment depth. This approach has two drawbacks: firstly, it increases the embedment depth of the support piles, leading to unnecessary resource waste and increased construction difficulty; secondly, it fails to consider the spatial anchoring effect of the embedded section, resulting in insufficient main reinforcement in the support piles, which is inherently unsafe. Summary of the Invention

[0004] The purpose of this invention is to provide a design method for a suspended pile support structure for a soil-rock combined foundation pit. This method takes into account factors such as economy and ease of construction, and proposes a "suspended pile" support system with the pile tip located above the bottom of the foundation pit. By reserving a certain width of rock shoulder in the pit to provide passive resistance, it participates in the design calculation of the support system, thereby shortening the rock embedment depth of the support pile, reducing construction difficulty, reducing construction costs, accelerating the construction progress of the foundation pit, and filling the gaps in the current specifications.

[0005] To achieve the above objectives, the present invention provides a design method for a suspended pile support structure for a soil-rock combined foundation pit. The suspended pile support structure includes support piles and a pre-reserved rock shoulder within the pit. The design method comprises the following steps:

[0006] Step 1: Establish a semi-infinite rock mass model and a finite-width rock mass model. The semi-infinite rock mass model satisfies the size effect requirement, and the actual finite-width rock mass model satisfies the boundary condition requirement. Submit the analysis and enter the post-processing module.

[0007] Step 2: Calculate the reduction factor of the finite rock mass horizontal resistance coefficient at each depth node of the rock mass based on the post-processing results, further determine the reduction factor of the proportional coefficient of the finite rock mass horizontal resistance coefficient, and substitute the reduction factor into the empirical formula to obtain the horizontal resistance coefficient in the actual design.

[0008] Step 3: Using the elastic resistance method calculation model, input relevant design parameters such as pile length, pile diameter, soil layer information, and foundation pit depth into the Tianhan Foundation Pit software. The base is defined as the top surface of the reserved rock shoulder. Passive zone reinforcement is carried out on the rock strata within the height range of the rock shoulder. Input the horizontal resistance coefficient ratio after reinforcement to ensure that it is equal to the horizontal resistance coefficient ratio calculated after substituting the reduction coefficient in Step 2. Further complete the displacement verification of the support piles, passive resistance safety factor verification, overturning resistance, and sliding resistance verification. Determine the optimal rock embedment depth H based on the verification results, and perform pile reinforcement according to the shear force and bending moment diagrams output by the software.

[0009] Step 4: Determine the design calculation parameters for the suspended piles, including the optimal rock embedment depth H, reserved rock shoulder width B, height Z, overlying soil unit weight γ1, cohesion c1, and internal friction angle determined in Step 3. Layer thickness h, bedrock unit weight γ, cohesion c, internal friction angle The external friction angle δ at the pile-rock interface is θ, which is the angle between the most dangerous slip surface and the horizontal plane under the ultimate limit state. Based on engineering experience, a reserved rock shoulder width B is determined, and this width is then substituted into the formula to verify the bearing capacity of the reserved rock shoulder, including verification of both shear and tensile bearing capacities. Both requirements must be met simultaneously. The specific verification process is as follows:

[0010] (1) When the reserved rock shoulder width B meets the following conditions, the shear bearing capacity of the reserved rock shoulder meets the design requirements:

[0011] a. When H≤Btanθ, according to the force equilibrium of the triangular sliding soil wedge: At this point, the width of the rock shoulder can be further reduced;

[0012] b. When Btanθ<H≤Z, the reserved rock shoulder width B must meet the following condition:

[0013]

[0014] In the formula:

[0015] (2) The tensile bearing capacity of the reserved rock shoulder meets the design requirements when the reserved rock shoulder width B meets the following conditions:

[0016]

[0017] In the formula: E a M is the resultant force of the active earth pressure on the retaining pile; M is the bending moment generated by the active earth pressure on the reserved rock shoulder, M = E a •a; a is the vertical distance from the point of application of the resultant force of the active earth pressure to the verification section; z is the vertical distance from the verification section to the top of the rock shoulder; σ f To reserve the uniaxial tensile strength of the rock for the rock shoulder section, it is generally taken as 1 / 10 to 1 / 30 of the tensile strength. The specific value should be based on the results of geotechnical tests. If there is no test data, it can be taken as 0.15 times the compressive strength.

[0018] Step 5: The rock shoulder width B in Step 4 should simultaneously meet the requirements of the reserved rock shoulder shear bearing capacity and the reserved rock shoulder tensile bearing capacity. If either condition is not met or there is a surplus, change the value of the rock shoulder width B and perform repeated trial calculations until the optimal rock embedment depth and rock shoulder width are determined.

[0019] The preferred technical solution of the present invention is as follows: In step one, the rock mass model adopts a plane strain model, and the model size is twice the calculation depth on both sides in the horizontal direction and twice the calculation depth in the vertical direction.

[0020] The preferred technical solution of the present invention is as follows: In step one, the rock mass model adopts the Hoek-Brown constitutive model, and the rock mass parameters, mesh, working conditions, loads and boundary conditions in the two models should be consistent.

[0021] A further technical solution of the present invention: the reduction factor λ of the finite rock mass horizontal resistance coefficient at each depth node in step two. z The calculation is as follows:

[0022]

[0023] Furthermore, the reduction factor λ for the proportionality coefficient of the horizontal resistance coefficient of the finite rock mass is calculated as follows:

[0024] Obtain the horizontal resistance coefficient in the actual design;

[0025]

[0026] Furthermore, the horizontal resistance coefficient k of the finite rock mass at different depths was determined in the actual design. h The calculation is as follows:

[0027] k h =λm(z-h0) ⑤

[0028] The m is calculated using the following empirical formula:

[0029] In the above formula: k 1z k is the horizontal resistance coefficient of the node at depth z in the semi-infinite rock mass model. 2z s represents the horizontal resistance coefficient of the node at depth z in the finite-width rock mass model; 1z s represents the horizontal displacement of the node at depth z in the semi-infinite rock mass model; 2z λ represents the horizontal displacement of the node at depth z in the finite-width rock mass model; λ is the reduction factor for calculating the m value of the finite rock mass; n represents the rock mass calculation node at multiple depths; z is the depth of the calculation point from the ground; h0 is the excavation depth of the foundation pit under the calculation condition. denoted as the internal friction angle of the rock; c is the cohesion of the rock; Δ is the displacement at the bottom of the pit, which can be taken as 10mm when there is no experience; ξ is an empirical coefficient, which can be taken as 1.0 for rock.

[0030] The preferred technical solution of the present invention is as follows: the value range of the rock shoulder width B in step four is 0.5 to 2m, and the initial value is usually taken as 1 to 1.5m during trial calculation;

[0031] A further technical solution of the present invention: when the overlying soil layer is multi-layered, the layered calculation is performed according to Rankine's earth pressure theory, and the reserved rock shoulder is a single rock layer, which is a relatively complete medium-hard rock or hard rock.

[0032] The beneficial effects of this invention are as follows: This invention proposes a "suspended pile" support system with the pile tip located above the bottom of the foundation pit. By reserving a rock shoulder of a certain width within the pit to provide passive resistance, this system participates in the design calculations of the support system, thereby shortening the rock embedment depth of the support piles, reducing construction difficulty, lowering construction costs, accelerating the foundation pit construction progress, and filling a gap in current specifications. The design method provided by this invention overcomes the shortcomings of traditional design specifications that calculate rock based on soil layers. This method is based on the Hoek-Brown strength criterion, which is more consistent with the properties of rock materials, and considers the embedment effect of the reserved rock shoulder to determine the appropriate rock embedment depth and rock shoulder width. The design steps are clear, the calculation formulas are simple, and it has certain application value for the design of suspended pile support systems. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the design method described in this invention;

[0034] Figure 2 This is a schematic diagram of a semi-infinite rock mass model that meets the model size effect requirements in this invention;

[0035] Figure 3 This is a schematic diagram of a real finite-width rock mass model considering boundary conditions in this invention;

[0036] Figure 4 This is the calculation interface of Tianhan software during the design of suspended piles;

[0037] Figure 5 It is a model for verifying and analyzing the bearing capacity of the reserved rock shoulder.

[0038] In the diagram: 1—Ground surface, 2—Support structure, 3—Reserved rock shoulder, 4—Base, 5—Shear failure surface. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The drawings are simplified illustrations of embodiments of the present invention to concisely and clearly illustrate the purpose of the embodiments. However, it should be understood that the scope of the specific embodiments of the present invention is not limited to the contents of the embodiments and can be implemented in various forms. These embodiments are provided solely for the purpose of more fully disclosing the content of the present invention.

[0040] In this invention, the same parameter symbols refer to the same parameter.

[0041] The design method for the soil-rock combined foundation pit suspended pile support structure provided by this invention includes the design of support piles and reserved rock shoulders. The design process is described in [reference needed]. Figure 1 This includes the following steps:

[0042] Step 1: Establish a semi-infinite rock mass model and an actual finite-width rock mass model. The semi-infinite rock mass model satisfies the size effect requirement, and the actual finite-width rock mass model satisfies the boundary condition requirements, such as... Figure 2 , Figure 3 As shown; the actual finite-width rock mass model meets the boundary condition requirements, is submitted for analysis, and enters the post-processing module; specifically, the rock mass model adopts a plane strain finite element model, considering the influence of model size effect, the calculation depth is twice that on both sides of the rock mass in the horizontal direction, and twice that in the vertical direction. The width of the rock shoulder can be initially assumed to be 1.0~1.5m for trial calculation; the rock layer thickness, parameters, mesh, working conditions, loads, and boundary conditions in the above two models should be consistent; the rock mass model adopts the Hoek-Brown constitutive model, and the mesh size is as fine as possible while ensuring the calculation speed; the load is a uniformly distributed load, acting on the node elements for calculating the horizontal resistance coefficient, in a horizontal direction, and the magnitude should be such that the analysis of the finite rock mass model converges.

[0043] Step 2: Calculate the reduction factor λ of the finite rock mass horizontal resistance coefficient at each depth node using formula ①. z :

[0044]

[0045] In the formula: k 1zk is the horizontal resistance coefficient of the node at depth z in the semi-infinite rock mass model. 2z s represents the horizontal resistance coefficient of the node at depth z in the finite-width rock mass model; 1z s represents the horizontal displacement of the node at depth z in the semi-infinite rock mass model; 2z This represents the horizontal displacement of the node at depth z in a rock mass model with a finite width.

[0046] The average value of the horizontal resistance coefficient reduction factor at each node at different depths is taken as the reduction factor for calculating the horizontal resistance coefficient of the finite rock mass, i.e., the value of m.

[0047]

[0048] In the formula: λ is the reduction factor for calculating the m value of a finite rock mass; n represents the rock mass calculation node at multiple depths.

[0049] Furthermore, the horizontal resistance coefficient of finite-width rock mass at different depths can be calculated:

[0050] k h =λm(z-h0) ③

[0051] In the formula: z is the depth of the calculation point from the ground, and h0 is the excavation depth of the foundation pit under the calculation condition.

[0052] m can be calculated using the following empirical formula:

[0053] In the formula: denoted as the internal friction angle of the rock; c is the cohesion of the rock; Δ is the displacement at the bottom of the pit, which can be taken as 10mm when there is no experience; ξ is an empirical coefficient, which can be taken as 1.0 for rock.

[0054] Step 3: Using the elastic resistance method calculation model, input relevant design parameters such as pile length, pile diameter, soil layer information, and foundation pit depth into the Tianhan Foundation Pit software. The base is defined as the top surface of the reserved rock shoulder. Passive zone reinforcement is performed on the rock strata within the rock shoulder height range. The proportional coefficient of the reinforced horizontal resistance coefficient is input, ensuring it is equal to the proportional coefficient of the horizontal resistance coefficient calculated in Step 2 after substituting the reduction factor. Further, the displacement calculation, passive resistance safety factor calculation, overturning resistance, and sliding resistance calculations of the support piles are completed. Based on the calculation results, the optimal rock embedment depth H is determined, and the pile reinforcement is calculated according to the shear force and bending moment diagrams output by the software. The software calculation interface is shown below. Figure 4 As shown.

[0055] Step 4: Determine the design calculation parameters for the suspended piles, including the optimal rock embedment depth H, reserved rock shoulder width B, height Z, overlying soil unit weight γ1, cohesion c1, and internal friction angle determined in Step 3. Layer thickness h, bedrock unit weight γ, cohesion c, internal friction angle The external friction angle δ at the pile-rock interface, θ is the angle between the most dangerous slip surface and the horizontal plane under the ultimate condition, E a E is the resultant force of the active earth pressure on the retaining pile. p The resultant passive earth pressure on the retaining piles; based on engineering experience, a reserved rock shoulder width B is determined, and the reserved rock shoulder width B is substituted into the formula to verify the bearing capacity of the reserved rock shoulder. The analysis model is as follows: Figure 5 As shown;

[0056] (1) Shear bearing capacity verification of reserved rock shoulder

[0057] The first step in verifying shear bearing capacity is to determine the most dangerous slip surface of the reserved rock shoulder. Based on Coulomb's earth pressure theory, the sliding soil wedge formed at the rock shoulder when the passive limit equilibrium state is reached can be analyzed in two cases according to the relationship between B and H, such as... Figure 5 As shown;

[0058] When aH≤Btanθ, according to the force equilibrium of the triangular sliding soil wedge:

[0059]

[0060] when At that time, E p Take the extreme value, at this time

[0061] In this case, there is room for further reduction in the width of the rock shoulder;

[0062] When Btanθ<H≤Z, according to the force balance of the trapezoidal sliding soil wedge:

[0063]

[0064] because E p As θ increases monotonically, E is equal to 0 when the slip surface is horizontal. p Take the minimum value, at this time

[0065] Based on the static equilibrium of the fractured body, we can obtain:

[0066]

[0067] In the formula: E a For calculating only the soil mass above the bedrock surface, the calculation can be performed using Rankine's earth pressure theory, as shown in the following formula:

[0068]

[0069] Where: K a For the active earth pressure coefficient, we have If there are multiple layers of soil above the bedrock surface, the resultant force should be calculated for each layer.

[0070] Further simplification yields:

[0071]

[0072] (2) The tensile bearing capacity verification shall conform to the following formula:

[0073]

[0074] Further simplification yields:

[0075]

[0076] In the formula: M is the bending moment generated by the active earth pressure on the reserved rock shoulder, and M = E a ·a, where a is the vertical distance from the point of application of the resultant force of the active earth pressure to the verification section; z is the vertical distance from the verification section to the top of the rock shoulder; σ f To reserve the uniaxial tensile strength of the rock shoulder, it is generally taken as 1 / 10 to 1 / 30 of the tensile strength. The specific value should be based on the results of geotechnical tests. If no test data is available, 0.15 times the compressive strength can be used.

[0077] The assumed rock shoulder width B in the finite element model should simultaneously meet the shear and tensile bearing capacity requirements of equations ④ and ⑤. If the verification results do not meet the requirements or have a surplus, the rock shoulder width B should be adjusted and the calculation returned to step one. Only after multiple iterations of trial calculations can the optimal rock embedment depth and rock shoulder width be determined.

[0078] The following is a comparative illustration using a specific example: In a soil-rock combined foundation pit project, the foundation pit is 8m deep and a cantilever pile support method is proposed. The exposed rock layer on the east side of the foundation pit is relatively shallow, 5m from the ground. The overlying soil layer is miscellaneous fill and silty clay. Considering the economic efficiency and ease of construction, a suspended pile support method is adopted. The relevant design parameters of the soil and rock layers are shown in Table 1. The method of this invention is used to design and calculate the support structure on the east side of the foundation pit.

[0079]

[0080] Establish semi-infinite rock mass models and finite-width rock mass models respectively, such as Figure 2 , Figure 3 As shown, the model dimensions are 15m wide and 6m high. A Hawke-Brown constitutive model is used. Based on engineering experience, a rock shoulder width of 1.5m and a calculation depth of 3m are assumed. A uniformly distributed load of 50kPa is considered to account for model convergence. The horizontal displacements on both sides of the model and the vertical and horizontal displacements at the bottom are constrained. The model is then meshed and submitted for calculation and analysis.

[0081] Extract the horizontal displacement of the rock mass nodes at each depth in the two models, and substitute it into formula ② to calculate the reduction factor of the proportional coefficient of the horizontal resistance coefficient of the finite rock mass: λ=0.088.

[0082] The horizontal resistance coefficient provided by the 1.5m wide rock mass reserved in front of the pile is 0.088 times that of the horizontal resistance coefficient calculated by the conventional m method.

[0083] In the Tianhan software, the embedding effect of finite rock mass is simulated by continuously setting internal supports in the embedded rock section. The passive resistance coefficient of finite rock mass is manually input as the support stiffness coefficient, and relevant design calculations are performed to determine the embedding depth as 1.8m.

[0084] By verifying the shear and tensile bearing capacities using equations ④ and ⑤ respectively, and substituting the relevant parameters from this example, the minimum rock shoulder width required to meet the bearing capacity requirement is calculated to be 1.485m. This means that the 1.5m rock shoulder width used in the finite element simulation meets the design requirements. Therefore, the rock embedment depth of this support section is 1.8m, and the reserved rock shoulder width is 1.5m.

[0085] The design method of this invention has a clear mechanical concept, is simple to calculate, and produces stable, reliable and concise calculation results. It solves the problem that current design software cannot accurately calculate and analyze the suspended pile support structure, and provides a feasible design method for the suspended pile support form of soil-rock combined foundation pit in actual engineering.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate specific implementations of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above examples, those skilled in the art should understand that various modifications and changes in form and detail can be made without departing from the spirit of the present invention and without deviating from the scope defined by the claims of the present invention.

Claims

1. A design method for a suspended pile support structure for a soil-rock combined foundation pit, wherein the suspended pile support structure includes support piles and a pre-reserved rock shoulder within the pit, characterized in that... The design methodology includes the following steps: Step 1: Establish a semi-infinite rock mass model and a finite-width rock mass model. The semi-infinite rock mass model satisfies the size effect requirement, and the finite-width rock mass model satisfies the boundary condition requirement. Submit the analysis and enter the post-processing module. Step 2: Calculate the reduction factor of the finite rock mass horizontal resistance coefficient at each depth node of the rock mass based on the post-processing results, further determine the reduction factor of the proportional coefficient of the finite rock mass horizontal resistance coefficient, and substitute the reduction factor into the empirical formula to obtain the horizontal resistance coefficient in the actual design. Step 3: Using the elastic resistance method calculation model, input the pile length, pile diameter, soil layer information, and relevant design parameters for the foundation pit depth into the Tianhan Foundation Pit software. The base is defined as the top surface of the reserved rock shoulder. Passive zone reinforcement is carried out on the rock strata within the height range of the rock shoulder. Input the horizontal resistance coefficient ratio after reinforcement to ensure that it is equal to the horizontal resistance coefficient ratio calculated after substituting the reduction coefficient in Step 2. Further complete the displacement verification of the support piles, passive resistance safety factor verification, overturning resistance and sliding resistance verification. Determine the optimal rock embedment depth H based on the verification results, and perform pile reinforcement according to the shear force and bending moment diagrams output by the software. Step 4: Determine the design calculation parameters for the suspended pile, including the optimal rock embedment depth H, reserved rock shoulder width B, height Z, overburden unit weight γ1, overburden cohesion c1, overburden internal friction angle φ1, layer thickness h, bedrock unit weight γ, rock cohesion c, rock internal friction angle φ, pile-rock interface external friction angle δ, and θ is the angle between the most dangerous slip surface and the horizontal plane under the ultimate condition. Based on engineering experience, determine a reserved rock shoulder width B, and substitute the reserved rock shoulder width B into formulas ① and ② to verify the bearing capacity of the reserved rock shoulder, including the verification of the shear bearing capacity and the tensile bearing capacity of the reserved rock shoulder, both of which should simultaneously meet the requirements. The specific verification process is as follows: (1) The shear bearing capacity of the reserved rock shoulder meets the design requirements when the reserved rock shoulder width B meets the following conditions: a.when At that time, according to the force equilibrium of the triangular sliding soil wedge, we have: At this point, the width of the rock shoulder can be further reduced; b. When When reserving the width B of the rock shoulder, the following conditions must be met: ① In the formula: , ; (2) The tensile bearing capacity of the reserved rock shoulder meets the design requirements when the reserved rock shoulder width B meets the following conditions: ② In the formula: E a M is the resultant force of the active earth pressure on the retaining piles; M is the bending moment generated by the active earth pressure on the reserved rock shoulder. ; a is the vertical distance from the point of application of the resultant force of the active earth pressure to the verification section; z is the vertical distance from the calculation point to the top of the rock shoulder; σ f To reserve the uniaxial tensile strength of the rock shoulder, take 1 / 10 to 1 / 30 of the tensile strength, refer to the results of geotechnical tests, and take 0.15 times the compressive strength when no test data is available; Step 5: The rock shoulder width B in Step 4 should simultaneously meet the requirements of the reserved rock shoulder shear bearing capacity and the reserved rock shoulder tensile bearing capacity. If either condition is not met or there is a surplus, change the value of the rock shoulder width B and perform repeated trial calculations until the optimal rock embedment depth and rock shoulder width are determined.

2. The design method for a soil-rock combined foundation pit suspended pile support structure according to claim 1, characterized in that: In step one, the rock mass model adopts a plane strain model, with the model dimensions taken as twice the calculation depth on both sides in the horizontal direction and twice the calculation depth in the vertical direction.

3. The design method for a soil-rock combined foundation pit suspended pile support structure according to claim 1, characterized in that: In step one, the rock mass model adopts the Hoek-Brown constitutive model, and the rock mass parameters, mesh, working conditions, loads and boundary conditions in the model are kept consistent.

4. The design method for a soil-rock combined foundation pit suspended pile support structure according to claim 1, characterized in that... In step two, the reduction factor λ of the finite rock mass horizontal resistance coefficient at each depth node of the rock mass z The calculation is as follows: ③ Furthermore, the reduction factor λ for the proportionality coefficient of the horizontal resistance coefficient of the finite rock mass is calculated as follows: Obtain the horizontal resistance coefficient in the actual design; ④ Furthermore, the horizontal resistance coefficients of finite rock masses at different depths were determined in the actual design. The calculation is as follows: ⑤ The m is calculated using the following empirical formula: ; In the above formula: k 1z k is the horizontal resistance coefficient of the node at depth z in the semi-infinite rock mass model. 2z s represents the horizontal resistance coefficient of the node at depth z in the finite-width rock mass model; 1z s represents the horizontal displacement of the node at depth z in the semi-infinite rock mass model; 2z λ represents the horizontal displacement of the node at depth z in the finite-width rock mass model; λ is the reduction factor for calculating the m value of the finite rock mass; n represents the rock mass calculation node at multiple depths; z is the depth of the calculation point from the ground; h0 is the excavation depth of the foundation pit under the calculation condition; φ is the internal friction angle of the rock; c is the cohesion of the rock; △ is the displacement at the bottom of the foundation pit, which is taken as 10mm when there is no experience. This is an empirical coefficient, taken as 1.0 for rocks.

5. The design method for a soil-rock combined foundation pit suspended pile support structure according to claim 1, characterized in that: The value of the rock shoulder width B in step four is 0.5~2m, and the initial value of 1~1.5m is used in the trial calculation.

6. A design method for a soil-rock combined foundation pit suspended pile support structure according to any one of claims 1 to 4, characterized in that: When the overlying soil layer is multi-layered, the layered calculation is based on Rankine's earth pressure theory. The reserved rock shoulder is a single rock layer, and it is a relatively complete medium-hard rock or hard rock.

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