A method for optimizing new anchor rod supporting system by expanding slope with residual anchor rods

Abstract

The present application relates to a kind of slope excavation new anchor rod supporting system optimization method using residual anchor rod.The method includes: according to the geometry of slope and anchor rod layout, preliminary selection multiple different excavation slope angle excavation scheme;The excavation area and residual length of anchor rod of each scheme are calculated;Theoretical pullout ultimate bearing capacity of residual anchor rod is calculated based on soil nail theory;The numerical simulation model of slope stability considering and not considering the influence of residual anchor rod reinforcement is established using Midas GTS NX software, and the safety factor and anchor rod axial force distribution are calculated;By comparing the maximum axial force of residual anchor rod calculated by numerical simulation with the theoretical calculation pullout ultimate bearing capacity, the authenticity of numerical simulation safety factor is determined, and the true safety factor is sought;According to true safety factor, the shear strength parameter adjustment coefficient of rock and soil mass is calculated, the enhanced shear strength parameter of rock and soil mass is obtained, input into geotechnical engineering design software, and new support structure design is carried out;Finally, the scheme is compared in technology and economy, and the optimal scheme is selected.

Description

Technical Field

[0001] This invention relates to the field of geotechnical disaster monitoring technology, and in particular to an optimization method for constructing a new anchor support system for slope excavation using residual anchor bolts. Background Technology

[0002] Early-built expressways are gradually reaching saturation levels, impacting their capacity and service quality. In the future, it will be essential to expand and upgrade busy sections of the national expressway network.

[0003] The safe construction of secondary excavation of road cut slopes is a key technical challenge during the reconstruction and expansion of operating highways, especially in mountainous areas. When conducting secondary excavation of slopes in reconstruction and expansion projects, the safety of highway operation and the environmental impact must be fully considered. Due to limitations in excavation and support methods, and the significant difficulties in traffic organization and construction management, the original support structure may be damaged during secondary excavation, creating a new exposed surface. If the newly constructed support structure fails to meet the requirements in terms of strength, stiffness, and support time, slope instability can easily occur, thereby affecting the safety of nearby operating highways.

[0004] Anchor bolt support is a common support method in road slope engineering. In traditional excavation processes, as excavation progresses from top to bottom and from the slope surface into the slope interior, some anchor bolts are damaged and removed along with the soil, leaving the remaining bolts permanently embedded in the slope. Traditional designs do not consider the reuse of these residual anchor bolts, resulting in significant resource waste. Summary of the Invention

[0005] This invention proposes a finite element numerical simulation method that fully considers the reuse of residual initial anchor bolts. Taking into account the reinforcement effect of residual anchor bolts, the method optimizes the support design of the anchor bolt system in slope excavation projects by increasing the excavation slope angle and adjusting parameters such as the prestress, density, and length of newly installed anchor bolts. This method can effectively reduce the excavation volume, decrease the land acquisition area, and control the cost of slope excavation support.

[0006] An optimized method for constructing a new anchor support system for slope excavation using residual anchor bolts includes the following steps:

[0007] Step 1: Based on the slope geometry and anchor bolt layout, select several excavation schemes initially, each with a different excavation slope angle;

[0008] Step 2: Based on the plane geometry, calculate the excavation area and the residual length of the initial anchor bolts after excavation for each excavation scheme;

[0009] Step 3: Based on the soil nail calculation theory, calculate the theoretical pull-out ultimate bearing capacity T of the residual anchor rod;

[0010] Step 4: Establish numerical simulation models of slope stability considering and not considering the influence of residual anchor reinforcement, and calculate the slope safety factor and anchor axial force distribution;

[0011] If the maximum axial force calculated by the numerical simulation of the residual anchor bolts is not greater than the theoretical ultimate tensile strength, then the slope stability safety factor considering the residual anchor bolts is determined to be the true safety factor k. nz Proceed directly to step 6; otherwise, it is a pseudo-safety factor k. nw Proceed to step 5;

[0012] Step 5: If the maximum axial force calculated from the numerical simulation of the residual anchor bolt is greater than the theoretical pull-out ultimate bearing capacity, calculate the maximum pseudo-safety factor reduction factor γ. nm ;

[0013] The maximum axial force is calculated using numerical simulation of the residual anchor bolts. If the maximum axial force calculated by numerical simulation of the residual anchor bolts is not greater than the theoretical ultimate tensile bearing capacity, then the safety factor calculated in this case is the true safety factor, and the process proceeds directly to step 6. Otherwise, step 5 is repeated until the maximum axial force calculated by numerical simulation of the residual anchor bolts is not greater than the theoretical ultimate tensile bearing capacity and the true safety factor is obtained.

[0014] Step 6: Based on the true safety factor, calculate the adjustment coefficient of the slope soil and rock shear strength parameters, and then obtain the enhanced soil and rock shear strength parameters; using the geotechnical engineering design software "Lizheng Geotechnical", input the enhanced soil and rock shear strength parameters, and design the new support structure for slopes with different slope angles in different excavation schemes, and obtain the prestress, diameter, length, and arrangement density and angle of the new anchor bolts;

[0015] Step 7: Conduct a technical and economic comparison of the new anchoring systems for each excavation scheme and select the most economical scheme.

[0016] In step 3, the formula for calculating the theoretical pull-out ultimate bearing capacity T of the residual anchor is:

[0017] T = πDq s L (1)

[0018] Where D is the diameter of the anchor body; q s It is the standard value of the ultimate skin friction between the anchor body and the soil; L is the length of the remaining anchor section.

[0019] In step 4, the calculation method for the slope safety factor and anchor bolt axial force distribution is as follows:

[0020] If the influence of residual anchor reinforcement is not considered, the slope geometry CAD drawing is imported into Midas GTS NX software to establish a numerical calculation model. Soil material and property parameters are set, the "Size Control" option is selected, and the "2D" option is used to generate the mesh. Boundary conditions are set to "Constraint" and gravity load is set to "Self-weight". Based on the excavation area of ​​each excavation scheme and the residual length of each initial anchor, the initial anchors are sequentially cut off to their residual length and the area of ​​the slope region where the cut anchors are located is excavated, according to the order of the initial anchors from top to bottom. These are used as analysis cases for each simulated construction stage. SRM is selected to calculate each analysis case, and the slope stability safety factor k for each simulated construction stage is obtained. n0 SRM refers to the strength reduction method; the attribute parameters include the specific weight, porosity, water content, cohesion, internal friction angle, Poisson's ratio, and standard value of ultimate bond strength of different formation materials, and the specific weight, elastic modulus, and Poisson's ratio of anchor bolts;

[0021] If the influence of residual anchor reinforcement is considered, the anchor is activated to obtain the calculation model. The subsequent steps are consistent with the numerical simulation modeling calculation process for slope stability without considering the influence of residual anchor reinforcement, and the slope stability safety factor k is obtained. nw Distribution of axial force on residual anchor bolts on slopes.

[0022] If the slope stability coefficient is less than 1, the excavation scheme is eliminated.

[0023] Step 5 includes:

[0024] Step 51. Initialize the reduction factor range, pseudo-safety factor reduction factor γ n The value range is (0,1), γ low =0,γ high =1; Calculate the median value of the reduction factor.

[0025] Step 52. Based on the median value of the reduction factor, perform slope numerical simulation modeling for each excavation scheme. The obtained shear strength parameters include the simulated cohesion C. n and simulated internal friction angle

[0026] c n =[k n0 +γ mid (k nw -k n0 )]C0 (2)

[0027]

[0028] Where c0 is the original slope cohesion. The original internal friction angle of the slope; k n0To disregard the safety factor for slope stability of residual anchor bolts, k nw To account for the pseudo-safety factor of slope stability due to residual anchor bolts;

[0029] Step 53. Place C n and Substituting the values ​​into the numerical simulation static load case calculation, the maximum axial force of the residual anchor bolt is obtained. If the maximum axial force is greater than the theoretical pull-out ultimate bearing capacity, it indicates that the current γ mid It's too small, it needs to be increased, i.e., γ low =γ mid Proceed to step 54;

[0030] If the maximum axial force is less than or equal to the theoretical ultimate tensile strength, then it indicates that the current γ mid The maximum pseudo-safety factor reduction factor γ nm Proceed to step 55;

[0031] Step 54. Repeat steps 51 to 53 until the maximum axial force obtained from the numerical simulation of the residual anchor bolt is less than or equal to the maximum pseudo-safety factor reduction factor γ of the theoretical pull-out ultimate bearing capacity. nm Proceed to step 55;

[0032] Step 55. Calculate the true safety factor k nz :

[0033] k nz =[k n0 +γ nm (k nw -k n0 (4)

[0034] Where, k nz For the true safety factor, k n0 To disregard the safety factor for slope stability of residual anchor bolts, k nw To account for the pseudo-safety factor of slope stability considering residual anchor bolts, γ nm Maximum pseudo-safety factor reduction factor.

[0035] Step 6 includes: adjusting the shear strength parameter α of the slope soil and rock mass. n The calculation method is as follows:

[0036] α n =k nz / k n0 (5)

[0037] Where, α n This refers to the adjustment coefficient for the shear strength parameters of the slope's soil and rock mass.

[0038] Based on the adjustment coefficient α of the slope soil and rock shear strength parameters nCalculate the shear strength parameters of the reinforced soil and rock mass:

[0039] C nt =α n C0 (6)

[0040]

[0041] Where c0 is the original slope cohesion. c is the original internal friction angle of the slope; nt For the enhanced cohesion in the nth excavation scheme, Let be the enhanced internal friction angle in the nth excavation scheme.

[0042] The beneficial effects of this invention mainly include the following:

[0043] Reduce excavation volume: By optimizing the excavation plan and selecting the plan with the least excavation volume as the optimal plan, unnecessary earthwork is reduced, construction costs are lowered, and environmental impact is reduced.

[0044] Controlling support costs: By utilizing residual anchor bolts, the number and length of newly constructed anchor bolts are reduced, thereby lowering the construction cost of the support structure.

[0045] Improve slope stability: Through numerical simulation and repeated calculation of the true safety factor, the stability of the slope during construction and after completion is ensured, thereby improving the safety of the project.

[0046] Optimize resource allocation: Make full use of existing anchor bolt resources, avoid resource waste, and improve resource utilization efficiency.

[0047] Improved design accuracy: Through numerical simulation and parameter adjustment, the accuracy of support design was improved, ensuring the rationality and reliability of the design scheme.

[0048] Enhanced engineering adaptability: This method is applicable to different geological conditions and engineering needs, and has strong adaptability and flexibility. Attached Figure Description

[0049] Figure 1 This is a schematic flowchart of the method of the present invention;

[0050] Figure 2 This is a schematic diagram of the original slope and excavation scheme in Example 1;

[0051] Figure 3 The diagram shows the process of importing the geometric model of Example 1 into Midas GTS software.

[0052] Figure 4 The Midas GTS software operation diagram for setting material parameters in Example 1;

[0053] Figure 5 Midas GTS software operation diagram for setting unit attributes in Example 1;

[0054] Figure 6 A diagram showing the operation of the Midas GTS software for size control in Example 1;

[0055] Figure 7 This is a diagram illustrating the operation of the Midas GTS software for mesh generation in Example 1.

[0056] Figure 8 Midas GTS software operation diagram for setting boundary conditions in Example 1;

[0057] Figure 9 The Midas GTS software operation diagram for setting gravity load in Example 1;

[0058] Figure 10 A diagram of the Midas GTS software operation during the construction phase is set up for Example 1;

[0059] Figure 11 The Midas GTS software operation diagram for setting up analysis conditions in Example 1;

[0060] Figure 12 The image shows the results of the slope safety factor calculation in Example 1 without considering the residual anchor reinforcement effect, displayed in Midas GTS software.

[0061] Figure 13 This is a screenshot of the Midas GTS software display when the anchor bolt is activated in Example 1;

[0062] Figure 14 The diagram shows the axial force of each excavation scheme in Example 1;

[0063] Figure 15 Correcting the geotechnical operation page of the geotechnical engineering design software;

[0064] Figure 16 This refers to the basic settings for the Lizheng Geotechnical Software in Example 1;

[0065] Figure 17 This refers to the slope ratio setting in the Lizheng Geotechnical Software for Example 1;

[0066] Figure 18 Inputting formation parameters for the Lizheng Geotechnical Software in Example 1;

[0067] Figure 19 Input the anchor bolt design parameters for the Lizheng Geotechnical Software in Example 1;

[0068] Figure 20 This is the display page showing the safety factor calculated by the Lizheng Geotechnical Software when no anchor bolt support is set in excavation scheme 1 of Example 1.

[0069] Figure 21 The page displays the safety factor calculated by the Lizheng Geotechnical Software when setting up anchor support for excavation scheme 2 in Example 1;

[0070] Figure 22 The page displays the safety factor calculated by the Lizheng Geotechnical Software when setting up anchor support for excavation scheme 3 in Example 1. Detailed Implementation

[0071] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0072] Technical terms

[0073] Anchored slope: refers to an engineering structure that connects the slope rock and soil mass to the stable strata through anchor bolts or other anchoring structures to improve the stability of the slope.

[0074] Safety factor: refers to the ratio of the anti-sliding force to the sliding force of a slope under design conditions, and is used to measure the stability of a slope.

[0075] Ultimate pull-out bearing capacity: refers to the maximum pull-out force that an anchor rod can withstand in the soil.

[0076] Numerical simulation of slopes: refers to the use of computer software Midas GTS NX to simulate and calculate the stability of slopes in order to predict the safety factor of slopes under different working conditions.

[0077] Pseudo-safety factor: In numerical simulation, the safety factor is obtained when the effect of residual anchor reinforcement is considered and the maximum axial force of the residual anchor is greater than the ultimate pull-out force of the residual anchor.

[0078] True safety factor: refers to the actual safety factor obtained after adjusting for the pseudo safety factor by reducing the pseudo safety factor.

[0079] Shear strength parameters: refer to the soil's ability to resist shear deformation, usually expressed by cohesion and internal friction angle.

[0080] Example 1

[0081] Taking the design of a first-level anchored slope excavation as an example, the steps of this invention will be described in detail.

[0082] The basic conditions of the slope are as follows: The slope safety level is Class II. The slope height is 8m, and the slope angle is 50°. Four layers of anchor bolts are installed on the slope, with each anchor bolt being 12m long, spaced 2m x 2m apart, and tilted at a 15° angle to the horizontal. The anchorage section and free section are each 6m long. The anchor bolt diameter is 25mm, the anchor body diameter is 150mm, and the prestress is 200kN. The anchorage section is the part of the anchor bolt that penetrates into the stable soil and rock mass, providing tensile strength through the bond or friction with the surrounding soil and rock mass. It is located in the stable soil and rock mass outside the theoretical sliding surface. The free section refers to the part from the anchor bolt head to the anchorage section, passing through the unstable soil and rock mass. Its main function is to transfer the tensile force from the anchor bolt head to the anchorage section.

[0083] The calculation parameters for slope strata and anchor materials are shown in Table 1:

[0084] Table 1. Calculation parameters for strata and anchor bolts

[0085]

[0086] Step 1. Initial selection of excavation plan, such as... Figure 2 As shown in figures a, b, c, and d, preliminary excavation schemes 1, 2, and 3 are selected. Blue represents the anchoring section of the anchor bolt, and black represents the free section. The magenta line segment represents the slope line after excavation. The slope angles between the slope line and the horizontal plane for preliminary excavation schemes 1, 2, and 3 are 70°, 60°, and 50°, respectively. The anchor bolts are numbered from top to bottom as Anchor Bolt 1, Anchor Bolt 2, Anchor Bolt 3, and Anchor Bolt 4.

[0087] Step 2. Calculate the excavation area and the remaining length of the initial anchor bolts: Based on the plane geometry, calculate the excavation area and the remaining length of the initial anchor bolts after excavation for each excavation scheme, as shown in Table 2:

[0088] Table 2. List of parameters for the preliminary excavation scheme

[0089]

[0090] Step 3. Based on soil nailing calculation theory, calculate the theoretical pull-out ultimate bearing capacity T of the residual anchor:

[0091] The theoretical pull-out ultimate bearing capacity of the residual anchor bolt is calculated according to Formula 1:

[0092] T = πDq s L (1)

[0093] Where D is the diameter of the anchor body (m); q s is the standard value of the ultimate skin friction between the anchor body and the soil (kPa), which is 95kPa in this embodiment; L is the length of the remaining anchor section (m).

[0094] In all three schemes, the anchor body of the anchor bolt was not removed by excavation, and the length of the remaining anchor body of the anchor bolt was 6m. Therefore, the theoretical ultimate tensile strength was 268.47kN.

[0095] Step 4. Numerical simulation modeling and calculation of slope:

[0096] Midas GTS NX is a professional geotechnical engineering simulation software. Based on different excavation schemes, Midas GTS NX software was used to establish numerical simulation models of slope stability considering and not considering the effects of residual anchor reinforcement, respectively, and to calculate the slope safety factor and anchor axial force distribution.

[0097] The numerical simulation modeling and calculation process for slope stability without considering the influence of residual anchor reinforcement is as follows:

[0098] like Figure 3 Import the CAD drawings of the slope geometry for each excavation scheme into Midas GTS NX software to establish a numerical calculation model, such as... Figure 4 The formation material is set as shown, and the attribute parameters are set according to Table 1, such as... Figure 5 The material properties are set to 2D properties as shown. Figure 6 As shown, select "Size Control". Figure 7 The image shows the mesh created using the "2D" option. Figure 8 The boundary conditions are set to the "Constraint" option as shown. Figure 9 Set the gravity load to the "self-weight" option, such as... Figures 10-11 The diagram shows the construction steps and analysis conditions for each excavation scheme. Based on the excavation area and the remaining length of each initial anchor bolt, the initial anchor bolts are sequentially cut to their remaining length and the area of ​​the slope where the cut anchor bolts are located is excavated, arranged from top to bottom. These are used as analysis conditions for each simulated construction stage. SRM is selected to calculate each analysis condition. Figure 12 The slope stability safety factor for each simulated construction stage is obtained in the "cloud map". Since the anchor body obtained in step 3 of this embodiment has not been excavated and removed, the influence of residual anchor reinforcement is not considered. Therefore, the anchor does not need to be activated in the entire calculation process.

[0099] SRM stands for Strength Reduction Method, used for slope stability analysis. Its basic principle is to gradually increase the reduction factor, correspondingly reducing the soil's shear strength indices (such as cohesion and internal friction angle), and repeatedly perform trial calculations on the slope until the slope reaches the critical state of limit equilibrium.

[0100] The numerical simulation modeling and calculation process for slope stability considering the influence of residual anchor reinforcement is as follows: Figure 13The calculation model is obtained by activating the anchor bolts as shown. The subsequent steps are consistent with the numerical simulation modeling calculation process for slope stability without considering the influence of residual anchor bolt reinforcement, as shown in Table 3 and... Figure 14 The results show the slope stability safety factor and the distribution of residual anchor force on the slope.

[0101] The slope stability safety factor should be greater than or equal to 1; otherwise, the temporary stability of the slope during excavation cannot be guaranteed. If the slope stability safety factor is less than 1, the excavation plan will be rejected.

[0102] Numerical simulations can provide the axial force at each point on the anchor bolt. By comparing the maximum axial force of the residual anchor bolt calculated in the numerical simulation with the theoretical pull-out bearing capacity under each analysis condition using SRM, if the maximum axial force of the residual anchor bolt calculated in the numerical simulation for the nth excavation scheme is less than the theoretical pull-out ultimate bearing capacity, it indicates that the stability safety factor in this scheme is the true safety factor k. nz If the maximum axial force calculated by the numerical simulation of the residual anchor bolt is greater than the theoretical pull-out limit bearing capacity, it indicates that the stability safety factor in this scheme is a pseudo-safety factor, and then proceed to step 5.

[0103] Table 3 Safety Factor, Maximum Axial Force, and Judgment of the Authenticity of Safety Factor

[0104]

[0105] As shown in Table 3, the slope stability safety factors of all three schemes meet the requirements.

[0106] The axial force diagrams of the residual anchors on the slope are shown in the original slope anchor diagram and the diagram considering the impact of residual anchor reinforcement on slope stability in the three excavation schemes. Figure 14 As shown.

[0107] Step 5. Maximum pseudo-safety factor reduction factor γ nm Trial calculation:

[0108] Step 51. Initialize the reduction factor range, pseudo-safety factor reduction factor γ n The value range is (0,1), γ low =0,γ high =1; Calculate the median value of the reduction factor.

[0109] Step 52. Based on the median value of the reduction factor, perform slope numerical simulation modeling for the nth excavation scheme. The obtained shear strength parameters include the simulated cohesion C. n and simulated internal friction angle

[0110] C n =[k n0 +γ mid (k nw -kn0 )]C0 (2)

[0111]

[0112] Where c0 is the original slope cohesion (kPa), The original internal friction angle of the slope (°); k n0 Let k be the slope stability safety factor for the nth excavation scheme, ignoring residual anchor bolts. nw The pseudo-safety factor for slope stability considering residual anchor bolts in the nth excavation scheme;

[0113] Step 53. Place C n and Substituting the values ​​of each analysis case into the numerical simulation static load calculation, the maximum axial force of the residual anchor bolt is obtained. If the maximum axial force is greater than the theoretical pull-out ultimate bearing capacity, it indicates that the current γ mid It's too small, it needs to be increased, i.e., γ low =γ mid Proceed to step 54;

[0114] If the maximum axial force is less than or equal to the theoretical ultimate tensile strength, then it indicates that the current γ mid The maximum pseudo-safety factor reduction factor γ nm Proceed to step 55;

[0115] Step 54. Repeat steps 51 to 53 until the maximum axial force obtained from the numerical simulation of the residual anchor bolt is less than or equal to the maximum pseudo-safety factor reduction factor γ of the theoretical pull-out ultimate bearing capacity. nm Proceed to step 55;

[0116] Step 55. Calculate the true safety factor k nz

[0117] At this time, k nz =[k n0 +γ nm (k nw -k n0 (4)

[0118] In the nth excavation scheme, the slope stability safety factor, excluding residual anchor bolts, is denoted as k. n0 The pseudo-safety factor is denoted as k. nw .

[0119] Step 6. After obtaining the true safety factor, design the new anchor bolt support system.

[0120] Calculate the adjustment coefficient for the shear strength parameter of the slope soil and rock mass in the nth excavation scheme:

[0121] α n =knz / k n0 (5)

[0122] Calculate the shear strength parameters of the reinforced soil and rock mass based on the adjustment coefficient of the slope soil and rock mass:

[0123] In the subsequent design of the new anchor bolt support system, the residual anchor bolts on the slope are left as soil nails in the slope to reinforce it. The reinforcement effect of the new anchor bolt support system is considered by increasing the shear strength parameters of the slope's soil and rock mass. The enhanced shear strength parameters of the soil and rock mass are as follows:

[0124] C nt =α n C0 (6)

[0125]

[0126] Among them, c nt Let be the enhanced cohesion (kPa) in the nth excavation scheme; α is the enhanced internal friction angle (°) in the nth excavation scheme; n This is the adjustment coefficient for the shear strength parameter of the slope soil and rock mass in the nth excavation scheme.

[0127] The true safety factor and the adjustment coefficient of the soil and rock shear strength parameters for different excavation schemes in this embodiment are shown in Table 4:

[0128] Table 4 Safety factors and adjustment coefficients for soil and rock shear strength parameters under different excavation schemes

[0129]

[0130] like Figures 15-22 As shown, using the geotechnical engineering design software "Lizheng Geotechnical", the shear strength parameters of the enhanced soil and rock mass (as shown in Table 5) were input to design new support structures for slopes with different angles under different excavation schemes. The design steps include: Figure 16 Set basic conditions, such as Figure 17 Set the slope ratio and input the geological parameters (as shown in Table 5). Figure 18 ),like Figure 19 Enter the anchor bolt design parameters, and finally click the calculate button to perform the calculation. For example... Figures 20-22 The overall stability calculation results of the three schemes were obtained. According to the "Specifications for Design of Highway Subgrade" (JTG D30-2015), the safety factor for slope stability of expressways and Class I highways should be greater than or equal to 1.20. The fact that the calculated safety factor after adding anchor bolts is greater than the specification requirement indicates that the design is feasible. The design of the new anchoring system for the three excavation schemes was carried out separately, and the parameters such as the diameter, length, arrangement density, and angle of the new anchor bolts were obtained, as shown in Table 6.

[0131] Table 5 Shear strength parameters of soil and rock masses enhanced by different excavation schemes

[0132]

[0133] The anchor bolt design parameters for the three excavation schemes are as follows:

[0134] Table 6 Design schemes for newly built anchorage support systems under different excavation methods

[0135]

[0136] Step 7: Technical and economic comparison and selection of the optimal solution.

[0137] Based on a longitudinal extension length of 20m for the slope, the cost for slope anchor bolt construction is 60 yuan / m, and the cost for earthwork excavation is 10 yuan / m. 3 Costing was conducted, and a technical and economic comparison was performed on the three options.

[0138] Table 7. Technical and economic comparison of newly constructed anchorage support systems under different excavation schemes.

[0139]

[0140] As shown in Table 7, excavation scheme 3 does not require anchor bolt support, has the lowest total cost, and has a shorter construction period than the other two schemes. Therefore, excavation scheme 3 should be the preferred option.

[0141] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An optimized method for constructing a new anchor support system in slope excavation using residual anchor bolts, characterized in that, Includes the following steps: Step 1: Based on the slope geometry and anchor bolt layout, select several excavation schemes initially, each with a different excavation slope angle; Step 2: Based on the plane geometry, calculate the excavation area and the residual length of the initial anchor bolts after excavation for each excavation scheme; Step 3: Based on the soil nail calculation theory, calculate the theoretical pull-out ultimate bearing capacity T of the residual anchor rod; Step 4: Establish numerical simulation models of slope stability considering and not considering the influence of residual anchor reinforcement, and calculate the slope safety factor and anchor axial force distribution; If the maximum axial force calculated by the numerical simulation of the residual anchor bolts is not greater than the theoretical ultimate tensile strength, then the slope stability safety factor considering the residual anchor bolts is determined to be the true safety factor k. nz Proceed directly to step 6; otherwise, it is a pseudo-safety factor k. nw Proceed to step 5; Step 5: If the maximum axial force calculated from the numerical simulation of the residual anchor bolt is greater than the theoretical pull-out ultimate bearing capacity, calculate the maximum pseudo-safety factor reduction factor γ. nm ; The maximum axial force is calculated using numerical simulation of the residual anchor bolts. If the maximum axial force calculated by numerical simulation of the residual anchor bolts is not greater than the theoretical ultimate tensile bearing capacity, then the safety factor calculated in this case is the true safety factor, and the process proceeds directly to step 6. Otherwise, step 5 is repeated until the maximum axial force calculated by numerical simulation of the residual anchor bolts is not greater than the theoretical ultimate tensile bearing capacity and the true safety factor is obtained. Step 6: Based on the true safety factor, calculate the adjustment coefficient of the slope soil and rock shear strength parameters, and then obtain the enhanced soil and rock shear strength parameters; using the geotechnical engineering design software "Lizheng Rock and Soil", input the enhanced soil and rock shear strength parameters, and design the new support structure for slopes with different slope angles in different excavation schemes, and obtain the prestress, diameter, length, and arrangement density and angle of the new anchor bolts; Step 7: Conduct a technical and economic comparison of the new anchoring systems for each excavation scheme and select the most economical scheme.

2. The method according to claim 1, characterized in that, In step 3, the theoretical pull-out ultimate bearing capacity T of the residual anchor is calculated using the following formula: T=πDq s L (1) Where D is the diameter of the anchor body; q s It is the standard value of the ultimate skin friction between the anchor body and the soil; L is the length of the remaining anchor section.

3. The method according to claim 1, characterized in that, In step 4, the calculation method for the slope safety factor and anchor bolt axial force distribution is as follows: If the influence of residual anchor reinforcement is not considered, the slope geometry CAD drawing is imported into Midas GTS NX software to establish a numerical calculation model. Soil material and property parameters are set, the "Size Control" option is selected, and the "2D" option is used to generate the mesh. Boundary conditions are set to "Constraint" and gravity load is set to "Self-weight". Based on the excavation area of ​​each excavation scheme and the residual length of each initial anchor, the initial anchors are sequentially cut off to their residual length and the area of ​​the slope region where the cut anchors are located is excavated, according to the order of the initial anchors from top to bottom. These are used as analysis cases for each simulated construction stage. SRM is selected to calculate each analysis case, and the slope stability safety factor k for each simulated construction stage is obtained. n0 SRM refers to the strength reduction method; the attribute parameters include the specific weight, porosity, water content, cohesion, internal friction angle, Poisson's ratio, and standard value of ultimate bond strength of different formation materials, and the specific weight, elastic modulus, and Poisson's ratio of anchor bolts; If the influence of residual anchor reinforcement is considered, the anchor is activated to obtain the calculation model. The subsequent steps are consistent with the numerical simulation modeling calculation process for slope stability without considering the influence of residual anchor reinforcement, and the slope stability safety factor k is obtained. nw Distribution of axial force on residual anchor bolts on slopes.

4. The method according to claim 3, characterized in that, If the slope stability coefficient is less than 1, the excavation scheme is eliminated.

5. The method according to claim 1, characterized in that, Step 5 includes: Step 51. Initialize the reduction factor range, pseudo-safety factor reduction factor γ n The value range is (0,1), γ low =0,γ high =1; Calculate the median value of the reduction factor. Step 52. Based on the median value of the reduction factor, perform slope numerical simulation modeling for each excavation scheme. The obtained shear strength parameters include the simulated cohesion C. n and simulated internal friction angle C n =[k n0 +γ mid (k nw -k n0 )]C0 (2) Where c0 is the original slope cohesion. The original internal friction angle of the slope; k n0 To disregard the safety factor for slope stability of residual anchor bolts, k nw To account for the pseudo-safety factor of slope stability due to residual anchor bolts; Step 53. Place C n and Substituting the values ​​into the numerical simulation static load case calculation, the maximum axial force of the residual anchor bolt is obtained. If the maximum axial force is greater than the theoretical pull-out ultimate bearing capacity, it indicates that the current γ mid It's too small, it needs to be increased, i.e., γ low =γ mid Proceed to step 54; If the maximum axial force is less than or equal to the theoretical ultimate tensile strength, then it indicates that the current γ mid The maximum pseudo-safety factor reduction factor γ nm Proceed to step 55; Step 54. Repeat steps 51 to 53 until the maximum axial force obtained from the numerical simulation of the residual anchor bolt is less than or equal to the maximum pseudo-safety factor reduction factor γ of the theoretical pull-out ultimate bearing capacity. nm Proceed to step 55; Step 55. Calculate the true safety factor k nz : k nz =[k n0 +γ nm (k nm -k n0 )] (4) Where, k nz For the true safety factor, k n0 To disregard the safety factor for slope stability of residual anchor bolts, k nw To account for the pseudo-safety factor of slope stability considering residual anchor bolts, γ nm Maximum pseudo-safety factor reduction factor.

6. The method according to claim 1, characterized in that, Step 6 includes: adjusting the shear strength parameter α of the slope soil and rock mass. n The calculation method is as follows: a n =k nz / k n0 (5) Where, α n This refers to the adjustment coefficient for the shear strength parameters of the slope's soil and rock mass. Based on the adjustment coefficient α of the slope soil and rock shear strength parameters n Calculate the shear strength parameters of the reinforced soil and rock mass: C nt =a n C0 (6) Where c0 is the original slope cohesion. c is the original internal friction angle of the slope; nt For the enhanced cohesion in the nth excavation scheme, Let be the enhanced internal friction angle in the nth excavation scheme.

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