Method for optimizing side slope expanding and excavating newly-built anchor rod supporting system through residual anchor rods

Abstract

The invention relates to a method for optimizing a newly-built anchor rod supporting system for slope expanding excavation by using residual anchor rods. The method comprises the following steps: preliminarily selecting a plurality of excavation schemes of different excavation slope angles according to the geometrical morphology of the side slope and the layout of anchor rods; calculating the excavation area and the residual length of the anchor rod of each scheme; calculating the theoretical ultimate uplift bearing capacity of the residual anchor rod based on the soil nail theory; midas GTS NX software is used for establishing a slope stability numerical simulation model considering and not considering the influence of residual anchor rod reinforcement, and a safety coefficient and anchor rod axial force distribution are calculated; by comparing the maximum axial force of the residual anchor rod obtained through numerical simulation calculation with the ultimate uplift bearing capacity obtained through theoretical calculation, the authenticity of the numerical simulation calculation safety coefficient is judged, and the true safety coefficient is sought; calculating a rock-soil body shear strength parameter adjustment coefficient according to the true safety coefficient to obtain an enhanced rock-soil body shear strength parameter, inputting the enhanced rock-soil body shear strength parameter into geotechnical engineering design software, and designing a newly-built support structure; and finally, technical and economic comparison and selection are carried out on the schemes, and the optimal scheme is selected.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical disaster monitoring, and particularly to an optimization method for a new anchor support system for slope excavation and reconstruction using residual anchor rods. Background Art

[0002] The traffic volume of early-built and opened highways is becoming increasingly saturated, affecting the road traffic capacity and service level. In the coming period, it is very necessary to promote the expansion and reconstruction of busy channels of the national highway.

[0003] During the reconstruction and expansion of operating highways, the safe construction of secondary excavation of cut slopes is a technical difficulty in the reconstruction and expansion of operating highways, especially in the reconstruction and expansion projects of mountain highways, and this problem is more prominent. When conducting secondary excavation of slopes in reconstruction and expansion projects, it is necessary to fully consider the safety of highway operation during construction and the impact on the environment. Due to the limitations of excavation and support construction means, and the large difficulty of traffic organization and construction management, during the secondary excavation of slopes, the original support structure may be damaged, forming a new free face. If the newly built support structure fails to meet the requirements in terms of strength, stiffness, and support time, it is extremely easy to cause slope instability, thus affecting the safety of nearby operating highways.

[0004] Anchor support is a common support means in road slope engineering. During the traditional excavation construction process, as the excavation progresses step by step from top to bottom and from the slope surface to the slope interior, some anchor rod bodies will be damaged and excavated and removed together with the soil, while the remaining part of the anchor rod will remain permanently in the slope body. In traditional designs, the reuse of these residual anchor rods is not considered, resulting in great waste of resources. Summary of the Invention

[0005] The present invention proposes a method based on finite element numerical simulation calculation, which fully considers the reuse of residual initial anchor rods. Considering the reinforcement effect of residual anchor rods, by increasing the excavation slope angle and adjusting parameters such as the prestress, layout density, and length of the newly built anchor rods, the support design of the anchor rod system in slope excavation projects is optimized. This method can effectively reduce the excavation volume, reduce the construction land acquisition area, and control the cost of support for the excavated slope.

[0006] An optimization method for a new anchor support system for slope excavation and reconstruction using residual anchor rods includes the following steps:

[0007] Step 1: According to the slope geometry and anchor rod layout, initially select multiple excavation plans, each with a different excavation slope angle;

[0008] Step 2: According to the plane geometric relationship, calculate the excavation area of each excavation plan and the residual length of the initial anchor rod after excavation;

[0009] Step 3: Calculate the theoretical ultimate tensile bearing capacity T of the residual anchor based on the soil nailing calculation theory;

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

[0011] If the maximum axial force calculated by numerical simulation of the residual anchor is not greater than the theoretical ultimate tensile bearing capacity, it is determined that the slope stability safety factor considering the residual anchor is the true safety factor k nz , and directly enter Step 6; otherwise, it is the pseudo-safety factor k nw Enter Step 5;

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

[0013] Using the maximum axial force calculated by numerical simulation of the residual anchor, if the maximum axial force calculated by numerical simulation of the residual anchor is not greater than the theoretical ultimate tensile bearing capacity, the safety factor calculated this time is the true safety factor, and directly enter Step 6; otherwise, repeat Step 5 until the maximum axial force calculated by numerical simulation of the residual anchor is not greater than the theoretical ultimate tensile bearing capacity, and obtain the true safety factor;

[0014] Step 6: According to the true safety factor, calculate the adjustment coefficient of the shear strength parameters of the slope rock and soil mass, and then obtain the enhanced shear strength parameters of the rock and soil mass; Using the geotechnical engineering design software "LiZheng Geotechnical", input the enhanced shear strength parameters of the rock and soil mass, and conduct the design of the new support structure for the slopes with different slope angles in each different excavation plan to obtain the prestress, diameter, length, and arrangement density and angle of the new anchor;

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

[0016] In the said Step 3, the calculation formula for the theoretical ultimate tensile 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 is the standard value of the ultimate frictional resistance between the anchor body and the soil; L is the anchorage section length of the residual anchor.

[0019] In the said Step 4, the calculation methods for the slope safety factor and the distribution of anchor shaft force are:

[0020] If the influence of residual anchor rod reinforcement is not considered, the geometric shape CAD drawing of the slope is imported into the Midas GTS NX software to establish a numerical calculation model. The formation material and property parameters are set. The "Size Control" option is selected and the "2D" option is used to divide the mesh. The boundary condition is set as the "Constraint" option and the gravity load is set as the "Self-weight" option. According to the excavation area of each excavation plan and the residual length of each initial anchor rod, in the order of the arrangement of each initial anchor rod from top to bottom, the residual length to which each initial anchor rod is truncated and the excavated area of the slope area where the truncated initial anchor rod is located are set successively as the analysis working conditions of each simulated construction stage. The SRM is selected to calculate each analysis working condition, and the slope stability safety factor k of each simulated construction stage is obtained. n0 ; SRM refers to the strength reduction method; the property parameters include the unit weight, porosity, water content, cohesion, internal friction angle, Poisson's ratio, standard value of ultimate bond strength of different formation materials, and the unit weight, elastic modulus, and Poisson's ratio of the anchor rod.

[0021] If the influence of residual anchor rod reinforcement is considered, the anchor rod is activated to obtain the calculation model. The subsequent steps are the same as the numerical simulation modeling calculation process of slope stability without considering the influence of residual anchor rod reinforcement, and the slope stability safety factor k is obtained. nw and the axial force distribution of the slope residual anchor rod.

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

[0023] The step 5 includes:

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

[0025] Step 52. According to the intermediate value of the reduction coefficient, conduct slope numerical simulation modeling for each excavation plan. The obtained shear strength parameters include the simulated cohesion C n and the simulated internal friction angle

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

[0027]

[0028] where, c0 is the cohesion of the original slope, is the internal friction angle of the original slope; k n0is the safety factor of slope stability without considering residual anchor bolts, k nw is the pseudo-safety factor of slope stability considering residual anchor bolts;

[0029] Step 53. Substitute C n and into the numerical simulation static condition calculation to obtain the maximum axial force of the residual anchor bolt in the numerical simulation calculation. If the maximum axial force is greater than the theoretical ultimate tensile bearing capacity, it indicates that the current γ mid is too small and needs to be increased, that is, γ low =γ mid , and enter Step 54;

[0030] If the maximum axial force is less than or equal to the theoretical ultimate tensile bearing capacity, it indicates that the current γ mid is the reduction coefficient γ nm of the maximum pseudo-safety factor, and enter Step 55;

[0031] Step 54. Repeat Steps 51 - 53 until the reduction coefficient γ nm of the maximum pseudo-safety factor when the maximum axial force of the residual anchor bolt in the numerical simulation calculation is less than or equal to the theoretical ultimate tensile bearing capacity is obtained, and enter 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 is the true safety factor, k n0 is the safety factor of slope stability without considering residual anchor bolts, k nw is the pseudo-safety factor of slope stability considering residual anchor bolts, and γ nm is the reduction coefficient of the maximum pseudo-safety factor.

[0035] The said Step 6 includes: The calculation method of the adjustment coefficient α n of the shear strength parameters of the slope rock and soil mass is:

[0036] α n =k nz / k n0 (5)

[0037] where α n is the adjustment coefficient of the shear strength parameters of the slope rock and soil mass;

[0038] According to the adjustment coefficient α n, calculate the enhanced shear strength parameters of the rock and soil mass:

[0039] C nt = α n C0 (6)

[0040]

[0041] where c0 is the cohesion of the original slope, is the internal friction angle of the original slope; c nt is the enhanced cohesion in the nth excavation plan, is the enhanced internal friction angle in the nth excavation plan.

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

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

[0044] Control the support cost: By utilizing the residual bolts, the number and length of newly built bolts are reduced, etc., and the construction cost of the support structure is lowered.

[0045] Improve the 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, and the safety of the project is improved.

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

[0047] Improve the design accuracy: Through numerical simulation and parameter adjustment, the accuracy of the support design is improved, and the rationality and reliability of the design plan are ensured.

[0048] Enhance the project adaptability: This method is applicable to different geological conditions and project requirements, and has strong adaptability and flexibility. Description of the Drawings

[0049] Figure 1 is the flow schematic diagram of the method of the present invention;

[0050] Figure 2 is the schematic diagram of the original slope and the excavation plan in Embodiment 1;

[0051] Figure 3 is the operation diagram of importing the geometric model of Embodiment 1 into the Midas GTS software;

[0052] Figure 4 is the operation diagram of setting material parameters in the Midas GTS software in Embodiment 1;

[0053] Figure 5 Unit property setting for Example 1, operation diagram of Midas GTS software

[0054] Figure 6 Dimension control setting for Example 1, operation diagram of Midas GTS software

[0055] Figure 7 Mesh generation for Example 1, operation diagram of Midas GTS software

[0056] Figure 8 Boundary condition setting for Example 1, operation diagram of Midas GTS software

[0057] Figure 9 Gravity load setting for Example 1, operation diagram of Midas GTS software

[0058] Figure 10 Construction stage setting for Example 1, operation diagram of Midas GTS software

[0059] Figure 11 Analysis case setting for Example 1, operation diagram of Midas GTS software

[0060] Figure 12 Calculation result of slope safety factor without considering the reinforcement effect of residual anchor bolts for Example 1, display diagram of Midas GTS software

[0061] Figure 13 Activation of anchor bolts in Example 1, display diagram of Midas GTS software

[0062] Figure 14 Axial force diagrams for each excavation plan in Example 1

[0063] Figure 15 Operation page of Lizheng Geotechnical Engineering Design Software

[0064] Figure 16 Basic condition setting of Lizheng Geotechnical Engineering Software for Example 1

[0065] Figure 17 Slope ratio setting of Lizheng Geotechnical Engineering Software for Example 1

[0066] Figure 18 Input of stratum parameters in Lizheng Geotechnical Engineering Software for Example 1

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

[0068] Figure 20 Display page of the calculated safety factor of Lizheng Geotechnical Engineering Software without setting anchor bolt support for Excavation Plan 1 in Example 1

[0069] Figure 21 The display page of the safety factor calculated by Lizheng Geotechnical Software when setting bolt support for the excavation plan 2 of Example 1;

[0070] Figure 22 The display page of the safety factor calculated by Lizheng Geotechnical Software when setting bolt support for the excavation plan 3 of Example 1. Specific implementation manners

[0071] In order to make the objectives, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are some but not all of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present disclosure without creative efforts shall fall within the scope of protection of the present disclosure.

[0072] Technical terms

[0073] Anchored slope: An engineering structure that connects the slope rock and soil mass with a stable stratum through bolts or other anchoring structures to improve the slope stability.

[0074] Safety factor: The ratio of the anti-sliding force to the sliding force of a slope under the designed working conditions, used to measure the slope stability.

[0075] Ultimate tensile bearing capacity: The maximum pulling-out force that a bolt can withstand in the soil.

[0076] Slope numerical simulation: Using the computer software Midas GTS NX to simulate and calculate the slope stability to predict the safety factor of the slope under different working conditions.

[0077] Pseudo safety factor: In numerical simulation, when considering the influence of residual bolt reinforcement and the maximum axial force of the residual bolt calculated by numerical simulation is greater than the ultimate tensile bearing capacity of the residual bolt, the obtained safety factor.

[0078] True safety factor: The true safety factor obtained after adjusting by the reduction factor of the pseudo safety factor.

[0079] Shear strength parameters: The ability of soil to resist shear deformation, usually expressed by cohesion and internal friction angle.

[0080] Example 1

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

[0082] The basic situation of the slope is as follows: The safety level of a certain slope is level 2. The height of the slope is 8m and the slope angle is 50°. There are 4 layers of anchors on the slope, the length of the anchors is 12m, the spacing between the anchors is 2m*2m, the inclination angle of the anchors to the horizontal direction is 15°, and the length of the anchoring section and the free section of the anchors are 6m each. The diameter of the anchor rod is 25mm, the diameter of the anchor body is 150mm, and the prestressing force of the anchor is 200kN. The anchoring section is the part of the anchor that penetrates into the stable rock and soil. It provides tensile resistance through the bonding force or friction between the surrounding rock and soil, and is located in the stable rock and soil outside the theoretical sliding surface. The free section refers to the section from the anchor head to the anchoring section, which passes through the unstable rock and soil. Its main function is to transfer the tension of the anchor head to the anchoring section.

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

[0084] Table 1 Calculation parameters of formation and anchor

[0085]

[0086] Step 1. Preliminary selection of excavation plan, such as Figure 2 As shown in a, b, c, and d in the figure, the preliminary excavation schemes 1, 2, and 3 are selected. In the figure, blue represents the anchor bolt anchoring section, and black represents the anchor bolt free section. The rose red line segment represents the slope line after excavation. The slope angles between the slope line and the horizontal plane of the 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 residual length of the initial anchor rod: According to the plane geometric relationship, calculate the excavation area of each excavation scheme and the residual length of the initial anchor rod after excavation, as shown in Table 2:

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

[0089]

[0090] Step 3. Based on the soil nail 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 is calculated according to formula 1:

[0092] T=πDq s L (1)

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

[0094] In the three solutions this time, the anchor rod anchor bodies were not excavated and removed, and the remaining lengths of the anchor rod anchor bodies were all 6m. Therefore, the theoretical ultimate tensile bearing capacities were all 268.47kN.

[0095] Step 4. Slope numerical simulation modeling and calculation:

[0096] Midas GTS NX is a professional geotechnical engineering simulation software. According to different excavation solutions, use the Midas GTS NX software to establish slope stability numerical simulation calculation models considering the influence of residual anchor rod reinforcement and without considering the influence of residual anchor rod reinforcement respectively, and calculate the slope safety factor and the distribution of anchor rod axial force.

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

[0098] As Figure 3 , import the CAD graphics of the slope geometry of each excavation solution into the Midas GTS NX software to establish a numerical calculation model. As Figure 4 shown, set the formation materials and set the property parameters according to Table 1. As Figure 5 shown, set the material property to 2D property. As Figure 6 shown, select "Dimension Control". As Figure 7 shown, select the "2D" option to divide the mesh. As Figure 8 shown, set the boundary condition to the "Constraint" option and as Figure 9 set the gravity load to the "Self-weight" option. As Figures 10 to 11 shown, set the construction steps and analysis working conditions of each excavation solution, that is, according to the excavation area of each excavation solution and the remaining length of each initial anchor rod, in the order of the arrangement of each initial anchor rod from top to bottom, set the remaining length of each initial anchor rod after being truncated and the excavated area of the slope area where the truncated initial anchor rod is located respectively as the analysis working conditions of each simulation construction stage, select SRM to calculate each analysis working condition. As Figure 12 , obtain the slope stability safety factor of each simulation construction stage in the "Contour Plot"; because it is obtained in step 3 of this embodiment that the anchor rod anchor bodies were not excavated and removed and the influence of residual anchor rod reinforcement is not considered, the anchor rods do not need to be activated during the whole calculation process.

[0099] SRM refers to the Strength Reduction Method, which is used for slope stability analysis. Its basic principle is to gradually increase the reduction factor, correspondingly reduce the shear strength indexes of the soil mass (such as cohesion and internal friction angle), and repeatedly calculate the slope until the slope reaches the critical state of ultimate equilibrium.

[0100] The process of numerical simulation modeling and calculation of slope stability considering the influence of residual anchor rod reinforcement is as follows: As Figure 13The calculation model is obtained for the activated bolts shown. The subsequent steps are the same as the numerical simulation modeling calculation process for slope stability without considering the influence of residual bolt reinforcement, as shown in Table 3 and Figure 14 the safety factor of slope stability and the distribution of axial forces of residual bolts in the slope are obtained as shown.

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

[0102] The axial force at each point of the bolt can be queried through numerical simulation calculation. Compare the maximum axial force of the residual bolts in the numerical simulation calculation with the theoretical calculated pull-out bearing capacity for each analysis condition in the SRM calculation. If the maximum axial force of the residual bolts in the numerical simulation calculation for the nth excavation plan is less than the theoretical pull-out ultimate bearing capacity, it indicates that the safety factor of stability in this plan is the true safety factor k nz and then proceed to step 6. If the maximum axial force of the residual bolts in the numerical simulation calculation is greater than the theoretical pull-out ultimate bearing capacity, it indicates that the safety factor of stability in this plan is a pseudo-safety factor, and then proceed to step 5.

[0103] Table 3 Safety factor, maximum axial force, and true / false judgment of safety factor

[0104]

[0105] As can be seen from Table 3, the safety factors of slope stability for all three plans meet the requirements.

[0106] The axial force diagrams of the residual bolts in the original slope bolts and the three excavation plans considering the influence of residual bolt reinforcement when considering slope stability are as shown in Figure 14 the figure.

[0107] Step 5. Reduction coefficient γ of the maximum pseudo-safety factor nm Trial calculation:

[0108] Step 51. Initialize the reduction coefficient range. The reduction coefficient γ of the pseudo-safety factor n has a value range of (0, 1), γ low = 0, γ high = 1; calculate the intermediate value of the reduction coefficient,

[0109] Step 52. Conduct numerical simulation modeling of the slope for the nth excavation plan according to the intermediate value of the reduction coefficient. The obtained shear strength parameters include the simulated cohesion C n and the simulated internal friction angle

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

[0111]

[0112] Among them, c0 is the cohesion of the original slope (kPa), is the internal friction angle of the original slope (°); k n0 is the safety factor of slope stability without considering residual anchor bolts in the nth excavation plan, k nw is the pseudo-safety factor of slope stability considering residual anchor bolts in the nth excavation plan;

[0113] Step 53. Substitute C n and into each analysis working condition for numerical simulation static working condition calculation to obtain the maximum axial force of the residual anchor bolt numerical simulation calculation. If the maximum axial force is greater than the theoretical ultimate tensile bearing capacity, it means that the current γ mid is too small and needs to be increased, that is, γ low =γ mid , and enter Step 54;

[0114] If the maximum axial force is less than or equal to the theoretical ultimate tensile bearing capacity, it means that the current γ mid is the reduction coefficient γ nm of the maximum pseudo-safety factor, and enter Step 55;

[0115] Step 54. Repeat Steps 51-53 until the reduction coefficient γ nm of the maximum pseudo-safety factor with the maximum axial force of the residual anchor bolt numerical simulation calculation less than or equal to the theoretical ultimate tensile bearing capacity is obtained, and enter 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] Among them, the safety factor of slope stability without considering residual anchor bolts in the nth excavation plan is denoted as k n0 , and the pseudo-safety factor is denoted as k nw .

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

[0120] Calculate the adjustment coefficient of the shear strength parameters of the slope rock and soil mass in the nth excavation plan:

[0121] α n =knz / k n0 (5)

[0122] Calculate the enhanced shear strength parameters of the rock and soil mass according to the adjustment coefficient of the shear strength parameters of the rock and soil mass of the slope:

[0123] During the subsequent design process of the newly built anchor bolt support system, the residual anchor bolts of the slope are retained in the slope as soil nails to reinforce the slope. During the design process of the newly built anchor bolt support system, its reinforcement effect is considered by increasing the shear strength parameters of the rock and soil mass of the slope. The enhanced shear strength parameters of the rock and soil mass are as follows:

[0124] C nt = α n C0 (6)

[0125]

[0126] where c nt is the enhanced cohesive force (kPa) in the nth excavation plan; is the enhanced internal friction angle (°) in the nth excavation plan; α n is the adjustment coefficient of the shear strength parameters of the rock and soil mass of the slope in the nth excavation plan.

[0127] The true safety factors and the adjustment coefficients of the shear strength parameters of the rock and soil mass for different excavation plans in this embodiment are shown in Table 4:

[0128] Table 4 Safety factors and adjustment coefficients of shear strength parameters of rock and soil mass for different excavation plans

[0129]

[0130] As Figures 15 to 22 shown, through the geotechnical engineering design software "LiZheng Geotechnical", input the enhanced shear strength parameters of the rock and soil mass (as shown in Table 5), and design the newly built support structure for slopes with different slope angles in each different excavation plan. The design steps include: As Figure 16 Set the basic conditions, such as Figure 17 Set the slope ratio of the slope surface, input the formation parameters (as shown in Table 5 and Figure 18 ), such as Figure 19 Input the design parameters of the anchor bolts, and finally click the calculation button to calculate. As Figures 20 to 22 The overall stability calculation results are obtained by designing the three plans respectively. According to the provisions of the "Code for Design of Highway Subgrades" (JTG D30 - 2015), the safety factor of slope stability for expressways and first-class highways should be greater than or equal to 1.20. If the calculated safety factor after adding anchor bolts is greater than the specification requirements, it indicates that the design is feasible. The design of the newly built anchoring system for the three excavation plans is carried out respectively, and the parameters such as the diameter, length, arrangement density and angle of the newly built anchor bolts are obtained, as shown in Table 6.

[0131] Table 5 Shear strength parameters of reinforced rock and soil mass under different excavation schemes

[0132]

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

[0134] Table 6 Design schemes of the newly built anchoring support system under different excavation schemes

[0135]

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

[0137] Taking the longitudinal extension length of the slope body as 20m, the construction cost of slope anchor bolts is 60 yuan / m, and the earthwork excavation is calculated at 10 yuan / m 3 for pricing, and a technical and economic comparison is made for the three schemes.

[0138] Table 7 Technical and economic comparison of the newly built anchoring support system under different excavation schemes

[0139]

[0140] As can be seen from Table 7, Excavation Scheme 3 does not require anchor bolt support, has the lowest total cost, and the construction period is shorter than the other two schemes. Therefore, Excavation Scheme 3 should be preferably selected.

[0141] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An optimization method for a newly built bolt support system in slope excavation and expansion using residual bolts, characterized in that, It includes the following steps: Step 1: According to the slope geometry and bolt layout, initially select multiple excavation plans, each of which has a different excavation slope angle; Step 2: Calculate the excavation area of each excavation plan and the residual length of the initial bolt after excavation according to the plane geometric relationship; Step 3: Based on the soil nail calculation theory, calculate the theoretical ultimate tensile capacity T of the residual bolt; Step 4: Respectively establish numerical simulation calculation models for slope stability considering and not considering the influence of residual bolt reinforcement, and calculate the slope safety factor and bolt axial force distribution; If the maximum axial force in the numerical simulation of the residual anchor bolt is not greater than the theoretical ultimate bearing capacity of uplift, it is determined that the safety factor of the slope stability considering the residual anchor bolt is the true safety factor k nz , and directly proceed to step 6. Otherwise, it is the false safety factor k nw Proceed to step 5; Step 5: If the maximum axial force calculated by the numerical simulation of the residual anchor bolt is greater than the theoretical ultimate tensile capacity, calculate the reduction coefficient γ of the maximum pseudo-safety factor nm ; Use the numerical simulation of the residual bolt to calculate the maximum axial force. If the maximum axial force calculated by the numerical simulation of the residual bolt is not greater than the theoretical ultimate tensile capacity, the safety factor calculated this time is the true safety factor, and then directly enter Step 6. Otherwise, repeat Step 5 until the maximum axial force calculated by the numerical simulation of the residual bolt is not greater than the theoretical ultimate tensile capacity, and obtain the true safety factor; Step 6: According to the true safety factor, calculate the adjustment coefficient of the shear strength parameters of the slope rock and soil mass, and then obtain the enhanced shear strength parameters of the rock and soil mass; Use the geotechnical engineering design software "LiZheng Geotechnical", input the enhanced shear strength parameters of the rock and soil mass, and design the new support structure for the slopes with different slope angles in each different excavation plan to obtain the prestress, diameter, length, and layout density and angle of the new bolt; Step 7: Conduct a technical and economic comparison of the new anchoring systems of each excavation plan and select the most economical plan.

2. The method according to claim 1, wherein In Step 3, the calculation formula for the theoretical ultimate tensile capacity T of the residual bolt is: T = πDq s L (1) Among them, D is the diameter of the anchor solid; q s is the standard value of the ultimate frictional resistance between the anchor solid and the soil; L is the residual anchorage length of the bolt.

3. The method according to claim 1, wherein In Step 4, the calculation method for the slope safety factor and bolt axial force distribution is: If the influence of residual bolt reinforcement is not considered, the geometric shape CAD drawing of the slope is imported into the Midas GTS NX software to establish a numerical calculation model, the formation material and property parameters are set, the "Size Control" option is selected and the "2D" option is used to divide the mesh, the boundary condition is set as the "Constraint" option and the gravity load is set as the "Self-weight" option. According to the excavation area of each excavation plan and the residual length of each initial bolt, in the order of the arrangement of each initial bolt from top to bottom, the residual length to which each initial bolt is truncated and the excavated area of the slope area where the truncated initial bolt is located are set successively, respectively as the analysis working conditions of each simulated construction stage. The SRM is selected to calculate each analysis working condition, and the slope stability safety factor k of each simulated construction stage is obtained. n0 ; SRM refers to the strength reduction method; the property parameters include the unit weight, porosity, water content, cohesion, internal friction angle, Poisson's ratio, standard value of ultimate bond strength of different formation materials, and the unit weight, elastic modulus, and Poisson's ratio of the bolt. If the influence of residual bolt reinforcement is considered, the bolts are activated to obtain the calculation model, and the subsequent steps are the same as those in the numerical simulation modeling calculation process of slope stability without considering the influence of residual bolt reinforcement, and the safety factor k of slope stability is obtained. nw And the distribution of axial forces of residual bolts in the slope.

4. The method according to claim 3, wherein If the slope stability coefficient is less than 1, this excavation plan is eliminated.

5. The method according to claim 1, wherein Step 5 includes: Step 51. Initialize the reduction coefficient range, the reduction coefficient γ of the pseudo safety factor n The value range is (0, 1), γ low = 0, γ high = 1; Calculate the intermediate value of the reduction coefficient Step 52. Carry out slope numerical simulation modeling for each excavation plan according to the intermediate value of the reduction coefficient, and the obtained shear strength parameters include the simulated cohesion C n and the simulated internal friction angle C n = [k n0 + γ mid (k nw - k n0 )]C0 (2) Among them, c0 is the cohesion of the original slope, and φ is the internal friction angle of the original slope; k n0 is the safety factor of slope stability without considering the residual anchor, and k nw is the pseudo-safety factor of slope stability considering the residual anchor; Step 53. Substitute C n and into the numerical simulation for the static condition calculation to obtain the maximum axial force of the residual anchor bolt from the numerical simulation calculation. If the maximum axial force is greater than the theoretical ultimate tensile bearing capacity, it indicates that the current γ mid is too small and needs to be increased, that is, γ low = γ mid , and proceed to Step 54; If the maximum axial force is less than or equal to the theoretical ultimate uplift bearing capacity, it indicates that the current γ mid is the reduction coefficient γ of the maximum pseudo safety factor nm , and proceed to step 55; Step 54. Repeat Steps 51 to 53 until the maximum pseudo-safety factor reduction coefficient γ is obtained such that the maximum axial force in the numerical simulation of the residual anchor bolt is less than or equal to the theoretical ultimate tensile bearing capacity, and then proceed to Step 55; nm , and proceed to Step 55; Step 55. Calculate the true safety factor k nz : k nz = [k n0 + γ nm (k nm - k n0 )] (4) Among them, k nz is the true safety factor, k n0 is the safety factor of slope stability without considering the residual anchor bolts, k nw is the pseudo safety factor of slope stability considering the residual anchor bolts, γ nm is the reduction factor of the maximum pseudo safety factor.

6. The method according to claim 1, wherein Step 6 includes: the shear strength parameter adjustment coefficient α of the slope rock and soil mass n The calculation method is as follows: α n = k nz / k n0 (5) Among them, α n is the adjustment coefficient of the shear strength parameter of the slope rock and soil mass; According to the adjustment coefficient α of the shear strength parameters of the slope rock and soil mass n , calculate the enhanced shear strength parameters of the rock and soil mass: C nt = α n C0 (6) Among them, c0 is the cohesion of the original slope, is the internal friction angle of the original slope; c nt is the enhanced cohesion in the nth excavation plan, is the enhanced internal friction angle in the nth excavation plan.

Images