Construction method for fully-weathered granite residual soil slope expanding and digging

Abstract

The invention discloses a safety construction method for side slope expanding excavation of fully-weathered granite residual soil, and provides an excavation process optimization method for a first-grade side slope close to an operation road on the basis of finite element simulation of the whole side slope expanding excavation construction process of the fully-weathered granite residual soil. The excavation safety construction method comprises the following steps that firstly, a temporary support is arranged, then a primary excavation procedure is designed, multiple sets of excavation parameter combinations are designed, then the slope state after secondary slope excavation is completed serves as the initial state, a finite element model of slope excavation is established for each scheme combination, excavation parameters are input, and a slope excavation result is obtained; and calculating the safety coefficient and the maximum displacement of the side slope after the side slope expanding excavation is completed under the excavation scheme, performing optimization according to the calculation result and the space requirement of the construction operation machinery, and finally determining the optimized expanding excavation parameters and the safe excavation process. According to the technical scheme, an optimized scheme can be provided for studying safe excavation of the fully-weathered granite residual soil slope.

Description

Technical Field

[0001] The invention belongs to the technical field of slope excavation, relates to finite element simulation technology, and particularly relates to a construction method for excavating a fully weathered granite residual soil slope. Background Technique

[0002] The reconstruction and expansion of mountain expressways are usually carried out while ensuring the normal operation of the existing roads. The mutual influence between traffic operation and expansion construction makes the safety control pressure of mountain expressways extremely prominent. Especially when high slopes are involved in the expansion project, the construction safety control faces huge technical challenges. The fully weathered granite residual soil is the product of a specific climate, geography, and geological environment. Its engineering geological properties are different from those of general soils and belong to regional special soils, which are relatively common in the southern region. High slope excavation projects in the road reconstruction and expansion projects in the South China region often involve fully weathered granite residual soils.

[0003] The fully weathered granite residual soil is the product of a specific climate, geography, and geological environment. Its engineering geological properties are different from those of general soils and belong to regional special soils, which are relatively common in the southern region. High slope excavation in the road reconstruction and expansion projects in the South China region often involves it. The original microcracks, high void ratio, and the lack of some intermediate particle sizes make the particle skeleton of the fully weathered granite residual soil present a special "block" - type structure, with weak cohesion and loose strata. It is prone to large deformations and significant strength attenuation under disturbances such as water, vibration, and stress unloading. Therefore, in the slope excavation construction of fully weathered granite residual soil, construction loads and rainfall effects are extremely likely to cause slope instability. Currently, for the slope excavation construction of fully weathered granite residual soil, the traditional construction method (as Figure 1 shown) is still adopted: auxiliary temporary measures are used for protection at the slope toe, and large-scale excavation is carried out from top to bottom, gradually advancing from the slope surface to the slope interior. Finally, the temporary retaining is removed to form a widened new lane. The traditional method has high construction risks because it directly constructs on the free slope surface adjacent to the operating road. Once a landslide or local collapse occurs and the temporary protection measures at the slope toe cannot provide effective support, it will inevitably endanger the operating expressway below the slope, causing serious casualties and economic losses. Summary of the Invention

[0004] Based on the above situation, the invention proposes a safe construction method for excavating a fully weathered granite residual soil slope, which specifically includes the following steps: For the excavation of slopes with a grade of two or above away from the operating road, the excavation steps are carried out layer by layer from top to bottom, and each layer of excavation steps is carried out step by step from the outer slope surface to the slope interior; For the remaining first-class slopes adjacent to the operating roads, expand and excavate them according to the optimized excavation process. The optimized excavation process includes: according to the overall height H of the first-class slope to be excavated, excavate in multiple layers of equal-height rock and soil layers from top to bottom. When excavating each layer of equal-height rock and soil layer, first excavate a placement pit on the side far from the operating road to form a rock and soil pile on the side close to the operating road, and then excavate the rock and soil pile. The distance from the side of the placement pit close to the second-class slope to the toe of the second-class slope after the expansion excavation is not less than the original berm width M. Before excavating each layer of placement pit, remove the anchor bolts implanted in the placement pit at the upper part of the first-class slope and the anchor bolt support structure connected to the anchor bolts; The transverse section of the placement pit in each layer of equal-height rock and soil layer is perpendicular to the slope surface of the first-class slope or the second-class slope and the extension direction of the berm. The shape of the transverse section is an inverted trapezoid with a bottom width smaller than the top width. The parameters of the placement pit are the same and include: b, h, α and β, where h and b are the height of the inverted trapezoid and the width of the bottom of the inverted trapezoid respectively, α / β is the inclination of the side of the inverted trapezoid close to the second-class slope / first-class slope relative to the operating road, α which is equal to the slope angle of the first-class slope provided by the design drawing; The parameters of the placement pit are obtained from the optimized placement pit parameters corresponding to the largest h selected from the optimized placement pit parameters. For the geometric model of the first-class slope after the 1st to nth excavation of the placement pit constructed according to the optimized placement pit parameters, after using Midas GTS to perform finite element numerical simulation calculations on the geometric model, the minimum safety factor of the geometric model after each excavation of the placement pit is not greater than 1.20 and the maximum displacement is less than 30 mm, and H / h = n.

[0005] At the same time, the optimized placement pit parameters are selected by the following steps: (1) Use Midas GTS software to calculate the maximum displacement after expanding and excavating the second-class slope or slopes above the second-class, calculate the safety factor through the strength reduction method, and set it as the initial state for the numerical simulation calculation in the subsequent step (4): Including: Import the original geometric model of the slope at the second level or above and the geometric models of each construction stage constructed according to the excavation steps into the Midas GTS software. Set the material parameters in the Midas GTS software and set the material property as 2D property. Select the "Dimension Control" option, then select the "2D" option to divide the mesh. Set the boundary condition as the "Constraint" option and the gravity load as the "Self-weight" option. Set the excavation calculation and analysis steps in sequence according to the original geometric model and the geometric models of each construction stage. Perform finite element numerical simulation calculations on each calculation step through Midas GTS to obtain the safety factor of the original slope. After excavating the slope at the second level or above of the upper part, obtain the maximum displacement after excavation of the slope at the second level or above through static calculation, obtain the safety factor through SRM calculation, and set the state after excavating the second-level slope as the initial state for the numerical simulation calculation in the subsequent step (4). (2) According to the overall excavation width B1 of the first-level slope, the overall height H of the first-level slope, and the spatial requirements of the excavation construction equipment, preliminarily design multiple groups of alternative pit parameters. All multiple groups of alternative pit parameters satisfy the following formula: B1 - b > hcotα + hcotβ, h < H, β ≥ α; (3) Arrange the multiple groups of alternative pit parameters in ascending order of h, and take the alternative pit parameters with the smallest h as the initial selected pit parameters. If the h values of multiple groups of alternative pit parameters are the same and are all the minimum values, then take them as the initial selected pit parameters at the same time. Calculate the number of cycles n for excavating the pit and clearing the rock and soil piles according to the ratio of H to h according to the preferred excavation process; (4) According to each group of initial selected pit parameters, respectively construct the geometric models of the first-level slope after excavating the pit for the 1st to nth times. Import the geometric models into the Midas GTS software. Set the material parameters in the Midas GTS software and set the material property as 2D property. Select the "Dimension Control" option, then select the "2D" option to divide the mesh. Set the boundary condition as the "Constraint" option and the gravity load as the "Self-weight" option. Establish the finite element numerical simulation calculation models after excavating the pit for the 1st to nth times. Set the excavation calculation and analysis steps according to the process of excavating the pit for the 1st to nth times of the first-level slope. Perform finite element numerical simulation calculations on each calculation step through the Midas GTS software to obtain the minimum safety factor and the maximum displacement of the geometric model after excavating the pit each time, and compare them with the safety factor and the maximum displacement required by the industry specifications. If they meet the requirements of the industry specifications, then execute step (5). If not, then terminate; (5) Return to step (3) and select the initial selected pit parameters from the multiple groups of alternative pit parameters with a larger h ranking, and repeat step (4); (6) According to the calculation results of steps (4) to (5), screen out all the accommodation pit parameters that meet the industry standard requirements, that is, the preferred accommodation pit parameters, and sort them in descending order of h; (7) Select the accommodation pit parameter with the largest h.

[0006] Further, before the excavation of the second-level or above slope, first remove the anchor bolts implanted in each layer of rock and soil blocks and the anchor bolt support structure on the slope surface of this layer of rock and soil blocks.

[0007] Further, the space requirements of the excavation construction equipment in step (2) mean that the bottom width of the accommodation pit and the top width of the rock and soil pile are not less than the width of the construction equipment mechanical vehicle.

[0008] Further, the material parameters in step (2) include the types of rock and soil, the unit weight of rock and soil, the porosity of rock and soil, the water content of rock and soil, the cohesion of rock and soil, the internal friction angle of rock and soil, the Poisson's ratio of rock and soil, and the elastic modulus of rock and soil.

[0009] Further, the meeting of the industry standard requirements in step (4) includes: The minimum safety factor of the geometric model after each excavation of the accommodation pit is not less than the safety factor required by the industry standard; And the maximum displacement of the geometric model after each excavation of the accommodation pit is less than the maximum displacement required by the industry standard.

[0010] Further, a system for a safe construction method for the excavation of a completely weathered granite residual soil slope includes a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the steps of the safe construction method for the excavation of the completely weathered granite residual soil slope are implemented.

[0011] The beneficial effects of the present invention compared with the prior art are as follows: 1. Without affecting the existing operation of the expressway, the present invention proposes a safe construction method for slope excavation of completely weathered granite residual soil on slopes of grade two or above. After the excavation construction of slopes of grade two or above is carried out according to the traditional excavation process, the excavation process of the remaining first-level slope adjacent to the operating road is optimized. According to the overall excavation width of the first-level slope to be excavated, from the slope interior to the slope surface, it is divided into a placement pit and a rock and soil pile, and the excavation is carried out in two rock and soil blocks. According to the overall height of the first-level slope, from the slope top to the slope bottom, from top to bottom, it is divided into multiple layers, and multiple rounds of excavation are carried out for the two rock and soil blocks of the placement pit and the rock and soil pile in each layer; the placement pit is a rock and soil block in an inverted trapezoid shape, and the rock and soil pile is a rock and soil block in a regular trapezoid shape; when excavating the rock and soil pile, the construction equipment is located at the top of the rock and soil pile, while pushing part of the rock and soil of the rock and soil pile into the placement pit, and at the same time clearing the rock and soil pushed into the placement pit. When clearing, the excavation direction of the excavation tool faces the filling side of the placement pit, so as to avoid excavation on the free face, resulting in the scattering or sliding of the soil mass onto the operating expressway.

[0012] 2. The present invention also designs and screens the excavation parameters of the placement pit of the first-level slope based on the finite element numerical simulation calculation model constructed by Midas GTS software for the excavation parameters of the remaining first-level slope adjacent to the operating road. The first step is to preliminarily determine multiple groups of alternative parameter combinations of the excavation bottom width b and the left excavation slope angle β when the value of the first group of single-excavation height h is the smallest according to factors such as the overall excavation width of the first-level slope, the overall height of the first-level slope, and the spatial requirements of the excavation construction equipment. A Midas GTS finite element calculation model of the parameter combination of the alternative plan when the value of the single-excavation height h is the minimum is constructed. The slope excavation stage is respectively simulated and calculated to obtain the safety factor and the maximum displacement. Through comparative analysis with the safety factor and the maximum displacement required by the industry standard, the parameter combination of the excavation bottom width b value and the left excavation slope angle β that meets the requirements is selected and enters the next round of screening after the single-excavation height h increases.

[0013] The second step is to gradually increase the value of the single-excavation height h in combination with the parameter combination of the bottom excavation width value b and the left excavation slope angle β screened in the first group to form a new group of excavation parameter combinations. A Midas GTS finite element calculation model is constructed. Through simulation calculation, the safety factor and the maximum displacement are obtained. Through comparison with the safety factor and the maximum displacement required by the industry standard, the parameter combination of the excavation bottom width b value and the left excavation slope angle β that meets the requirements is selected.

[0014] The third step is to select the larger value of the single-excavation height h in the new group of excavation parameter combinations under the condition of meeting the requirements of the safety factor and the maximum displacement to ensure the continuity of the excavation construction, reduce equipment relocation, and improve the excavation efficiency.

[0015] In summary, the proposed safe construction method of the present invention has the following advantages: it comprehensively considers the construction convenience and safety; the excavation construction parameters given by the numerical simulation-assisted calculation are accurate, detailed and highly operable; the given excavation construction control indicators can be directly applied to the on-site actual monitoring and control, providing accurate early warnings for safe construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the traditional excavation construction process; Figure 2 It is a schematic diagram of the traditional excavation construction process of the secondary slope; Figure 3 It is a schematic diagram of the optimized construction process after the overall slope is combined with the traditional excavation; Figure 4 It is a schematic diagram of the excavation of the accommodation pit (rock and soil block No. 7) on the inner side of the first-level slope; Figure 5 It is a schematic diagram of the excavation of the rock and soil pile (rock and soil block No. 8) on the outer side of the first-level slope; Figure 6 It is a flow chart for screening the excavation plan of the first-level slope; Figure 7 It is a schematic sectional view of Example 1; Figure 8 It is an operation diagram of the Midas GTS software for setting unit properties in Example 1; Figure 9 It is an operation diagram of the Midas GTS software for setting dimension control in Example 1; Figure 10 It is an operation diagram of the Midas GTS software for mesh generation in Example 1; Figure 11 It is an operation diagram of the Midas GTS software for setting boundary conditions and gravity loads in Example 1; Figure 12 It is a display diagram of the calculation result of the safety factor of the original slope in Example 1 shown by the Midas GTS software; Figure 13 It is a display result diagram of the calculation results of the maximum displacement and safety factor after the secondary slope excavation in Example 1 shown by the Midas GTS software; Figure 14 It is the numerical simulation calculation process of six excavation stages of Plan 1-1 in the first group of plans; Figure 15 It is the numerical simulation calculation process of four excavation stages of Plan 2-1 in the second group of plans; Figure 16 It is a schematic sectional view after the secondary slope excavation in Example 1; Figure 17It is the excavation displacement nephogram of Scheme 2-1 in the second group of schemes. Detailed implementation manners

[0018] The various exemplary implementation manners of the present invention will be described in detail below. This detailed description should not be construed as a limitation on the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0019] Term explanation A bench is a buffer zone between different levels of slopes in slope engineering, facilitating construction and maintenance, helping with drainage, and increasing the overall stability of the slope.

[0020] The first-level slope generally refers to the first-level slope starting from the road surface, located at the bottom, directly adjacent to the operating road, and is the level closest to the road in the entire slope system.

[0021] The second-level slope refers to the next-level slope above the first-level slope, separated from the first-level slope by a bench (platform), and is farther from the operating road than the first-level slope.

[0022] A high-level slope refers to a relatively high slope, usually a slope that needs to be excavated in stages. Due to the large height of the slope, in order to ensure stability, it is divided into multiple levels (multiple steps), and the "level" refers to the number of steps into which the slope is divided.

[0023] The excavation width refers to the distance between the slope surface before excavation and the slope surface after excavation along the horizontal plane.

[0024] In this embodiment, for the excavation of a second-level or higher-level completely weathered granite residual soil slope above the first-level slope adjacent to the road surface, a method is proposed that uses Midas GTS finite element numerical simulation technology to finely optimize the excavation process of the completely weathered granite residual soil slope, and gives specific excavation safety construction parameters and control indicators, so as to achieve the purpose of safe construction. The following takes the excavation of the second-level slope and the first-level slope as examples to illustrate the implementation steps of the present invention.

[0025] Before preparing for excavation, it is necessary to remove the pre-embedded reinforcement and support components in the slope, and then carry out the excavation construction. The specific steps are as follows: Step 1: Excavate the second-level slope far from the operating road. In this step, since the second-level slope is relatively far from the operating highway and is separated from the first-level slope by the original bench as a buffer zone, the excavation of the second-level slope still follows the traditional excavation process. Determine the excavation width B2 of the second-level slope according to the design drawings, and the excavation sequence is from the slope surface to the slope interior, from top to bottom, and gradually carried out in sections. Specifically, as Figure 2 shown.

[0026] In this step, before the excavation of the secondary slope, according to the excavation width B2, the part to be excavated of the secondary slope is evenly divided into two layers by line segments parallel to the slope surface, and then evenly divided into multiple blocks from bottom to top. Each block of the area to be excavated is a rhombus with the same shape, and the excavation width of each block is the same. As Figure 2 shown, the secondary slope is divided into Rock and Soil Block No. 1 to Rock and Soil Block No. 6. During the excavation process, from the slope surface to the slope interior, and from top to bottom, each of the Rock and Soil Blocks No. 1 to 6 is excavated and cleared one by one. Before the excavation of each layer of rock and soil blocks, the anchor bolts implanted in the rock and soil blocks and the anchor bolt support structure on the slope surface of this layer of rock and soil blocks are removed first. After all the rock and soil blocks are excavated, the surface of the secondary slope is close to parallel to the original surface of the secondary slope, and the whole is translated a certain excavation width away from the operating road. The excavation width B2 is not less than twice the width M of the original access road, and a geometric model of the original slope form is constructed.

[0027] Step 2: Excavate the primary slope adjacent to the operating road. If the excavation of the primary slope still follows the traditional excavation process, it is prone to instability and cause safety risks. Therefore, the excavation process of the primary slope needs to be optimized, specifically as Figure 3 shown.

[0028] Step 2.1: After the excavation of the secondary slope in Step 1 is completed, the excavation of the primary slope is carried out on the newly formed access road after widening. The designed excavation width of the primary slope is B2. According to the overall height of the primary slope, it is excavated in multiple layers of equal-height rock and soil layers from top to bottom. In each layer of equal-height rock and soil layer, first, a placement pit (Rock and Soil Area No. 7) is excavated on the side far from the operating road, and a rock and soil pile is formed on the outside of the placement pit, that is, on the side close to the operating road, and then the rock and soil pile (Rock and Soil Area No. 8) is excavated. Before the excavation of each placement pit, according to the excavation depth of the placement pit, that is, the single excavation height h, the anchor bolts implanted in the placement pit at the upper part of the primary slope and the anchor bolt support structure connected to the anchor bolts are removed, and the distance between the side of the placement pit (Rock and Soil Area No. 7) close to the secondary slope and the toe of the secondary slope after the excavation in Step 1 is controlled to be not less than the width M of the original access road, so that the width of the access road between the primary slope and the secondary slope after the excavation is not less than the width M of the original access road.

[0029] Step 2.2: When the excavation of the placement pit (Rock and Soil Area No. 7) in Step 2.1 is completed and the excavation of the rock and soil pile (Rock and Soil Area No. 8) starts, while part of the rock and soil of the rock and soil pile (Rock and Soil Area No. 8) is pushed into the placement pit (Rock and Soil Area No. 7), the rock and soil pushed into the placement pit is cleared, and the excavation direction of the excavation tool during the clearing is towards the filling side of the placement pit. This avoids the excavation of the primary slope on the free face, resulting in the scattering or sliding of the rock and soil to the operating expressway.

[0030] Step 2.3: Repeat Steps 2.1 to 2.2, layer by layer from top to bottom, excavate and clear each layer of rock and soil in the primary slope until the excavation of the primary slope is completed.

[0031] In step 2.1 above, before excavating each layer of accommodation pits, it is necessary to finely design the parameters of the accommodation pits through finite element numerical simulation calculation using Midas GTS. In the transverse profile direction of the first-level slope or the second-level slope, as Figure 4 and Figure 5 shown, the transverse profile of the accommodation pit is an inverted trapezoid with a bottom width smaller than the top width. The parameters of the accommodation pit include: the width of the bottom of the inverted trapezoid is b, the height of the inverted trapezoid is h, and the inclination of the side of the inverted trapezoid close to the second-level slope relative to the operating road is α , α determined according to the slope angle of the first-level slope provided by the design drawings, and the inclination of the side of the inverted trapezoid close to the first-level slope relative to the operating road is β; the transverse profile is perpendicular to the extension direction of the slope surface and the berm of the first-level slope or the second-level slope.

[0032] The parameters of the accommodation pit are used to ensure the overall stability of the slope body and the local stability of the rock and soil heap. The parameters of the accommodation pit are substituted into Midas GTS for finite element numerical simulation calculation to evaluate the stability of the first-level slope and the rock and soil heap, obtain the optimal results of the safety factor and the maximum displacement, and then screen the parameters of the accommodation pit in combination with the space requirements of the construction machinery.

[0033] According to 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. In this method, the safety factor of slope stability is greater than or equal to 1.20, that is, it is judged that the slope is overall stable. The local stability of the rock and soil heap is evaluated according to the displacement value. According to the "Technical Specification for Monitoring of Highway Cutting Slopes" (DBJ53 / T-156-2023), when the maximum displacement of the rock and soil heap is greater than or equal to 30 mm, it is judged that there is a risk of local instability.

[0034] The commonly used formula for calculating the safety factor of slope stability by the strength reduction method is as follows: Among them: k is the safety factor; is the actual cohesion of the soil; is the actual internal friction angle of the soil; is the value when the cohesion is automatically reduced by MidasGTS to the slip limit state of the slope body; is the value when the internal friction angle is automatically reduced by Midas GTS to the slip limit state of the slope body.

[0035] When solving the safety factor of the slope in Midas GTS software, the following three judgment criteria can be used to determine the limit state: (1)Displacement convergence criterion: During the slope stability analysis, it refers to whether the displacement rate of the maximum displacement of the monitoring nodes at the top of the slope surface is continuously accelerating before and after a fixed number of time steps. If the maximum displacement rate of the nodes at the top of the slope surface continues to increase within a continuous fixed number of time steps, it is considered that the deformation of the slope is intensifying and is about to reach or has exceeded its stable limit state; (2)Velocity convergence criterion: During the slope stability analysis, it refers to whether the difference in the deformation rate of the slope before and after a fixed time step is continuously greater than a certain ratio. If the difference in the deformation rate (usually referring to the displacement rate) of the slope continues to be greater than the set ratio within a continuous fixed number of time steps, it is considered that the deformation rate of the slope is continuously increasing and may be approaching or has reached the limit state; (3)Generalized shear strain or plastic strain penetration criterion: In the Midas GTS software, through the post-processing function, it is observed that a continuous high-strain region is formed by the generalized shear strain or plastic strain in the slope soil mass, indicating that significant generalized shear strain or plastic deformation has occurred inside the slope soil mass and may be approaching or reaching the limit state.

[0036] The fixed time step refers to a fixed time step length set in the Midas GTS software during the numerical simulation process. Within this time step length, the Midas GTS software will perform a calculation iteration to simulate the deformation and stress changes of the slope within this time step.

[0037] When using Midas GTS to perform elastoplastic finite element method calculations on the slope, if it is determined that the slope reaches the limit state according to the instability judgment criterion, the ratio of the actual cohesion before reduction to the cohesion after reduction according to the reduction coefficient, or the ratio of the tangent value of the actual internal friction angle before reduction to the tangent value of the internal friction angle after reduction according to the reduction coefficient, is the overall safety factor. Otherwise, repeat the reduction according to the newly assumed reduction coefficient until the slope reaches the critical limit equilibrium state. This calculation process is automatically executed by the software.

[0038] As Figure 6 shown, the preferred process of the containment pit parameters in the above steps is as follows.

[0039] (1)Set the geotechnical physical parameters of the first-level slope. Determine α according to the slope angle of the first-level slope provided by the design drawings. Based on factors such as the overall excavation width B1 of the first-level slope, the overall height H of the first-level slope, and the space requirements of the excavation vehicle, preliminarily design multiple groups of alternative containment pit parameters, namely h, b, and β.

[0040] (2)Sort the multiple groups of alternative pit placement parameters in ascending order of h, and take the alternative pit placement parameter with the smallest h as the preliminary selected pit placement parameter. If the h values of multiple groups of alternative pit placement parameters are the same and are all the minimum values, they are simultaneously used as the preliminary selected pit placement parameters. Calculate the number of cycles n for excavating the pit and clearing the rock and soil piles according to the ratio of H to h in steps 2.1 - 2.2.

[0041] (3)According to each group of preliminary selected pit placement parameters, construct the geometric models of the first - n times of pit excavation for the first - level slope respectively. Import the geometric models into Midas GTS. Set the material parameters in the Midas GTS software and set the material property to 2D property. Select the "Size Control" option, then select the "2D" option to divide the mesh. Set the boundary condition as the "Constraint" option and the gravity load as the "Self - weight" option to establish the finite - element numerical simulation calculation models after the first - n times of pit excavation. According to the process of the first - n times of pit excavation for the first - level slope, set the excavation calculation analysis steps, and perform finite - element numerical simulation calculations for each calculation step through the Midas GTS software to obtain the minimum safety factor and the maximum displacement of the geometric model after each pit excavation, and compare them with the safety factor and the maximum displacement required by the industry specifications. If the industry specification requirements are met, execute step (4); if not, terminate.

[0042] (4)Return to step (2), select the preliminary selected pit placement parameters from the multiple groups of alternative pit placement parameters with a larger h sorting, and repeat step (3).

[0043] (5)According to the calculation results of steps (3) - (4), screen out all the pit placement parameters that meet the industry specification requirements, that is, the optimized pit placement parameters, and sort them in descending order of h.

[0044] (6)Select the pit placement parameter with the largest h, and construct the geometric models of the first - n times of pit excavation for the first - level slope according to the selected pit placement parameter as the overall excavation step to ensure the continuity of the excavation construction, reduce equipment relocation, and improve the excavation efficiency.

[0045] Example 1 The following takes a specific example to explain the specific steps and the process of scheme optimization of the safe construction method for the excavation of the completely weathered granite residual soil slope.

[0046] Case: Due to the need for expansion, a certain expressway conducts the excavation of the second - level slope. The slopes of the two - level original slope are both 45°, the height H of the two - level slope is 6m, and the width M of the berm in the middle of the two - level slope is 4m. The excavation widths B1 and B2 are 8m, and the slope shape after excavation is the same as the original slope. The upper part of this area is completely weathered granite residual soil, and the lower part is strongly weathered granite. The formation parameters are shown in Table 1, and the slope profile is as Figure 7As shown, the geotechnical parameters within the original slope are set according to the properties of completely weathered granite, and the geotechnical parameters under the operating road are set according to the properties of strongly weathered granite.

[0047] Table 1 Main formation calculation parameters input in the software First, perform the excavation calculation for the upper secondary slope: Import the geometric model of the original slope form drawn on the CAD drawing (as Figure 7 shown) and the geometric models of each construction stage constructed according to the excavation steps into the Midas GTS software. In the Midas GTS software, set the material parameters according to Table 1 and set the material property as 2D property, as Figure 8 shown. Select the "Dimension Control" option (as Figure 9 shown), and then select the "2D" option to divide the mesh (as Figure 10 shown). Set the boundary condition as the "Constraint Option" and the gravity load as the "Self-weight" option (as Figure 11 shown). Set the excavation calculation analysis steps in sequence according to the original geometric model and the geometric models of each construction stage. Through the finite element numerical simulation calculation of each calculation step by Midas GTS, the safety factor of the original slope is 1.20 (as Figure 12 shown). After excavating the upper secondary slope, the maximum displacement obtained through static calculation is 18.5 mm (as Figure 13 shown), and the safety factor obtained through SRM calculation is 1.31 (as Figure 13 shown). Set the state after excavating the secondary slope as the initial state for the subsequent step (3) numerical simulation calculation. The software operation method for the subsequent excavation calculation of the primary slope is the same as that for the excavation construction of the secondary slope.

[0048] 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 perform trial calculations on the slope until the slope reaches the critical state of ultimate equilibrium.

[0049] Secondly, perform the excavation calculation for the primary slope near the operating road at the bottom. In this embodiment, mainly optimize the excavation plan for the primary slope near the operating road at the bottom. The optimization process is as follows: (1) Initial selection of single-excavation construction parameters: The slope angle of the primary slope provided by the design drawing is 45°, so determine α = 45°. According to factors such as the excavation width B1, slope height H, and space requirements of the excavation construction equipment, initially determine multiple groups of alternative (single-excavation height h, bottom width b, β) parameter combinations. The parameter combinations are shown in Table 2.

[0050] Since B1 - b > hcotα + hcotβ, h < H, and β ≥ α, when β = 45° and h = 3m, with the given excavation width B1 = 8m and berm width M = 4m, during each round of excavation, it is not possible to simultaneously meet the requirements for the excavator passage space (≥1.5m) at the bottom of the accommodation pit during the first excavation and the excavator construction space requirements (≥2m) at the top during the second excavation. Therefore, the combination related to β = 45° did not enter the preliminary selection of the second set of parameter combinations.

[0051] Table 2 First set of single - excavation schemes In the above - mentioned first set of parameter combinations, in Scheme 1 - 1, when h = 2m, b = 2m, and β = 45°, the accommodation pit (Rock and Soil Area 7) inside the first - layer excavation area and the outer rock and soil heap (Rock and Soil Area 8) are exactly the same shape. In Scheme 1 - 1, on the one hand, when h = 2m and β = 45° remain unchanged and b is enlarged, the excavation construction space of the outer rock and soil heap will change. When b = 2.5, the top operation width of the outer trapezoidal soil block 8 is only 1.5m, which is not conducive to the operation of construction equipment. On the other hand, when h = 2m and b = 2m remain unchanged and β is decreased, the excavation construction space of the outer rock and soil heap will change. When β = 30°, the top operation width of the outer rock and soil heap will be less than 2m, which is not conducive to the operation of construction equipment. Therefore, for Scheme 1 - 1, there is only this one parameter combination, and no more examples are given.

[0052] Therefore, in the first set of schemes, under the condition of h = 2m, b and β need to be adjusted simultaneously, that is, when b increases, β also increases, in order to meet the requirements during each round of rock and soil block excavation, that is, to simultaneously meet the construction space requirements at the bottom of the accommodation pit during the first excavation and the construction space requirements at the top of the rock and soil heap during the second excavation.

[0053] When b and β increase simultaneously, the surface where the inner accommodation pit (Rock and Soil Area 7) and the outer rock and soil heap (Rock and Soil Area 8) contact gradually becomes steeper, which is also not conducive to the safety of construction operations, that is, β is less than or close to 75°.

[0054] In the preliminary design of the above - mentioned accommodation pit parameters, multiple relatively reasonable schemes are given, and then analyzed and compared to select a better scheme. The design of the accommodation pit parameters does not require continuous change because continuous change does not conform to engineering reality. If the single - excavation h is too small, the number of excavation cycles is too many, and construction is inconvenient. The single - excavation h is set as an integer with a difference of 1m based on the convenience of on - site construction.

[0055] (2)Preliminary selection of overall excavation plan: Excavate the accommodation pit and remove the rock and soil pile according to the first group of combined excavation (Plan 1-1, Plan 1-2, Plan 1-3, Plan 1-4). According to the slope height H of 6m and h of 2m, as Figure 14 shown, repeat steps 2.1 to 2.2 three times to complete the excavation of the first-level slope; Excavate the accommodation pit and remove the rock and soil pile according to the second group of combined excavation (Plan 2-1, Plan 2-2, Plan 2-3). According to the slope height H of 6m and h of 3m, as Figure 15 shown, repeat steps 2.1 to 2.2 twice to complete the excavation of the first-level slope.

[0056] (3)Taking Plans 1-1, 1-2, 1-3, and 1-4 as examples in turn, construct a finite element calculation model according to the slope shape after the excavation of the second-level slope (as Figure 16 shown). Set the material parameters in the Midas GTS software and set the material properties to 2D properties. Select the "Size Control" option, then select the "2D" option to divide the mesh. Set the boundary condition as the "Constraint" option and the gravity load as the "Self-weight" option. Establish a finite element numerical simulation calculation model after the excavation of the accommodation pit for the 1st to nth times. According to the process of excavating the accommodation pit for the 1st to nth times of the first-level slope, set the excavation calculation analysis steps. Perform finite element numerical simulation calculations on each calculation step through the Midas GTS software to obtain the minimum safety factor and the maximum displacement of the geometric model after each excavation of the accommodation pit, that is, as shown in Table 3, and obtain the safety factors and maximum displacements of 4 different combined plans.

[0057] Table 3 Safety factors and maximum displacements at each excavation stage of the numerical simulation calculation of the first group of plans As can be seen from Table 3, for the accommodation pit parameters of the four plans designed in the first group in Table 2, the safety factors and maximum displacements obtained through the Midas GTS finite element numerical simulation calculation model all meet the requirements.

[0058] (4)Increase the excavation depth h = 3m and design the accommodation pit parameters of the second group. Taking Plans 2-1, 2-2, and 2-3 shown in Table 4 as examples in turn, according to the slope shape after the excavation of the second-level slope (as Figure 16A finite element calculation model was constructed (as shown), material parameters were set in the Midas GTS software, and the material properties were set as 2D properties. The "Size Control" option was selected, and then the "2D" option was used to divide the mesh. The boundary condition was set as the "Constraint" option and the gravity load was set as the "Self-weight" option. A finite element numerical simulation calculation model was established after the excavation of the accommodation pit for the 1st to nth times. According to the process of excavating the accommodation pit for the 1st to nth times of the first-level slope, the excavation calculation analysis steps were set. The finite element numerical simulation calculation was carried out for each calculation step through the Midas GTS software, and the minimum safety factor and the maximum displacement of the geometric model after each excavation of the accommodation pit were obtained. That is, as shown in Table 4, the safety factors and the maximum displacements of three different combination schemes were obtained through calculation.

[0059] As can be seen from Table 4, among the accommodation pit parameters of the three schemes designed in the second group in Table 2, only Scheme 2-1 meets the requirements through the Midas GTS finite element numerical simulation calculation model.

[0060] Table 4 Safety factors and maximum displacements at each excavation stage of the numerical simulation calculation of the second group of schemes Moreover, in the second group of schemes, the safety factor in Excavation Stage 1 has reached the critical value required by the specification. When the single excavation height h is further increased, it will surely no longer meet the safety factor requirements.

[0061] At the same time, for Scheme 2-1, the excavation displacement nephogram was obtained through the Midas GTS software, as Figure 17 shown. It is the displacement nephograms of 4 different excavation stages, visualizing and quantifying the influence of underground excavation on the displacement of the surrounding rock and soil masses. The displacement nephogram represents the displacement amount of different regions through color coding, and the change of color reflects the magnitude and direction of the displacement. There is a series of numerical values beside the displacement nephogram of each stage, and these numerical values represent the colors corresponding to different displacement amounts. For example, the minimum displacement is blue, while the maximum displacement is red. These numerical values are expressed in actual displacement amount (m). Among them, the displacement nephograms from Excavation Stage 1 to Excavation Stage 4 show the displacement conditions of the rock and soil masses after the completion of Excavation Stage 1 to Excavation Stage 4 respectively, which are consistent with the results in Table 5, indicating that when excavating the first-level slope according to the second group of schemes, the displacement amounts of the rock and soil are within the safe range.

[0062] (5) Determination of the optimal scheme: It can be seen from step (3) that when the single excavation height h = 3m, it is preferred that the bottom excavation width b = 1.5m and the left slope angle β = 56.3°. Scheme 2-1 not only meets the requirements of the safety factor and the maximum displacement, but also meets the requirement of selecting a large value for the single excavation height h, ensuring the continuity of the excavation construction, reducing equipment relocation, and improving the excavation efficiency.

[0063] A system for a safe construction method of excavating a fully weathered granite residual soil slope, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the steps of the safe construction method of excavating the fully weathered granite residual soil slope are implemented. The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle scope of the present invention shall be included within the protection scope of the present invention.

Claims

1. A safe construction method for excavating a slope of fully weathered granite residual soil, characterized in that: The following steps are involved: Excavation of the second-level or higher slope away from the operating road; The remaining primary slope adjacent to the operating road is excavated in multiple layers of rock and soil with equal heights from top to bottom. When excavating each layer of rock and soil with equal heights, a receiving pit is first excavated on the side away from the operating road to form a rock and soil pile on the side close to the operating road, and then the rock and soil pile is excavated. The distance from the receiving pit close to the side of the secondary slope to the foot of the secondary slope after the excavation is completed is not less than the original bridleway width M. Before excavating each layer of receiving pit, the anchor rods implanted in the receiving pit on the upper part of the primary slope and the anchor rod support structure connected to the anchor rods are removed; The transverse section of the accommodation pit in each equal-height rock and soil layer is perpendicular to the first-level slope or the second-level slope and the extension direction of the bridleway. The transverse section shape is an inverted trapezoid with a bottom width smaller than the top width. The accommodation pit parameters are the same and include: b, h, α and β, h and b are the height and width of the bottom of the inverted trapezoid respectively, α / β are the inclinations of the side of the inverted trapezoid close to the secondary slope / primary slope relative to the operating road, α Equal to the slope angle of the first-level slope provided in the design drawings; The pit parameters are obtained by screening the preferred pit parameters corresponding to the largest h from the preferred pit parameters. The geometric model of the first-level slope after the 1st to nth excavation of the pit is constructed according to the preferred pit parameters. After finite element numerical simulation calculation is performed on the geometric model using Midas GTS, the minimum safety factor of the geometric model after each excavation of the pit is not greater than 1.20 and the maximum displacement is less than 30 mm, H / h=n.

2. The safe construction method for excavating a fully weathered granite residual soil slope according to claim 1 is characterized in that: The preferred containment pit parameters are screened by the following steps: (1) Use Midas GTS software to calculate the maximum displacement after excavating the secondary or higher slope, calculate the safety factor using the strength reduction method, and set it as the initial state of the numerical simulation calculation in step (4); (2) Based on the overall excavation width B1 of the first-level slope, the overall height H of the first-level slope, and the space requirements for excavation construction equipment, multiple sets of alternative containment pit parameters are preliminarily designed, and B1-b>hcotα+hcotβ, h <H,β≥α; (3) The candidate pit parameter with the smallest h is used as the primary pit parameter. If the h of multiple sets of candidate pit parameters are the same and are all minimum values, they are used as the primary pit parameters at the same time. The number of cycles n of excavating the pit and removing the rock and soil pile according to the preferred excavation process is calculated based on the ratio of H to h. (4) According to each group of preliminary pit parameters, the geometric model of the first-level slope after the 1st to nth excavation of the pit is constructed respectively, and the Midas GTS software is imported to establish the finite element numerical simulation calculation model after the 1st to nth excavation of the pit. The minimum safety factor and maximum displacement of the geometric model after each excavation of the pit are obtained, and compared with the safety factor and maximum displacement required by the industry specification. If the requirements of the industry specification are met, step (5) is executed; if not, the process is terminated; (5) Return to step (3) and select the primary pit parameters from the multiple groups of candidate pit parameters with a larger h ranking, and repeat step (4); (6) Based on the calculation results of steps (4) to (5), all the containment pit parameters that meet the requirements of industry specifications are screened out, i.e., the optimal containment pit parameters are selected, and they are sorted from the largest to the smallest according to h; (7) Select the pit parameters with the largest h.

3. The safe construction method for excavating a fully weathered granite residual soil slope according to claim 1 is characterized in that: After the geometric model is imported into the Midas GTS software, step (1) and step (4) also include: setting material parameters and setting material properties as 2D properties in the Midas GTS software, selecting the "Size Control" option, then selecting the "2D" option to divide the mesh, setting the boundary condition to the "Constraint" option and the gravity load to the "Self-Weight" option.

4. The safe construction method for excavating a fully weathered granite residual soil slope according to claim 1, characterized in that: Before excavating the second-level or higher slopes, the anchor rods implanted in the rock and soil blocks and the anchor rod support structure on the slope surface of the rock and soil blocks shall be removed first.

5. The safe construction method for excavating a fully weathered granite residual soil slope according to claim 2, characterized in that: The space requirement for excavation construction equipment in step (2) means that the bottom width of the accommodation pit and the top width of the rock and soil pile are not less than the width of the construction equipment and mechanical vehicle.

6. The safe construction method for excavating a fully weathered granite residual soil slope according to claim 2, characterized in that: The material parameters in step (2) include rock and soil type, rock and soil density, rock and soil porosity, rock and soil moisture content, rock and soil cohesion, rock and soil internal friction angle, rock and soil Poisson's ratio, and rock and soil elastic modulus.

7. The safe construction method for excavating a fully weathered granite residual soil slope according to claim 2, characterized in that: Meeting the industry standard requirements in step (4) includes: The minimum safety factor of the geometric model after each excavation of the accommodation pit shall not be less than the safety factor required by industry standards; Furthermore, the maximum displacement of the geometric model after each excavation of the accommodation pit is less than the maximum displacement required by industry standards.

8. The safe construction method for excavating a fully weathered granite residual soil slope according to claim 1, characterized in that: The excavation steps for the second-level or higher slopes away from the operating road are to excavate layer by layer from top to bottom, and the excavation steps for each layer are gradually divided into sections from the outer slope surface to the inner slope.

9. A system for generating a safe construction method for excavating a slope of fully weathered granite residual soil, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 8 are implemented.

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