Construction method for full-weathered granite residual soil slope extension

Abstract

The application discloses a safe construction method for slope expansion and excavation of full-weathered granite residual soil, which is based on finite element simulation of the whole process of slope expansion and excavation of full-weathered granite residual soil, and proposes an excavation process optimization method for a first-level slope near an operating road. The safe construction method for expansion and excavation comprises the following steps: firstly, setting a temporary retaining support, then designing a primary excavation process, and designing multiple sets of excavation parameter combinations, taking the slope state after the expansion and excavation of a second-level slope are completed as an initial state, establishing a finite element model for the expansion and excavation of the slope for each scheme combination, inputting the excavation parameters, and calculating the safety factor and the maximum displacement of the slope after the expansion and excavation of the slope under the excavation scheme, and optimizing according to the calculation results and the space requirement of construction operation machinery, and finally determining the optimized expansion and excavation parameters and the safe excavation process. The technical scheme disclosed by the application can provide an optimized scheme for the safe expansion and excavation of full-weathered granite residual soil.

Description

Technical Field

[0001] This invention belongs to the field of slope excavation technology, and involves finite element simulation technology, specifically a construction method for excavating a slope with residual soil from completely weathered granite. Background Technology

[0002] The reconstruction and expansion of mountain highways are usually carried out while ensuring the normal operation of existing roads. The interaction between traffic flow and expansion construction results in significant pressure on safety management of mountain highways. In particular, when expansion projects involve widening high slopes, construction safety control faces enormous technical challenges. Completely weathered granite residual soil is a product of specific climate, geography, and geological environments. Its engineering geological properties differ from ordinary soil, making it a regionally unique soil type, more common in southern regions. High slope excavation projects in road expansion projects in South China often involve completely weathered granite residual soil.

[0003] Completely weathered granite residual soil is a product of specific climate, geography, and geological environments. Its engineering geological properties differ from ordinary soil, classifying it as a regionally unique soil. It is more common in southern regions and frequently involves high slope excavation in road widening projects in South China. The presence of primary micro-fractures, high void ratio, and a lack of intermediate particle size results in a unique "building block" structure in the particle skeleton of completely weathered granite residual soil. This leads to weak cohesion, loose strata, and a tendency for large deformation and significant strength reduction under disturbances such as water exposure, vibration, and stress unloading. Therefore, during slope excavation construction using completely weathered granite residual soil, construction loads and rainfall can easily cause slope instability. Currently, slope excavation construction using completely weathered granite residual soil still employs traditional construction methods (such as...). Figure 1 (As shown): Temporary protective measures are provided at the toe of the slope. The large-scale excavation proceeds gradually from top to bottom, from the slope surface inwards, until the temporary supports are removed, creating a widened new lane. Traditional construction methods are risky because construction is carried out directly on an open slope adjacent to the operating road. If a landslide or partial collapse occurs, and the temporary protective measures at the toe of the slope cannot provide effective support, it will inevitably endanger the operating highway below, causing serious casualties and economic losses. Summary of the Invention

[0004] Based on the above-mentioned situation, this invention proposes a safe construction method for excavating slopes with residual soil from completely weathered granite, specifically including the following steps:

[0005] For the excavation of slopes at or above level two that are far from the operating road, the excavation steps shall be carried out layer by layer from top to bottom, and the excavation steps of each layer shall be carried out step by step from the outer slope surface to the inside of the slope.

[0006] The remaining primary slope adjacent to the operating road is excavated according to the preferred excavation procedure. The preferred excavation procedure includes: according to the overall height H of the primary slope to be excavated, excavating in multiple layers of equal height soil and rock from top to bottom. When excavating each layer of equal height soil and rock, first excavate a accommodating pit on the side away from the operating road, so that a soil and rock pile is formed on the side closer to the operating road, and then excavate the soil and rock pile. The distance from the side of the accommodating pit close to the secondary slope to the toe of the secondary slope after the excavation is completed is not less than the original width M of the horse trail. Before excavating each layer of accommodating pit, remove the anchor rods and anchor rod support structures connected to the anchor rods that are embedded in the accommodating pits on the upper part of the primary slope.

[0007] The transverse profile of the embankment pit in each layer of equal-height soil and rock is perpendicular to the slope surface of the first or second-level slope and the extension direction of the horse trail. The transverse profile shape is an inverted trapezoid with a bottom width smaller than the top width. The parameters of the embankment pit are the same and include: b, h, α and β. h and b are the height and bottom width of the inverted trapezoid, respectively. α / β are the inclination of the side of the inverted trapezoid closest to the second-level slope / first-level slope relative to the operating road. α is equal to the slope angle of the first-level slope provided in the design drawings.

[0008] The parameters of the accommodating pit are obtained by selecting the optimal accommodating pit parameter corresponding to the largest h from the optimal accommodating pit parameters. The geometric model of the first-level slope after the first to nth excavation of the accommodating pit is constructed according to the optimal accommodating pit parameters. After the geometric model is calculated by finite element numerical simulation using Midas GTS, the minimum safety factor of the geometric model after each excavation of the accommodating pit is not greater than 1.20 and the maximum displacement is less than 30mm, H / h=n.

[0009] Meanwhile, the preferred accommodating pit parameters are selected using the following steps:

[0010] (1) Calculate the maximum displacement after excavating a level 2 or higher slope using Midas GTS software, obtain the safety factor by strength reduction method, and set it as the initial state for the subsequent numerical simulation calculation (4):

[0011] This includes: importing the original geometric model of the secondary or higher slope and the geometric model of each construction stage constructed according to the excavation steps into the Midas GTS software; setting material parameters and 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 conditions as the "constraint" option and the gravity load as the "self-weight" option; setting the excavation calculation and analysis steps in sequence according to the original geometric model and the geometric model of each construction stage; obtaining the original slope safety factor by performing finite element numerical simulation calculations on each calculation step through Midas GTS; obtaining the maximum displacement of the secondary or higher slope after excavation through static calculations after excavation through SRM calculations; setting the state after excavation of the secondary slope as the initial state for subsequent step (4) numerical simulation calculations.

[0012] (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, a preliminary design of multiple sets of alternative embankment parameters is made. All sets of alternative embankment parameters satisfy the following formula: B1-b>hcotα+hcotβ, h <H,β≥α;

[0013] (3) Sort the multiple sets of candidate pit parameters in order of h from small to large, and take the candidate pit parameter with the smallest h as the initial selection pit parameter. If the h of multiple sets of candidate pit parameters is the same and is the minimum value, then they are all taken as the initial selection pit parameters. Calculate the number of cycles n for excavating the pit and clearing the soil and rock pile according to the ratio of H to h.

[0014] (4) According to the parameters of each initial selection of the containment pit, construct the geometric model of the first to nth excavation of the containment pit of the first-level slope respectively, import it into the Midas GTS software, set the material parameters and set the material properties to 2D properties in the Midas GTS software, select the “size control” option, and then select the “2D” option to divide the mesh, set the boundary conditions to the “constraint” option and the gravity load to the “self-weight” option, establish the finite element numerical simulation calculation model after the first to nth excavation of the containment pit, set the excavation calculation analysis steps according to the process of the first to nth excavation of the containment pit of the first-level slope, and perform finite element numerical simulation calculation on each calculation step through the Midas GTS software to obtain the minimum safety factor and maximum displacement of the geometric model after each excavation of the containment pit, and compare it with the safety factor and maximum displacement required by the industry standard. If the industry standard requirements are met, then execute step (5); if not, then terminate.

[0015] (5) Return to step (3) and select the initial selection of the accommodating pit parameters from the multiple sets of candidate pit parameters with larger h sorting, and repeat step (4).

[0016] (6) Based on the calculation results of steps (4) to (5), select all the accommodating pit parameters that meet the industry standard requirements, that is, select the preferred accommodating pit parameters, and sort them from largest to smallest according to h;

[0017] (7) Select the accommodating pit parameter with the largest h.

[0018] Furthermore, before excavation of slopes of level two or above, the anchor bolts embedded in each layer of rock and soil and the anchor bolt support structure on the slope surface of that layer of rock and soil should be removed.

[0019] Furthermore, in step (2), the space requirement for excavation construction equipment refers to the fact that the width of the bottom of the accommodating pit and the width of the top of the soil and rock pile are not less than the width of the construction equipment and machinery vehicles.

[0020] Furthermore, the material parameters in step (2) include soil type, soil unit weight, soil porosity, soil water content, soil cohesion, soil internal friction angle, soil Poisson's ratio, and soil elastic modulus.

[0021] Furthermore, meeting industry standard requirements in step (4) includes:

[0022] The minimum safety factor of the geometric model after each excavation of the containment pit shall not be less than the safety factor required by industry standards.

[0023] Furthermore, the maximum displacement of the geometric model after each excavation of the containment pit is less than the maximum displacement required by industry standards.

[0024] Furthermore, a system for generating a safe construction method for excavating a completely weathered granite residual soil slope includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the safe construction method for excavating a completely weathered granite residual soil slope.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. This invention proposes a safe construction method for excavating slopes of secondary or higher-grade completely weathered granite residual soil without affecting existing highway operations. After excavating secondary or higher-grade slopes according to traditional excavation procedures, this method optimizes the excavation process for the remaining primary slopes adjacent to the operating road. Based on the overall excavation width of the primary slope to be excavated, it divides the slope from the inside to the fracture surface into a containment pit and a soil-rock pile, excavating them as two separate soil-rock blocks. The excavation is based on the overall height of the primary slope. The process is divided into multiple layers from top to bottom, with multiple rounds of excavation for each layer, including the containment pit and the two rock and soil blocks in each layer. The containment pit consists of inverted trapezoidal rock and soil blocks, while the rock and soil pile consists of regular trapezoidal rock and soil blocks. When excavating the rock and soil pile, the construction equipment is positioned at the top of the rock and soil pile. While pushing part of the rock and soil pile into the containment pit, the rock and soil pushed into the containment pit are also removed. During removal, the excavation tools are excavated in the direction of the filling side of the containment pit to avoid excavation on the free face, which could cause the soil to scatter or slide onto the operating highway.

[0027] 2. In addition to the excavation parameters of the remaining primary slopes adjacent to the operating roads, this invention also designed and screened the excavation parameters of the containment pits for the primary slopes using a finite element numerical simulation model built with MidasGTS software.

[0028] The first step is to preliminarily determine the parameter combinations of the bottom width b and the left excavation slope angle β of multiple alternative options when the first group of single excavation height h is minimized, based on factors such as the overall excavation width of the first-level slope, the overall height of the first-level slope, and the space requirements of the excavation equipment. A Midas GTS finite element calculation model is constructed for the parameter combinations of alternative schemes when the single excavation height h is minimized. The slope excavation stage is simulated and calculated to obtain the safety factor and maximum displacement. By comparing and analyzing with the safety factor and maximum displacement required by industry standards, the parameter combinations of the bottom width b and the left excavation slope angle β that meet the requirements are selected and proceeded to the next round of selection after the single excavation height h is increased.

[0029] The second step involves combining the bottom excavation width value b and the left excavation slope angle β selected in the first set of parameters, gradually increasing the single excavation height value h to form a new set of excavation parameter combinations. A Midas GTS finite element calculation model is then constructed, and the safety factor and maximum displacement are obtained through simulation calculations. By comparing these with the safety factor and maximum displacement required by industry standards, the parameter combinations of the bottom excavation width b and the left excavation slope angle β that meet the requirements are selected.

[0030] Thirdly, while meeting the requirements of safety factor and maximum displacement, a single excavation height h with a larger value is selected from a new set of excavation parameter combinations to ensure the continuity of excavation construction, reduce equipment relocation, and improve excavation efficiency. In summary, the safe construction method proposed in this invention has the following advantages: it comprehensively considers both construction convenience and safety; the excavation construction parameters given by numerical simulation-assisted calculation are accurate, detailed, and highly operable; and the given excavation construction control indicators can be directly applied to actual on-site monitoring and control, providing accurate early warnings for safe construction. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the traditional trenching construction process;

[0032] Figure 2 This is a schematic diagram of the traditional excavation and widening construction process for a secondary slope;

[0033] Figure 3 A schematic diagram illustrating the optimized construction process for a whole slope combined with traditional excavation.

[0034] Figure 4 This is a schematic diagram of the excavation of the containment pit (block 7) on the inner side of the first-level slope;

[0035] Figure 5 This 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;

[0036] Figure 6 A flowchart for selecting excavation schemes for a first-level slope;

[0037] Figure 7 This is a schematic cross-sectional view of Example 1;

[0038] Figure 8 Midas GTS software operation diagram for setting unit attributes in Example 1;

[0039] Figure 9 A diagram showing the operation of the Midas GTS software for size control in Example 1;

[0040] Figure 10 This is a diagram illustrating the operation of the Midas GTS software for mesh generation in Example 1.

[0041] Figure 11 Midas GTS software operation diagram for setting boundary conditions and gravity loads for Example 1;

[0042] Figure 12 The image shows the calculation results of the original slope safety factor in Example 1, displayed using Midas GTS software.

[0043] Figure 13The figure shows the calculation results of the maximum displacement and safety factor after the secondary slope excavation in Example 1, displayed by Midas GTS software.

[0044] Figure 14 The numerical simulation calculation process for the six excavation stages of Scheme 1-1 in the first group of schemes;

[0045] Figure 15 The numerical simulation calculation process for the four excavation stages of Scheme 2-1 in the second group of schemes;

[0046] Figure 16 This is a schematic cross-sectional view of the secondary slope after excavation in Example 1; Figure 17 This is the excavation displacement cloud map for Scheme 2-1 in the second group of schemes. Detailed Implementation

[0047] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0048] Terminology Explanation

[0049] Horse trails serve as buffer zones between different slope levels in slope engineering, facilitating construction and maintenance, aiding drainage, and increasing the overall stability of the slope.

[0050] A first-level slope typically refers to the first-level slope measured from the road surface. It is located at the bottom and is directly adjacent to the operating road. It is the first-level slope closest to the road in the entire slope system.

[0051] A secondary slope is a slope that is one level below a primary slope. It is separated from the primary slope by a walkway (platform) and is farther from the operating road than the primary slope.

[0052] Advanced slopes refer to higher slopes that typically require tiered excavation. Due to their greater height, slopes are divided into multiple levels (multi-stage steps) to ensure stability. The "levels" refer to the number of steps the slope is divided into.

[0053] Excavation width refers to the horizontal distance between the slope surface before and after excavation.

[0054] This embodiment addresses the excavation of secondary or higher-level completely weathered granite residual soil slopes above primary slopes adjacent to road surfaces. It proposes a method using Midas GTS finite element numerical simulation technology to refine and optimize the excavation process, providing specific safety construction parameters and control indicators to achieve safe construction. The implementation steps of this invention are illustrated below using the excavation of secondary and primary slopes as examples.

[0055] Before excavation, the pre-embedded reinforcement and support components in the slope need to be removed, and then the excavation can be carried out. The specific steps are as follows:

[0056] Step 1: Excavate the secondary slope away from the operating highway. In this step, because the secondary slope is relatively far from the operating highway and is separated from the primary slope by the original bridle path serving as a buffer zone, the secondary slope excavation will still follow the traditional excavation procedure. The excavation width B2 of the secondary slope will be determined according to the design drawings. The excavation sequence will proceed gradually from the slope surface to the inside of the slope, and from top to bottom, as detailed below. Figure 2 As shown.

[0057] In this step, before excavating the secondary slope, the section of the secondary slope to be excavated is divided into two layers using line segments parallel to the slope surface, based on the excavation width B2. These layers are then further divided into multiple equal sections from bottom to top. Each section to be excavated is a rhombus of the same shape, and each section has the same excavation width. Figure 2 As shown, the secondary slope is divided into rock and soil blocks No. 1 to No. 6. The excavation process proceeds from the slope surface to the inside of the slope, and from top to bottom, excavating and clearing rock and soil blocks No. 1 to No. 6 one by one. Before excavation, the anchor rods embedded in the rock and soil blocks and the anchor rod support structure on the slope surface of each rock and soil block are removed. After all rock and soil blocks are excavated, the surface of the secondary slope is nearly parallel to the original surface of the secondary slope, and the entire slope is shifted away from the operating road by a certain excavation width. The excavation width B2 is not less than twice the original width of the horse trail M, and a geometric model of the original slope shape is constructed.

[0058] Step 2: Excavate the primary slope adjacent to the operating road. If the excavation of the primary slope is carried out according to the traditional excavation procedure, it is prone to instability and safety risks. Therefore, the excavation procedure for the primary slope needs to be optimized, specifically as follows: Figure 3 As shown. Step 2.1: After the secondary slope widening in Step 1 is completed, the primary slope is widened on the newly formed ramp. The designed primary slope widening width is B1. Based on the overall height of the primary slope, multiple layers of equal-height soil and rock are excavated from top to bottom. In each layer of equal-height soil and rock, a containment pit (Soil and Rock Area No. 7) is first excavated on the side away from the operating road. A soil and rock pile is formed on the outside of the containment pit, i.e., the side closer to the operating road. Then, the soil and rock pile (Soil and Rock Area No. 8) is excavated. Before excavating each layer of containment pit, based on the excavation depth of the containment pit, i.e., the single excavation height h, the anchor rods implanted in the containment pit at the top of the primary slope and the anchor rod support structure connected to the anchor rods are removed. The distance from the side of the containment pit (Soil and Rock Area No. 7) close to the secondary slope to the toe of the secondary slope after the widening in Step 1 is not less than the original ramp width M, so that the ramp width between the primary slope and the secondary slope after the widening is not less than the original ramp width M.

[0059] Step 2.2: After the excavation of the containment pit (No. 7 soil and rock area) in Step 2.1 is completed, when excavating the soil and rock pile (No. 8 soil and rock area), some of the soil and rock from the pile (No. 8 soil and rock area) is pushed into the containment pit (No. 7 soil and rock area) while the soil and rock pushed into the containment pit are removed. During removal, the excavation tools are facing the filling side of the containment pit. This avoids the need for primary slope excavation on the free face, which could lead to soil and rock scattering or sliding onto the operating highway.

[0060] Step 2.3: Repeat steps 2.1 to 2.2, excavating and removing each layer of soil and rock within the first-level slope from top to bottom, until the first-level slope excavation is completed.

[0061] In step 2.1 above, before excavating each layer of the containment pit, it is necessary to use Midas GTS finite element numerical simulation to calculate and refine the design parameters of the containment pit, in the transverse cross-section direction of the primary or secondary slope, such as... Figure 4 and Figure 5 As shown, the transverse section of the embankment pit is an inverted trapezoid with a bottom width smaller than the top width. The parameters of the embankment pit include: the width of the bottom of the inverted trapezoid is b, the height of the inverted trapezoid is h, the inclination of the side of the inverted trapezoid closest to the secondary slope relative to the operating road is α, α is determined according to the slope angle of the primary slope provided in the design drawings, and the inclination of the side of the inverted trapezoid closest to the primary slope relative to the operating road is β; the transverse section is perpendicular to the slope surface of the primary or secondary slope and the extension direction of the bridle path.

[0062] The parameters of the containment pit are used to ensure the overall stability of the slope and the local stability of the soil and rock pile. The parameters of the containment pit are substituted into Midas GTS for finite element numerical simulation calculations to evaluate the stability of the primary slope and the soil and rock pile, obtain the optimal results for the safety factor and maximum displacement, and then filter the containment pit parameters in combination with the space requirements of construction machinery.

[0063] According to the "Specifications for Design of Highway Subgrade" (JTG D30-2015), the slope stability safety factor for expressways and Class I highways should be greater than or equal to 1.20. In this method, a slope stability safety factor greater than or equal to 1.20 is considered to indicate overall slope stability. The local stability of the soil and rock pile is assessed based on displacement values. According to the "Technical Specification for Monitoring Slopes of Highway Cuts" (DBJ53 / T-156-2023), when the maximum displacement of the soil and rock pile is greater than or equal to 30 mm, a risk of local instability is considered. The commonly used strength reduction method for calculating the slope stability safety factor is as follows: ,

[0064] Where: k is the safety factor; It is the actual cohesion of the soil; It is the actual internal friction angle of the soil; It is the value of cohesion automatically reduced to the slope's slip limit state by MidasGTS; It is the value of the internal friction angle automatically reduced to the slope's slip limit state by the Midas GTS.

[0065] When calculating the safety factor of a slope in Midas GTS software, the following three criteria can be used to determine the limit state:

[0066] (1) Displacement convergence criterion: In the process of slope stability analysis, it is used to monitor whether the maximum displacement rate of the top node of the slope continuously accelerates before and after a fixed number of time steps. If the maximum displacement rate of the top node of the slope 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 already exceeded its stability limit state;

[0067] (2) Velocity convergence criterion: In the process of slope stability analysis, it is monitored whether the difference between the deformation rates of the slope before and after a fixed time step is continuously greater than a certain proportion. If the difference between the deformation rates (usually displacement rates) of the slope is continuously greater than the set proportion within a continuous fixed time step, it is considered that the deformation rate of the slope is constantly increasing and may be approaching or has reached the limit state;

[0068] (3) The criterion for the continuity of generalized shear strain or plastic strain: In the Midas GTS software, through the post-processing function, it is observed that the generalized shear strain or plastic strain forms a continuous high strain region in the slope soil, indicating that significant generalized shear strain or plastic deformation has occurred inside the slope soil, and it may be close to or reach the limit state.

[0069] A fixed time step refers to a fixed time step set in the Midas GTS software during numerical simulation. Within this time step, the Midas GTS software performs one calculation iteration to simulate the deformation and stress changes of the slope within that time step.

[0070] The slope was calculated using the elastoplastic finite element method with Midas GTS. If the slope was determined to have reached its limit state according to the instability criterion, the ratio of the actual cohesion before reduction to the cohesion after reduction by the reduction factor, or the ratio of the actual tangent of the internal friction angle before reduction to the tangent of the internal friction angle after reduction by the reduction factor, was the overall safety factor. Otherwise, the reduction was repeated using a newly assumed reduction factor until the slope reached the critical limit equilibrium state. This calculation process was performed automatically by the software.

[0071] like Figure 6 As shown, the optimal process for determining the accommodating pit parameters in the above steps is as follows.

[0072] (1) Set the geophysical parameters of the first-level slope. Determine α based on the slope angle of the first-level slope provided in 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, design a number of alternative accommodating pit parameters, namely h, b and β.

[0073] (2) Sort the multiple sets of candidate pit parameters in order of h from smallest to largest, and take the candidate pit parameter with the smallest h as the initial selection pit parameter. If the h of multiple sets of candidate pit parameters is the same and is the minimum value, then they are all taken as the initial selection pit parameters. Calculate the number of cycles n for excavating the pit and clearing the soil pile according to steps 2.1~2.2 based on the ratio of H to h.

[0074] (3) According to the parameters of each group of initially selected burial pits, construct the geometric model after the first to nth excavation of burial pits on the first-level slope. Import the geometric model into Midas GTS. In the Midas GTS software, set the material parameters and set the material properties to 2D properties. Select the “Size Control” option and then select the “2D” option to divide the mesh. Set the boundary conditions to the “Constraint” option and the gravity load to the “Self-weight” option. Establish the finite element numerical simulation calculation model after the first to nth excavation of burial pits. According to the process of the first to nth excavation of burial pits on the first-level slope, set the excavation calculation and analysis steps. Perform finite element numerical simulation calculations on each calculation step through the Midas GTS software to obtain the minimum safety factor and maximum displacement of the geometric model after each excavation of burial pits. Compare it with the safety factor and maximum displacement required by the industry standard. If the industry standard requirements are met, proceed to step (4). If not, terminate.

[0075] (4) Return to step (2) and select the initial selection of the accommodating pit parameters from the multiple sets of candidate pit parameters with larger h sorting, and repeat step (3).

[0076] (5) Based on the calculation results of steps (3) to (4), select all the accommodating pit parameters that meet the industry standard requirements, that is, select the preferred accommodating pit parameters, and sort them from largest to smallest according to h. (6) Select the accommodating pit parameter with the largest h, and construct the geometric model of the first to nth excavation of the accommodating pit of the first-level slope according to the selected accommodating pit parameters, as the overall excavation steps. This is to ensure the continuity of excavation construction, reduce equipment relocation, and improve excavation efficiency.

[0077] Example 1

[0078] The following specific examples illustrate the detailed steps and optimization process of the safe construction method for excavating residual soil slopes of completely weathered granite.

[0079] Case Study: A highway underwent secondary slope widening for expansion. The original slope had two levels, each with a 45° slope and a height H of 6m. The crosswalk width M between the two slopes was 4m. The widening widths B1 and B2 were 8m, resulting in a slope shape identical to the original slope. The upper part of the area consisted of completely weathered granite residual soil, while the lower part consisted of strongly weathered granite. Stratigraphic parameters are shown in Table 1, and the slope profile is shown below. Figure 7 As shown, the soil and rock parameters within the original slope are set according to the properties of completely weathered granite, while the soil and rock parameters under the operating road are set according to the properties of strongly weathered granite.

[0080] Table 1. Main stratigraphic calculation parameters input into the software

[0081]

[0082] First, perform the excavation calculation for the upper secondary slope: This involves creating a geometric model of the original slope shape drawn on the CAD drawings (such as...). Figure 7 (As shown) and the geometric models of each construction stage constructed according to the excavation steps are imported into Midas GTS software. In Midas GTS software, material parameters are set according to Table 1 and material properties are set as 2D properties, such as... Figure 8 As shown, select the "Size Control" option (e.g.) Figure 9 As shown), then select the "2D" option to divide the mesh (as shown). Figure 10 As shown), set the boundary conditions to "Constraint Options" and the gravity load to "Self-Weight" (as shown). Figure 11 As shown), the excavation calculation and analysis steps were set sequentially based on the original geometric model and the geometric models of each construction stage. Finite element numerical simulations were performed on each calculation step using Midas GTS to obtain the original slope safety factor of 1.20 (as shown). Figure 12 As shown), after the upper secondary slope was excavated, the maximum displacement was found to be 18.5 mm through static calculations (as shown). Figure 13 As shown), the safety factor calculated using SRM is 1.31 (as shown). Figure 13 (As shown). The state after the secondary slope excavation is completed is set as the initial state for the numerical simulation calculation in the subsequent step (3). The software operation method for the subsequent primary slope excavation calculation is the same as the software operation method for the secondary slope excavation construction.

[0083] SRM stands for Strength Reduction Method, used for slope stability analysis. Its basic principle is to gradually increase the reduction factor, correspondingly decreasing the soil's shear strength parameters (such as cohesion and internal friction angle), and repeatedly perform trial calculations on the slope until the slope reaches the critical state of limit equilibrium.

[0084] Secondly, perform the excavation calculation for the first-level slope near the operating road at the bottom. In this embodiment, the main purpose is to optimize the excavation plan for the first-level slope near the operating road at the bottom. The optimization process is as follows:

[0085] (1)初选单次开挖施工参数: 设计图纸提供的一级边坡坡角为45°, 因此确定α = 45°. 根据拓挖宽度B1、边坡高度H及开挖施工设备空间需求等因素, 初步确定多组备选的(单次开挖高度h、底部宽度b、β)参数组合, 参数组合如表2所示。

[0086] 由于B1 - b > hcotα + hcotβ, h < H, β ≥ α, 因此β = 45°, 且h = 3m时, 在既定的拓挖宽度B1 = 8m, 马道宽度M = 4m时, 在每一轮开挖过程中, 不能同时满足第一次开挖的容置坑底部的挖机通行空间需求(≥1.5m)及第二次开挖顶部的挖机施工空间需求(≥2m), 故β = 45°相关的组合未能进入第二组参数组合初选中。

[0087] Table 2 The first set of single-excavation schemes

[0088]

[0089] In the above first set of parameter combinations, in Scheme 1-1, when h = 2m, b = 2m, and β = 45°, the accommodation pit (Rock Soil Area 7) inside the first-layer excavation area and the outer rock soil pile (Rock 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 soil pile 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 reduced, the excavation construction space of the outer rock soil pile will change. When β = 30°, the top operation width of the outer rock soil pile 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 other examples are given.

[0090] 因此, 在第一组方案中, 在h = 2m的条件下, b、β需要同时调整, 即b增大、β也变大, 才能满足每一轮的岩土块开挖过程中需求, 即同时满足第一次开挖时容置坑底部的施工空间的需求和第二次开挖时岩土堆顶部的施工空间需求。

[0091] It should be noted that in the translation of item (3), there is an inaccuracy in the original Chinese expression. The correct English translation should be: (1) Preliminary selection of single-excavation construction parameters: The slope angle of the first-level slope provided in the design drawing is 45°, so α = 45° is determined. According to factors such as the excavation width B1, slope height H, and the space requirements of the excavation construction equipment, multiple groups of alternative (single-excavation height h, bottom width b, β) parameter combinations are initially determined. The parameter combinations are shown in Table 2.As b and β increase simultaneously, the contact surface between the inner containment pit (No. 7 soil and rock area) and the outer soil and rock pile (No. 8 soil and rock area) gradually becomes steeper, which is also not conducive to the safety of construction operations, i.e. β is less than or close to 75°.

[0092] In the preliminary design of the aforementioned embankment parameters, several relatively reasonable schemes were presented. These schemes were then analyzed and compared to select the optimal one. The embankment parameters should not be continuously varied, as this is not practical for engineering. If the single excavation interval h is too small, the number of excavation cycles will be too high, making construction inconvenient. Setting the single excavation interval h to an integer with a difference of 1 meter is based on the convenience of on-site construction.

[0093] (2) Preliminary selection of overall excavation scheme: According to the first group of combinations, the excavation of the containment pit and the removal of soil and rock piles are carried out (Scheme 1-1, Scheme 1-2, Scheme 1-3, Scheme 1-4). Based on the slope height H being 6m and h being 2m, as follows... Figure 14 Repeat steps 2.1 to 2.2 three times as shown to complete the excavation of the first-level slope;

[0094] According to the second group of combinations, the excavation of the containment pit and the removal of soil and rock piles are carried out (Scheme 2-1, Scheme 2-2, Scheme 2-3). Based on the slope height H being 6m and h being 3m, as follows... Figure 15 Repeat steps 2.1 to 2.2 twice to complete the excavation of the first-level slope.

[0095] (3) Taking schemes 1-1, 1-2, 1-3, and 1-4 as examples, the slope morphology after the secondary slope excavation is completed (e.g.) Figure 16 As shown, a finite element calculation model was constructed. In the Midas GTS software, material parameters were set and material properties were set to 2D properties. The "Size Control" option was selected, and then the "2D" option was used to generate the mesh. The boundary conditions were set to the "Constraint" option and the gravity load was set to the "Self-weight" option. A finite element numerical simulation calculation model was established after the first to nth excavation of the containment pit. According to the process of the first to nth excavation of the containment pit of the first-level slope, the excavation calculation and analysis steps were set. Finite element numerical simulation calculations were performed on each calculation step using the Midas GTS software to obtain the minimum safety factor and maximum displacement of the geometric model after each excavation of the containment pit, as shown in Table 3. The safety factor and maximum displacement of four different combination schemes were obtained.

[0096] Table 3. Safety factors and maximum displacement at each excavation stage in the numerical simulation calculation of the first scheme.

[0097]

[0098] As shown in Table 3, the safety factor and maximum displacement of the four schemes in the first group of designs in Table 2 all meet the requirements, as calculated by the Midas GTS finite element numerical simulation model.

[0099] (4) Increase the excavation depth h=3m and design the parameters for the second set of containment pits. Taking schemes 2-1, 2-2, and 2-3 shown in Table 4 as examples, the slope morphology after the secondary slope widening is completed (e.g., Figure 16 As shown, a finite element calculation model was constructed. In the Midas GTS software, material parameters were set and material properties were set to 2D properties. The "Size Control" option was selected, and then the "2D" option was used to generate the mesh. The boundary conditions were set to the "Constraint" option and the gravity load was set to the "Self-weight" option. A finite element numerical simulation calculation model was established after the first to nth excavations of the containment pit. According to the process of the first to nth excavations of the containment pit on the first-level slope, the excavation calculation and analysis steps were set. Finite element numerical simulation calculations were performed on each calculation step using the Midas GTS software to obtain the minimum safety factor and maximum displacement of the geometric model after each excavation of the containment pit, as shown in Table 4. The safety factor and maximum displacement of three different combination schemes were obtained through calculation.

[0100] As shown in Table 4, among the three schemes in the second group of designs in Table 2, only scheme 2-1 meets the requirements for the accommodating pit parameters through the Midas GTS finite element numerical simulation model.

[0101] Table 4. Safety factors and maximum displacement at each excavation stage in the numerical simulation calculation of the second scheme.

[0102]

[0103] Furthermore, in the second scheme, the safety factor of excavation stage 1 has reached the critical value required by the specification. When the single excavation height h increases further, the safety factor requirement will no longer be met.

[0104] Meanwhile, for Scheme 2-1, its excavation displacement cloud map was obtained using Midas GTS software, such as... Figure 17The diagram shows displacement contour maps for four different excavation stages, visualizing and quantifying the impact of underground excavation on the displacement of the surrounding soil and rock. The displacement contour maps use color coding to represent the displacement in different areas; color changes reflect the magnitude and direction of the displacement. Each stage's displacement contour map is accompanied by a series of values, representing the color corresponding to different displacement amounts. For example, the smallest displacement is blue, while the largest is red. These values ​​are expressed in actual displacement (m). Specifically, the displacement contour maps for excavation stages 1 to 4 show the displacement of the soil and rock after the completion of each stage, consistent with the results in Table 4, indicating that the displacement of the soil and rock is within a safe range when using the second scheme for excavating the first-level slope.

[0105] (5) Determination of the preferred scheme: As can be seen from step (3), when the single excavation height h=3m, the preferred bottom excavation width b=1.5m and the left slope angle β=56.3° are both met by the safety factor and the maximum displacement requirements, and the single excavation height h is selected to be the largest value, which ensures the continuity of excavation construction, reduces equipment relocation, and improves excavation efficiency.

[0106] A system for generating a safe construction method for excavating a completely weathered granite residual soil slope includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the safe construction method for excavating a completely weathered granite residual soil slope.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A safe construction method for excavating a slope with residual soil from completely weathered granite, characterized in that, Includes the following steps: Excavate slopes of level 2 or above that are far from operating roads; The remaining primary slope adjacent to the operating road will be excavated in multiple layers of equal-height soil and rock from top to bottom. When excavating each layer of equal-height soil and rock, a containment pit will be excavated first on the side away from the operating road, so that a soil and rock pile is formed on the side closer to the operating road. Then the soil and rock pile will be excavated. The distance from the side of the containment pit close to the secondary slope to the toe of the secondary slope after the excavation is completed shall not be less than the original width M of the horse trail. Before excavating each layer of containment pit, the anchor rods implanted in the containment pit on the upper part of the primary slope and the anchor rod support structure connected to the anchor rods will be removed. The transverse profile of the embankment pit in each layer of equal-height soil and rock is perpendicular to the slope surface of the first or second-level slope and the extension direction of the horse trail. The transverse profile shape is an inverted trapezoid with a bottom width smaller than the top width. The parameters of the embankment pit are the same and include: b, h, α and β. h and b are the height and bottom width of the inverted trapezoid, respectively. α / β are the inclination of the side of the inverted trapezoid closest to the second-level slope / first-level slope relative to the operating road. α is equal to the slope angle of the first-level slope provided in the design drawings. The parameters of the accommodating pit are obtained by selecting the optimal accommodating pit parameter corresponding to the largest h from the optimal accommodating pit parameters. The geometric model of the first-level slope after the first to nth excavation of the accommodating pit is constructed according to the optimal accommodating pit parameters. After the geometric model is calculated by finite element numerical simulation using Midas GTS, the minimum safety factor of the geometric model after each excavation of the accommodating pit is not less than 1.20 and the maximum displacement is less than 30mm. H / h=n, where H is the overall height of the first-level slope.

2. The safe construction method for excavating a slope with residual soil from completely weathered granite according to claim 1, characterized in that, The preferred accommodating pit parameters are selected using the following steps: (1) Use Midas GTS software to calculate the maximum displacement after excavating the second-level or higher slope, calculate the safety factor by strength reduction method, and set it as the initial state for 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 equipment, a preliminary design of multiple sets of alternative embankment parameters is made, where B1-b>hcotα+hcotβ, h <H,β≥α; (3) The candidate pit parameter with the smallest h is used as the initial pit parameter. If multiple candidate pit parameters have the same h and are all the smallest, they are used as initial pit parameters. The number of cycles n for excavating the pit and clearing the soil pile according to the preferred excavation procedure is calculated based on the ratio of H to h. (4) According to the parameters of each group of initial selection of the accommodating pit, construct the geometric model of the first-level slope after the first to nth excavation of the accommodating pit, import it into the Midas GTS software, establish the finite element numerical simulation calculation model after the first to nth excavation of the accommodating pit, obtain the minimum safety factor and maximum displacement of the geometric model after each excavation of the accommodating pit, and compare it with the safety factor and maximum displacement required by the industry standard. If the industry standard requirements are met, proceed to step (5); otherwise, terminate. (5) Return to step (3) and select the initial selection of the accommodating pit parameters from the multiple sets of candidate pit parameters with larger h sorting, and repeat step (4). (6) Based on the calculation results of steps (4) to (5), select all the accommodating pit parameters that meet the industry standard requirements, that is, select the preferred accommodating pit parameters, and sort them from largest to smallest according to h; (7) Select the accommodating pit parameter with the largest h.

3. The safe construction method for excavating a slope with residual soil from completely weathered granite according to claim 2, characterized in that, Steps (1) and (4) after importing the geometric model into the Midas GTS software also include: setting material parameters and setting material properties to 2D properties in the Midas GTS software, selecting the "Dimension Control" option, then selecting the "2D" option to generate the mesh, setting the boundary conditions to the "Constraint" option and the gravity load to the "Self-weight" option.

4. The safe construction method for excavating a slope with residual soil from completely weathered granite according to claim 1, characterized in that, Before excavation of slopes of grade II or above, the anchor bolts embedded in the rock and soil blocks and the anchor bolt support structure on the slope surface of the rock and soil blocks should be removed.

5. A safe construction method for excavating a slope with residual soil from completely weathered granite according to claim 2, characterized in that, In step (2), the space requirement for excavation construction equipment refers to the fact that the width of the bottom of the accommodating pit and the width of the top of the soil and rock pile are not less than the width of the construction equipment and machinery vehicles.

6. A safe construction method for excavating a slope with residual soil from completely weathered granite according to claim 3, characterized in that, The material parameters include soil type, soil unit weight, soil porosity, soil moisture content, soil cohesion, soil internal friction angle, soil Poisson's ratio, and soil elastic modulus.

7. A safe construction method for excavating a slope with residual soil from completely weathered granite according to claim 2, characterized in that, The requirements for meeting industry standards in step (4) include: The minimum safety factor of the geometric model after each excavation of the containment 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 containment pit is less than the maximum displacement required by industry standards.

8. A safe construction method for excavating a slope with residual soil from completely weathered granite according to claim 1, characterized in that, The excavation steps for slopes of level 2 or above that are far from the operating road shall be carried out layer by layer from top to bottom, and the excavation steps for each layer shall be carried out step by step from the outer slope surface to the inside of the slope.

9. A system for generating a safe construction method for excavating a slope with residual soil from completely weathered granite, 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, it implements the steps of the method according to any one of claims 1 to 8.

Images