A deep ditch slope expansion excavation decision optimization method considering red layer soft rock strength attenuation

Abstract

The present application relates to the technical field of expressway capacity expansion slope disaster prevention, and more particularly to a deep cutting slope expansion decision optimization method considering red layer soft rock strength attenuation, first, according to the actual engineering conditions, the existing slope form and the red layer soft rock attenuation characteristics, the suitable support form including strong support, gentle slope rate, wide platform and composite structure is established, then, the rock mass parameter attenuation law is obtained by means of indoor test and embedded into the finite element model, the stability safety factor of the slope in the construction period and the long-term operation process is simulated. Through repeated iteration calculation, the safety analysis is carried out on different support parameters and slope form, so as to control the support structure and engineering quantity under the premise of ensuring the stability of the slope, and the safety reliability and engineering economy are synergistically optimized.

Description

Technical Field

[0001] This invention relates to the field of slope disaster prevention technology for highway expansion, and in particular to an optimization method for deep trench slope expansion decisions that takes into account the strength decay of red bed soft rock. Background Technology

[0002] With the continuous deepening of urban technological development, the demand for road network capacity is increasing day by day. The traffic efficiency of early expressways can no longer meet the travel and transportation needs. In the future, promoting the expansion and upgrading of expressways is an inevitable measure to ensure the service capacity of the transportation system.

[0003] Carrying out secondary excavation of an operational highway will face many challenges. Excavation work must be carried out while ensuring the normal passage of the existing road. Construction conditions are significantly limited, and the selection of support methods is narrow. It is necessary to scientifically choose an appropriate excavation plan to balance daily traffic and on-site construction safety.

[0004] Red bed soft rock is a type of rock mass with significant engineering geological characteristics. It has a low degree of cementation and low mechanical strength. Under repeated effects of rainfall, sunshine and high temperature, it is prone to softening and disintegration, especially in the shallow surface part, where it often breaks down and collapses. This makes the red bed slope more prone to instability and affects the traffic safety of nearby highways.

[0005] Anchored (cable) frame beam support and gentle slope ratio are commonly used support methods in road cut slope engineering. During the secondary excavation of slopes, reliable support measures must be set up to ensure slope stability and road traffic safety. However, traditional protection design schemes have problems such as excessive support leading to high engineering costs, or insufficient protection due to the strength decay of soft rock, leaving significant safety risks. These pose great hidden dangers to the long-term durability of slope engineering. Summary of the Invention

[0006] This invention proposes a slope widening design method based on finite element numerical simulation. The design selects appropriate support schemes (strong support, gentle slope ratio, wide platform, composite type) according to actual working conditions to ensure the long-term stability of red bed slopes. Furthermore, the design method fully considers the impact of the strength decay characteristics of soft red bed rock on slope stability to reduce the risk of geological disasters and ensure traffic safety. Through scheme optimization, indoor collapse tests, and numerical simulation, the support system is quantitatively analyzed, effectively controlling the support cost during slope widening and achieving a balance between safety and economy.

[0007] To achieve the above objectives, this invention provides an optimization method for deep trench slope widening decisions considering the strength attenuation of red bed soft rock, comprising the following steps: S1. Based on the detailed engineering geological survey data of the deep trench slope, the existing support structure design drawings and current status test report, the reconstruction and expansion design requirements and the construction environment survey report, obtain the basic conditions and constraints for the excavation. S2. Select one or more excavation support schemes suitable for the current engineering scenario from the preset typical excavation mode library; determine whether the excavation support scheme meets the decision screening conditions for deep trench slopes. If it meets the decision screening conditions, execute S3. If it does not meet the decision screening conditions, re-screen the excavation support scheme. S3. Based on the characteristics of red bed soft rock being easily softened and disintegrated when exposed to water, indoor disintegration tests and triaxial strength tests were conducted to simulate the stress state and hydrological cycle under different burial depth conditions. The attenuation data of the shear strength parameters of the rock and soil as the burial depth changed were obtained. Based on the attenuation data and regression analysis algorithm, a mathematical attenuation model reflecting the change of the strength parameters of red bed soft rock with depth was established. S4. A realistic geological model including topography, strata and preliminary excavation support form is constructed using Rhino 3D geological modeling software. The realistic geological model is then imported into finite element software. Based on the strength attenuation formula given by the mathematical attenuation model, a constitutive model of the rock and soil mass of the corresponding soil layer is assigned to simulate the spatiotemporal deterioration effect of rock mass strength during and after the excavation process. The strength reduction algorithm is used to perform numerical simulation calculation of the stability of the excavation scheme to obtain the stability safety factor of the excavation scheme. S5, Adjust the stability safety factor Compared with the standard value of the engineering design safety factor Conduct comparative analysis, and obtain a feasible solution that has passed the verification based on the results of the comparative analysis; S6. Based on feasible solutions, conduct an economic evaluation of the entire life cycle technology to obtain the target excavation support scheme.

[0008] In some embodiments of this application, in S1, the decision screening conditions include at least: Whether it is a thin-skin excavation, that is, whether the excavation thickness is at the critical value; Whether the slope reaches its top after widening, i.e., whether it has been widened to the top of the mountain; Can excavated waste be used as roadbed fill material for resource utilization? Verify the access routes for construction machinery, the conditions for setting up work platforms, and the feasibility of constructing access roads; Whether there are important structures such as high-voltage towers, pipelines, and buildings on the top of the slope, and to determine the impact level of construction vibration and deformation on its safe operation.

[0009] In some embodiments of this application, in S2, the typical expansion mining mode library includes: Wide platform type excavation mode, gentle slope type excavation mode, strong support type excavation mode, and composite combination type excavation mode; Wide platform type excavation mode includes: by setting up a wide tiered platform, reducing the single-level slope height, and using the platform unloading and foot pressure effect to improve overall stability, it is suitable for open terrain and scenarios where the requirements for slope appearance are not high. The gentle slope type of widening excavation mode includes: adopting a gentler final slope to directly reduce the sliding force, which is suitable for scenarios with relaxed land acquisition conditions but not sensitive to the amount of excavation. Strong support type widening excavation mode includes: maintaining a relatively steep slope, but providing anti-sliding force through a dense, high-strength active support system, which is suitable for scenarios where land use is limited and the excavation range needs to be strictly controlled; Composite excavation mode includes: combining the characteristics of gentle slope excavation mode and strong support excavation mode, using a medium slope and supplemented with appropriate support.

[0010] In some embodiments of this application, in S3, the shear strength parameters of the soil and rock mass include cohesion and internal friction angle.

[0011] In some embodiments of this application, in S3, the expression for establishing a mathematical attenuation model reflecting the change of the strength parameter of red bed soft rock with depth is as follows: ; in, The soil-rock cohesion at a burial depth of h. Let h be the internal friction angle at a burial depth of h. The depth of burial at the ground surface is represented by A, B, and C, which are all fitted parameter values.

[0012] In some embodiments of this application, in S4, the finite element software used is FLAC3D.

[0013] In some embodiments of this application, in step S4, a strength reduction algorithm is used to perform numerical simulation calculations on the stability of the excavation widening scheme, and the resulting stability safety factor of the excavation widening scheme includes: The FLAC3D software gradually reduces the shear strength parameter of the slope soil and rock mass until it reaches the failure state, determines the range between stability and instability, and narrows the range through trial calculations until the stability and instability are within a tolerance range, thus completing the calculation. Among them, the shear strength parameters of slope rock and soil include cohesion, internal friction angle, and tensile strength; Using the principle of bisection, the intermediate value between the current stability coefficient and the instability coefficient is used for trial calculation. Assuming that the intermediate value is the stable value of the safety coefficient, the new range is the intermediate value minus the previous instability coefficient. The bisection is repeated to reduce the range. The formula for calculating the reduction in each nth iteration is: ; ; in, The initial cohesion, To calculate the reduced cohesion in the nth iteration, The initial internal friction angle, Calculate the reduced internal friction angle for the nth iteration; In Rhino software, the support structure is drawn and meshed. It is then imported into FLAC3D software to build a calculation model. The initial stress field is generated by fixing the boundary conditions through the command flow. The property parameters of the formation material and the support structure are assigned. The safety factor is solved by the model-factor-of-safety command. The support structure includes at least the three-dimensional geometry of the slope and the anchor frame beam.

[0014] In some embodiments of this application, in S4, the attribute parameters include constitutive models, unit weight, elastic modulus, cohesion, internal friction angle, Poisson's ratio, and tensile strength of different soil materials; Young's modulus, tensile strength, cross-sectional area, cement grout stiffness per unit length, cement grout bond strength per unit length, grouting hole perimeter, and cement grout friction angle of anchor bolts; and Young's modulus, Poisson's ratio, cross-sectional area, y-axis moment of inertia, z-axis moment of inertia, and polar moment of inertia of frame beams.

[0015] In some embodiments of this application, in S5, the stability safety factor is... Compared with the standard value of the engineering design safety factor Comparative analysis was conducted, and the feasible solutions that passed the verification based on the comparative analysis results include: like In If the value is within a reasonable range, the solution is deemed usable, and step S6 is executed. like < If the slope is deemed unstable, the support measures should be strengthened, and the process should return to step S4 for recalculation. like > If the design is deemed too conservative, the support parameters are reduced, and the process returns to step S4 for recalculation until... The requirements are met.

[0016] The advantages and beneficial effects of this invention compared to the prior art are: 1. This invention enables the rational selection of excavation schemes. By comparing and analyzing various excavation schemes, the scheme most suitable for the foundation conditions of the deep trench slope is selected as the basis for implementation, thereby significantly reducing unnecessary engineering measures, saving construction costs, and reducing interference with the surrounding environment.

[0017] 2. This invention effectively controls the cost of support structures. By evaluating and optimizing the excavation support system, it minimizes the number and density of support structures, thereby controlling the construction investment of the support system. 3. This invention improves the stability performance of slopes throughout their entire life cycle by using numerical simulation and iterative verification based on the stability safety factor to ensure that the slope has a reliable stable state and enhances the overall safety margin of the project.

[0018] 4. This invention improves the precision of support design by forming a more accurate support scheme based on numerical simulation and multi-parameter feedback adjustment, thus ensuring the dual quality of the design in terms of mechanical rationality and engineering reliability.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a flowchart of a deep trench slope widening decision optimization method considering the strength attenuation of red bed soft rock in an embodiment of the present invention; Figure 2 This is a schematic diagram of the original slope with a gradient of 60° according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the indoor disintegration and triaxial test according to an embodiment of the present invention; Figure 4 This is a graph showing the attenuation of cohesion with depth in an embodiment of the present invention. Figure 5 This is a graph showing the attenuation of the friction angle with depth according to an embodiment of the present invention. Figure 6 This is a diagram of the Rhino software interface according to an embodiment of the present invention; Figure 7 This is a three-dimensional terrain slope diagram with a gentle slope ratio of 40°, according to an embodiment of the present invention. Figure 8 This is a composite three-dimensional terrain slope map according to an embodiment of the present invention; Figure 9 This is a structural diagram of a composite anchor frame beam according to an embodiment of the present invention; Figure 10 This is a diagram illustrating the FLAC3D software operation for importing external meshes according to an embodiment of the present invention. Figure 11 This is a FLAC3D mesh model with a gentle slope of 40°, as described in an embodiment of the present invention. Figure 12 This is a FLAC3D mesh model of the composite anchor frame beam according to an embodiment of the present invention; Figure 13 This is a diagram of the FLAC3D software interface operation according to an embodiment of the present invention; Figure 14This is a command flow diagram for calculating the stability safety factor using the strength reduction method with a gentle slope of 40°, as described in an embodiment of the present invention. Figure 15 This is a command flow diagram for a composite anchored frame beam according to an embodiment of the present invention; Figure 16 This is an optimized and adjusted three-dimensional terrain slope and mesh model with a gentle slope of 30° according to an embodiment of the present invention; Figure 17 This is an optimized and adjusted composite three-dimensional terrain slope and mesh model according to an embodiment of the present invention. Detailed Implementation

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] like Figure 1 As shown, this invention provides an optimization method for deep trench slope widening decisions considering the strength attenuation of red bed soft rock, comprising the following steps: S1. Based on the detailed engineering geological survey data of the deep trench slope, the existing support structure design drawings and current status test report, the renovation and expansion design requirements, and the construction environment survey report, obtain the basic conditions and constraints for the excavation.

[0024] S2. Select one or more excavation support schemes suitable for the current engineering scenario from the preset typical excavation mode library; determine whether the excavation support scheme meets the decision screening conditions for deep trench slopes. If it meets the decision screening conditions, execute S3. If it does not meet the decision screening conditions, re-screen the excavation support scheme.

[0025] In the decision-making process for widening the excavation, if there are important structures at the top of the slope, strong support is generally adopted; if there is a need for excavation relocation and backfilling, a gentle slope ratio is generally adopted. This step will generate a set of schemes containing one or more pre-selected widening support methods and proceed to the next stage of detailed analysis.

[0026] S3. Based on the characteristics of red bed soft rock being easily softened and disintegrated when exposed to water, indoor disintegration tests and triaxial strength tests were conducted to simulate the stress state and hydrological cycle under different burial depth conditions. The attenuation data of the shear strength parameters of the rock and soil as the burial depth changed were obtained. Based on the attenuation data and regression analysis algorithm, a mathematical attenuation model reflecting the change of the strength parameters of red bed soft rock with depth was established.

[0027] Specifically, the mathematical attenuation model established in this step provides quantitative input for intensity degradation in subsequent numerical analysis.

[0028] S4. A realistic geological model including topography, strata, and preliminary excavation support morphology is constructed using Rhino 3D geological modeling software. The realistic geological model is then imported into finite element software. Based on the strength attenuation formula given by the mathematical attenuation model, a constitutive model of the rock and soil mass for the corresponding soil layer is assigned to simulate the spatiotemporal deterioration effect of rock mass strength during and after the excavation process. The strength reduction algorithm is used to perform numerical simulation calculations on the stability of the excavation scheme to obtain the stability safety factor of the excavation scheme.

[0029] S5, Adjust the stability safety factor Compared with the standard value of the engineering design safety factor A comparative analysis was conducted, and a feasible solution that passed the verification was obtained based on the results of the comparative analysis.

[0030] S6. Based on feasible solutions, conduct an economic evaluation of the entire life cycle technology to obtain the target excavation support scheme.

[0031] It should be noted that this application aims to optimize the secondary excavation decision for deep trench slopes.

[0032] In this step, a comprehensive life-cycle techno-economic comparison is conducted on all verified "feasible solutions" to select the most economical widening and support solution. If only one solution meets all the conditions, that solution is directly selected.

[0033] This invention enables the rational selection of excavation schemes. By comparing and analyzing various excavation schemes, the scheme most suitable for the foundation conditions of deep trench slopes is selected as the basis for implementation, thereby significantly reducing unnecessary engineering measures. While saving construction costs, it also reduces interference with the surrounding environment and effectively controls the cost of support structures. Through the evaluation and optimization of the excavation support system, the number and density of support structures are minimized, thereby controlling the construction investment of the support system.

[0034] In some embodiments of this application, in S1, the decision screening conditions include at least: Whether it is a thin-skin excavation, that is, whether the excavation thickness is at the critical value; Whether the slope reaches its top after widening, i.e., whether it has been widened to the top of the mountain; Can excavated waste be used as roadbed fill material for resource utilization? Verify the access routes for construction machinery, the conditions for setting up work platforms, and the feasibility of constructing access roads; Whether there are important structures such as high-voltage towers, pipelines, and buildings on the top of the slope, and to determine the impact level of construction vibration and deformation on its safe operation.

[0035] In some embodiments of this application, in S2, the typical expansion mining mode library includes: Wide platform type excavation mode, gentle slope type excavation mode, strong support type excavation mode, and composite combination type excavation mode; Wide platform type excavation mode includes: by setting up a wide tiered platform, reducing the single-level slope height, and using the platform unloading and foot pressure effect to improve overall stability, it is suitable for open terrain and scenarios where the requirements for slope appearance are not high. The gentle slope type of widening excavation mode includes: adopting a gentler final slope to directly reduce the sliding force, which is suitable for scenarios with relaxed land acquisition conditions but not sensitive to the amount of excavation. Strong support excavation mode includes: maintaining a relatively steep slope, but providing anti-sliding force through a dense, high-strength active support system (such as long anchor cables, high-strength anchor frames, etc.), which is suitable for scenarios where land use is limited and the excavation range needs to be strictly controlled; Composite excavation mode includes: combining the characteristics of gentle slope excavation mode and strong support excavation mode, using a medium slope and supplemented with appropriate support.

[0036] In one embodiment, based on experience from an implemented expansion project, a slope database is established using a large amount of slope data. The weights of various factors in S1 are considered, and a slope prediction model is built based on the slope database and a machine learning algorithm. The decision conditions in S1 are then input to obtain preliminary selection results. The machine learning algorithm can be either a Support Vector Machine (SVM) or a Random Forest algorithm.

[0037] In some embodiments of this application, in S3, the shear strength parameters of the soil and rock mass include cohesion and internal friction angle.

[0038] In some embodiments of this application, in S3, the expression for establishing a mathematical attenuation model reflecting the change of the strength parameter of red bed soft rock with depth is as follows: ; in, The soil-rock cohesion at a burial depth of h. Let h be the internal friction angle at a burial depth of h. The depth of burial at the ground surface is represented by A, B, and C, which are all fitted parameter values.

[0039] In some embodiments of this application, in S4, the finite element software used is FLAC3D.

[0040] In some embodiments of this application, in step S4, a strength reduction algorithm is used to perform numerical simulation calculations on the stability of the excavation widening scheme, and the resulting stability safety factor of the excavation widening scheme includes: The FLAC3D software gradually reduces the shear strength parameter of the slope soil and rock mass until it reaches the failure state, determines the range between stability and instability, and narrows the range through trial calculations until the stability and instability are within a tolerance range, thus completing the calculation. Among them, the shear strength parameters of slope rock and soil include cohesion, internal friction angle, and tensile strength; Using the principle of bisection, the intermediate value between the current stability coefficient and the instability coefficient is used for trial calculation. Assuming that the intermediate value is the stable value of the safety coefficient, the new range is the intermediate value minus the previous instability coefficient. The bisection is repeated to reduce the range. The formula for calculating the reduction in each nth iteration is: ; ; in, The initial cohesion, To calculate the reduced cohesion in the nth iteration, The initial internal friction angle, Calculate the reduced internal friction angle for the nth iteration; In Rhino software, the support structure is drawn and meshed. It is then imported into FLAC3D software to build a calculation model. The initial stress field is generated by fixing the boundary conditions through the command flow. The property parameters of the formation material and the support structure are assigned. The safety factor is solved by the model-factor-of-safety command. The support structure includes at least the three-dimensional geometry of the slope and the anchor frame beam.

[0041] In some embodiments of this application, in S4, the attribute parameters include constitutive models, unit weight, elastic modulus, cohesion, internal friction angle, Poisson's ratio, and tensile strength of different soil materials; Young's modulus, tensile strength, cross-sectional area, cement grout stiffness per unit length, cement grout bond strength per unit length, grouting hole perimeter, and cement grout friction angle of anchor bolts; and Young's modulus, Poisson's ratio, cross-sectional area, y-axis moment of inertia, z-axis moment of inertia, and polar moment of inertia of frame beams.

[0042] In some embodiments of this application, in S5, the stability safety factor is... Compared with the standard value of the engineering design safety factor Comparative analysis was conducted, and the feasible solutions that passed the verification based on the comparative analysis results include: like In If the value is within a reasonable range, the solution is deemed usable, and step S6 is executed. like < If the slope is deemed unstable, the support measures should be strengthened, and the process should return to step S4 for recalculation. Enhanced support measures include adjusting the density, length, or prestress of anchor bolts (cables), or increasing the distribution density of the support structure; like > If the design is deemed too conservative, the support parameters are reduced, and a more economical solution is sought while ensuring safety. The process then returns to step S4 for recalculation until... The requirements are met.

[0043] It is important to note that the adjustment range is for reference. / Determined by the ratio The method of this invention improves engineering applicability and flexibility, has a systematic analysis framework and adjustment mechanism, can adapt to diverse geological environments and engineering constraints, and exhibits good universality and scalability.

[0044] The following experimental verification is conducted in conjunction with the embodiments.

[0045] Technical terms include: Anchored frame beam slope: A support system that uses anchor bolts and frame beams to connect potential slip bodies with deep stable rock and soil to improve the overall stability of the slope.

[0046] Stability safety factor: Under given working conditions, the ratio of the overall anti-sliding moment (or resistance) to the sliding moment (or sliding force) of a slope is a key indicator for evaluating the stability of a slope.

[0047] Design safety factor: The range of values ​​for slope stability safety factor determined according to the relevant provisions of the "Highway Subgrade Design Specification" and the highway grade.

[0048] Numerical simulation of slopes: A geomechanical model of the slope is established based on the finite element software FLAC3D. The stress, deformation and stability safety factor of the slope under various loads and working conditions are predicted through calculation and analysis.

[0049] Shear strength parameters: mechanical indicators that characterize the ability of soil and rock to resist shear failure, mainly including cohesion and internal friction angle.

[0050] The following section uses the widening and excavation project of an existing slope with a height of 30m as an example to illustrate the implementation steps of the present invention step by step.

[0051] The original basic conditions of the excavated slope are as follows: vertical height of the slope is 30m, slope angle is 60°, width is 30m, and the overall structure of the slope is shown in the figure. Figure 2 As shown.

[0052] Step 1: Based on the on-site investigation of the deep trench slope, the selection criteria for the proposed scheme are shown in Table 1.

[0053] Table 1. Selection criteria for the scheme

[0054] Step 2, preliminary selection of excavation schemes: Based on the screening conditions listed in Table 1, the feasibility of each excavation scheme is compared. As shown in Table 2, through the preliminary selection and comparative analysis of the model library, it can be seen that the gentle slope type of excavation scheme 2 and the composite type of excavation scheme 4 meet the conditions. Therefore, the gentle slope type and the composite support scheme are further calculated and analyzed.

[0055] Table 2 List of Preliminary Excavation Schemes

[0056] Excavation scheme 2 is a gentle slope type, with a preliminary design widening slope of 40°. The geotechnical material parameters are shown in Table 3.

[0057] Table 3 Geotechnical Material Parameters

[0058] In Flac3D, the bulk modulus K and shear modulus G are derived from the elastic modulus E and Poisson's ratio μ, and their calculation formulas are as follows: ; ; Excavation scheme 4 is a composite type, with an excavation slope of 50°, followed by the application of anchor frame beams.

[0059] The support system adopts an anchored frame beam structure. The frame beams are arranged in 11 layers both horizontally and along the slope, with a horizontal spacing of 3m and a slope-direction spacing of 3.92m. Anchors are installed at the intersections of the horizontal and vertical frame beams, in the upper 8 rows and without anchors in the lower 3 rows. Each anchor is 12m long and installed vertically along the slope. The anchor length extends at least 3m into the stable soil and rock layer outside the potential sliding surface, providing pull-out resistance through the bond between the grout and the surrounding soil and rock. Anchor calculation parameters are shown in Table 4 below, and frame beam calculation parameters are shown in Table 5 below.

[0060] Table 4 Anchor Bolt Calculation Parameters

[0061] Table 5 Calculation parameters for frame beams

[0062] Step 3: Based on indoor disintegration and triaxial tests, the mathematical attenuation model of the strength parameters of red bed soft rock at different depths is obtained as follows: ; Indoor disintegration and triaxial testing, such as Figure 3 As shown; the attenuation law of cohesion with depth is as follows: Figure 4 As shown; the attenuation law of the internal friction angle with depth is as follows: Figure 5 As shown.

[0063] Step 4, in Rhino geological modeling software (such as...) Figure 6 A three-dimensional model of the gentle slope ratio and composite slope is drawn in the figure (shown). The three-dimensional topographical diagram of the gentle slope ratio is shown in the figure. Figure 7 As shown, the composite three-dimensional terrain diagram Figure 8 And draw the anchor rods and frame beam structure in Rhino, such as... Figure 9 As shown, the excavated slope is then meshed using the Griddle plugin in Rhino software for numerical calculations. The meshed slope and support components are then imported into the finite element software FLAC3D (e.g., ...). Figure 10 For gentle slope ratios and composite mesh models, see [link / reference]. Figure 11 , 12 As shown. In the FLAC3D software interface (such as...) Figure 13 Simulation is performed via command flow (e.g.) Figure 14 First, the boundary displacements of the four sides and bottom are fixed. Then, the initial geostress field is realized through the elastic solution method: the constitutive model of the material is set to an elastic model, and the bulk modulus and shear modulus are set to their maximum values, and then the initial geostress field is generated. Next, the Mohr-Coulomb model is assigned to the soil and the property parameters are assigned. The soil material properties are shown in Table 3. The cohesion and internal friction angle are calculated using the strength attenuation model in step 3. Then, the calculation parameters of the anchor rod and frame beam are assigned according to Tables 4 and 5 respectively. The command flow for importing and generating the anchor rod and frame beam is shown below. Figure 15 Finally, the stability safety factor of the widened slope is calculated using the command flow `modelfactor-of-safety`. The calculated slope ratio and stability safety factor of the composite widened slope are shown in Table 6 below.

[0064] Table 6 Calculated values ​​of stability safety factor

[0065] Step 5: According to the "Highway Subgrade Design Specifications" and the highway grade, the slope stability safety factor Fa is determined to be in the range of 1.20~1.30. Comparing the stability safety factor Fs calculated in Step 4 with the standard value Fa of the engineering design safety factor, it is found that the safety factor of the widened slope with a gentle slope ratio is too small, while the safety factor of the composite slope is too large, failing to meet the control conditions. The ratios of Fs / Fa are 0.92 and 1.136, respectively. Therefore, the design of the gentle slope ratio and the composite slope is optimized and adjusted, with the adjustment range determined with reference to the Fs / Fa ratio. After adjustment, the excavation slope of the gentle slope type in excavation scheme 2 is 30°. Figure 16 As shown in (a) and (b), the excavation slope of the composite excavation scheme 4 remains 50°, but the support structure is adjusted. Anchor frame beams are still used, arranged in 9 layers horizontally and along the slope, with a horizontal spacing of 3.75m and a slope-direction spacing of 4.90m. Anchors are installed at the intersection of the horizontal and vertical frame beams, in the upper 7 rows and without anchors in the lower 2 rows. Each anchor is 12m long and installed vertically along the slope. The redesigned anchor frame beam structure is as follows: Figure 17 As shown in (a), the optimized composite slope model is as follows: Figure 17 As shown in (b). Then, the optimized and adjusted slope ratio and the composite widened slope are returned to step 4 for calculation to obtain the stability safety factor, as shown in Table 7 below. The safety factor Fa value requirement is met, so proceed to the next step.

[0066] Table 7. Adjusted Stability Safety Factor Calculation Values

[0067] Step 6: Conduct a comprehensive comparison and selection of the "feasible solutions".

[0068] The longitudinal length of the slope is 30m. Assuming the comprehensive unit price for anchor bolt installation is 60 yuan / m, the comprehensive unit price for frame beam installation is 500 yuan / m, and the comprehensive unit price for earthwork excavation is 10 yuan / m. 3 The calculated excavation volume based on the gentle slope ratio is 13754 m³. 3 The combined excavation volume is 3540 m³. 3 The technical and economic comparison of slope excavation and support schemes is shown in Table 8.

[0069] Table 8. Comparative Analysis of the Technical and Economic Feasibility of Support Systems under Different Excavation Schemes

[0070] According to the comparative analysis in Table 8, excavation scheme 2 does not require additional support structures and has the lowest total cost. From an economic perspective, a gentle slope ratio should be chosen. However, the red bed soft rock has the characteristic of disintegration, and the excavation slope is relatively gentle with a large excavation volume, which poses greater challenges to construction operations and site conditions. Excavation scheme 4 improves the safety factor by adding support. Therefore, from the perspective of safety and long-term stability, a composite excavation slope support system should be given priority.

[0071] In summary, this invention proposes a dynamic support design method for secondary excavation slopes designed to address the strength decay characteristics of soft red rock. By integrating indoor disintegration test data with finite element numerical simulation, it achieves a support response that addresses the long-term stability of the slope under varying strength decay, overcoming the safety hazards caused by neglecting the time-dependent strength degradation of the rock mass in traditional designs. Furthermore, this invention constructs a slope excavation support scheme comparison and optimization system based on multi-condition numerical simulation. While ensuring existing traffic flow, it quantitatively analyzes the engineering applicability of measures such as "strong support - gentle slope ratio - wide platform - composite type," achieving a balance between safety and economy in strictly constrained construction environments. This overcomes the problems of insufficient or excessive support in traditional empirical designs.

[0072] The above embodiments are merely illustrative of the present invention. Those skilled in the art can make various adjustments, modifications, or equivalent transformations without departing from the principles and core ideas of the present invention. The scope of protection of the present invention is determined by the claims and their equivalents.

[0073] In this application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In case of any inconsistency, the meaning set forth in this specification or derived from the content described herein shall prevail. Furthermore, the terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit the scope of this application.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for optimizing decision-making in widening deep trench slopes, considering the strength attenuation of soft red bed rock, characterized in that, Includes the following steps: S1. Based on the detailed engineering geological survey data of the deep trench slope, the existing support structure design drawings and current status test report, the reconstruction and expansion design requirements and the construction environment survey report, obtain the basic conditions and constraints for the excavation. S2. Select one or more excavation support schemes suitable for the current engineering scenario from the preset typical excavation mode library; determine whether the excavation support scheme meets the decision screening conditions for deep trench slopes. If it meets the decision screening conditions, execute S3. If it does not meet the decision screening conditions, re-screen the excavation support scheme. S3. Based on the characteristics of red bed soft rock being easily softened and disintegrated when exposed to water, indoor disintegration tests and triaxial strength tests were conducted to simulate the stress state and hydrological cycle under different burial depth conditions. The attenuation data of the shear strength parameters of the rock and soil as the burial depth changed were obtained. Based on the attenuation data and regression analysis algorithm, a mathematical attenuation model reflecting the change of the strength parameters of red bed soft rock with depth was established. In S3, the expression for establishing a mathematical attenuation model reflecting the change of strength parameters of red bed soft rock with depth is as follows: ； in, The soil-rock cohesion at a burial depth of h. Let h be the internal friction angle at a burial depth of h. This refers to the burial depth at the ground surface. , , All are fitting parameter values ​​for soil-rock cohesion. , , All are fitting parameter values ​​for the internal friction angle; S4. A realistic geological model including topography, strata and preliminary excavation support form is constructed using Rhino 3D geological modeling software. The realistic geological model is then imported into finite element software. Based on the strength attenuation formula given by the mathematical attenuation model, a constitutive model of the rock and soil mass of the corresponding soil layer is assigned to simulate the spatiotemporal deterioration effect of rock mass strength during and after the excavation process. The strength reduction algorithm is used to perform numerical simulation calculation of the stability of the excavation scheme to obtain the stability safety factor of the excavation scheme. S5, Adjust the stability safety factor Compared with the standard value of the engineering design safety factor Conduct comparative analysis, and obtain a feasible solution that has passed the verification based on the results of the comparative analysis; S6. Based on feasible solutions, conduct an economic evaluation of the entire life cycle technology to obtain the target excavation support scheme.

2. The method for optimizing deep trench slope widening decisions considering the strength attenuation of soft red bed rock as described in claim 1, characterized in that, In S1, the decision screening conditions include at least the following: Whether it is a thin-skin excavation, that is, whether the excavation thickness is at the critical value; Whether the slope reaches its top after widening, i.e., whether it has been widened to the top of the mountain; Can excavated waste be used as roadbed fill material for resource utilization? Verify the access routes for construction machinery, the conditions for setting up work platforms, and the feasibility of constructing access roads; Whether there are important structures such as high-voltage towers, pipelines, and buildings on the top of the slope, and to determine the impact level of construction vibration and deformation on its safe operation.

3. The method for optimizing deep trench slope widening decisions considering the strength attenuation of soft red bed rock according to claim 2, characterized in that, In S2, the typical expansion mining mode library includes: Wide platform type wide excavation mode, gentle slope type wide excavation mode, strong support type wide excavation mode, and composite combination type wide excavation mode; The wide platform type excavation mode includes: reducing the single-level slope height by setting up a wide tiered platform, and improving the overall stability by utilizing the platform unloading and foot pressure effect. It is suitable for scenarios with open terrain and low requirements for slope appearance. The gentle slope type widening excavation mode includes: adopting a gentler final slope to directly reduce the sliding force, which is suitable for scenarios with relaxed land acquisition conditions but not sensitive to the excavation volume; The strong support type of widening excavation mode includes: maintaining a relatively steep slope, but providing anti-sliding force through a dense, high-strength active support system, which is suitable for scenarios where land use is limited and the excavation range needs to be strictly controlled; The composite excavation mode includes: combining the characteristics of the gentle slope excavation mode and the strong support excavation mode, adopting a medium slope and supplementing it with appropriate support.

4. The method for optimizing deep trench slope widening decisions considering the strength attenuation of soft red bed rock according to claim 3, characterized in that, In S3, the shear strength parameters of the soil and rock mass include cohesion and internal friction angle.

5. The method for optimizing deep trench slope widening decisions considering the strength attenuation of soft red bed rock according to claim 4, characterized in that, In S4, the finite element software used is FLAC3D.

6. The method for optimizing deep trench slope widening decisions considering the strength attenuation of soft red bed rock according to claim 5, characterized in that, In step S4, a strength reduction algorithm is used to perform numerical simulation calculations on the stability of the excavation widening scheme, and the resulting stability safety factor of the widening scheme includes: The FLAC3D software gradually reduces the shear strength parameter of the slope soil and rock mass until it reaches the failure state, determines the range between stability and instability, and narrows the range through trial calculations until the stability and instability are within a tolerance range, thus completing the calculation. Among them, the shear strength parameters of slope rock and soil include cohesion, internal friction angle, and tensile strength; Using the principle of bisection, the intermediate value between the current stability coefficient and the instability coefficient is used for trial calculation. Assuming that the intermediate value is the stable value of the safety coefficient, the new range is the intermediate value minus the previous instability coefficient. The bisection is repeated to reduce the range. The formula for calculating the reduction in each nth iteration is: ； ； in, The initial cohesion, To calculate the reduced cohesion in the nth iteration, The initial internal friction angle, Calculate the reduced internal friction angle for the nth iteration; In Rhino software, the support structure is drawn and meshed. It is then imported into FLAC3D software to build a calculation model. The initial stress field is generated by fixing the boundary conditions through the command flow. The property parameters of the formation material and the support structure are assigned. The safety factor is solved by the model-factor-of-safety command. The support structure includes at least the three-dimensional geometry of the slope and the anchor frame beam.

7. The method for optimizing deep trench slope widening decisions considering the strength attenuation of soft red bed rock according to claim 6, characterized in that, In S4, the attribute parameters include constitutive models, unit weight, elastic modulus, cohesion, internal friction angle, Poisson's ratio, and tensile strength of different soil materials; Young's modulus, tensile strength, cross-sectional area, cement grout stiffness per unit length, cement grout bond strength per unit length, grouting hole perimeter, and cement grout friction angle of anchor bolts; and Young's modulus, Poisson's ratio, cross-sectional area, y-axis moment of inertia, z-axis moment of inertia, and polar moment of inertia of frame beams.

8. The method for optimizing deep trench slope widening decisions considering the strength attenuation of soft red bed rock according to claim 7, characterized in that, In S5, the stability safety factor Compared with the standard value of the engineering design safety factor Comparative analysis was conducted, and the feasible solutions that passed the verification based on the comparative analysis results include: like In If the value is within a reasonable range, the solution is deemed usable, and step S6 is executed. like < If the slope is deemed unstable, the support measures should be strengthened, and the process should return to step S4 for recalculation. like > If the design is deemed too conservative, the support parameters are reduced, and the process returns to step S4 for recalculation until... The requirements are met.

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