Optimization method for primary support of shallow-buried unsymmetrical pressure tunnel

Abstract

The invention discloses an optimization method for a primary support of a shallow-buried and unsymmetrical-pressure tunnel, and belongs to the field of tunnel engineering.The optimization method for the primary support of the shallow-buried and unsymmetrical-pressure tunnel comprises the steps that a stratum-tunnel-support structure three-dimensional calculation model is established, and displacement and stress distribution conditions of surrounding rock and the primary support of the tunnel after excavation are calculated; and safe, economic and reasonable asymmetric optimization design is carried out on the tunnel primary support. According to the scheme, possible dangers in the excavation period of the shallow-buried unsymmetrical-pressure large-section tunnel can be predicted in advance, corresponding control measures are provided, and an ideal scheme considering construction safety and economy can be provided for the construction process through scheme optimization.

Description

Technical Field

[0001] The invention relates to the field of tunnel engineering construction, and in particular to an optimization method for initial support of a shallow-buried bias-pressure tunnel. Background Art

[0002] Shallow buried bias pressure is a common undesirable phenomenon in tunnel construction, which will cause asymmetric stress deformation of the tunnel and the supporting structure. If the support method is inappropriate, it is easy to cause large deformation of the surrounding rock, local stress concentration and other problems, which seriously endangers the construction safety. At present, the research on the initial support of shallow buried bias pressure tunnels is mainly to verify the feasibility of the original design scheme, or to dynamically adjust the support scheme according to the monitoring data of the surrounding rock and initial support in actual construction. However, such methods often have lags, cannot detect possible problems in advance, and cannot effectively ensure the safety and stability of the tunnel excavation process.

[0003] In view of the above defects, the present invention adopts numerical simulation to simulate the changes of indicators such as surrounding rock displacement and initial support stress under different asymmetric initial support schemes to compare the impact of different schemes on tunnel safety. On this basis, a method is proposed that can take into account construction safety and improve support performance as much as possible. Summary of the invention

[0004] This scheme can predict in advance the dangers that may occur during the excavation of shallow-buried, biased, large-section tunnels and propose corresponding countermeasures. Through the optimization of the support scheme, an ideal solution that takes into account both construction safety and economy can be provided for the construction process.

[0005] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] The present invention provides a method for optimizing the initial support of a shallow-buried bias-pressure tunnel. The method for optimizing the initial support of a shallow-buried bias-pressure tunnel comprises the following steps:

[0007] Step S1: The server obtains stratum data, tunnel data and initial support data from a database or an external data source, wherein the stratum data includes geological structure and mechanical parameters of rock and soil, the tunnel data includes tunnel dimensions, and the initial support data includes anchor position and anchor length and shotcrete thickness;

[0008] The main purpose of step S1 is to obtain the basic data required for tunnel construction from various data sources so as to subsequently establish a three-dimensional calculation model and perform numerical simulation analysis.

[0009] Database: usually refers to the database system established within the enterprise, which stores data on previous projects, geological survey reports, design documents, etc.

[0010] External data sources: including Internet resources, data provided by other institutions or units, on-site survey data, etc.

[0011] The stratigraphic data include the following:

[0012] Geological structure: describes the geological conditions of the area through which the tunnel passes, including the type, distribution, direction, inclination, etc. of the rock formations.

[0013] Mechanical parameters of rock and soil: physical and mechanical properties of rock and soil, such as density, elastic modulus, Poisson's ratio, internal friction angle, cohesion, etc. These parameters are crucial to tunnel excavation and support design.

[0014] Tunnel data includes the following:

[0015] Tunnel dimensions: including the tunnel's cross-sectional shape, dimensions (such as width, height), longitudinal slope, curvature, etc. These data are the basis for establishing a tunnel model.

[0016] The initial support data include the following:

[0017] Shotcrete thickness: The specific thickness of shotcrete in the tunnel support structure. This is directly related to the strength and support effect of the shotcrete structure.

[0018] Anchor position: The specific position information of the anchor in the tunnel support structure, such as the arrangement angle and spacing of the anchor.

[0019] Anchor length: The buried length of the anchor in the rock and soil, which is directly related to the support effect of the anchor.

[0020] According to the project requirements, clarify which databases or external data sources need to be used to obtain data. Data query and extraction: Use database query languages ​​(such as SQL) or external data interfaces (such as API) to extract the required data from the specified data source. Verify the extracted data to ensure its integrity and accuracy, and convert and organize the data format as needed. Store the verified and organized data in the local server or designated data storage system for use in subsequent steps.

[0021] Step S1 is the basis for all subsequent analysis and optimization work. Only by ensuring the accuracy and completeness of the data can an accurate three-dimensional calculation model be established and reliable numerical simulation results be obtained.

[0022] Step S2: Use finite element software to establish a three-dimensional calculation model of the stratum-tunnel on the server side. The three-dimensional calculation model of the stratum-tunnel is used to calculate the terrain bias effect and perform linear generalization processing on the terrain. Use finite difference software to establish a three-dimensional calculation model of the initial support on the server side, including shell unit simulation, cable unit simulation and beam unit simulation;

[0023] Step S2 involves using finite element software and finite difference software to establish a three-dimensional calculation model of stratum-tunnel-initial support on the server side. The following is a detailed analysis of this step:

[0024] Step S2: Based on the data obtained in step S1, a three-dimensional calculation model that accurately reflects the actual size of the stratum and the tunnel is constructed using finite element software, and a three-dimensional calculation model of the initial support that conforms to the actual engineering situation is constructed using finite difference software to facilitate subsequent numerical simulation analysis.

[0025] Choose appropriate finite element software and finite difference software according to project requirements, such as ABAQUS, FLAC3D, etc. These software usually have powerful modeling and computing capabilities and can handle complex engineering problems.

[0026] According to the geological structure and terrain characteristics, the terrain is linearly generalized to simplify the model and facilitate calculation. At the same time, the influence of terrain bias effect on tunnel and support structure is considered. According to the formation data, the formation model is constructed. This includes defining the physical and mechanical parameters of different rock formations, such as density, elastic modulus, Poisson's ratio, internal friction angle, cohesion, etc. According to the tunnel data, the geometric model of the tunnel is established. Including the cross-sectional shape, size, longitudinal slope, curvature, etc. of the tunnel.

[0027] Initial support modeling:

[0028] Shell unit simulation of shotcrete: As an important part of the initial support, shotcrete is simulated using shell units. This can accurately reflect the thickness, stiffness and strength of shotcrete.

[0029] Cable unit simulation anchor rod: Anchor rods are used to reinforce surrounding rock and initial support structure, and are simulated using cable units. The reinforcement effect of anchor rods is reflected by defining parameters such as the length, diameter, and material properties of the anchor rods.

[0030] Beam element simulation of steel arch: If the initial support includes a steel arch structure, the beam element is used for simulation. The beam element can accurately simulate the bending and shear deformation of the steel arch.

[0031] After the model is built, it is necessary to verify the model to ensure its accuracy and reliability. This includes comparison and verification with known geological conditions, engineering experience or experimental data. According to the verification results, the model is adjusted and optimized as necessary to improve the accuracy and applicability of the model.

[0032] The verified 3D computational model is stored on the server side to facilitate numerical simulation analysis in subsequent steps. If the model needs to be shared with other team members or partners, model sharing and collaboration can be carried out through the network or dedicated software platform.

[0033] The three-dimensional calculation model established in step S2 is the basis for subsequent numerical simulation analysis. The accuracy and reliability of the model directly affect the accuracy and credibility of the subsequent analysis results. Therefore, in the modeling process, it is necessary to fully consider the geological conditions, terrain characteristics, actual conditions of the tunnel and support structure, so that the model can truly reflect the actual engineering situation.

[0034] Through the above steps, a calculation model that accurately reflects the three-dimensional relationship of stratum-tunnel-initial support can be constructed, providing strong support for subsequent safety and economic analysis.

[0035] Step S3: Use finite difference software (such as FLAC3D) to perform numerical simulation on the three-dimensional calculation model, calculate the displacement and stress distribution of the surrounding rock and the tunnel support structure after the excavation is completed, evaluate the bias effect of the tunnel structure after the excavation is completed and the safety during the construction process, receive different preset shotcrete thickness schemes, anchor rod length schemes and anchor rod spacing schemes, use the preset shotcrete simulation model, perform numerical simulation on different schemes respectively, compare the displacement and stress changes of the surrounding rock and the support structure under different shotcrete thicknesses, and select the optimal thickness combination;

[0036] Step S3 involves numerical simulation of the three-dimensional computational model using finite difference software to evaluate the stability and safety of the tunnel after excavation is completed, and to determine the optimal combination of shotcrete thickness by comparing different support schemes. The following is a detailed analysis of this step:

[0037] Step S3: Through numerical simulation, the displacement and stress distribution after tunnel excavation under different support schemes are analyzed to evaluate the bias effect of the tunnel structure and the safety during the construction process, and then determine the optimal combination of shotcrete thickness, anchor length and anchor spacing.

[0038] Commonly used finite difference software such as FLAC3D can efficiently handle complex mechanical problems in geotechnical engineering and underground engineering.

[0039] The three-dimensional calculation model established in step S2 is imported into FLAC3D, and simulation parameters such as boundary conditions and loading methods are set as needed.

[0040] Excavation simulation: The excavation process of the tunnel is simulated by the NULL model or other appropriate methods, and the displacement and stress distribution of the surrounding rock and tunnel support structure after excavation are calculated.

[0041] Support scheme simulation: Receive different preset shotcrete thickness schemes, anchor length schemes, and anchor spacing schemes. For each scheme, set the corresponding model parameters (such as shotcrete thickness, anchor length and spacing) and perform numerical simulation calculations.

[0042] Result extraction and analysis: Extract the vertical displacement cloud map of the rock mass after excavation and the internal force distribution cloud map of the initial support to analyze the deformation and stress of the tunnel structure. Compare the displacement and stress changes of the surrounding rock and support structure under different shotcrete thicknesses, and evaluate the impact of different thickness combinations on tunnel stability and safety. Consider construction safety and economy comprehensively, and select the optimal shotcrete thickness combination.

[0043] In addition to the thickness of shotcrete, similar analysis and comparison are also required for anchor length and anchor spacing. The final optimized support scheme is determined by comprehensively considering the impact of different support parameters on tunnel stability and safety, as well as factors such as construction cost.

[0044] Step S3 uses numerical simulation analysis to predict possible problems encountered during tunnel excavation in advance and provide support for decision-making during construction. At the same time, by comparing the effects of different support schemes, a support scheme that meets construction safety requirements and is economically reasonable can be found.

[0045] By comparing the displacement and stress distribution cloud maps under different support schemes, the support effect can be intuitively evaluated. Prioritize the support scheme that can significantly reduce tunnel deformation and stress. Under the premise of meeting the construction safety requirements, consider factors such as the cost of support materials and construction difficulty, and select economically reasonable support parameters. Comprehensively consider multiple aspects such as construction safety, economy and support effect to determine the final optimized support scheme.

[0046] Through the precise numerical simulation and comprehensive analysis of the above steps, scientific basis and technical support can be provided for the initial support design of shallow-buried bias-loaded tunnels.

[0047] Step S4: extracting the vertical displacement cloud map of the rock and soil mass after excavation and the internal force distribution cloud map of the initial support, analyzing the characteristics of shotcrete thickness, anchor length and anchor spacing of different support schemes, and comparing the optimization effects of different schemes. The comparison of the optimization effects of different schemes includes comparing the displacement and stress distribution of the support structure, and determining the final optimization scheme. The final optimization scheme includes the optimal shotcrete thickness, anchor length and anchor spacing;

[0048] Step S4 involves detailed analysis and evaluation of the numerical simulation results to determine the final optimized support solution. The following is a detailed analysis of step S4:

[0049] Step S4: By analyzing the vertical displacement cloud map of the rock mass after excavation and the internal force distribution cloud map of the initial support, the characteristics of shotcrete thickness, anchor length and anchor spacing of different support schemes are extracted and compared, and then the optimal support scheme is determined. The vertical displacement cloud map of the rock mass after excavation and the internal force distribution cloud map of the initial support are extracted from the numerical simulation results. The displacement and stress data of key positions such as the arch crown and spandrel under different support schemes are derived.

[0050] Thickness characteristics of shotcrete: Analyze the influence of different thicknesses on the supporting effect of shotcrete, and record the thickness distribution of shotcrete and its supporting effect on the tunnel structure.

[0051] Anchor length characteristics: Evaluate the reinforcement effect and stress conditions of the anchor on the surrounding rock under different anchor lengths, and understand the role of the anchor in the tunnel support system.

[0052] Anchor spacing characteristics: explore the impact of changes in anchor spacing on the overall stability of the tunnel support system and analyze the reasonable spacing of anchor arrangements.

[0053] The comparison of the plans specifically includes the following:

[0054] Comparison of displacement and stress distribution: Compare the displacement differences between the deep buried side and the shallow buried side of the rock and soil mass under each support scheme to evaluate the control effect of the support scheme on tunnel deformation.

[0055] Comparison of internal forces of support structures: Analyze the stress states of shotcrete and anchor rods in the internal force distribution cloud diagram of the initial support structure, extract and record the maximum compressive stress of shotcrete and the maximum axial force of anchor rods, and compare the changes in stress values ​​under different support schemes.

[0056] Safety and economic evaluation: Comprehensively consider factors such as the safety, stability and construction cost of the support structure, and evaluate the optimization effects of different support schemes.

[0057] According to the above analysis results, the optimal combination of shotcrete thickness, anchor length and anchor spacing is determined, so that the final optimization scheme can meet the construction safety requirements and achieve economic rationality.

[0058] The analysis result of step S4 is directly related to the effectiveness and economy of the support scheme. Through scientific analysis and evaluation, reliable technical support can be provided for the construction process to ensure the safe and smooth progress of tunnel construction.

[0059] Make scientific and reasonable decisions based on detailed numerical simulation results and data analysis. While meeting construction safety requirements, pursue the economy of support solutions. Improve the overall effect of tunnel support by continuously optimizing support parameters and solutions.

[0060] Through the detailed analysis and comprehensive evaluation of the above steps, the final optimized support scheme can be made both safe and economical, providing a strong guarantee for the initial support of shallow-buried biased tunnels.

[0061] Step S5: Output the final optimization solution to a report, which includes specific values ​​of shotcrete thickness, anchor length and anchor spacing, as well as a tunnel support structure schematic diagram and related charts.

[0062] Furthermore, the optimization method for initial support of a shallow-buried biased tunnel provided by the present invention comprises, in step S2:

[0063] The 3D calculation model of stratum-tunnel-initial support combines the terrain bias effect to make a linear generalization of the terrain;

[0064] The shotcrete is simulated by shell elements, the anchor rods are simulated by cable elements, and the steel arches are simulated by beam elements.

[0065] Furthermore, in the optimization method for initial support of a shallow-buried biased tunnel provided by the present invention, the step S3 comprises:

[0066] The different shotcrete thickness design schemes include: deep burial 29cm and shallow burial 23cm, deep burial 32cm and shallow burial 20cm, and deep burial 35cm and shallow burial 17cm.

[0067] The specific design schemes for different anchor lengths include: deep buried 4.0m and shallow buried 3.0m, deep buried 4.5m and shallow buried 2.5m, and deep buried 5.0m and shallow buried 2.0m.

[0068] The specific design schemes for different anchor bolt spacings include: deep buried measurement of 0.9×0.6m and shallow buried measurement of 1.1×0.6m, deep buried measurement of 0.8×0.6m and shallow buried measurement of 1.2×0.6m, and deep buried measurement of 0.6×0.6m and shallow buried measurement of 1.4×0.6m.

[0069] Furthermore, the optimization method for initial support of a shallow-buried biased tunnel provided by the present invention comprises, in step S4:

[0070] Shotcrete thickness characteristics: used to record the thickness distribution of shotcrete and its supporting effect on the tunnel structure for each support scheme;

[0071] Anchor length characteristics: used to analyze the reinforcement effect and stress conditions of the anchor on the surrounding rock under different anchor lengths;

[0072] Anchor spacing characteristics: used to evaluate the impact of changes in anchor spacing on the overall stability of the tunnel support system.

[0073] Furthermore, the optimization method for initial support of a shallow-buried biased tunnel provided by the present invention comprises, in step S4:

[0074] The vertical displacement cloud diagram of the rock mass after excavation and the distribution cloud diagram of the initial support internal force are extracted from the numerical simulation results, and the displacement and stress data of the arch crown and spandrel under different support schemes are derived;

[0075] Compare the displacement differences between the deep buried side and the shallow buried side of the rock and soil mass under each support scheme;

[0076] Analyze the stress states of shotcrete and anchors in the internal force distribution cloud diagram of the initial support structure, extract and record the maximum compressive stress of shotcrete and the maximum axial force of anchors, compare the changes in stress values ​​under different support schemes, evaluate the optimization effect of stress distribution, and determine the optimal shotcrete thickness, anchor length, and anchor spacing.

[0077] Furthermore, the optimization method for initial support of a shallow-buried biased tunnel provided by the present invention, in the step S5, further comprises:

[0078] The calculation data, simulation results and optimization solutions are stored in the server-side database for query and audit, and an API interface or web interface is provided for users to access and download relevant data and results.

[0079] Beneficial effects of the invention: The present invention relates to an optimization method for initial support of shallow-buried biased tunnels: a three-dimensional calculation model is established using ABAQUS software in the finite element software, and the model is imported into the finite difference software FLAC3D to calculate the displacement and stress distribution of the surrounding rock and initial support after the excavation is completed. According to the numerical simulation results, an asymmetric optimization scheme based on shotcrete thickness, anchor length, and anchor spacing is designed, and different schemes are compared according to the stress and deformation conditions of the surrounding rock and support structure. This scheme can predict in advance the dangers that may occur during the excavation of shallow-buried biased large-section tunnels and propose corresponding countermeasures. Through the optimization of the support scheme, an ideal scheme that takes into account both construction safety and economy can be provided for the construction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0081] Figure 1 It is a schematic diagram of the three-dimensional computational model of the stratum-tunnel;

[0082] Figure 2 It is the model detail drawing of the initial support;

[0083] Figure 3 Vertical displacement cloud diagram of rock and soil

[0084] Figure 4 Initial support internal force distribution cloud map

[0085] Figure 5 Compressive stress distribution of shotcrete at different shotcrete thicknesses

[0086] Figure 6 Compressive stress distribution of shotcrete under different anchor lengths

[0087] Figure 7 Anchor axial force distribution under different anchor spacing DETAILED DESCRIPTION

[0088] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure. And the scope of the present disclosure can be fully conveyed to those skilled in the art.

[0089] Step 1: Create a 3D finite element model

[0090] The embodiment of the present invention provides an optimization method for initial support of a shallow-buried biased tunnel. The large-scale general finite difference software FLAC3D is used as a calculation tool, and the NULL model is applied to simulate the excavation process of the tunnel. The soil is simulated using the Mohr-Coulomb constitutive method. Considering the actual engineering and simulation conditions, the model is processed as follows:

[0091] According to the actual engineering situation, the terrain is linearly generalized, such as Figure 1 shown.

[0092] The shotcrete is simulated by shell elements, the anchor rods are simulated by cable elements, and the steel arches are simulated by beam elements. Figure 2 As shown;

[0093] Since the secondary lining is generally used as a safety reserve and is subjected to little or even no stress during tunnel structure analysis, it is not considered during simulation.

[0094] The optimization of initial support adopts an asymmetric design method, which can be divided into asymmetric optimization design of shotcrete thickness, anchor length, and anchor spacing.

[0095] Statistics on the changes in surrounding rock displacement and initial support internal force under different schemes

[0096] In order to analyze the bias pressure effect of shallow buried bias pressure large cross-section tunnel, the vertical displacement distribution cloud map of rock and soil mass and the initial support internal force distribution cloud map after excavation are extracted, such as Figure 3 , Figure 4 shown.

[0097] By changing the thickness of shotcrete on both sides of the tunnel, the designed concrete thickness is 29cm for deep burial and 23cm for shallow burial, 32cm for deep burial and 20cm for shallow burial, and 35cm for deep burial and 17cm for shallow burial. The distribution cloud map of the compressive stress of shotcrete after excavation is extracted, as shown in the figure below. Figure 5 shown.

[0098] By changing the anchor lengths on both sides of the tunnel, the designed anchor lengths are 4.0m deep and 3.0m shallow, 4.5m deep and 2.5m shallow, and 5.0m deep and 2.0m shallow. The compressive stress distribution cloud of shotcrete after excavation is extracted, as shown in the figure below. Figure 6 shown.

[0099] By changing the anchor spacing on both sides of the tunnel, the anchor spacing is designed to be 0.9×0.6m for deep burial and 1.1×0.6m for shallow burial, 0.8×0.6m for deep burial and 1.2×0.6m for shallow burial, and 0.6×0.6m for deep burial and 1.4×0.6m for shallow burial. The axial force distribution cloud map of the anchor after excavation is extracted, as shown in the figure below. Figure 7 shown.

[0100] Scheme comparison and selection;

[0101] The selection of support schemes should consider both the safety of construction and the economy of construction. Figure 3-Figure 7 The conclusions obtained are listed as follows to reflect the optimization ideas of the solution of the present invention:

[0102] from Figure 3 It can be seen that the tunnel asymmetry phenomenon is significant under the shallow buried bias pressure condition, which is specifically manifested in that the deformation value of the deep buried side is greater than that of the shallow buried side. The maximum vertical displacement value at the left spandrel is 106.7mm, while the maximum vertical displacement value at the right spandrel is 74.3mm. The final settlement value difference between the left and right spandrels is 32.4mm. It can be seen that the original symmetrical support scheme cannot effectively control the deformation difference between the left and right sides of the tunnel structure, and is prone to local large deformation, collapse and other problems. Figure 4 It can be seen that the compressive stress of shotcrete and the axial force distribution of anchor rods are obviously asymmetric due to the influence of shallow buried bias pressure. The maximum compressive stress of shotcrete on the shallow buried side of the tunnel is 6.89MPa, which is 28.4% of the ultimate compressive strength of shotcrete (24.3MPa). The maximum axial force of the anchor rod is 61.1kN, which is 30.9% of the ultimate tensile strength of the anchor rod (197.6kN). The compressive performance of concrete on the shallow buried side and the tensile performance of anchor rods are not fully utilized.

[0103] In summary, the original symmetrical support scheme not only failed to give full play to the performance of the shallow buried side support structure of the tunnel, but also failed to effectively control the difference in stress and deformation between the deep and shallow sides of the tunnel, which easily led to tunnel instability. Therefore, in order to ensure the economy and safety of construction, the initial support structure needs to be optimized, as shown in Table 1.

[0104] Table 1 Optimization design of initial support

[0105]

[0106] Table 2 shows the settlement of the tunnel vault under different shotcrete thicknesses. Figure 5 It can be seen that as the thickness of the shotcrete on the left side increased from 26cm to 35cm, the settlement of the arch on the deep buried side only decreased by 1.3%, while the maximum compressive stress of the concrete was greatly reduced by 16.7%. When the thickness of the shotcrete on the right side decreased from 26cm to 17cm, the settlement of the arch on the shallow buried side only increased slightly by 1.9%, while the maximum compressive stress of the concrete increased significantly by 44.3%. The above results show that changing the thickness of shotcrete has a weak control effect on the arch settlement, but it can effectively reduce the force difference on both sides of the support structure, improve the stability of the tunnel structure, and the performance of the shallow buried concrete is fully utilized, which greatly improves the economy of the construction. Figure 5 It can also be seen that when the concrete thickness on the deep buried side is greater than 32 cm, the maximum compressive stress decreases slightly, indicating that increasing the concrete thickness is no longer effective in reducing the stress on the support structure. At the same time, considering that a certain concrete thickness should be reserved on the shallow buried side of the biased tunnel as a safety reserve, when optimizing the shotcrete thickness, the concrete thickness on the left side of the tunnel can be set to 32 cm and the concrete thickness on the right side can be set to 20 cm.

[0107] Table 2 Tunnel vault settlement under different shotcrete thickness

[0108]

[0109] Table 3 shows the settlement of the tunnel vault under different anchor rod lengths. It can be seen that the settlement of the vault on the deep buried side is 6.4mm less in condition 4 than in the original condition, with a reduction of 6.0%; it is 3.1mm less in condition 5 than in condition 4, with a reduction of 3.1%; and it is only 0.6mm less in condition 6 than in condition 5, with a reduction of 0.6%. This shows that under the asymmetric support scheme, increasing the anchor rod length can effectively control the large deformation on the deep buried side, the settlement difference on both sides of the vault gradually decreases, and the eccentric deformation of the tunnel gradually improves. However, when the anchor rod length reaches 4.5m, the reduction in the vault settlement is small, so the tunnel deformation cannot be controlled indefinitely by increasing the anchor rod length. Figure 6It can be seen that compared with the original support scheme, the maximum compressive stress of the shotcrete on the deep buried side under the optimized scheme decreased by 0.59MPa, 0.45MPa and 0.33MPa respectively, while the maximum compressive stress of the concrete on the shallow buried side increased by 0.37MPa, 0.54MPa and 0.63MPa respectively. The force difference on both sides of the support structure gradually decreased, and the bias phenomenon gradually weakened. Therefore, considering the practicality and economy, the anchor length on the left side of the tunnel can be set to 4.5m, and the anchor length on the right side can be set to 3.0m.

[0110] Table 3 Tunnel crown settlement under different anchor lengths

[0111]

[0112] Step 304: Table 4 shows the settlement of the tunnel crown under different anchor spacings. It can be seen that as the anchor spacing on the left side is increased from the original 1.0m to 0.8m, the settlement of the crown on the deep buried side decreases by 5.4mm, a decrease of 5.1%, while when the anchor spacing is increased from 0.8m to 0.6m, the settlement only decreases by 0.8mm, a decrease of 0.8%. This shows that increasing the anchor spacing has a certain effect on controlling tunnel deformation, but when the anchor spacing is less than 0.8m, the trend of decreasing crown settlement is no longer obvious, because the rock and soil around the tunnel has basically been reinforced by anchor grouting. When the anchor spacing on the right side is greater than 1.2m, the rate of increase of the crown settlement on the shallow buried side is significantly accelerated, and the anchor cannot effectively control the stability of the tunnel on this side. Figure 7 It can be seen that with the change of anchor bolt spacing, the maximum axial force of the deep-buried side anchor bolts decreased by 10.7%, 7.0% and 3.2% respectively, while the maximum axial force of the shallow-buried side anchor bolts increased by 5.2%, 7.9% and 12.5% ​​respectively. The force difference between the left and right sides of the anchor bolts gradually decreased, and the bias pressure phenomenon of the support structure gradually weakened. At the same time, considering that too dense anchor bolt spacing will increase the difficulty of construction, lead to an extension of the construction period and cause waste of the support structure. After comprehensive consideration, it is recommended to select the left anchor bolt spacing of 0.8m×0.6m and the right anchor bolt spacing of 1.2m×0.6m as the final optimization solution.

[0113] Table 4 Tunnel vault settlement under different anchor spacing

[0114]

[0115] The present invention provides an optimization method for initial support of a shallow-buried biased tunnel, which solves the technical problems faced by initial support of a shallow-buried biased tunnel in the following ways:

[0116] Shallow buried bias pressure is a common adverse geological phenomenon in tunnel construction. Shallow buried bias pressure will cause asymmetric stress deformation of the tunnel and the support structure. If the support method is improper, it is easy to cause large deformation of the surrounding rock, local stress concentration and other problems, which will endanger the safety of construction. Existing solutions mainly rely on verifying the feasibility of the original design plan or dynamically adjusting the support plan according to monitoring data during the construction process, but these methods have lags and cannot predict and effectively respond to risks that may be encountered during construction in advance.

[0117] In order to solve the above problems, the present invention adopts the following technical solutions:

[0118] Establish a three-dimensional calculation model: Use finite element software (such as ABAQUS) and finite difference software (such as FLAC3D) to establish a three-dimensional calculation model of the stratum-tunnel-support structure, fully consider the terrain bias effect, and perform linear generalization on the terrain.

[0119] Asymmetric optimization design: In view of the characteristics of shallow buried bias pressure, the initial support is designed asymmetric in terms of shotcrete thickness, anchor length, anchor spacing, etc. Through numerical simulation, the displacement and stress distribution of surrounding rock and tunnel support structure under different support schemes are analyzed.

[0120] Numerical simulation and scheme comparison: Use finite difference software (such as FLAC3D) to perform numerical simulation on the three-dimensional calculation model, calculate the displacement and stress distribution of the surrounding rock and tunnel support structure after excavation, and evaluate the eccentric pressure effect of the tunnel structure and the safety during construction.

[0121] Design multiple groups of different shotcrete thickness, anchor length, anchor spacing schemes, and conduct numerical simulation comparisons. By comparing the support effects under different schemes, select the best scheme.

[0122] Determine the final optimization plan: According to the numerical simulation results and scheme comparison, the final optimization plan is determined by comprehensively considering the construction safety and economy. The optimization plan includes the optimal shotcrete thickness, anchor length and anchor spacing.

[0123] Output optimization plan report: The final optimization plan is output to the report, which includes the specific values ​​of shotcrete thickness, anchor length and anchor spacing, as well as the tunnel support structure diagram and related charts. At the same time, the calculation data, simulation results and optimization plan are stored in the server-side database for subsequent query and audit.

[0124] The present invention predicts the possible dangers during the excavation of a shallow biased tunnel in advance through numerical simulation, and proposes corresponding control measures, thus avoiding the lag of traditional methods.

[0125] Asymmetric design: In view of the characteristics of shallow buried bias pressure, an asymmetric support design is adopted to effectively control the difference in stress and deformation between the deep and shallow sides of the tunnel and improve the stability of the tunnel structure. By comparing multiple groups of schemes, the construction safety and economy are comprehensively considered to determine the optimal support scheme, ensuring the support effect while reducing the construction cost.

[0126] Through the above technical measures, the present invention effectively solves the technical problems faced by the initial support of shallow-buried biased tunnels, and provides a safer, more economical and reasonable support solution for tunnel construction.

[0127] The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solution and inventive concept of the present invention within the scope disclosed by the present invention, which shall fall within the protection scope of the present invention.

Claims

1. An optimization method for initial support of a shallow-buried bias-pressure tunnel, characterized in that: The optimization method for initial support of shallow-buried biased tunnel comprises the following steps: Step S1: The server obtains stratum data, tunnel data and initial support data from a database or an external data source, wherein the stratum data includes geological structure and mechanical parameters of rock and soil, the tunnel data includes tunnel dimensions, and the initial support data includes anchor position, anchor length and shotcrete thickness; Step S2: Use finite element software to establish a three-dimensional calculation model of the stratum-tunnel on the server side. The three-dimensional calculation model of the stratum-tunnel is used to calculate the terrain bias effect and perform linear generalization processing on the terrain. Use finite difference software to establish a three-dimensional calculation model of the initial support on the server side, including shell unit simulation, cable unit simulation and beam unit simulation; Step S3: Use finite difference software to perform numerical simulation on the three-dimensional calculation model, calculate the displacement and stress distribution of the surrounding rock and the tunnel support structure after the excavation is completed, evaluate the bias effect of the tunnel structure after the excavation is completed and the safety during the construction process, receive different preset shotcrete thickness schemes, anchor rod length schemes and anchor rod spacing schemes, use the preset shotcrete simulation model, perform numerical simulation on different schemes respectively, compare the displacement and stress changes of the surrounding rock and the support structure under different shotcrete thicknesses, and select the optimal thickness combination; Step S4: extracting the vertical displacement cloud map of the rock and soil mass after excavation and the internal force distribution cloud map of the initial support, analyzing the characteristics of shotcrete thickness, anchor length and anchor spacing of different support schemes, and comparing the optimization effects of different schemes. The comparison of the optimization effects of different schemes includes comparing the displacement and stress distribution of the support structure, and determining the final optimization scheme. The final optimization scheme includes the optimal shotcrete thickness, anchor length and anchor spacing; Step S5: Output the final optimization solution to a report, which includes specific values ​​of shotcrete thickness, anchor length, and anchor spacing, as well as a tunnel support structure schematic diagram and related charts.

2. The optimization method for initial support of a shallow-buried biased tunnel according to claim 1 is characterized by: The step S2 includes: The 3D calculation model of stratum-tunnel-initial support combines the terrain bias effect to make a linear generalization of the terrain; The shotcrete is simulated by shell elements, the anchor rods are simulated by cable elements, and the steel arches are simulated by beam elements.

3. The optimization method for initial support of a shallow-buried biased tunnel according to claim 1 is characterized by: The step S3 comprises: The different shotcrete thickness design schemes include: deep buried 29cm and shallow buried 23cm, deep buried 32cm and shallow buried 20cm, and deep buried 35cm and shallow buried 17cm. The specific design schemes for different anchor lengths include: deep buried 4.0m and shallow buried 3.0m, deep buried 4.5m and shallow buried 2.5m, and deep buried 5.0m and shallow buried 2.0m. The specific design schemes for different anchor bolt spacings include: deep buried measurement of 0.9×0.6m and shallow buried measurement of 1.1×0.6m, deep buried measurement of 0.8×0.6m and shallow buried measurement of 1.2×0.6m, and deep buried measurement of 0.6×0.6m and shallow buried measurement of 1.4×0.6m.

4. The optimization method for initial support of a shallow-buried bias-pressure tunnel according to claim 1 is characterized by: The step S4 includes: Shotcrete thickness characteristics: used to record the thickness distribution of shotcrete and its supporting effect on the tunnel structure for each support scheme; Anchor length characteristics: used to analyze the reinforcement effect and stress conditions of the anchor on the surrounding rock under different anchor lengths; Anchor spacing characteristics: used to evaluate the impact of changes in anchor spacing on the overall stability of the tunnel support system.

5. The optimization method for initial support of a shallow-buried biased tunnel according to claim 4 is characterized by: The step S4 includes: The vertical displacement cloud diagram of the rock mass after excavation and the distribution cloud diagram of the initial support internal force are extracted from the numerical simulation results, and the displacement and stress data of the arch crown and spandrel under different support schemes are derived; Compare the displacement differences between the deep buried side and the shallow buried side of the rock and soil mass under each support scheme; Analyze the stress states of shotcrete and anchors in the internal force distribution cloud diagram of the initial support structure, extract and record the maximum compressive stress of shotcrete and the maximum axial force of anchors, compare the changes in stress values ​​under different support schemes, evaluate the optimization effect of stress distribution, and determine the optimal shotcrete thickness, anchor length, and anchor spacing.

6. The optimization method for initial support of a shallow-buried bias-pressure tunnel according to claim 1, characterized in that: The step S5 further includes: The calculation data, simulation results and optimization solutions are stored in the server-side database for query and audit, and an API interface or web interface is provided for users to access and download relevant data and results.

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