Optimization method for calculating surrounding rock pressure of deep buried four-hole tunnel with small clearance

Abstract

The present invention relates to the technical field of surrounding rock pressure calculation, and in particular, to a method for optimizing the calculation of surrounding rock pressure of a deep-buried four-hole tunnel with a small net spacing. The method comprises the following steps: collecting geological parameters and support parameters; calculating the radius of the anchor reinforcement zone based on the geological parameters and support parameters; calculating the synthetic surrounding rock contact pressure value based on the radius of the anchor reinforcement zone using dynamic plastic superposition, introducing a porosity attenuation factor to quantify the influence of the pore structure on the rock mass stiffness in the process of calculating the synthetic surrounding rock contact pressure value, and introducing a gradation correction coefficient to optimize and dynamically adjust the sensitivity of the plastic zone expansion to the particle gradation; establishing a graded contact pressure correction model to correct the contact pressure error caused by the interference of multiple caverns to obtain the optimized surrounding rock contact pressure value. The design of the present invention comprehensively considers the mutual influence between multiple caverns, the synergistic effect of the support structure, and the dynamic changes during the construction process, and introduces the dynamic plastic superposition theory, dual-field coupling stress analysis, and a graded correction model.

Description

Technical Field

[0001] The present invention relates to the technical field of surrounding rock pressure calculation, in particular to a surrounding rock pressure calculation optimization method for a deep-buried four-hole tunnel with a small clearance distance. Background Art

[0002] Due to the close distances between the chambers in a four-hole, closely spaced tunnel, the construction of one chamber can significantly impact adjacent chambers during excavation. Traditional calculation models often analyze each chamber separately, ignoring the actual impact of this interaction on surrounding rock pressure and stability. In the case of multi-chamber excavation, stress concentration areas and overlapping plastic zones are prone to occur, which complicates the local stress state and increases the risk of surrounding rock instability. Traditional calculation methods struggle to accurately capture these complex stress variations. Existing calculation methods often fail to fully consider the synergistic effects between support measures (such as anchors and linings) and the surrounding rock, resulting in inappropriate support design, potentially wasting resources, or insufficient support strength. The physical and mechanical properties of surrounding rock vary significantly under the same geological conditions, making it challenging to adjust the surrounding rock pressure calculation model based on specific geological parameters to suit different engineering environments. Furthermore, the effects of factors such as porosity and particle size distribution on surrounding rock stiffness also need to be considered. Therefore, an optimized method for calculating surrounding rock pressure in deep, four-hole, closely spaced tunnels is presented. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for optimizing the calculation of surrounding rock pressure of a deep-buried four-hole tunnel with a small net spacing, so as to solve the problems of mutual influence of multiple caverns, stress concentration and redistribution, and complexity of geological conditions raised in the above-mentioned background technology.

[0004] To achieve the above object, the present invention provides a method for optimizing the calculation of surrounding rock pressure of a deep-buried four-hole tunnel with small clearance, comprising the following steps:

[0005] S1. Collect geological parameters and support parameters;

[0006] S2. Calculate the radius of the anchor reinforcement area based on geological parameters and support parameters;

[0007] S3. Based on the radius of the anchor reinforcement zone, dynamic plastic superposition is used to calculate the synthetic surrounding rock contact pressure value. In the process of calculating the synthetic surrounding rock contact pressure value, a porosity attenuation factor is introduced to quantify the influence of pore structure on rock mass stiffness, and a gradation correction coefficient is introduced to optimize and dynamically adjust the sensitivity of plastic zone expansion to particle gradation.

[0008] S4. Establish a graded contact pressure correction model to correct the contact pressure error caused by multi-cavity interference to obtain the optimized surrounding rock contact pressure value.

[0009] As a further improvement of the present technical solution, in S2, the radius of the anchor reinforcement area is calculated based on geological parameters and support parameters, including the following steps:

[0010] S2.1. Determine the computational domain based on geological parameters and support parameters, and divide the computational domain into non-uniformly encrypted grids;

[0011] S2.2. Calculate the radius of the anchor reinforcement area based on the three-dimensional anchor ring model.

[0012] As a further improvement of the present technical solution, in S2.2, the radius of the anchor reinforcement area is calculated based on the three-dimensional anchoring ring model, including the following steps:

[0013] S2.21. Obtain the anchor length used in the current cavern;

[0014] S2.22. Use the three-dimensional anchoring circle model including the anchor installation angle and surrounding rock strength parameters to calculate the anchor reinforcement area radius, and output the anchor reinforcement area radius.

[0015] As a further improvement of the present technical solution, in S3, the calculation of the synthetic surrounding rock contact pressure value by dynamic plastic superposition includes the following steps:

[0016] S3.1. Divide the construction phases according to the timing of support application and construct a spatiotemporal correlation matrix for the excavation sequence of each cavern;

[0017] S3.2. For each cavern, after excavation, calculate the radius of the plastic zone of the cavern using the YoHoek-Brown criterion based on the surrounding rock properties;

[0018] S3.3. When the plastic zones of two caverns overlap, the plastic superposition correction mechanism is triggered;

[0019] S3.4. Use the dual-field coupling algorithm to construct the dynamic superposition of the surrounding rock stress field, and introduce the time-space attenuation factor to adjust the stress contribution of each position in the surrounding rock stress field;

[0020] S3.5. Calculate the equivalent contact pressure at each node in the non-uniformly refined mesh;

[0021] S3.6. Based on the equivalent contact pressure and the introduction of the support synergy factor, the final surrounding rock contact pressure value is calculated using the contact pressure formula.

[0022] As a further improvement of the technical solution, in S3.2, the plastic zone radius of the cavern is calculated using the YoHoek-Brown criterion, including the following steps:

[0023] S3.21. Determine the initial in-situ stress at the location of the cavern;

[0024] S3.22. Determine whether the surrounding rock will enter a plastic state when a specific stress is applied;

[0025] S3.23. Analyze the changes in internal stress of the surrounding rock before and after excavation and identify the plastic zone;

[0026] S3.24. Combined with the failure envelope provided by the YoHoek-Brown criterion, the distance from the cavern wall to the maximum stress limit that the surrounding rock can withstand is estimated. A porosity attenuation factor is introduced into the elastic modulus term of the YoHoek-Brown criterion to quantify the effect of pore structure on rock stiffness, and a gradation correction coefficient is introduced to optimize and dynamically adjust the sensitivity of plastic zone expansion to particle gradation.

[0027] As a further improvement of this technical solution, in S3.4, a dual-field coupling algorithm is used to construct a dynamic superposition stress field of the surrounding rock, and a spatiotemporal attenuation factor is introduced to adjust the stress contribution of each position in the surrounding rock stress field, including the following steps:

[0028] S3.41. Based on the non-uniformly refined grid, the spatial position of each node in the grid is clarified;

[0029] S3.42. Based on the linear elastic theory, simulate the stress redistribution of the surrounding rock after excavation and unloading, and construct the plastic zone field according to whether each node enters the plastic state;

[0030] S3.43, coupling the elastic stress field with the plastic damage field, and combining the information of the elastic stress field and the plastic damage field to form a comprehensive stress field;

[0031] S3.44. Define the spatiotemporal attenuation factor based on the distance between the node and the nearest cavern center;

[0032] S3.45. Dynamically update the stress field to obtain a dynamic superimposed stress field that changes with time and space;

[0033] S3.46. Output the final stress value.

[0034] As a further improvement of the present technical solution, in S3.5, calculating the equivalent contact pressure on each node in the non-uniform encrypted grid includes the following steps:

[0035] S3.51. For each node in the non-uniformly refined grid, specify the node's spatial coordinates and the distance to the nearest cavern center;

[0036] S3.52. Extract the normal stress contribution of each cavity to the node based on the dynamic superposition stress field generated by the dual-field coupling algorithm;

[0037] S3.53. For each cavern's stress contribution to the node, apply the corresponding spatiotemporal attenuation factor for adjustment;

[0038] S3.54. Accumulate the adjusted stress contributions of all caverns to the node to obtain a preliminary equivalent rock contact pressure value. Combined with the stress value corrected by plastic superposition, further refine the equivalent rock contact pressure value at the node.

[0039] As a further improvement of this technical solution, in S3.6, the calculation of the final surrounding rock contact pressure value based on the equivalent contact pressure and the introduction of the support synergy factor includes the following steps:

[0040] S3.61. Obtain the equivalent surrounding rock contact pressure value;

[0041] S3.62. Combine the equivalent contact pressure at each node with the support synergy factor and use the contact pressure formula to calculate the final surrounding rock contact pressure value at that node;

[0042] S3.63. Based on the calculated preliminary and final surrounding rock contact pressure values, further adjust them by applying the lining stiffness correction factor;

[0043] S3.64. Output the final surrounding rock contact pressure value result.

[0044] As a further improvement of the present technical solution, in S4, a hierarchical contact pressure correction model is established to correct the contact pressure error caused by multi-chamber interference, including the following steps:

[0045] S4.1. Collect measured contact pressure data, surrounding rock displacement monitoring data, and support structure strain data after excavation of each cavern;

[0046] S4.2. Identify typical interference patterns based on the spatial position relationship of the cavern;

[0047] S4.3. Based on the clear distance between the caverns and the radius of their respective plastic zones, define weight coefficients reflecting the strength of the interaction between the caverns, and organize all the interaction weight coefficients between any two caverns into a matrix form;

[0048] S4.4. For each node in the grid, calculate the composite interference stress caused by each cavity based on its location and the distribution of surrounding cavities;

[0049] S4.5. Construct a graded contact pressure correction model to eliminate the elastic error, plastic damage deviation and geometric distortion caused by multi-cavity interference, and obtain the optimized surrounding rock contact pressure value.

[0050] As a further improvement of the present technical solution, in S4.5, constructing a graded contact pressure correction model includes the following steps:

[0051] S4.51. Use a nonlinear decay function to correct the error caused by the overestimation of contact pressure by traditional elastic theory.

[0052] S4.52. Introduce damage variables to quantify the strength loss of surrounding rock due to plastic deformation, and adjust the surrounding rock contact pressure value accordingly;

[0053] S4.53. Based on the geometric characteristics of the four-chamber spatial layout, a curvature correction coefficient is introduced to compensate for the stress distortion caused by the shape and arrangement of the chambers.

[0054] S4.54, output the final corrected surrounding rock contact pressure value.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] 1. This method for optimizing the calculation of surrounding rock pressure in deep-buried four-hole tunnels with small clearances comprehensively considers the mutual influence between multiple chambers, the synergistic effect of support structures, and dynamic changes during construction. By introducing dynamic plastic superposition theory, dual-field coupled stress analysis, and a graded correction model, it effectively corrects the problem of traditional methods easily overestimating or underestimating surrounding rock pressure in complex multi-hole systems, thereby improving the accuracy of surrounding rock pressure calculations and providing a more scientific basis for tunnel support design.

[0057] 2. This method for optimizing the calculation of surrounding rock pressure in a deep, four-hole, closely spaced tunnel utilizes multi-dimensional parametric modeling techniques, including non-uniform mesh densification, spatiotemporal attenuation factors, lining stiffness corrections, and damage variables. This method flexibly addresses the influence of varying geological conditions, support parameters, and excavation sequences. In particular, under a multi-hole layout with close spacing, it accurately captures phenomena such as overlapping plastic zones, stress redistribution, and rock mass weakening. This improves the computational model's adaptability to actual engineering scenarios, facilitating safe and economical tunnel construction and operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 The figure is a flow chart of the overall method of the present invention. DETAILED DESCRIPTION

[0059] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0060] Example: See Figure 1As shown, this embodiment provides a method for optimizing the calculation of surrounding rock pressure of a deep-buried four-hole tunnel with small clearance, including the following steps:

[0061] S1. Collect geological parameters and support parameters. Geological parameters include surrounding rock density. , internal friction angle , cohesion , burial depth , Excavation width of four chambers , Net distance between adjacent caverns , support parameters include anchor length , lining stiffness and support construction timing ;

[0062] S2. Calculate the radius of the anchor reinforcement area based on geological parameters and support parameters;

[0063] In this embodiment, the radius of the anchor reinforcement area is calculated based on geological parameters and support parameters, including the following steps:

[0064] S2.1. Determine the computational domain based on geological and support parameters, and create a non-uniform mesh within the computational domain to precisely define the boundary conditions of the study area. Consider the impact of different geological conditions and support measures on the stability of the surrounding rock mass, and use non-uniform meshing technology to improve computational accuracy, especially in areas with stress concentration or high structural complexity.

[0065] When determining the computational domain range, the boundary in the X direction is set as , the Y direction is set to , the Z direction extends from the surface to , close to the cave surface The near field area within the range uses a fixed density grid with a grid size not exceeding , while in the area far away from the cave, the grid size is increased according to the exponential function. The specific formula is: , Indicates the distance from the point to the nearest cavern, represents the exponential growth rate per meter;

[0066] S2.2. To quantify the impact of the support structure on the surrounding rock stability, the radius of the anchor reinforcement area is calculated based on the three-dimensional anchor circle model;

[0067] Calculating the radius of the anchor reinforcement area based on the three-dimensional anchor ring model includes the following steps:

[0068] S2.21. Obtain the anchor length used in the current cavern;

[0069] S2.22. Use the three-dimensional anchoring circle model including the anchor installation angle and surrounding rock strength parameters to calculate the anchor reinforcement zone radius, and output the anchor reinforcement zone radius. The anchor forms a reinforcement influence zone around it through its length and the friction characteristics of the rock mass in which it is located. The reinforcement zone radius reflects the spatial range in which the anchor can effectively enhance the stability of the surrounding rock. The anchor reinforcement zone is expanded from a two-dimensional plane to a three-dimensional ellipsoid. Its spatial influence range is calculated by equivalently calculating the anchor reinforcement zone radius. express;

[0070] Among them, the three-dimensional anchor circle model is used to calculate the radius of the anchor reinforcement area for: , is the anchor installation angle, is the surrounding rock strength parameter.

[0071] S3. Dynamic plastic superposition is used to calculate the synthetic surrounding rock contact pressure value based on the radius of the anchor reinforcement zone. The porosity attenuation factor is introduced in the calculation process to quantify the influence of pore structure on rock mass stiffness, and the gradation correction coefficient is introduced to optimize the dynamic adjustment of the sensitivity of the plastic zone expansion to the particle gradation. Due to the special geometric layout of the deep-buried four-hole tunnel with a small clearance distance (due to the close distance between the four caverns), the construction of one cavern during excavation will have a significant impact on the adjacent caverns. Therefore, the results obtained from the individual analysis of each cavern are integrated using the principle of dynamic plastic superposition.

[0072] In this embodiment, the dynamic plastic superposition is used to calculate the synthetic surrounding rock contact pressure value, including the following steps:

[0073] S3.1. According to the timing of support construction Divide the construction phases and construct a spatiotemporal correlation matrix of the excavation sequence of each cavern. The matrix records the status of each cavern at different construction stages (including whether it is being excavated and whether support has been applied). Each row of the matrix represents a cavern, and each column represents a construction phase. Matrix elements include information such as excavation time and support application time. This matrix is ​​used in subsequent analysis to determine the interactions between caverns and their changes over time.

[0074] S3.2. For each cavern, after excavation, calculate the radius of the plastic zone of the cavern using the YoHoek-Brown criterion based on the surrounding rock properties;

[0075] The calculation of the plastic zone radius of the cavern using the YoHoek-Brown criterion includes the following steps:

[0076] S3.21. Determine the initial geostress at the location of the cavern, involving vertical stress (primarily caused by the weight of the overlying strata) and horizontal stress (possibly affected by tectonic activity).

[0077] S3.22. Determine whether the surrounding rock will enter a plastic state when a specific stress is applied. Based on the surrounding rock characteristic parameters (rock quality index, geological strength index, and material constants), use the Hoek-Brown criterion to estimate the surrounding rock failure threshold under different stress conditions.

[0078] S3.23. Analyze the changes in internal stress of the surrounding rock before and after excavation and identify the plastic zone;

[0079] S3.24. Combined with the failure envelope provided by the YoHoek-Brown criterion, the distance from the cavern wall to the maximum stress limit that the surrounding rock can withstand is estimated. This distance is the radius of the plastic zone. The porosity attenuation factor is introduced into the elastic modulus term of the YoHoek-Brown criterion to quantify the effect of pore structure on rock stiffness, and the gradation correction coefficient is introduced to optimize the dynamic adjustment of the sensitivity of the plastic zone expansion to the particle gradation (the porosity attenuation factor is used to quantify the effect of pore structure on rock stiffness. The presence of pores will reduce the effective stress transfer capacity of the rock, thereby affecting its overall strength and stability. By introducing the porosity attenuation factor, the elastic modulus of the surrounding rock can be adjusted more accurately. modulus, thereby more realistically simulating the mechanical behavior of rock materials under different porosity conditions; the gradation correction coefficient is used to optimize and dynamically adjust the sensitivity of the plastic zone expansion to the particle gradation. Different particle size distributions will affect the stability and failure mode of the rock's internal structure. Introducing the gradation correction coefficient can better consider the impact of the rock's internal particle distribution characteristics on the expansion of the plastic zone. Especially under complex geological conditions, rock is not a homogeneous medium, and its internal particle size, shape, and arrangement will significantly affect the rock's failure mechanism. By adjusting this coefficient, the YoHoek-Brown criterion can be better applied to various rock types and geological conditions, providing more accurate prediction results of the plastic zone radius);

[0080] The YoHoek-Brown criterion is an optimization of the Hoek-Brown criterion. The YoHoek-Brown criterion retains the core framework of the Hoek-Brown criterion (such as the form of the failure envelope). The YoHoek-Brown criterion formula is:

[0081] ;

[0082] After introducing the porosity attenuation factor and gradation correction coefficient into the YoHoek-Brown criterion, it is:

[0083] ;

[0084] Where, represents the porosity attenuation factor, represents the porosity, represents the gradation correction coefficient, represents the fractal dimension of particle distribution (calculated based on particle screening data), Indicates the support delay time, It is expressed (the empirical value range is 0.01 to 0.1), which is used to reflect the incremental effect of support delay on the softening of surrounding rock and the development of plastic zone.

[0085] S3.3. When the plastic zones of two chambers overlap, the plastic superposition correction mechanism is triggered. The plastic superposition correction mechanism is as follows: if the distance between the two chambers is less than the sum of the radii of their respective plastic zones, the plastic zones of the two chambers are considered to overlap. For the overlapping area, the stress state of the area is reassessed, and the impact of the plastic zone superposition is taken into account, and the local material properties or stress distribution are adjusted;

[0086] S3.4. A dual-field coupling algorithm is used to construct a dynamic superposition of the surrounding rock stress field. (The dual-field coupling algorithm dynamically superimposes the elastic field (based on linear elasticity theory) and the plastic field (based on the improved Hoek-Brown criterion and damage variables), combined with a spatiotemporal attenuation factor and construction phase iteration to accurately describe the stress redistribution, plastic failure, and multi-cavity interference effects of the surrounding rock.) A spatiotemporal attenuation factor is introduced to adjust the stress contribution of each location in the surrounding rock stress field, reflecting the influence of distance on the propagation of surrounding rock stress. During tunnel construction, stress changes caused by excavation activities gradually weaken with distance from the cavern center or the passage of time. The spatiotemporal attenuation factor quantifies this effect, making the stress analysis more realistic.

[0087] Among them, the plastic superposition correction mechanism has a direct impact on the updating of the elastic field and the plastic field. When the plastic zones of the two caverns overlap (triggered by step S3.3), the plastic superposition correction mechanism dynamically adjusts the stress distribution in the elastic field and the damage variables in the plastic field by re-evaluating the stress state of the overlapping area. Specifically, in the elastic field, the initial elastic stress solution of the superimposed area will be reduced according to the expansion amplitude of the plastic zone to reflect the weakening of rock strength; in the plastic field, the damage variable will be updated according to the equivalent plastic strain increment after the superposition of the plastic zone, thereby quantifying the cumulative damage effect. This process realizes the two-way interaction between elastic response and plastic failure by coupling the dynamic correction of the elastic modulus and the nonlinear evolution of the damage variable;

[0088] The dual-field coupling algorithm is used to construct the dynamic superposition of the surrounding rock stress field, and the spatiotemporal attenuation factor is introduced to adjust the stress contribution of each position in the surrounding rock stress field. The following steps are included:

[0089] S3.41. Based on the non-uniformly refined grid, the spatial position of each node in the grid is clarified;

[0090] S3.42. Based on linear elasticity theory, simulate the stress redistribution of the surrounding rock after excavation and unloading. Based on whether each node enters the plastic state, construct a plastic zone field reflecting the weakening of the surrounding rock strength and irreversible deformation, which is used to record plastic strain and damage degree.

[0091] S3.43. Coupling the elastic stress field and the plastic damage field, combining the information of the elastic stress field and the plastic damage field to form a comprehensive stress field that can simultaneously reflect the elastic response and plastic failure effects;

[0092] S3.44. Define a spatiotemporal attenuation factor based on the distance of a node from the nearest cavern center. The farther the distance or the longer the time, the smaller the stress disturbance of the surrounding rock on the node, and thus its stress contribution is weakened accordingly.

[0093] Among them, the spatiotemporal attenuation factor is: , represents the rheological coefficient of the surrounding rock, Indicates the distance from the measuring point to the nearest cavern;

[0094] S3.45. Dynamically update the stress field to obtain a dynamic superimposed stress field that changes with time and space. As the construction phase progresses, each time a new cavern is excavated or support measures are implemented, the stress state of all nodes in the current phase is recalculated, the elastic and plastic fields are updated, and the dual-field coupling is re-performed. The spatiotemporal attenuation factor is synchronously updated to ensure that the stress contribution of each node always matches the current construction state.

[0095] S3.46. Output the final stress value.

[0096] S3.5. Calculate the equivalent contact pressure at each node in the non-uniform refined grid , taking into account the multi-cavity excavation and plastic superposition effects, specifically: ,in, Indicates the The contribution of each chamber to the normal stress of the node is: Indicates the The spatiotemporal attenuation factor of each chamber, represents the plastic superposition coefficient, represents the damage tensile stress;

[0097] The calculation of the equivalent contact pressure at each node in the non-uniform refined grid includes the following steps:

[0098] S3.51. For each node in the non-uniformly refined grid, specify the node's spatial coordinates and the distance to the nearest cavern center;

[0099] S3.52. Extract the normal stress contribution of each cavern to the node (i.e., the stress perpendicular to the cavern wall) based on the dynamic superposition stress field generated by the dual-field coupling algorithm.

[0100] S3.53. For each cavern's stress contribution to the node, the corresponding spatiotemporal attenuation factor is applied to adjust the stress. The farther the distance or the longer the time, the smaller the stress contribution.

[0101] S3.54. Accumulate the adjusted stress contributions of all caverns to the node to obtain a preliminary equivalent rock contact pressure value. Combined with the stress value corrected by plastic superposition, further refine the equivalent rock contact pressure value at the node. The specific steps of refinement are: identify which nodes are located in the overlapping area of ​​the plastic zones of two or more caverns, and introduce plastic superposition coefficients for these nodes to adjust their stress states to reflect the weakening of rock strength and stress redistribution caused by the superposition of plastic zones; then, combine the normal stress contributions of each cavern to the node after adjustment by the time-space attenuation factor with the stress value corrected by plastic superposition, comprehensively consider the influence of factors such as cohesion and internal friction angle, and accumulate all relevant stress contributions to obtain a more accurate equivalent contact pressure at the node.

[0102] S3.6, based on equivalent contact pressure and introducing support synergy factor (The support synergy factor quantifies and reflects the synergistic effect of anchors and linings) The final surrounding rock contact pressure value is calculated using the contact pressure formula. The main function of introducing the support synergy factor when calculating the equivalent contact pressure is to quantify and reflect the interaction between the support structure (such as anchors and linings) and the surrounding rock, so as to more accurately evaluate the actual bearing pressure of the surrounding rock. The support synergy factor can reflect the enhancement effect of the support measures on the stability of the surrounding rock. By combining parameters such as the radius of the anchor reinforcement area and the stiffness of the lining, this factor reflects how the support structure effectively shares and reduces the pressure on the surrounding rock, thereby improving the safety of the overall structure; the support synergy factor helps to more accurately simulate the redistribution of internal stress in the surrounding rock during excavation. Especially in multi-chamber tunnel projects, due to the mutual influence between the chambers, it is crucial to reasonably consider the role of the support structure in predicting the stress state of the surrounding rock;

[0103] Furthermore, the support synergistic factor for: , is the elastic modulus of surrounding rock, is the net distance between adjacent caverns, is the characteristic length, which is used for normalization to ensure that the entire exponential term is dimensionless;

[0104] Among them, based on the equivalent contact pressure and the introduction of support synergy factor Calculating the final surrounding rock contact pressure value includes the following steps:

[0105] S3.61. Obtain the equivalent surrounding rock contact pressure value;

[0106] S3.62. Combine the equivalent contact pressure at each node with the support synergy factor and use the contact pressure formula to calculate the final surrounding rock contact pressure value at that node;

[0107] S3.63. Based on the calculated preliminary and final surrounding rock contact pressure values, further adjustments are made using the lining stiffness correction factor. This adjustment ensures that the final surrounding rock contact pressure values ​​fully account for the support provided by the lining, thereby reducing the actual bearing pressure of the surrounding rock.

[0108] Among them, the contact pressure formula is used to calculate the surrounding rock contact pressure value Specifically: , It represents the lining stiffness correction coefficient. The higher the stiffness of the lining structure is relative to the surrounding rock stiffness, the stronger its ability to restrain the deformation of the surrounding rock is. Therefore, the lining stiffness correction coefficient is defined to reflect this relative effect. , represents the lining stiffness, is the elastic modulus of surrounding rock;

[0109] S3.64. Output the final surrounding rock contact pressure value result.

[0110] S4. Establishing a graded contact pressure correction model to correct the contact pressure error caused by multi-cavity interference to obtain the optimized surrounding rock contact pressure value;

[0111] In this embodiment, a hierarchical contact pressure correction model is established to correct the contact pressure error caused by multi-chamber interference, including the following steps:

[0112] S4.1. Collect measured contact pressure data (pressure sensor readings), surrounding rock displacement monitoring data (multi-point displacement meter, fiber optic monitoring), and support structure strain data (rebar gauge, concrete strain gauge) after excavation of each cavern;

[0113] S4.2. Based on the spatial relationship between the caverns, identify typical interference patterns, including: lateral compression (adjacent cavern sidewalls compress each other), roof unloading (excavation of the upper cavern causes stress release in the lower cavern roof), and central column eccentricity (abnormal stress concentration in the central rock column area).

[0114] S4.3. Based on the clear distance between the chambers and the radius of their respective plastic zones, define a weight coefficient reflecting the strength of the interaction between the chambers (the weight coefficient is: ,in, Indicates a cave and The net distance, Indicates a cave The plastic zone radius, is the attenuation coefficient; this coefficient decreases with increasing distance, indicating that the mutual influence between distant caverns is small). The interaction weight coefficients between all two caverns are organized into a matrix form (this matrix helps quantify the superposition effect of stresses from different directions on each node);

[0115] S4.4. For each node in the grid, calculate the composite interference stress caused by each cavern based on its location and the distribution of surrounding caverns. This process comprehensively considers the primary and secondary stress field components and includes the influence of spatiotemporal attenuation effects.

[0116] Among them, the synthetic interference stress for:

[0117] ;

[0118] Where, represents the principal stress field components, represents the secondary stress field component (including time and space attenuation effect);

[0119] S4.5. Construct a graded contact pressure correction model to eliminate elastic errors, plastic damage deviations, and geometric distortions caused by multi-cavity interference, resulting in an optimized surrounding rock contact pressure value. This optimized surrounding rock contact pressure value reflects the actual pressure borne by the tunnel surrounding rock under specific support measures after a series of corrections and adjustments. This value comprehensively considers the mutual interference between multiple caverns, the overlapping effect of plastic zones, the synergistic effect of support structures (such as anchors and linings), and the impact of complex geological conditions on surrounding rock stability.

[0120] Furthermore, a graded contact pressure correction model is constructed, including the following steps:

[0121] S4.51. Use a nonlinear attenuation function to correct errors caused by overestimation of contact pressure in traditional elastic theory. (The purpose of using a nonlinear attenuation function to correct errors caused by overestimation of contact pressure in traditional elastic theory is to improve the accuracy of surrounding rock contact pressure calculations and reflect the phenomenon of reduced surrounding rock pressure caused by factors such as stress redistribution and plastic deformation in actual engineering projects. By introducing a nonlinear attenuation function, the calculation model can be adjusted according to the actual deformation and failure characteristics of the surrounding rock, effectively eliminating the overestimation of contact pressure caused by traditional elastic theory when dealing with complex geological conditions.)

[0122] Among them, the nonlinear attenuation function correction process is:

[0123] ;

[0124] Where, It represents the surrounding rock contact pressure value after preliminary correction, represents the contact pressure calculated by elastic theory, represents the maximum curvature, Represents the empirical coefficient, which is used to adjust the weakening effect of curvature on the contact pressure of surrounding rock. Indicates the reference curvature (unit: 1 / m), which is used to normalize the maximum curvature;

[0125] S4.52. Introduce a damage variable to quantify the strength loss of the surrounding rock due to plastic deformation, and adjust the surrounding rock contact pressure value accordingly. This step ensures a more realistic description of the stress state in the plastic zone of the surrounding rock. (Introducing a damage variable to quantify the strength loss of the surrounding rock due to plastic deformation is intended to more realistically reflect the mechanical degradation process of the surrounding rock after excavation disturbance. As the surrounding rock enters the plastic state and undergoes continuous deformation, its internal structure is damaged and its bearing capacity gradually decreases. Traditional elastic or ideal plastic models cannot accurately describe this process. By introducing a damage variable, the cumulative damage effect of the surrounding rock can be incorporated into the contact pressure calculation, thereby dynamically correcting the actual stress state of the surrounding rock, improving the reliability of the calculation results and engineering applicability.)

[0126] After introducing the damage variable, the nonlinear attenuation function is:

[0127] ;

[0128] Where, represents the surrounding rock contact pressure value after further correction, represents the dimensionless adjustment coefficient, which is obtained based on the fitting of damage variables and surrounding rock cohesion;

[0129] S4.53. Based on the geometric characteristics of the four-chamber spatial layout, a curvature correction factor is introduced to compensate for stress distortion caused by the chamber shape and arrangement. This correction helps to more accurately predict the surrounding rock pressure distribution under complex geological conditions. (The curvature correction factor is defined to compensate for the stress distortion caused by the unique geometric characteristics of the four-chamber spatial layout. Its function is to accurately adjust the errors in the surrounding rock contact pressure calculation caused by the chamber shape and arrangement. In complex multi-chamber tunnel projects, the relative position, spacing, and shape of the chambers can cause local stress concentration or dispersion, resulting in differences between the actual stress distribution and the ideal model prediction. By introducing the curvature correction factor, the influence of these geometric factors on the surrounding rock stress state can be effectively reflected, thereby optimizing the contact pressure assessment.)

[0130] Curvature correction coefficient for:

[0131] ;

[0132] Where, Indicates the minimum clearance distance, Indicates the maximum excavation width; Anchor rod installation angle;

[0133] S4.54, output the final corrected surrounding rock contact pressure value;

[0134] Final corrected surrounding rock contact pressure value for:

[0135] .

[0136] The basic principles, main features, and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited to the above-described embodiments. The above-described embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention claimed.

Claims

1. A method for optimizing the calculation of surrounding rock pressure for a deep-buried four-hole tunnel with small clearance, characterized by: The following steps are involved: S1. Collect geological parameters and support parameters; S2. Calculate the radius of the anchor reinforcement area based on geological parameters and support parameters; S3. Based on the radius of the anchor reinforcement zone, dynamic plastic superposition is used to calculate the synthetic surrounding rock contact pressure value. In the process of calculating the synthetic surrounding rock contact pressure value, a porosity attenuation factor is introduced to quantify the influence of pore structure on rock mass stiffness, and a gradation correction coefficient is introduced to optimize and dynamically adjust the sensitivity of plastic zone expansion to particle gradation. The dynamic plastic superposition is used to calculate the synthetic surrounding rock contact pressure value, which includes the following steps: S3.

1. Divide the construction phases according to the timing of support application and construct a spatiotemporal correlation matrix for the excavation sequence of each cavern; S3.

2. For each cavern, after excavation, calculate the radius of the plastic zone of the cavern using the YoHoek-Brown criterion based on the surrounding rock properties; The YoHoek-Brown criterion is an optimization of the Hoek-Brown criterion. The YoHoek-Brown criterion retains the failure envelope form of the Hoek-Brown criterion. Furthermore, the plastic zone radius of the cavern is calculated using the YoHoek-Brown criterion, which includes the following steps: S3.

21. Determine the initial in-situ stress at the location of the cavern; S3.

22. Determine whether the surrounding rock will enter a plastic state when a specific stress is applied; S3.

23. Analyze the changes in internal stress of the surrounding rock before and after excavation and identify the plastic zone; S3.

24. Based on the failure envelope provided by the YoHoek-Brown criterion, the distance from the cavern wall to the maximum stress limit that the surrounding rock can withstand is estimated. A porosity attenuation factor is introduced into the elastic modulus term of the YoHoek-Brown criterion to quantify the effect of pore structure on rock mass stiffness. A gradation correction factor is also introduced to optimize and dynamically adjust the sensitivity of plastic zone expansion to particle gradation. S3.

3. When the plastic zones of two caverns overlap, the plastic superposition correction mechanism is triggered; S3.

4. Use a dual-field coupling algorithm to construct a dynamic superposition of the surrounding rock stress field, and introduce a spatiotemporal attenuation factor to adjust the stress contribution of each position in the surrounding rock stress field. The dual fields refer to the elastic stress field and the plastic damage field. S3.

5. Calculate the equivalent contact pressure at each node in the non-uniformly refined mesh; S3.

6. Based on the equivalent contact pressure and the introduction of the support synergy factor, the final surrounding rock contact pressure value is calculated using the contact pressure formula; S4. Establish a graded contact pressure correction model to correct the contact pressure error caused by multi-cavity interference to obtain the optimized surrounding rock contact pressure value.

2. The method for calculating and optimizing surrounding rock pressure of a deep-buried four-hole tunnel with small clearance distance according to claim 1 is characterized in that: In S2, the radius of the anchor reinforcement area is calculated based on the geological parameters and the support parameters, including the following steps: S2.

1. Determine the computational domain based on geological parameters and support parameters, and divide the computational domain into non-uniformly encrypted grids; S2.

2. Calculate the radius of the anchor reinforcement area based on the three-dimensional anchor ring model.

3. The method for calculating and optimizing surrounding rock pressure of a deep-buried four-hole tunnel with small clearance distance according to claim 2 is characterized in that: In S2.2, the calculation of the radius of the anchor reinforcement area based on the three-dimensional anchoring circle model includes the following steps: S2.

21. Obtain the anchor length used in the current cavern; S2.

22. Use the three-dimensional anchoring circle model including the anchor installation angle and surrounding rock strength parameters to calculate the anchor reinforcement area radius, and output the anchor reinforcement area radius.

4. The method for calculating and optimizing surrounding rock pressure of a deep-buried four-hole tunnel with small clearance distance according to claim 1 is characterized in that: In S3.4, a dual-field coupling algorithm is used to construct a dynamic superposition of the surrounding rock stress field, and a spatiotemporal attenuation factor is introduced to adjust the stress contribution of each position in the surrounding rock stress field, including the following steps: S3.

41. Based on the non-uniformly refined grid, the spatial position of each node in the grid is clarified; S3.

42. Based on the linear elastic theory, simulate the stress redistribution of the surrounding rock after excavation unloading, and construct the plastic zone field according to whether each node enters the plastic state; S3.43, coupling the elastic stress field with the plastic damage field, and combining the information of the elastic stress field and the plastic damage field to form a comprehensive stress field; S3.

44. Define the spatiotemporal attenuation factor based on the distance between the node and the nearest cavern center; S3.

45. Dynamically update the stress field to obtain a dynamic superimposed stress field that changes with time and space; S3.

46. Output the final stress value.

5. The method for calculating and optimizing surrounding rock pressure of a deep-buried four-hole tunnel with small clearance distance according to claim 1 is characterized in that: In S3.5, the equivalent contact pressure on each node in the non-uniform refined grid is calculated, including the following steps: S3.

51. For each node in the non-uniformly refined grid, specify the node's spatial coordinates and the distance to the nearest cavern center; S3.

52. Extract the normal stress contribution of each cavity to the node based on the dynamic superposition stress field generated by the dual-field coupling algorithm; S3.

53. For each cavern's stress contribution to the node, apply the corresponding spatiotemporal attenuation factor for adjustment; S3.

54. Accumulate the adjusted stress contributions of all caverns to the node to obtain a preliminary equivalent rock contact pressure value. Combined with the stress value corrected by plastic superposition, further refine the equivalent rock contact pressure value at the node.

6. The method for calculating and optimizing surrounding rock pressure of a deep-buried four-hole tunnel with small clearance distance according to claim 1 is characterized in that: In S3.6, the calculation of the final surrounding rock contact pressure value based on the equivalent contact pressure and the introduction of the support synergy factor includes the following steps: S3.

61. Obtain the equivalent surrounding rock contact pressure value; S3.

62. Combine the equivalent contact pressure at each node with the support synergy factor and use the contact pressure formula to calculate the final surrounding rock contact pressure value at that node. S3.

63. Based on the calculated preliminary and final surrounding rock contact pressure values, further adjust them by applying the lining stiffness correction factor; S3.

64. Output the final surrounding rock contact pressure value result.

7. The method for calculating and optimizing surrounding rock pressure of a deep-buried four-hole tunnel with small clearance distance according to claim 1 is characterized in that: In S4, a hierarchical contact pressure correction model is established to correct the contact pressure error caused by multi-chamber interference, including the following steps: S4.

1. Collect measured contact pressure data, surrounding rock displacement monitoring data, and support structure strain data after excavation of each cavern; S4.

2. Identify typical interference patterns based on the spatial position relationship of the cavern; S4.

3. Based on the clear distance between the caverns and the radius of their respective plastic zones, define weight coefficients reflecting the strength of the interaction between the caverns, and organize all the interaction weight coefficients between any two caverns into a matrix form; S4.

4. For each node in the grid, calculate the composite interference stress caused by each cavity based on its location and the distribution of surrounding cavities; S4.

5. Construct a graded contact pressure correction model to eliminate the elastic error, plastic damage deviation and geometric distortion caused by multi-cavity interference, and obtain the optimized surrounding rock contact pressure value.

8. The method for calculating and optimizing surrounding rock pressure of a deep-buried four-hole tunnel with small clearance distance according to claim 7 is characterized in that: In said S4.5, constructing a graded contact pressure correction model comprises the following steps: S4.

51. Use a nonlinear decay function to correct the error caused by the overestimation of contact pressure by traditional elastic theory. S4.

52. Introduce damage variables to quantify the strength loss of surrounding rock due to plastic deformation, and adjust the surrounding rock contact pressure value accordingly; S4.

53. Based on the geometric characteristics of the four-chamber spatial layout, a curvature correction coefficient is introduced to compensate for the stress distortion caused by the shape and arrangement of the chambers. S4.54, output the final corrected surrounding rock contact pressure value.

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