Method for calculating and optimizing surrounding rock pressure of deeply-buried four-hole small-clear-distance tunnel

Abstract

The invention relates to the technical field of surrounding rock pressure calculation, in particular to a deep-buried four-hole small-clear-distance tunnel surrounding rock pressure calculation optimization method. The method comprises the following steps: collecting geological parameters and support parameters; calculating the radius of an anchor rod reinforcing area based on the geological parameters and the support parameters; a synthetic surrounding rock contact pressure value is calculated by adopting dynamic plastic superposition based on the radius of an anchor rod reinforcing area, a porosity attenuation factor is introduced in the process of calculating the synthetic surrounding rock contact pressure value to quantify the influence of a pore structure on the rock mass rigidity, and a grading correction coefficient is introduced to optimize and dynamically adjust the sensitivity of plastic area expansion to grain grading; and establishing a graded contact pressure correction model to correct a contact pressure error caused by multi-cavern interference to obtain an optimized surrounding rock contact pressure value. According to the design, the mutual influence among multiple caverns, the synergistic effect of a supporting structure and the dynamic change in the construction process are comprehensively considered, and a dynamic plastic superposition theory, double-field coupling stress analysis and a grading correction model are introduced.

Description

Technical Field

[0001] The present invention relates to the technical field of surrounding rock pressure calculation, and more specifically, to an optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel. Background Technique

[0002] Due to the relatively short distance between the chambers in a four-hole small clear distance tunnel, the construction of one chamber during excavation will have a significant impact on adjacent chambers. Traditional calculation models often analyze each chamber separately, ignoring the actual impact of this interaction on the surrounding rock pressure and stability; in the case of multi-chamber excavation, stress concentration areas and overlapping plastic zones are likely to occur, which will lead to the complication of the local stress state and increase the risk of surrounding rock instability. Traditional calculation methods are difficult to accurately capture these complex stress changes; existing calculation methods usually do not fully consider the synergy effect between support measures (such as bolts, linings, etc.) and the surrounding rock, resulting in unreasonable support design, which may cause problems such as waste of resources or insufficient support strength; the physical and mechanical properties of the surrounding rock vary greatly under the same geological conditions. How to adjust the surrounding rock pressure calculation model according to specific geological parameters to adapt to different engineering environments is a challenge. In addition, the influence of factors such as porosity and particle size distribution on the stiffness of the surrounding rock also needs to be considered; therefore, an optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel is provided. Summary of the Invention

[0003] The purpose of the present invention is to provide an optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel to solve the problems of multi-chamber interaction, stress concentration and redistribution, and geological condition complexity mentioned in the above background technique.

[0004] To achieve the above purpose, the present invention aims to provide an optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel, including the following steps: S1. Collect geological parameters and support parameters; S2. Calculate the radius of the bolt reinforcement area based on the geological parameters and support parameters; S3. Calculate the synthetic surrounding rock contact pressure value by using dynamic plastic superposition based on the radius of the bolt reinforcement area. During the calculation of the synthetic surrounding rock contact pressure value, a porosity attenuation factor is introduced to quantify the influence of the pore structure on the rock mass stiffness, and a grading correction coefficient is introduced to optimize the dynamic adjustment of the sensitivity of the plastic zone expansion to the particle size distribution; S4. Establish a hierarchical contact pressure correction model to correct the contact pressure error caused by multi-chamber interference to obtain the optimized surrounding rock contact pressure value.

[0005] As a further improvement of this technical solution, in S2, calculating the synthetic surrounding rock contact pressure value by using dynamic plastic superposition based on the radius of the bolt reinforcement area includes the following steps: S2.1. Determine the range of the calculation domain according to geological parameters and support parameters, and divide a non-uniformly encrypted grid within the calculation domain; S2.2. Calculate the radius of the bolt reinforcement area based on the three-dimensional anchoring layer model.

[0006] As a further improvement of this technical solution, in S2.2, calculating the radius of the bolt reinforcement area based on the three-dimensional anchoring layer model includes the following steps: S2.21. Obtain the length of the bolts used in the current cavern; S2.22. Use the three-dimensional anchoring layer model including the bolt installation angle and surrounding rock strength parameters to calculate the radius of the bolt reinforcement area, and output the radius of the bolt reinforcement area.

[0007] As a further improvement of this technical solution, in S3, calculating the combined surrounding rock contact pressure value using dynamic plastic superposition includes the following steps: S3.1. Divide the construction stages according to the support application timing, and construct a spatio-temporal correlation matrix of the excavation sequence of each cavern; S3.2. For each cavern, calculate the plastic zone radius of the cavern using the Hoek-Brown criterion according to the surrounding rock characteristics after its excavation; S3.3. When the plastic zones of two caverns overlap, trigger the plastic superposition correction mechanism; S3.4. Use the dual-field coupling algorithm to construct the stress field of the dynamically superposed surrounding rock, and introduce a spatio-temporal attenuation factor to adjust the stress contribution of each position in the surrounding rock stress field; S3.5. Calculate the equivalent contact pressure at each node in the non-uniformly encrypted grid; S3.6. Calculate the final surrounding rock contact pressure value based on the equivalent contact pressure and introduce a support cooperation factor using the contact pressure formula.

[0008] As a further improvement of this technical solution, in S3.2, calculating the plastic zone radius of the cavern using the Hoek-Brown criterion 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 the plastic state when a specific stress is applied; S3.23. Analyze the change in the internal stress of the surrounding rock before and after excavation, and identify the plastic zone; S3.24. Combine the failure envelope provided by the Hoek-Brown criterion to estimate the distance from the cavern wall to the maximum stress limit that the surrounding rock can withstand. Introduce a porosity attenuation factor in the elastic modulus term of the Hoek-Brown criterion to quantify the influence of the pore structure on the rock mass stiffness, and introduce a grading correction coefficient to optimize the dynamic adjustment of the sensitivity of the plastic zone expansion to the particle grading.

[0009] As a further improvement of this technical solution, in S3.4, a dual-field coupling algorithm is adopted to construct the stress field of the dynamically superimposed surrounding rock, and a space-time attenuation factor is introduced to adjust the stress contributions of each position in the surrounding rock stress field, including the following steps: S3.41. Based on the non-uniformly encrypted grid, clarify the spatial positions of each node in the grid; S3.42. Based on the linear elastic theory, simulate the stress redistribution of the surrounding rock after excavation unloading, and construct a plastic zone field according to whether each node enters the plastic state; S3.43. Couple the elastic stress field and the plastic damage field, and form a comprehensive stress field by combining the information of the elastic stress field and the plastic damage field; S3.44. Define a space-time attenuation factor according to the distance of the node from the center of the nearest cavern; S3.45. Dynamically update the stress field to obtain a dynamically superimposed stress field that changes with time and space; S3.46. Output the final stress value.

[0010] As a further improvement of this technical solution, in S3.5, calculate the equivalent contact pressure on each node in the non-uniformly encrypted grid, including the following steps: S3.51. For each node in the non-uniformly encrypted grid, clarify the node spatial coordinates and the distance from the center of the nearest cavern; S3.52. According to the dynamically superimposed stress field generated by the dual-field coupling algorithm, extract the normal stress contribution of each cavern to this node; S3.53. For the stress contribution of each cavern to this node, apply the corresponding space-time attenuation factor for adjustment; S3.54. Accumulate the adjusted stress contributions of all caverns to this node to obtain a preliminary equivalent surrounding rock contact pressure value, and combine it with the stress value corrected by plastic superposition to further refine the equivalent surrounding rock contact pressure value at this node.

[0011] As a further improvement of this technical solution, in S3.6, calculate the final surrounding rock contact pressure value based on the equivalent contact pressure and introduce a support cooperation factor, including the following steps: S3.61. Obtain the equivalent surrounding rock contact pressure value; S3.62. Combine the equivalent contact pressure on each node with the support cooperation factor, and use the contact pressure formula to calculate the final surrounding rock contact pressure value at this node; S3.63. On the basis of the preliminary final surrounding rock contact pressure value obtained by calculation, further adjust it by applying the lining stiffness correction coefficient; S3.64. Output the result of the final surrounding rock contact pressure value.

[0012] As a further improvement of this technical solution, in S4, a hierarchical contact pressure correction model is established to correct the contact pressure error caused by the interference of multiple chambers, including the following steps: S4.1. Collect the measured contact pressure data, surrounding rock displacement monitoring data, and support structure strain data after the excavation of each chamber; S4.2. Identify typical interference patterns according to the spatial position relationship of the chambers; S4.3. Based on the net distance between the chambers and their respective plastic zone radii, define a weight coefficient reflecting the interaction intensity between the chambers, and organize the interaction weight coefficients between all pairs of chambers into a matrix form; S4.4. For each node in the grid, calculate the combined interference stress caused by each chamber according to its position and the distribution of the surrounding chambers; S4.5. Construct a hierarchical contact pressure correction model to eliminate the elastic error, plastic damage deviation, and geometric distortion caused by the interference of multiple chambers, and obtain the optimized surrounding rock contact pressure value.

[0013] As a further improvement of this technical solution, in S4.5, constructing a hierarchical contact pressure correction model includes the following steps: S4.51. Use a nonlinear attenuation function to correct the error caused by the overestimation of the contact pressure by the traditional elastic theory; S4.52. Introduce a damage variable to quantify the strength loss suffered by the surrounding rock due to plastic deformation, and adjust the surrounding rock contact pressure value accordingly; S4.53. For the geometric characteristics of the spatial layout of four chambers, introduce a curvature correction coefficient 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.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. In this optimized method for calculating the surrounding rock pressure of a deep-buried four-hole small clear distance tunnel, the mutual influence between multiple chambers, the cooperative effect of the support structure, and the dynamic changes during the construction process are comprehensively considered. By introducing the dynamic plastic superposition theory, dual-field coupled stress analysis, and hierarchical correction model, the problem that the traditional method is prone to overestimate or underestimate the surrounding rock pressure in a complex multi-chamber system is effectively corrected, thereby improving the accuracy of the surrounding rock pressure calculation and providing a more scientific basis for the tunnel support design.

[0015] 2. In the optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel, multi-dimensional parameter modeling means such as non-uniformly encrypted grids, spatio-temporal attenuation factors, lining stiffness correction, and damage variables are adopted, which can flexibly cope with the influences of different geological conditions, support parameters, and excavation sequences. Especially in the layout of small clear distance multi-tunnels, it can accurately capture phenomena such as overlapping plastic zones, stress redistribution, and weakening of rock mass strength, improving the adaptability of the calculation model to actual engineering scenarios and facilitating the realization of safe and economical tunnel construction and operation. Brief Description of the Drawings

[0016] Figure 1 This is the overall method flow chart of the present invention. Detailed Embodiments

[0017] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] Embodiment: Please refer to Figure 1 As shown, this embodiment provides an optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel, including the following steps: S1. Collect geological parameters and support parameters. The geological parameters include the unit weight of the surrounding rock , the internal friction angle , the cohesion , the burial depth , the excavation width of the four chambers , the clear distance between adjacent chambers , and the support parameters include the bolt length , the lining stiffness , and the timing of support application ; S2. Calculate the radius of the bolt reinforcement area based on the geological parameters and support parameters; In this embodiment, based on the radius of the bolt reinforcement area, the combined surrounding rock contact pressure value is calculated by dynamic plastic superposition, including the following steps: S2.1. Determine the calculation domain range according to the geological parameters and support parameters, and divide non-uniformly encrypted grids within the calculation domain to accurately define the boundary conditions of the research area. Considering the influence of different geological conditions and support measures on the stability of the surrounding rock, in order to improve the calculation accuracy, non-uniformly encrypted grid technology is adopted, especially in places where stress concentration or structural complexity is high; Among them, when determining the calculation domain range, the boundary in the X direction is set as , and the Y direction is set as , the Z - direction extends from the ground surface to , in the near - field area close to the chamber surface , a fixed - density grid is adopted within a range, and the grid size does not exceed , while in the area far from the chamber, the grid size is increased according to the exponential - function - increasing method. The specific formula is , represents the distance from this point to the nearest chamber, represents the exponential growth rate per meter; S2.2. To quantify the influence of the support structure on the stability of surrounding rock, calculate the radius of the bolt reinforcement area based on the three - dimensional anchoring layer model; Among them, calculating the radius of the bolt reinforcement area based on the three - dimensional anchoring layer model includes the following steps: S2.21. Obtain the length of the bolts used in the current chamber; S2.22. Use the three - dimensional anchoring layer model including the bolt installation angle and surrounding - rock strength parameters to calculate the radius of the bolt reinforcement area, and output the radius of the bolt reinforcement area. The bolt forms a reinforcement influence area around it through its length and the friction characteristics of the rock mass it is in. The radius of the reinforcement area reflects the spatial range where the bolt can effectively enhance the stability of the surrounding rock, and the bolt reinforcement area is extended from a two - dimensional plane to a three - dimensional ellipsoid, and its spatial influence range is represented by the equivalent calculated radius of the bolt reinforcement area ; Among them, using the three - dimensional anchoring layer model to calculate the radius of the bolt reinforcement area is: , is the bolt installation angle, is the surrounding - rock strength parameter.

[0019] S3. Based on the radius of the bolt reinforcement area, use dynamic plastic superposition to calculate the synthetic surrounding - rock contact pressure value. During the process of calculating the synthetic surrounding - rock contact pressure value, introduce the porosity attenuation factor to quantify the influence of the pore structure on the rock mass stiffness, and introduce the gradation correction coefficient to optimize the dynamic adjustment of the sensitivity of the plastic zone expansion to the particle gradation. For the deep - buried four - hole small - clear - distance tunnel, due to its special geometric layout (because the distance between the four chambers is relatively close), the construction of one chamber during the excavation process will have a significant impact on the adjacent chambers. Therefore, integrate the results obtained from the individual analysis of each chamber through the principle of dynamic plastic superposition; In this embodiment, using dynamic plastic superposition to calculate the synthetic surrounding - rock contact pressure value includes the following steps: S3.1. According to the timing of support application Divide the construction stages, construct a spatio-temporal correlation matrix for the excavation sequence of each chamber. The matrix is used to record the state of each chamber at different construction stages (including whether it is under excavation and whether support has been applied). Each row of the matrix represents a chamber, each column represents a construction stage, and the matrix elements include information such as excavation time and support application time. This matrix is used to determine the interaction between chambers and its change over time in subsequent analysis; S3.2. For each chamber, after its excavation, calculate the radius of the plastic zone of the chamber according to the surrounding rock characteristics using the Hoek-Brown criterion; Among them, calculating the radius of the plastic zone of the chamber using the Hoek-Brown criterion includes the following steps: S3.21. Determine the initial in-situ stress at the location of the chamber, which involves vertical stress (mainly caused by the weight of overlying rock strata) and horizontal stress (possibly affected by tectonic activities); S3.22. Determine whether the surrounding rock will enter the plastic state when a specific stress is applied. According to the surrounding rock characteristic parameters (rock quality designation, geological strength index, and material constants), use the Hoek-Brown criterion to estimate the failure threshold of the surrounding rock under different stress conditions; S3.23. Analyze the change in the internal stress of the surrounding rock before and after excavation and identify the plastic zone; S3.24. Combine the failure envelope provided by the Hoek-Brown criterion to estimate the distance from the chamber wall outward until it reaches the maximum stress limit that the surrounding rock can withstand. This distance is the radius of the plastic zone. Introduce a porosity attenuation factor into the elastic modulus term of the Hoek-Brown criterion to quantify the influence of the pore structure on the stiffness of the rock mass, and introduce a grading correction coefficient to optimize and dynamically adjust the sensitivity of the plastic zone expansion to the particle grading (the porosity attenuation factor is used to quantify the influence of the pore structure on the stiffness of the rock mass. The existence of pores will reduce the effective stress transfer ability of the rock, thus affecting its overall strength and stability. By introducing the porosity attenuation factor, the elastic modulus of the surrounding rock can be adjusted more precisely, and then the mechanical behavior of the rock material under different porosity conditions can be simulated more realistically; the grading correction coefficient is used to optimize and dynamically adjust the sensitivity of the plastic zone expansion to the particle grading. Different particle size distributions will affect the stability and failure mode of the internal structure of the rock. Introducing the grading correction coefficient can better consider the influence of the internal particle distribution characteristics of the rock on the plastic zone expansion, especially in complex geological conditions where the rock is not a homogeneous medium, and the internal particle size, shape, and arrangement will significantly affect the failure mechanism of the rock. By adjusting this coefficient, the Hoek-Brown criterion can be better applied to various different rock types and geological conditions, providing more accurate prediction results for the radius of the plastic zone); 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 formula of the YoHoek-Brown criterion is: ; After introducing the porosity attenuation factor and the gradation correction coefficient into the YoHoek-Brown criterion, it becomes: ; In the formula, represents the porosity attenuation factor, represents the porosity, represents the gradation correction coefficient, represents the fractal dimension of particle size distribution (calculated based on particle screening data), represents the support delay time, represents (the empirical value range is 0.01 - 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.

[0020] S3.3. When the plastic zones of two caverns overlap, trigger the plastic superposition correction mechanism. The plastic superposition correction mechanism is as follows: If the distance between two caverns is less than the sum of their respective plastic zone radii, it is considered that the plastic zones of these two caverns overlap. For the overlapping area, re-evaluate the stress state of this area, consider the influence brought by the superposition of plastic zones, and adjust the local material properties or stress distribution; S3.4. Use the dual-field coupling algorithm to construct the stress field of the dynamically superimposed surrounding rock (the dual-field coupling algorithm accurately describes the stress redistribution, plastic failure and multi-cavern interference effect of the surrounding rock through the dynamic superposition of the elastic field (based on linear elastic theory) and the plastic field (based on the improved Hoek-Brown criterion and damage variable), combined with the space-time attenuation factor and construction stage iteration). And introduce the space-time attenuation factor to adjust the stress contribution of each position in the stress field of the surrounding rock, reflecting the influence of distance on the stress propagation of the surrounding rock. During the tunnel construction process, the stress change caused by the excavation activity will gradually weaken as it moves away from the center of the cavern or with the passage of time. The space-time attenuation factor quantifies this effect, making the stress analysis closer to the actual situation; Among them, the plastic superposition correction mechanism has a direct impact on the update of the elastic field and the plastic field. When the plastic zones of the two chambers overlap (triggered by step S3.3), the plastic superposition correction mechanism dynamically adjusts the stress distribution in the elastic field and the damage variable in the plastic field by re-evaluating the stress state in the overlapping area. Specifically, in the elastic field, the initial elastic stress solution in the superposition area is reduced according to the expansion amplitude of the plastic zone to reflect the weakening of rock strength; in the plastic field, the damage variable is updated according to the equivalent plastic strain increment after the superposition of the plastic zones, so as to quantify the cumulative damage effect. This process realizes the two-way interaction between elastic response and plastic failure through the dynamic correction of the elastic modulus and the non-linear evolution of the damage variable; The stress field of the dynamically superimposed surrounding rock is constructed by using the dual-field coupling algorithm, and the stress contribution of each position in the surrounding rock stress field is adjusted by introducing the space-time attenuation factor, including the following steps: S3.41. Based on the non-uniformly encrypted grid, clarify the spatial position of each node in the grid; S3.42. Based on the linear elastic theory, simulate the stress redistribution of the surrounding rock after excavation unloading, and construct a plastic zone field reflecting the weakening of the surrounding rock strength and irreversible deformation according to whether each node enters the plastic state, which is used to record the plastic strain and the degree of damage; S3.43. Couple the elastic stress field and the plastic damage field, and form a comprehensive stress field that can simultaneously reflect the elastic response and the plastic failure effect by combining the information of the elastic stress field and the plastic damage field; S3.44. Define the space-time attenuation factor according to the distance of the node from the center of the nearest chamber. The farther the distance or the longer the time, the smaller the stress disturbance of the surrounding rock to the node, so its stress contribution is correspondingly weakened; Among them, the space-time attenuation factor is: , represents the rheological coefficient of the surrounding rock, represents the distance from the measuring point to the nearest chamber; S3.45. Dynamically update the stress field to obtain the dynamically superimposed stress field that changes with time and space. As the construction stage progresses, whenever a new chamber is excavated or a support measure is applied, recalculate the stress state of all nodes in the current stage, update the elastic field and the plastic field, and re-perform the dual-field coupling, and synchronously update the space-time attenuation factor to ensure that the stress contribution of each node always matches the current construction state; S3.46. Output the final stress value.

[0021] S3.5. Calculate the equivalent contact pressure on each node in the non-uniformly encrypted grid , which comprehensively considers the multi-chamber excavation and the plastic superposition effect. Specifically: , Among them, Indicates the normal stress contribution of the th chamber to this node, Indicates the spatio-temporal attenuation factor of the th chamber, Indicates the plastic superposition coefficient, Indicates the damage tensile stress; Among them, calculating the equivalent contact pressure at each node in the non-uniformly refined grid includes the following steps: S3.51. For each node in the non-uniformly refined grid, clarify the node spatial coordinates and the distance to the center of the nearest chamber; S3.52. According to the dynamic superposition stress field generated by the dual-field coupling algorithm, extract the normal stress contribution of each chamber to this node (i.e., the stress perpendicular to the chamber wall surface); S3.53. For the stress contribution of each chamber to this node, apply the corresponding spatio-temporal attenuation factor for adjustment. The farther the distance or the longer the time, the smaller the stress contribution; S3.54. Accumulate the adjusted stress contributions of all chambers to this node to obtain a preliminary equivalent surrounding rock contact pressure value. Combine the stress value corrected by plastic superposition to further refine the equivalent surrounding rock contact pressure value at this node. The specific steps of refinement are as follows: Identify which nodes are located in the overlapping area of the plastic zones of two or more chambers, and introduce a plastic superposition coefficient for these nodes to adjust their stress states, reflecting the weakening of rock strength and stress redistribution caused by the superposition of plastic zones; Then, combine the normal stress contributions of each chamber to the node adjusted by the spatio-temporal 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.

[0022] S3.6. Based on the equivalent contact pressure and introducing a support cooperation factor (The support cooperation factor quantifies and reflects the cooperation effect between bolts and linings) Use the contact pressure formula to calculate the final surrounding rock contact pressure value. The main role of introducing the support cooperation factor when calculating the equivalent contact pressure is to quantify and reflect the interaction between the support structure (such as bolts and linings) and the surrounding rock, so as to more accurately evaluate the actual bearing pressure of the surrounding rock. The support cooperation 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 bolt reinforcement area and the lining stiffness, this factor reflects how the support structure effectively shares and reduces the pressure borne by the surrounding rock, thereby improving the safety of the overall structure; The support cooperation factor helps to more accurately simulate the redistribution of internal stress in the surrounding rock during the excavation process. Especially in multi-chamber tunnel projects, due to the mutual influence between chambers, reasonably considering the role of the support structure is crucial for predicting the stress state of the surrounding rock; Furthermore, the support cooperation factor is: , is the elastic modulus of the surrounding rock, is the net distance between adjacent cavities, is the characteristic length, which is used for normalization to ensure that the entire exponential term is dimensionless; Among them, based on the equivalent contact pressure and introducing the support cooperation factor to calculate the final surrounding rock contact pressure value, including 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 cooperation factor, and use the contact pressure formula to calculate the final surrounding rock contact pressure value at this node; S3.63. On the basis of the initially calculated final surrounding rock contact pressure value, further adjust it by applying the lining stiffness correction coefficient. This adjustment ensures that the final surrounding rock contact pressure value fully considers the support effect provided by the lining, thereby reducing the actual bearing pressure of the surrounding rock; Among them, use the contact pressure formula to calculate the surrounding rock contact pressure value Specifically: , represents the lining stiffness correction coefficient. The higher the stiffness of the lining structure relative to the surrounding rock stiffness, the stronger its ability to restrain the deformation of the surrounding rock. Therefore, the lining stiffness correction coefficient is defined to reflect this relative effect, , represents the lining stiffness, is the elastic modulus of the surrounding rock; S3.64. Output the result of the final surrounding rock contact pressure value.

[0023] S4. Establish a hierarchical contact pressure correction model to correct the contact pressure error caused by multi-cavity interference to obtain the optimized surrounding rock contact pressure value; In this embodiment, establishing a hierarchical contact pressure correction model to correct the contact pressure error caused by multi-cavity interference includes the following steps: S4.1. Collect the measured contact pressure data (pressure sensor readings), surrounding rock displacement monitoring data (multi-point displacement meters, fiber optic monitoring), and support structure strain data (rebar meters, concrete strain gauges) after the excavation of each cavity; S4.2. According to the spatial position relationship of the cavities, identify typical interference patterns, including: lateral extrusion type (the side walls of adjacent cavities squeeze each other), roof unloading type (the excavation of the upper cavity causes the stress release of the roof of the lower cavity), and middle column eccentric compression type (abnormal stress concentration in the middle rock pillar area); S4.3. Based on the net distance between the cavities and their respective plastic zone radii, define the weight coefficient reflecting the interaction strength between the cavities (the weight coefficient is: , where, Denote the cavern and the net distance of, Denote the cavern the radius of the plastic zone of, is the attenuation coefficient; this coefficient decreases with the increase of distance, indicating that the mutual influence between caverns at a long distance is small), and the interaction weight coefficients between all pairs of caverns are arranged in matrix form (this matrix helps to quantify the stress superposition effect received by each node from different directions); S4.4. For each node in the grid, calculate the synthetic interference stress caused by each cavern according to its position and the distribution of surrounding caverns. This process comprehensively considers the components of the principal stress field and the secondary stress field, and includes the influence of the spatio-temporal attenuation effect; Among them, the synthetic interference stress is: ; In the formula, represents the component of the principal stress field, represents the component of the secondary stress field (including the spatio-temporal attenuation effect); S4.5. Construct a hierarchical contact pressure correction model to eliminate the elastic error, plastic damage deviation and geometric distortion caused by multi-cavern interference, and obtain the optimized surrounding rock contact pressure value. The 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 multi-caverns, the overlapping effect of plastic zones, the synergistic effect of support structures (such as bolts and linings), and the influence of complex geological conditions on the stability of surrounding rocks; Furthermore, construct a hierarchical contact pressure correction model, including the following steps: S4.51. Use a non-linear attenuation function to correct the error caused by the overestimation of the contact pressure by the traditional elastic theory (using a non-linear attenuation function to correct the error caused by the overestimation of the contact pressure by the traditional elastic theory is mainly to improve the accuracy of the calculation of the surrounding rock contact pressure and reflect the phenomenon of the reduction of the surrounding rock pressure caused by factors such as stress redistribution and plastic deformation in actual engineering. By introducing a non-linear attenuation function, the calculation model can be adjusted according to the actual deformation and failure characteristics of the surrounding rock, and effectively eliminate the overestimation of the contact pressure by the traditional elastic theory when dealing with complex geological conditions); Among them, the non-linear attenuation function correction process is: ; In the formula, represents the preliminary corrected surrounding rock contact pressure value, represents the contact pressure calculated by the 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. represents the reference curvature (unit: 1 / m), which is used for normalizing the maximum curvature. S4.52. Introduce a damage variable to quantify the strength loss suffered by the surrounding rock due to plastic deformation, and adjust the contact pressure value of the surrounding rock 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 caused by plastic deformation of the surrounding rock serves 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 are difficult to accurately describe this process. By introducing a damage variable, the cumulative damage effect of the surrounding rock can be incorporated into the calculation of contact pressure, thereby dynamically correcting the actual stress state of the surrounding rock and improving the reliability and engineering applicability of the calculation results); After introducing the damage variable, the non-linear attenuation function is: ; In the formula, represents the value of the contact pressure of the surrounding rock after further correction. represents the dimensionless adjustment coefficient, which is obtained by fitting based on the damage variable and the cohesion of the surrounding rock. S4.53. Aiming at the geometric characteristics of the four-chamber spatial layout, introduce a curvature correction coefficient to compensate for the stress distortion caused by the shape and arrangement of the chambers. This correction helps to more accurately predict the distribution of surrounding rock pressure under complex geological conditions (defining a curvature correction coefficient to compensate for the stress distortion caused by the unique geometric characteristics of the four-chamber spatial layout, its role is to accurately adjust the error in the calculation of the contact pressure of the surrounding rock caused by the shape and arrangement of the chambers. In complex multi-chamber tunnel projects, the relative position, spacing and shape between chambers will cause local stress concentration or dispersion, resulting in a difference between the actual stress distribution and the prediction result of the ideal model. By introducing a curvature correction coefficient, the influence of these geometric factors on the stress state of the surrounding rock can be effectively reflected, and the contact pressure assessment can be optimized); The curvature correction coefficient is: ; In the formula, represents the minimum net distance. represents the maximum excavation width. is the installation angle of the bolt. S4.54. Output the value of the finally corrected contact pressure of the surrounding rock; The value of the finally corrected contact pressure of the surrounding rock is:

[0024] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and the descriptions in the specification are only preferred examples of the present invention, which are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and all these changes and improvements fall within the scope of the present invention claimed.

Claims

1. An optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel, characterized in that, It includes the following steps: S1. Collect geological parameters and support parameters; S2. Calculate the radius of the bolt reinforcement area based on the geological parameters and support parameters; S3. Calculate the synthetic surrounding rock contact pressure value using dynamic plastic superposition based on the radius of the bolt reinforcement area. During the calculation of the synthetic surrounding rock contact pressure value, introduce a porosity decay factor to quantify the influence of the pore structure on the rock mass stiffness, and introduce a grading correction coefficient to optimize the dynamic adjustment of the sensitivity of the plastic zone expansion to the particle grading; S4. Establish a grading contact pressure correction model to correct the contact pressure error caused by multi - chamber interference to obtain the optimized surrounding rock contact pressure value.

2. The optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel according to claim 1, characterized in that: In S2, calculating the synthetic surrounding rock contact pressure value using dynamic plastic superposition based on the radius of the bolt reinforcement area includes the following steps: S2.

1. Determine the calculation domain range according to the geological parameters and support parameters, and divide non - uniformly encrypted grids within the calculation domain; S2.

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

3. The optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel according to claim 2, characterized in that: In S2.2, calculating the radius of the bolt reinforcement area based on the three - dimensional anchor layer model includes the following steps: S2.

21. Obtain the bolt length used in the current chamber; S2.

22. Use the three - dimensional anchor layer model including the bolt installation angle and surrounding rock strength parameters to calculate the radius of the bolt reinforcement area and output the radius of the bolt reinforcement area.

4. The optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel according to claim 1, wherein: In S3, calculating the synthetic surrounding rock contact pressure value using dynamic plastic superposition includes the following steps: S3.

1. Divide the construction stages according to the support construction timing, and construct a spatio - temporal correlation matrix of the excavation sequence of each chamber; S3.

2. For each chamber, after its excavation, calculate the plastic zone radius of the chamber according to the surrounding rock characteristics using the Hoek - Brown criterion; S3.

3. When the plastic zones of two chambers overlap, trigger the plastic superposition correction mechanism; S3.

4. Use the dual - field coupling algorithm to construct the stress field of the dynamically superimposed surrounding rock, and introduce a spatio - temporal decay factor to adjust the stress contribution of each position in the surrounding rock stress field; S3.

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

6. Based on the equivalent contact pressure and introducing a support cooperation factor, calculate the final surrounding rock contact pressure value using the contact pressure formula.

5. The optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel according to claim 4, characterized in that: In S3.2, calculating the plastic zone radius of the chamber using the Hoek - Brown criterion includes the following steps: S3.

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

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

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

24. Combine the failure envelope provided by the Hoek - Brown criterion to estimate the distance from the chamber wall surface outward until it reaches the maximum stress limit that the surrounding rock can withstand. Introduce a porosity decay factor in the elastic modulus term of the Hoek - Brown criterion to quantify the influence of the pore structure on the rock mass stiffness, and introduce a grading correction coefficient to optimize the dynamic adjustment of the sensitivity of the plastic zone expansion to the particle grading.

6. The optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel according to claim 4, characterized in that: In S3.4, a dual-field coupling algorithm is used to construct the stress field of the dynamically superimposed surrounding rock, and a spatio-temporal attenuation factor is introduced to adjust the stress contributions at various positions in the surrounding rock stress field, including the following steps: S3.

41. Based on the non-uniformly refined grid, clarify the spatial positions of each node in the grid; S3.

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

43. Couple the elastic stress field and the plastic damage field, and form a comprehensive stress field by combining the information of the elastic stress field and the plastic damage field; S3.

44. Define the spatio-temporal attenuation factor according to the distance of the node from the center of the nearest cavern; S3.

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

46. Output the final stress value.

7. The optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear-span tunnel according to claim 4, characterized in that: In S3.5, calculate the equivalent contact pressure at each node in the non-uniformly refined grid, including the following steps: S3.

51. For each node in the non-uniformly refined grid, clarify the node spatial coordinates and the distance from the center of the nearest cavern; S3.

52. Extract the normal stress contribution of each cavern to this node according to the dynamically superimposed stress field generated by the dual-field coupling algorithm; S3.

53. Adjust the stress contribution of each cavern to this node by applying the corresponding spatio-temporal attenuation factor; S3.

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

8. The optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel according to claim 4, characterized in that: In S3.6, calculate the final surrounding rock contact pressure value based on the equivalent contact pressure and introduce a support cooperation factor, including 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 cooperation factor, and calculate the final surrounding rock contact pressure value at this node using the contact pressure formula; S3.

63. On the basis of the initially calculated final surrounding rock contact pressure value, further adjust it by applying the lining stiffness correction coefficient; S3.

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

9. The optimized method for calculating the surrounding rock pressure of a deeply buried four-hole small clear distance tunnel according to claim 1, characterized in that: In S4, establish a hierarchical contact pressure correction model to correct the contact pressure error caused by multi-cavern interference, including the following steps: S4.

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

2. Identify typical interference patterns according to the spatial position relationship of the caverns; S4.

3. Based on the net distance between caverns and their respective plastic zone radii, define the weight coefficients reflecting the interaction strength between caverns, and organize the interaction weight coefficients between all pairs of caverns into a matrix form; S4.

4. For each node in the grid, calculate the combined interference stress caused by each cavern according to its position and the distribution of surrounding caverns; S4.

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

10. The optimized method for calculating the surrounding rock pressure of a deeply buried four-hole closely spaced tunnel according to claim 9, characterized in that: In S4.5, a hierarchical contact pressure correction model is constructed, including the following steps: S4.

51. Use a non-linear attenuation function to correct the error caused by the overestimation of contact pressure by traditional elastic theory; S4.

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

53. For the geometric characteristics of the four-chamber spatial layout, introduce a curvature correction coefficient to compensate for the stress distortion caused by the shape and arrangement of the chambers; S4.

54. Output the finally corrected contact pressure value of the surrounding rock.

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