Method for determining mountainside depth of mountainside tunnel in alpine and valley region based on rockburst risk

Abstract

The invention relates to the technical field of hard surrounding rock hillside tunnel burial depth design in the field of tunnel engineering, in particular to a hillside tunnel hillside depth determination method based on rockburst risk in a high mountain and valley region, which comprises the following steps: determining the superposition influence range of a tectonic stress field and a valley stress field; determining a strong rockburst limit caused by the burial depth; and determining the safe burial depth range of the near-mountain tunnel by integrating the influence ranges of the tectonic stress fields in the step 1 and the step 2 and the influence ranges of the valley stress fields and the strong rockburst limit caused by the burial depth. According to the method for determining the mountainside depth of the mountainside tunnel in the alpine and valley region based on the rockburst risk, for the first time, for the hard surrounding rock mountainside tunnel under the complex crustal stress condition, multiple factors such as the complex geological environment, the high-energy-storage rock mass, the high-level tectonic stress field, the valley stress field and the large burial depth are comprehensively considered, and the comprehensive burial depth determining method is provided; the scientificity of tunnel burial depth determination is ensured, and the technical blank in the field is filled.

Description

Technical Field

[0001] The present invention relates to the technical field of buried depth design for hard surrounding rock mountainside tunnels in the field of tunnel engineering, and in particular to a method for determining the mountainside depth of mountainside tunnels based on rock burst risks in alpine canyon areas. Background Art

[0002] With the continued expansion and optimization of the national highway and rail network, traversing mountainous terrain has become unavoidable. Mountainside tunnels, as an efficient and safe engineering solution, have been widely used in mountain transportation construction. They not only significantly reduce risks during construction and operation, improve efficiency, and reduce costs, but also maximize protection of the surrounding natural environment, achieving the goal of harmonious coexistence between man and nature.

[0003] However, mountainside tunnel construction, particularly hard-rock tunnels located in high mountain valleys, faces an extremely complex geological environment. These areas often feature variable geological conditions, complex geostress states, and the unique stress fields created by the ravine terrain, significantly increasing the difficulty of tunnel design and construction. In particular, the behavior of hard surrounding rock under complex geostress conditions—such as the stability of high-energy-storage rock masses, the combined effects of tectonic stress and ravine stress fields, and the severe rockburst risk associated with deep burial depths—becomes a key factor limiting the safety and economic viability of tunnel construction.

[0004] Rockburst, a common geological hazard during tunnel construction in hard surrounding rock, has a complex mechanism and is influenced by numerous factors, including the physical and mechanical properties of the rock, the ground stress state, the tunnel depth, and the excavation method. In mountainous canyon areas, the steep terrain and intense rock compression often lead to high ground stress levels. Furthermore, the hard surrounding rock has a high energy storage capacity. Once tunnel excavation disrupts the existing stress balance, rockburst is highly likely to occur, posing a serious threat to the safety of construction workers, the integrity of equipment, and the stability of the tunnel structure.

[0005] Currently, the determination of the buried depth of mountainside tunnels primarily relies on geological survey data and engineering geological environment analysis during the empirical design phase, estimated through engineering analogy. While this approach does account for the influence of geological conditions to a certain extent, its limitations are increasingly evident when dealing with hard surrounding rock tunnels in high mountain canyon areas with complex geostress conditions. Geological conditions vary significantly across regions, and even similar geological structures can result in vastly different engineering responses due to differences in local stress states, rock properties, and other factors. Therefore, empirical analogy alone makes it difficult to accurately assess the impact of tunnel buried depth on rockburst risk, making it difficult to ensure the safety and economic efficiency of tunnel design.

[0006] Therefore, there is an urgent need for a more scientific, reasonable and efficient method to determine the buried depth of mountainside tunnels in hard surrounding rock under complex ground stress conditions, to minimize the risk of tunnel crossing, and to provide technical support for mountainside tunnel design in the design stage. Summary of the Invention

[0007] In order to solve the above problems, the present invention provides a method for determining the mountainside depth of mountainside tunnels in high mountain canyon areas based on rock burst risks. This method for determining the mountainside depth of mountainside tunnels in high mountain canyon areas based on rock burst risks is the first to target hard surrounding rock mountainside tunnels under complex ground stress conditions. It comprehensively considers multiple factors such as complex geological environment, high-energy storage rock mass, high-level tectonic stress field, valley stress field and large burial depth, and proposes a comprehensive burial depth determination method, which ensures the comprehensiveness of tunnel burial depth determination and fills the technical gap in this field.

[0008] The technical solutions of the present invention are as follows:

[0009] A method for determining the mountainside depth of a mountainside tunnel in a high mountain canyon area based on rock burst risk comprises the following steps:

[0010] Step 1: Determine the superposition influence range of tectonic stress field and valley stress field;

[0011] Step 2: Determine the boundary of strong rock burst caused by burial depth;

[0012] Step 3: Determine the safe burial depth range of the mountainside tunnel by combining the tectonic stress field of steps 1 and 2, the influence range of the valley stress field, and the boundary of the strong rock burst caused by the burial depth.

[0013] In step one, the influence depths of tectonic stress and valley stress field are preliminarily determined through measured geostress data in the tunnel site area; then numerical simulation is used to verify and optimize the preliminarily determined influence depths of tectonic stress and valley stress field.

[0014] In step 2, rock physics and mechanics tests are conducted at the tunnel site to determine the statistical average value of the saturated uniaxial compressive strength; typical sections of the tunnel site are selected for stress field simulation; and based on the strength-stress ratio method, σmax = Rc / 2 is used as the criterion to determine the limit of severe rockburst caused by burial depth.

[0015] Measured geostress data obtained using hydraulic fracturing.

[0016] The verification and optimization of the impact depth of the preliminarily determined tectonic stress and valley stress field using numerical simulation includes the following steps: model selection; model construction; loading; parameter assignment; result reliability analysis; and analysis of the stress field distribution characteristics on the slope.

[0017] A typical section in the tunnel area that can reflect the general characteristics of the slope stress field is selected as the numerical calculation model.

[0018] In constructing the model, the swept mesh generation technology is used to decompose it into several 8-node hexahedral elements.

[0019] The ideal elastic-plastic constitutive model that obeys the Mohr-Cou l omb yield criterion and associated flow law is adopted in constructing the model.

[0020] The boundary conditions are set as follows: horizontal stress constraints are applied to the four boundaries of the model, and vertical displacement constraints are applied to the bottom surface.

[0021] Loading methods include: self-weight stress simulation, structural action simulation, boundary load adjustment method and static equilibrium state simulation.

[0022] The parameter assignment is as follows: Make full use of existing survey data and existing literature, and determine the rock physical and mechanical parameters of the tunnel site according to the different weathering degrees of the rock mass.

[0023] The reliability analysis of the results is as follows: the measured ground stress data of the boreholes near the tunnel site are compared with the numerical simulation results, the error is defined, and the error at different depths is analyzed. The error range is usually between 15% and 30%, which indicates that the numerical simulation has high reliability.

[0024] The stress field distribution characteristics of the slope are analyzed as follows: the change in stress direction from the surface to the inside of the slope is analyzed through the principal stress cloud map, and the area of the slope prone to overall shear failure is analyzed through the maximum shear strain increment cloud map, thereby comprehensively determining the depth of the superposition of the valley stress field and the tectonic stress field.

[0025] The beneficial effects of the present invention are:

[0026] 1. The present invention discloses a method for determining the mountainside depth of mountainside tunnels in high mountain canyon areas based on rock burst risk. This method is the first to target hard surrounding rock mountainside tunnels under complex geostress conditions. It comprehensively considers multiple factors such as complex geological environment, high-energy storage rock mass, high-level tectonic stress field, valley stress field, and large burial depth, and proposes a comprehensive burial depth determination method, ensuring the comprehensiveness of tunnel burial depth determination and filling the technical gap in this field.

[0027] 2. The present invention discloses a method for determining the mountainside depth of a mountainside tunnel in a high mountain canyon area based on the risk of rock burst. The method for determining the mountainside depth of a mountainside tunnel in a high mountain canyon area based on the risk of rock burst accurately determines the influence range of tectonic stress and valley stress field by combining the statistics of measured ground stress data from drilling with numerical simulation, thereby improving the accuracy and reliability of burial depth determination. By utilizing rock physics and mechanics tests and stress field simulation, the boundary of severe rock burst caused by burial depth is scientifically and rationally delineated, thereby effectively avoiding the risk of severe rock burst in the design stage.

[0028] 3. The present invention discloses a method for determining the mountainside depth of a mountainside tunnel in a high mountain canyon area based on the risk of rock burst. The method for determining the mountainside depth of a mountainside tunnel in a high mountain canyon area based on the risk of rock burst minimizes the optimization idea of the deep buried section, reduces the project cost and construction difficulty, and improves the economy of the project.

[0029] 4. The present invention discloses a method for determining the mountainside depth of a mountainside tunnel in a high mountain canyon area based on the risk of rock burst. The method is suitable for mountainside tunnels with hard surrounding rocks under complex ground stress conditions, provides a scientific idea and method for determining the tunnel burial depth in the design stage, and has broad practicality and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram for determining the safe burial depth range of mountainside tunnels

[0031] Figure 2 Drilling plane distribution map

[0032] Figure 3 Variation of maximum horizontal principal stress with depth in a plateau canyon area

[0033] Figure 4 Variation of minimum horizontal principal stress with depth in a plateau canyon area

[0034] Figure 5 Section 1-1 Numerical calculation model

[0035] Figure 6 The plane position relationship between section 1-1 and horizontal hole SPZ-1

[0036] Figure 7 Comparative analysis of simulated data and measured maximum principal stress data

[0037] Figure 8 Variation of errors at different locations with horizontal burial depth

[0038] Figure 9 Distribution of maximum principal stress in the stress field at the slope

[0039] Figure 10 Minimum principal stress distribution of stress field on slope

[0040] Figure 11 Cloud diagram of the maximum shear strain increment when the slope undergoes overall shear failure under the superposition of tectonic stress and self-weight stress

[0041] Figure 12 The maximum principal stress limit is 40 MPa

[0042] Figure 13 The corresponding hole positions of each scheme

[0043] Figure 14 Maximum principal stress distribution under unsupported excavation conditions DETAILED DESCRIPTION

[0044] The present invention will be further described in detail below by means of specific embodiments in conjunction with the accompanying drawings. Similar elements in different embodiments are numbered with associated similar elements. In the following embodiments, many detailed descriptions are provided to enable the present application to be better understood. However, those skilled in the art will readily appreciate that some of the features may be omitted in different circumstances, or may be replaced by other elements, materials, or methods. In some cases, some operations related to the present application are not shown or described in the specification. This is to avoid the core portion of the present application being overwhelmed by excessive descriptions, and for those skilled in the art, it is not necessary to describe these related operations in detail. They will fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0045] In addition, the features, operations, or characteristics described in the specification may be combined in any appropriate manner to form various embodiments. Furthermore, the steps or actions in the method description may be reordered or adjusted in a manner readily apparent to those skilled in the art. Therefore, the various sequences in the specification and drawings are provided solely for the purpose of clearly describing a particular embodiment and are not intended to be mandatory, unless otherwise specified.

[0046] The method for determining the mountainside depth of mountainside tunnels in alpine canyon areas based on rockburst risk includes the following steps:

[0047] 1. Determination of the influence range of tectonic stress and valley stress field

[0048] (1) Preliminary determination: Based on the statistical results of the measured ground stress data from the boreholes in the slope zone of the canyon area, the influence depth of the tectonic stress and the valley stress field was preliminarily determined.

[0049] Due to the unique topography of canyon regions, their geostress fields are often influenced by both tectonic stress and valley stress. Tectonic stress is primarily caused by crustal movement and plate interaction, while valley stress is related to factors such as topography, surface erosion, and riverbed incision. Measured geostress data can directly reflect the geostress characteristics of alpine canyon regions under the combined influence of tectonic and valley stress fields. This data can be used to clarify the extent of the combined influence of these two stress fields.

[0050] Take a typical canyon area on the plateau as an example. The slope rock type is mainly granite. Under the combined action of gravity geology and dynamic geology of marine glaciers, the canyon area has a narrow terrain and steep terrain. The relative height difference of the terrain is 1500m to 3000m, and the average slope of the slope is greater than 60°. A total of 17 deep-hole ground stress test boreholes were laid in the slope area of the canyon area. The borehole plane distribution is as follows: Figure 2 shown.

[0051] On-site geostress measurements were conducted using hydraulic fracturing, with measuring points spaced approximately 50 meters apart and the depth range of the geostress test from 54.75 to 958.05 meters. Preliminary statistical analysis of the test data revealed that the maximum horizontal principal stress (SH) ranged from 4.77 to 26.1 MPa, and the minimum horizontal principal stress (Sh) ranged from 3.89 MPa to 18.41 MPa. With increasing burial depth, the relationship between the three principal stresses shifted from SH > Sh > SV to SH > SV > Sh. The geostress state was dominated by regional tectonic stress, with the dominant direction of the maximum horizontal principal stress being from N10°E to N52°E, with a predominantly NE orientation.

[0052] The measured ground stress data in the slope area are plotted as a scatter plot, and the maximum and minimum horizontal principal stresses in the canyon vary with horizontal depth, as shown in Figure 2. Figure 3 and Figure 4 As can be seen, within the horizontal depth range of 0 to 400m, the measured values of the maximum and minimum principal stresses are 14.19MPa and 12.12MPa, respectively. Within this range, the growth gradient of the geostress is steep, and the test results fluctuate significantly, indicating that the superposition of tectonic stress and valley stress fields in this area is quite strong. However, when the depth exceeds 400m, the distribution of the horizontal principal stress shows a steady increasing trend with increasing horizontal depth.

[0053] Statistical analysis of geostress data indicates that the combined influence of the slope stress field and tectonic stress field in this canyon region reaches a depth of 400 meters. This means that the stress complex zone begins at a horizontal depth of 400 meters, and beyond that, the stress enters a stable zone. These statistical results reflect the regularity of stress variations in canyon slopes, consistent with existing academic understanding.

[0054] 2. Verification and optimization of the influence range of tectonic stress and valley stress field

[0055] (1) Deficiencies in determining the influence range of slope stress field based on measured ground stress data

[0056] When analyzing the depth of slope stress, various industries generally rely on field-measured geostress data. These tests generally employ hydraulic fracturing. However, hydraulic fracturing has three significant drawbacks when conducting geostress testing:

[0057] 1) A basic assumption of hydraulic fracturing is that the direction of the principal stress is consistent with the borehole axis, but the principal stress value in this direction is estimated. In areas with complex topography and geological conditions, this assumption may lead to significant differences between the measured data and the actual ground stress;

[0058] 2) When fine cracks are developed in the tunnel site area and primary cracks exist in the measurement section, the water pressure changes during the measurement process will be abnormal, and the measured value will deviate from the actual value;

[0059] 3) The measurement process of hydraulic fracturing involves multiple steps and parameter selections. Each small error in these steps may accumulate, resulting in a deviation between the final measured value and the actual value.

[0060] Taking all of the above factors into account, it can be concluded that the in-situ stress data measured by hydraulic fracturing may underestimate the actual in-situ stress level, while the actual depth of influence of the slope stress field may be deeper than the analysis results based on the measured in-situ stress data. Therefore, relying solely on measured in-situ stress data to determine the influence range of the slope stress field may pose a safety hazard. To more accurately assess the influence depth of the slope stress field, it is necessary to combine it with numerical simulation results and make corrections.

[0061] (2) Calibration optimization

[0062] The tectonic stress background and topographic conditions of the canyon area are similar. Considering the topographic data, structural geology and engineering geology data of the tunnel site, a typical valley profile 1-1 was selected for stress analysis. The location of profile 1-1 is shown in Figure 2 .

[0063] 1) Model selection

[0064] Taking the canyon area as an example, a typical section 1-1 of the tunnel site area is established as a numerical calculation model to reflect the general characteristics of the slope stress field. The section model is shown in Figure 5 .

[0065] 2) Model construction

[0066] ① Stratigraphic structure: From the surface to the inside, there are strongly weathered layer, weakly weathered layer, slightly weathered layer and unweathered layer.

[0067] ②Model size: 7355.7m long, 3010-3810m high, 600m wide.

[0068] ③ Mesh division: Using the swept mesh generation technology, it is decomposed into 1613787 8-node hexahedral elements.

[0069] ④Material constitutive model: The granite mass adopts the ideal elastic-plastic constitutive model that obeys the Mohr-Cou l omb yield criterion and the associated flow law.

[0070] ⑤ Tectonic stress direction: Under long-term geological action, the tectonic stress direction is stable (north-east direction), and the equation of the horizontal stress regression curve is px=-0.0289y+6.66 (MPa).

[0071] ⑥ Boundary conditions: There are five main factors that have a greater impact on the current ground stress field: a: Y-direction self-weight stress, b: X-direction compression structure, c: Z-direction compression structure, d: horizontal X-direction shear structure, and e: horizontal Z-direction shear structure.

[0072] Given that hydraulic fracturing measurements revealed no vertical shear stress, and given that engineering geological analysis indicated that shear tectonic activity in the study area is insignificant, the following boundary conditions were set: horizontal stress constraints were applied to the front, back, left, and right boundaries of the model, and vertical displacement constraints were applied to the bottom surface.

[0073] 3) Loading method

[0074] ① Self-weight stress simulation: Simulation is performed by assigning different granites with different degrees of weathering different weights.

[0075] ② Tectonic action simulation: This is achieved by applying stress boundary conditions on the corresponding boundary surfaces of the model.

[0076] ③ Boundary load adjustment method: According to the tectonic position and dynamic background of the study area, surface loads are added to the model in the east-west, south-north and north-south directions, and inversion calculations are performed with reference to the measured ground stress data to determine the optimal boundary loading method and value.

[0077] ④ Static equilibrium state simulation: After the calculation is completed, all node velocities are reset to zero to simulate the static equilibrium state of rock and soil under the action of the ground stress field.

[0078] 4) Parameter assignment

[0079] During numerical simulations, ensuring the reliability of material parameters is key to obtaining reliable results. The material parameters used in this simulation were determined by fully utilizing existing survey data and extensively referencing key data such as rock density, uniaxial compressive strength, and Poisson's ratio from similar projects.

[0080] The material parameters shown in Table 1, including granite's deformation modulus E, Poisson's ratio ν, and density, are the core foundation of model construction. These parameters ensure the model's accuracy and reliability in reflecting actual geomechanical properties.

[0081] Table 1 Model material parameters

[0082] Lithology Deformation modulus (GPa) Poisson's ratio Density (g / cm3) Cohesion (kPa) Internal friction angle (°) Strongly weathered granite 6 0.30 2.60 450 38 Weakly weathered granite 10 0.28 2.62 800 46 Slightly weathered granite 20 0.24 2.65 1500 52.5 Unweathered granite 30 0.24 2.65 1700 54.6

[0083] 5) Result reliability analysis

[0084] In order to verify the reliability of the simulation results, the measured ground stress data of the adjacent horizontal hole SPZ-1 were selected for comparative analysis with the numerical simulation results.

[0085] Figure 6 The horizontal hole and the 1-1 section are located on the same bank slope, and their strikes are approximately parallel. The horizontal hole is projected onto the 1-1 section, and the ground stress simulation data at the projected position is extracted and compared with the measured maximum principal stress data. The relevant results are plotted on Figure 7 It can be seen that with the increase of horizontal burial depth, the maximum principal stresses of both simulation and measurement show a monotonically increasing trend, but the numerical simulation results are larger than the measured values. The error is defined as follows: the difference between the simulation value and the measured value at a certain depth and the percentage of the measured value. The relationship between the error at different positions and the horizontal burial depth is plotted on Figure 8 The relative error range between the two is 17.5% to 48.4%, and the normal error range is 15% to 30%. When the horizontal burial depth exceeds 1150m, the error is less than 20%. In other words, as the burial depth increases, the numerical simulation can more accurately reflect the actual ground stress conditions.

[0086] It should be noted that in the shallow layer of the slope, the numerical simulation results are 48.4% larger than the measured maximum principal stress. The main reasons for this error are the following two aspects: (1) the external dynamic geological action in the shallow layer is strong, various cracks are developed in the rock mass, and the unloading of the rock mass causes the ground stress level to decrease; (2) the numerical simulation fails to reflect the development of cracks in the rock mass.

[0087] In addition, the numerical simulation results are generally 15% to 30% higher than the measured values. In addition to the defects of the hydraulic fracturing method itself, from the perspective of numerical simulation analysis: a: During the numerical simulation, the granite body was assumed to be a homogeneous and isotropic geological body, and an ideal elastic-plastic constitutive model obeying the Mohr-Coulom yield criterion and associated flow law was adopted. This failed to reflect the cracks, local folds and structures existing within the rock mass; b: The application of tectonic stress in section 1-1 comprehensively considered the measured geostress data of the entire tunnel site and adopted statistically significant data regression analysis. Therefore, local differences may occur.

[0088] Overall, this numerical simulation reflects the general laws of the geostress field at the tunnel site with high reliability. Especially under deep burial conditions, the accuracy of the numerical simulation is significantly improved. Based on these simulation results, we will now conduct a systematic analysis of the relevant laws of the geostress field.

[0089] 6) Stress field distribution characteristics of slope parts

[0090] The stress field on the slope shows a distinct differentiation phenomenon from the surface to the inside. Due to the presence of high and steep terrain and the free surface, within the burial depth range of 0 to 200 m, from the valley to the slope, the maximum principal stress gradually approaches parallel to the slope surface; the minimum principal stress is nearly orthogonal to the slope surface. In this area, the maximum principal stress level is relatively low, which constitutes an important feature of the shallow surface stress field on the slope. Figure 9 and Figure 10 Within the range of 200 to 500 m, the stress direction is chaotic and the stress state changes dramatically. Specifically, the principal stress trace deflects, transforming from the original stress direction system parallel to the slope to a horizontal-vertical stress direction system. After the horizontal burial depth exceeds 500 m, the principal stress direction differentiation gradually weakens, and the principal stress direction tends to a stable state (horizontal-vertical). This phenomenon indicates that in the Parlung Tsangpo Canyon area, the superimposed influence of topography and tectonic stress on the slope stress field does not exceed a depth of 500 m.

[0091] The depth of the superimposed influence of topography and tectonic stress on the slope stress field can also be analyzed from another perspective. The stress difference between the maximum principal stress and the minimum principal stress in the stress concentration area is large, forming a large shear stress increase zone. The existence of this stress difference makes the stress concentration area an area in the slope prone to overall shear failure. Figure 11 The figure shows the maximum shear strain increment contour when the slope experiences overall shear failure under the superposition of tectonic stress and self-weight stress. The figure shows that the maximum failure thickness during overall shear failure is approximately 400 to 500 meters. This analysis is consistent with the conclusions drawn from the perspective of principal stress directional heterogeneity.

[0092] Based on the measured ground stress data and the simulation results of the typical profile stress field, it is determined that the depth of influence of the superposition of the slope stress field and the tectonic stress field in the canyon area is 400 to 500 meters.

[0093] As the vertical depth of a mountainside tunnel increases, ground stresses increase, with the increase in maximum principal stress being particularly significant. According to the first strength theory, when the maximum principal stress exceeds the strength limit of the surrounding rock, a rockburst may occur. To assess the risk and severity of a rockburst, the rock strength-stress ratio method is widely used in the industry.

[0094] The strength-stress ratio method for predicting rockbursts is based on rock mechanics and stress field theory. It is a tunnel (hole) rockburst assessment method explicitly specified in the industry standard "Code for Design of Railway Tunnels" (TB10003-2016) and the national standard "Code for Geological Investigation of Hydropower Engineering" (GB 50287-2016). This method assesses the risk of rockburst by comparing the maximum principal stress of the surrounding rock with the uniaxial compressive strength of the rock. This theoretical method has been widely used in the field of underground engineering technology and has been verified by multiple research and engineering examples. In actual projects, the strength-stress ratio method has been successfully applied to predict rockbursts. For example, in projects such as Tianshengqiao and Erlangshan Tunnel, this method was used to successfully predict the occurrence of rockbursts, demonstrating its effectiveness in practical applications.

[0095] Generally speaking, when the strength-stress ratio exceeds a certain critical value, the rock may be damaged, thereby causing a rock burst. The judgment criteria can be found in the above two specifications.

[0096] Based on the statistical results of the compressive strength of granite in the tunnel site, the characteristic value of the saturated uniaxial compressive strength of rock is taken as 80 MPa. According to the strength-stress ratio method, when the surrounding rock strength-stress ratio Rc / max is less than 2, the risk of severe rock burst in the tunnel (hole) is very high. Therefore, the maximum principal stress limit for severe rock burst in the tunnel site is determined to be 40 MPa.

[0097] Numerical simulation shows that the maximum principal stress limit is 40 MPa. Figure 12 As shown, it can be seen that the maximum principal stress is the limit of 40Mpa ( Figure 12 The black dashed line in the middle is approximately parallel to the topographic line, but is generally gentler than the topographic line; the slope topography abrupt change zone has a vertical distance from the ground surface that is shallower than the gentle zone.

[0098] 4. Optimization of the hole position

[0099] Based on the inversion of the original ground stress field, the full-section unsupported excavation condition was used to simulate the stress redistribution and stress concentration near the tunnel body when the tunnel body was located at different positions within the safe burial depth range. Taking the 1-1 section as an example, after comprehensively considering various practical factors, three schemes were formulated for the mountain tunnel. The corresponding tunnel body positions of each scheme are as follows: Figure 13 As shown in the figure, since the tunnel size is negligible compared with the horizontal distance of different schemes, the tunnels at three locations are excavated simultaneously, and it is assumed that the stress fields do not affect each other.

[0100] Figure 14The figure shows the distribution of maximum principal stresses under unsupported excavation conditions. It can be seen that stress concentration is located at the arch waist for all three schemes. Scheme III has the most significant stress concentration, followed by Scheme II. Scheme I has significantly less stress concentration near the tunnel than the other two schemes. Furthermore, under unsupported excavation conditions, the maximum principal stress for Scheme III is approximately 85 MPa, for Scheme II is approximately 70 MPa, and for Scheme I is approximately 60 MPa.

[0101] It can be concluded that when the tunnel body is within the safe burial depth range, Scheme I has the lowest rock burst risk. Compared with Schemes II and III, Scheme I is the best.

[0102] The above examples are used to illustrate the present invention, which are only used to help understand the present invention and are not intended to limit the present invention. Those skilled in the art can make several simple deductions, modifications or substitutions based on the concept of the present invention.

Claims

1. A method for determining the mountainside depth of a mountainside tunnel in a high mountain canyon area based on rockburst risk, characterized in that: The following steps are involved: Step 1: Determine the superposition influence range of tectonic stress field and valley stress field; Step 2: Determine the boundary of strong rock burst caused by burial depth; Step 3: Determine the safe burial depth range of the mountainside tunnel by combining the tectonic stress field of steps 1 and 2, the influence range of the valley stress field, and the boundary of the strong rock burst caused by the burial depth.

2. The method for determining the mountainside depth of a mountainside tunnel based on rockburst risk in a high mountain canyon area according to claim 1, characterized in that: In step one, the influence depths of tectonic stress and valley stress field are preliminarily determined through measured geostress data in the tunnel site area; then numerical simulation is used to verify and optimize the preliminarily determined influence depths of tectonic stress and valley stress field.

3. The method for determining the mountainside depth of a mountainside tunnel based on rockburst risk in a high mountain canyon area according to claim 1, characterized in that: In step 2, rock physics and mechanics tests are carried out in the tunnel area to determine the statistical average of the saturated uniaxial compressive strength; a typical section of the tunnel area is selected for stress field simulation; and σ is converted to max =Rc / 2 is used as the criterion to determine the limit of severe rock burst caused by burial depth.

4. The method for determining the mountainside depth of a mountainside tunnel based on rockburst risk in a high mountain canyon area according to claim 2, wherein: Measured geostress data obtained using hydraulic fracturing.

5. The method for determining the mountainside depth of a mountainside tunnel based on rockburst risk in a high mountain canyon area according to claim 2, characterized in that: The verification and optimization of the impact depth of the preliminarily determined tectonic stress and valley stress field using numerical simulation includes the following steps: model selection; model construction; loading; parameter assignment; result reliability analysis; and analysis of the stress field distribution characteristics on the slope.

6. The method for determining the mountainside depth of a mountainside tunnel based on rockburst risk in a high mountain canyon area according to claim 5, characterized in that: A typical section in the tunnel area that can reflect the general characteristics of the slope stress field is selected as the numerical calculation model.

7. The method for determining the mountainside depth of a mountainside tunnel based on rockburst risk in a high mountain canyon area according to claim 5, characterized in that: The boundary conditions are set as follows: horizontal stress constraints are applied to the four boundaries of the model, and vertical displacement constraints are applied to the bottom surface.

8. The method for determining the mountainside depth of a mountainside tunnel based on rockburst risk in a high mountain canyon area according to claim 5, characterized in that: Loading methods include: self-weight stress simulation, structural action simulation, boundary load adjustment method and static equilibrium state simulation.

9. The method for determining the mountainside depth of a mountainside tunnel based on rockburst risk in a high mountain canyon area according to claim 5, characterized in that: The reliability analysis of the results is as follows: the measured ground stress data of the boreholes near the tunnel site are compared with the numerical simulation results, the error is defined, and the error at different depths is analyzed. The error range is usually between 15% and 30%, which indicates that the numerical simulation has high reliability.

10. The method for determining the mountainside depth of a mountainside tunnel based on rockburst risk in a high mountain canyon area according to claim 5, characterized in that: The stress field distribution characteristics of the slope are analyzed as follows: the change in stress direction from the surface to the inside of the slope is analyzed through the principal stress cloud map, and the area of the slope prone to overall shear failure is analyzed through the maximum shear strain increment cloud map, thereby comprehensively determining the depth of the superposition of the valley stress field and the tectonic stress field.

Images