Optimal selection method for axis of underground cavern

Abstract

The invention provides an underground cavern axis optimization method, and relates to the field of water conservancy and hydropower engineering, the initial stress condition range of surrounding rock before cavern excavation is obtained through regression and inversion calculation of a crustal stress field, and an indoor true triaxial loading test is carried out for simulation; parameters such as crack initiation stress, damage stress and peak stress in different stress states and damage evolution characteristics are obtained, so that the damage risk coefficient range of each damage mode is obtained, finite element analysis is carried out on each cavern axis scheme based on the damage risk coefficient range of each damage mode, and the damage evolution characteristic of each cavern axis scheme is obtained. According to the method, the spatial range of the damage mode of each cavern axis scheme is obtained, the corresponding cavern axis scheme is screened out according to the damage mode and the corresponding spatial range, so that the corresponding underground cavern axis is obtained, the problem that how to select the underground cavern axis is not clear in the prior art is solved, and the method is suitable for underground cavern axis selection.

Description

Technical Field

[0001] This invention relates to the field of water conservancy and hydropower engineering, and in particular to a method for optimizing the axis of large underground caverns. Background Technology

[0002] Underground engineering is developing towards "deep burial, high stress, and large scale," and the construction environment of underground caverns is becoming more complex. How to achieve efficient and safe construction of underground engineering projects in the future has attracted widespread attention from society.

[0003] The most critical issue affecting the safe and efficient construction of underground caverns is the control of the stability of the surrounding rock. This directly relates to the safety of personnel and equipment, the construction period and investment, and ultimately determines the success or failure of the project.

[0004] The selection of the axis of an underground cavern is one of the most critical technical issues in controlling the stability of the surrounding rock, especially for deeply buried underground caverns. Excavation can release enormous amounts of energy and cause large deformations of the rock mass towards the open space, leading to widespread rock bursts, spalling, and unloading relaxation—all brittle failure phenomena that severely impact the project. Different axis schemes result in significantly different mechanical responses of the surrounding rock mass to excavation and blasting; therefore, the optimal selection of the underground cavern axis is of paramount importance.

[0005] How to scientifically and rationally select the tunnel axis to improve the stability of the surrounding rock has always been a key issue in the design of water conservancy and hydropower projects. To this end, numerous universities, research institutions, and design units in China have conducted extensive research, resulting in relevant theoretical achievements and industry standards. In the current "Design Code for Hydropower Station Powerhouses," the direction of the initial maximum principal stress of the rock mass is usually used as the main basis for tunnel layout, explicitly stating that the angle between the main tunnel axis and this direction should not exceed 30°. This method, based on the initial ground stress measured in the field, emphasizes the dominant role of the initial maximum principal stress, and to a certain extent ensures the overall stability of the surrounding rock. However, in complex geological environments and under deep burial conditions, the stress redistribution phenomenon caused by excavation disturbance in the surrounding rock is significant, especially in brittle rock masses, easily inducing severe local failure. Therefore, the existing code does not adequately consider the three-dimensional evolution characteristics of the secondary stress field after excavation and its impact on failure modes, leaving room for optimization.

[0006] In recent years, some scholars and research institutions have gradually recognized the important role of the spatial three-dimensional characteristics of ground stress in cavern layout. For example, Chinese invention patent application number 201611016626.7 proposed a layout method based on the direction of the maximum horizontal principal stress, further expanding traditional design ideas. However, in future high-stress, deep underground caverns, excavation-induced brittle failure is more sensitive. Simply using the initial stress direction as the layout benchmark cannot quantitatively evaluate its failure effect, and it is difficult to comprehensively assess and compare the substantial impact of different schemes on the stability of the surrounding rock. Especially under conditions dominated by brittle failure, how to introduce more targeted evaluation indicators to quantitatively analyze and evaluate the differences in the degree of failure of different schemes, thereby achieving more effective optimization, is currently a blank area. Summary of the Invention

[0007] The technical problem solved by the present invention: The present invention provides a method for selecting the axis of an underground cavern, which solves the problem in the prior art that it is unclear how to select the axis of an underground cavern.

[0008] The technical solution adopted by this invention to solve the above-mentioned technical problems is a method for optimizing the axis of underground caverns, comprising the following steps: S1. Based on the measured points on site, perform regression and inversion calculations of the geostress field to obtain the stress condition range of the surrounding rock before the excavation of the tunnel. S2. Based on the stress conditions of the surrounding rock, conduct indoor true triaxial loading tests to obtain the initiation stress, damage stress and peak stress of the surrounding rock, and calculate the failure risk coefficient based on the initiation stress, damage stress and peak stress. S3. Compare the failure risk coefficients under different stress conditions to obtain the range of failure risk coefficients for each failure mode. S4. Based on the range of failure risk coefficients for each failure mode, finite element analysis is performed on each tunnel axis scheme to obtain the failure mode and corresponding spatial range of each tunnel axis scheme. S5. Based on the failure mode and the corresponding spatial range, select the corresponding cavern axis scheme to obtain the corresponding underground cavern axis.

[0009] Furthermore, the stress condition range of the surrounding rock is the initial stress field, including the direction and numerical range of the maximum principal stress, the direction and numerical range of the intermediate principal stress, and the direction and numerical range of the minimum principal stress.

[0010] Furthermore, in S2, the indoor true triaxial loading test includes the following steps: The indoor true triaxial loading test includes the following steps: S21. Select intact, hard rock samples without damage or defects, and prepare them into specimens of 50mm×50mm×100mm, with the surface flatness of the specimens controlled within ±0.02 mm. S22. Apply stress to the specimen from three directions, namely the direction of minimum principal stress, the direction of intermediate principal stress, and the direction of maximum principal stress, and apply the stress at a rate of 0.5 MPa / s until the value of minimum principal stress is reached; S23. Keep the stress value in the direction of minimum principal stress unchanged, and continue to apply stress in the direction of intermediate principal stress and the direction of maximum principal stress until the stress is applied to the value of intermediate principal stress. S24. Keep the stress value in the middle principal stress direction unchanged, and continue to apply stress in the direction of maximum principal stress until the specimen fails tensilely. Record the initiation stress, damage stress and peak stress, and calculate the failure risk coefficient based on the initiation stress, damage stress and peak stress. S25. Change the values ​​of the minimum principal stress and the intermediate principal stress, and repeat S21 to S24 to obtain the failure risk coefficient of the surrounding rock under different stress conditions.

[0011] Furthermore, the failure modes include shear failure, tensile-shear combined failure, and tensile failure.

[0012] Furthermore, in S2, the formula for calculating the damage risk coefficient is as follows: ,in, Indicates the risk factor of damage. Indicates the crack initiation stress. Indicates damage stress, This indicates the peak stress.

[0013] Furthermore, in S3, the failure risk coefficient ranges for each failure mode include: the failure risk coefficient range for shear failure is A < 0.15; the failure risk coefficient range for tensile-shear combined failure is 0.15 ≤ A ≤ 0.5; and the failure risk coefficient range for tensile failure is A > 0.5.

[0014] Furthermore, in S4, FLAC3D software was used to perform finite element analysis on the axis schemes of each cavern. During the simulated excavation process, the failure risk coefficient was updated in real time to obtain the failure mode and corresponding spatial range of each cavern axis scheme.

[0015] Furthermore, in S5, based on the failure mode and the corresponding spatial range, the corresponding cavern axis scheme is selected to obtain the corresponding underground cavern axis, including: selecting the cavern axis scheme with the smallest spatial range corresponding to tensile failure as the underground cavern axis.

[0016] The beneficial effects of this invention are as follows: This invention provides a method for optimizing the axis of an underground cavern. By regressing and inverting the geostress field, the initial stress condition range of the surrounding rock before cavern excavation is obtained. A true triaxial loading test is conducted indoors to simulate the stress, obtaining parameters such as initiation stress, damage stress, and peak stress under different stress states, as well as the failure evolution characteristics. This yields the range of failure risk coefficients for each failure mode. Based on the range of failure risk coefficients for each failure mode, finite element analysis is performed on each cavern axis scheme to obtain the spatial range of failure modes for each cavern axis scheme. Based on the failure mode and the corresponding spatial range, the appropriate cavern axis scheme is selected, thus obtaining the corresponding underground cavern axis. This solves the problem in the prior art of not knowing how to select the axis of an underground cavern. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating a method for optimizing the axis of an underground cavern provided by the present invention. Detailed Implementation

[0018] This invention addresses the challenge of selecting a better axis scheme for existing underground caverns by providing a method for optimizing the axis of underground caverns, such as... Figure 1 As shown, it includes the following steps: S1. Based on the measured points on site, perform regression and inversion calculations of the geostress field to obtain the stress condition range of the surrounding rock before the excavation of the tunnel.

[0019] Specifically, the stress condition range of the surrounding rock is the initial stress field, including the direction and numerical range of the maximum principal stress, the direction and numerical range of the intermediate principal stress, and the direction and numerical range of the minimum principal stress.

[0020] S2. Based on the stress conditions of the surrounding rock, conduct indoor true triaxial loading tests to obtain the initiation stress, damage stress, and peak stress of the surrounding rock, and calculate the failure risk coefficient based on the initiation stress, damage stress, and peak stress.

[0021] Specifically, the formula for calculating the damage risk factor is as follows: ,in, Indicates the risk factor of damage. Indicates the crack initiation stress. Indicates damage stress, Indicates peak stress. This indicates the energy storage capacity during the resilience phase. This indicates the energy storage capacity as it expands from microscopic defects to macroscopic degradation.

[0022] The indoor true triaxial loading test includes the following steps: S21. Select intact, hard rock samples without damage or defects, and prepare them into specimens of 50mm×50mm×100mm, with the surface flatness of the specimens controlled within ±0.02 mm.

[0023] S22. Apply stress to the specimen from three directions, namely the direction of minimum principal stress, the direction of intermediate principal stress, and the direction of maximum principal stress, and apply the stress at a rate of 0.5 MPa / s until the value of minimum principal stress is reached.

[0024] S23. Keep the stress value in the direction of minimum principal stress unchanged, and continue to apply stress in the direction of intermediate principal stress and the direction of maximum principal stress until the stress is applied to the value of intermediate principal stress.

[0025] S24. Keep the stress value in the middle principal stress direction unchanged, and continue to apply stress in the direction of maximum principal stress until the specimen fails tensilely. Record the initiation stress, damage stress and peak stress, and calculate the failure risk coefficient based on the initiation stress, damage stress and peak stress.

[0026] Specifically, the initiation stress is the critical stress value in the elastic stress stage of the specimen, the damage stress is the critical value for the expansion of micro-defects inside the specimen to macro-deterioration, and the peak stress is the ultimate bearing capacity of the specimen.

[0027] S25. Change the values ​​of the minimum principal stress and the intermediate principal stress, and repeat S21 to S24 to obtain the failure risk coefficient of the surrounding rock under different stress conditions.

[0028] S3. Compare the failure risk coefficients under different stress conditions to obtain the range of failure risk coefficients for each failure mode.

[0029] Specifically, the failure risk coefficients under different stress conditions are normalized for easier comparison. The failure modes include shear failure, tensile-shear failure, and tensile failure. Tensile failure is also known as brittle failure. When tensile failure occurs, the indoor true triaxial loading test ends.

[0030] The minimum principal stress of a certain surrounding rock is 5 MPa. Through indoor true triaxial loading tests, the failure risk coefficient range of each failure mode was obtained by comparing different intermediate principal stresses. Based on the failure modes, it can be seen that the failure risk coefficient range of shear failure is A < 0.15; the failure risk coefficient range of tensile-shear combined failure is 0.15 ≤ A ≤ 0.5; and the failure risk coefficient range of tensile failure is A > 0.5.

[0031] S4. Based on the aforementioned failure risk coefficient threshold, perform finite element analysis on each cavern axis scheme to obtain the spatial range of failure modes for each cavern axis scheme.

[0032] Specifically, FLAC3D software was used to perform finite element analysis on the axis schemes of each cavern. During the simulated excavation process, the failure risk coefficient was updated in real time to obtain the failure mode and corresponding spatial range of each cavern axis scheme.

[0033] Specifically, it includes: S31: Establish a three-dimensional finite element model: Based on the FLAC3D software platform, construct a three-dimensional numerical model of the underground cavern that conforms to the actual engineering situation. The model should include the division of the surrounding rock area, the spatial layout of the cavern, boundary constraints, and mechanical parameter settings. The surrounding rock is given strength parameters and constitutive models consistent with true triaxial tests, and the cavern excavation is simulated using the static unloading method.

[0034] S32: Setting up multiple cavern axis schemes and stress boundary conditions: For different cavern axis layout schemes to be compared, corresponding model versions are established, and initial triaxial geostress conditions are applied based on field measurements and inversion results. The initial stress includes the numerical range and spatial direction of the maximum principal stress, intermediate principal stress, and minimum principal stress to ensure that the simulation conditions are consistent with the actual measurement environment.

[0035] S33: Introducing the calculation program corresponding to the formula for the failure risk coefficient: The formula for calculating the failure risk coefficient is embedded into the numerical model through the FISH script. During the simulation, the principal stress information of each calculation unit is extracted in real time, its failure risk coefficient is calculated, and it is stored in the zone.extra() variable; combined with the failure risk coefficient range of each failure mode, the failure mode of each unit is determined.

[0036] S34: Simulate tunnel excavation and extract failure results: Simulate the tunnel excavation process according to each axis scheme, and record the failure mode and corresponding spatial range. Classify and statistically analyze the failure modes under different schemes for scheme comparison.

[0037] S5. Based on the failure mode and the corresponding spatial range, select the corresponding cavern axis scheme to obtain the corresponding underground cavern axis.

[0038] Specifically, the cavern axis scheme with the smallest spatial range corresponding to tensile failure is selected to obtain the corresponding underground cavern axis. Alternatively, the spatial range corresponding to tensile failure is taken as the main factor, and the spatial range corresponding to tensile-shear combined failure is taken as the secondary factor. A comprehensive consideration is made to select the corresponding cavern axis scheme to obtain the corresponding underground cavern axis.

[0039] Example: Taking a 480m vertically buried underground cavern as an example, the stress conditions of the surrounding rock before the excavation of the underground cavern are as follows: initial maximum principal stress The numerical range of the principal stress is 17.5 MPa to 30 MPa, with a horizontal projection azimuth of N80°W. The numerical range of the intermediate principal stress is 12 MPa to 20 MPa, with a horizontal projection azimuth of N18°W. The numerical range of the minimum principal stress is 7.5 MPa to 15 MPa, with a horizontal projection azimuth of N85°E. Scheme 1 for the cavern axis is N50°W, which is consistent with the initial maximum principal stress. With an included angle of 30°, the second option for the cavern axis is: N35°W, with an included angle of 45° with the initial stress field.

[0040] Through indoor true triaxial loading tests and comparisons, it was found that when the failure risk coefficient is greater than 0.5, there is a risk of brittle failure. Finite element analysis showed that the volume of the brittle failure zone in Scheme 1 is about 52,000 cubic meters, while the volume of the brittle failure zone in Scheme 2 is about 41,000 cubic meters. Therefore, Scheme 2 is the more favorable scheme, and the corresponding underground cavern axis of Scheme 2 was obtained.

Claims

1. A method for optimizing the axis of an underground cavern, characterized in that, Includes the following steps: S1. Based on the measured points on site, perform regression and inversion calculations of the geostress field to obtain the stress condition range of the surrounding rock before the excavation of the tunnel. S2. Based on the stress conditions of the surrounding rock, conduct indoor true triaxial loading tests to obtain the initiation stress, damage stress and peak stress of the surrounding rock, and calculate the failure risk coefficient based on the initiation stress, damage stress and peak stress. S3. Compare the failure risk coefficients under different stress conditions to obtain the range of failure risk coefficients for each failure mode. S4. Based on the range of failure risk coefficients for each failure mode, finite element analysis is performed on each tunnel axis scheme to obtain the failure mode and corresponding spatial range of each tunnel axis scheme. S5. Based on the failure mode and the corresponding spatial range, select the corresponding cavern axis scheme to obtain the corresponding underground cavern axis.

2. The method for optimizing the axis of an underground cavern according to claim 1, characterized in that, The stress conditions of the surrounding rock are defined as the initial stress field, which includes the direction and numerical range of the maximum principal stress, the direction and numerical range of the intermediate principal stress, and the direction and numerical range of the minimum principal stress.

3. The method for optimizing the axis of an underground cavern according to claim 2, characterized in that, In S2, the indoor true triaxial loading test includes the following steps: S21. Select intact, hard rock samples without damage or defects, and prepare them into specimens of 50mm×50mm×100mm, with the surface flatness of the specimens controlled within ±0.02 mm. S22. Apply stress to the specimen from three directions, namely the direction of minimum principal stress, the direction of intermediate principal stress, and the direction of maximum principal stress, and apply the stress at a rate of 0.5 MPa / s until the value of minimum principal stress is reached; S23. Keep the stress value in the direction of minimum principal stress unchanged, and continue to apply stress in the direction of intermediate principal stress and the direction of maximum principal stress until the stress is applied to the value of intermediate principal stress. S24. Keep the stress value in the middle principal stress direction unchanged, and continue to apply stress in the direction of maximum principal stress until the specimen fails tensilely. Record the initiation stress, damage stress and peak stress, and calculate the failure risk coefficient based on the initiation stress, damage stress and peak stress. S25. Change the values ​​of the minimum principal stress and the intermediate principal stress, and repeat S21 to S24 to obtain the failure risk coefficient of the surrounding rock under different stress conditions.

4. The method for optimizing the axis of an underground cavern according to claim 3, characterized in that, The failure modes include shear failure, tensile-shear combined failure, and tensile failure.

5. The method for optimizing the axis of an underground cavern according to claim 4, characterized in that, In S2, the formula for calculating the damage risk coefficient is: ,in, Indicates the risk factor of damage. Indicates the crack initiation stress. Indicates damage stress, This indicates the peak stress.

6. The method for optimizing the axis of an underground cavern according to claim 5, characterized in that, In S3, the failure risk coefficient ranges for each failure mode are as follows: the failure risk coefficient range for shear failure is A < 0.15; the failure risk coefficient range for tensile-shear combined failure is 0.15 ≤ A ≤ 0.5; and the failure risk coefficient range for tensile failure is A > 0.

5.

7. The method for optimizing the axis of an underground cavern according to claim 6, characterized in that, In S4, FLAC3D software was used to perform finite element analysis on the axis schemes of each cavern. During the simulated excavation process, the failure risk coefficient was updated in real time to obtain the failure mode and corresponding spatial range of each cavern axis scheme.

8. The method for optimizing the axis of an underground cavern according to claim 7, characterized in that, In S5, based on the failure mode and the corresponding spatial range, the corresponding cavern axis scheme is selected to obtain the corresponding underground cavern axis, including: selecting the cavern axis scheme with the smallest spatial range corresponding to tensile failure, thereby obtaining the corresponding underground cavern axis.

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