A numerical simulation method for evaluating stability of narrow rock pillar in underground cavern

Abstract

The underground cavern narrow rock pillar stability evaluation numerical simulation method disclosed by the application comprises the following steps: for a narrow rock pillar with a width-height ratio of 1, RS2 numerical simulation software is used to establish an underground cavern numerical model; ground stress is applied to the boundary of the numerical model; the underground cavern excavation process is completed in the numerical model, the average value of the new safety factor of the narrow rock pillar defined from the shear stress angle and reaching a preset target value in the numerical model is obtained, and the average stress value of the narrow rock pillar is obtained; for different narrow rock pillars with a width-height ratio less than 1, underground cavern numerical models are respectively established and the average stress value of the narrow rock pillar is obtained; a narrow rock pillar new safety factor curve is drawn; and the stability of the narrow rock pillar of the underground cavern is evaluated. The method combines the new safety factor defined from the shear stress angle with the numerical simulation method, can accurately evaluate the stability of the narrow rock pillar of the underground cavern, helps to optimize the thickness design of the narrow rock pillar, and has guiding application value for the reasonable arrangement and design of the underground cavern group.

Description

Technical Field

[0001] This invention relates to the field of stability evaluation of rock columns in underground caverns, and specifically to a numerical simulation method for stability evaluation of narrow rock columns in underground caverns. Background Technology

[0002] In underground engineering construction, parallel arrangements of tunnels or underground chambers are frequently encountered. The rock mass between these chambers is called a rock column, and its stability needs to be properly assessed before excavation to avoid affecting the normal excavation and operation of the chamber. Given a fixed chamber height, the thickness of the rock column affects the stability of the chamber itself and the surrounding rock. If the rock mass is thick, meaning the chambers are far apart, construction costs are higher, and the normal function of the chambers may be affected. Conversely, if the rock column is thin, meaning the chambers are close together, construction of adjacent chambers may interact, which is detrimental to the stability and safety of both the rock column and the chamber. Therefore, selecting an appropriate rock column thickness is crucial for the stability and safety of the rock column and adjacent chambers. Narrow rock columns are generally defined as those with a width-to-height ratio between two chambers not exceeding 1, and their stability evaluation has always been a key focus and challenge.

[0003] Currently, the stability evaluation of narrow rock columns mainly adopts empirical methods. First, according to the traditional definition of the safety factor, the ratio of the rock column's strength to its stress is defined as the safety factor. Then, this safety factor is compared with a safety factor determined based on previous engineering cases. If the former is greater than the latter, the rock column is judged to be in a stable state; if the former is not greater than the latter, the rock column is judged to be in an unstable state, prone to failure and instability. However, because rock columns may have natural joints or internal cracks due to tunnel blasting, accurately estimating the rock column strength using traditional safety factors is difficult. Moreover, considering that specific engineering cases may differ significantly from previous engineering experience (e.g., different geological conditions, rock mass mechanical properties, in-situ stress, etc.), the safety factor determined based on previous engineering experience may not be applicable to specific engineering cases. Therefore, specific engineering problems require specific analysis, and the stability of the rock column should be analyzed specifically according to the characteristics of the engineering case. Furthermore, such as... Figure 1 As shown, the traditional safety factor is the ratio of rock column strength to stress defined from the perspective of normal stress. However, narrow rock columns often experience shear failure under uniaxial compression conditions, which is closely related to shear stress. Figure 1 As shown, the new safety factor, defined from the perspective of shear stress as the ratio of rock column strength to stress, better aligns with the failure mechanism of narrow rock columns and can more accurately describe their stability and safety. Therefore, this invention proposes a numerical simulation method for evaluating the stability of narrow rock columns in underground caverns. By analyzing engineering problems through a customized approach, it combines the new safety factor defined from the perspective of shear stress with numerical simulation methods to plot the new safety factor curve for narrow rock columns in specific engineering projects, thus serving the stability evaluation of narrow rock columns. This method is innovative. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a numerical simulation method for evaluating the stability of narrow rock columns in underground caverns, which addresses the shortcomings of existing technologies. By combining a new safety factor defined from the perspective of shear stress with the numerical simulation method, the stability of narrow rock columns in underground caverns can be accurately evaluated, which helps to optimize the design of narrow rock column thickness and has guiding application value for the rational layout and design of underground cavern groups.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a numerical simulation method for evaluating the stability of narrow rock columns in underground caverns, comprising the following steps;

[0006] S1. For a narrow rock column with a width-to-height ratio of 1, an underground cavern numerical model is established using RS2 numerical simulation software;

[0007] S2. Obtain the rock mass specific gravity, lateral pressure coefficient, and intact rock strength of the area where the underground cavern is located through geological exploration. Apply in-situ stress to the boundary of the numerical model based on the rock mass specific gravity and lateral pressure coefficient.

[0008] S3. Complete the underground cavern excavation process in the numerical model, conduct elastoplastic stress analysis and calculation, and obtain the average value of the new safety factor of the narrow rock column defined from the perspective of shear stress in the numerical model. If the average value of the new safety factor of the narrow rock column reaches the preset target value, obtain the average stress value of the narrow rock column; if the average value of the new safety factor of the narrow rock column does not reach the preset target value, keep the lateral pressure coefficient unchanged in the numerical model, adjust the geostress value, so that the average value of the new safety factor of the narrow rock column reaches the preset target value, and obtain the average stress value of the narrow rock column.

[0009] S4. For different narrow rock columns with a width-to-height ratio of less than 1, repeat the above steps S1-S3 respectively to establish the numerical model of the underground cavern and obtain the average stress value of the narrow rock column.

[0010] S5. Based on the average stress value of the narrow rock column obtained under different width-to-height ratios, and combined with the intact rock strength obtained in step S2, plot the new safety factor curve of the narrow rock column. The horizontal axis is the width-to-height ratio of the narrow rock column, and the vertical axis is the ratio of the average stress value of the narrow rock column to the corresponding intact rock strength.

[0011] S6. Obtain the average stress value of the narrow rock column after excavation of the underground cavern to be evaluated. Combined with the intact rock strength of the underground cavern to be evaluated, calculate the ratio of the average stress value of the narrow rock column after excavation to its intact rock strength. Combined with the width-to-height ratio of the narrow rock column of the underground cavern to be evaluated, determine the data point and compare it with the plotted new safety factor curve of the narrow rock column to evaluate the stability of the narrow rock column of the underground cavern. The evaluation criteria are: if the data point is below the new safety factor curve of the narrow rock column, the narrow rock column is evaluated as stable; otherwise, the narrow rock column is evaluated as unstable.

[0012] Preferably, in step S1, the boundary conditions of the underground cavern numerical model are set to fixed displacement boundaries around the perimeter, so as to adjust the in-situ stress values ​​and make the average value of the new safety factor of the narrow rock column reach the target value. In this case, the in-situ stress is directly applied to the boundary of the numerical model, so the numerical model does not need to consider the actual burial depth of the cavern, and is therefore suitable for both shallow and deep caverns.

[0013] Preferably, in step S3, the average value of the new safety factor for the narrow rock column is the average value of the new safety factors at several points located at half the height of the narrow rock column, and the average stress value of the narrow rock column is the average value of the stress values ​​at these several points. Because the excavation of the tunnel causes a redistribution of stress in the narrow rock column, the stress distribution is uneven from the surface to the center of the narrow rock column at half its height. Therefore, we use the average value of the new safety factors at several points within the width range of the narrow rock column of the same height as the average value of the new safety factor for the narrow rock column to avoid overestimating or underestimating the stability of the rock column by using the new safety factor value at a single point. Similarly, after the average value of the new safety factor for the narrow rock column reaches the preset target value, the stress values ​​at several points corresponding to the narrow rock column are obtained, and their average value is taken as the average stress value of the narrow rock column.

[0014] As a preferred option, in step S3, the preset target value of the new safety factor for the narrow rock column is determined based on known engineering design specifications and in combination with specific engineering geological conditions.

[0015] Preferably, in step S3, the preset target value for the new safety factor of the narrow rock column is 1.3 to 1.5.

[0016] Preferably, in step S1, the intact rock strength obtained is the uniaxial compressive strength of the rock. The method for obtaining the uniaxial compressive strength of the rock is as follows: after sampling the rock mass in the area where the underground cavern is located, a uniaxial compression test is conducted according to the standard ASTM D7012-23. To reduce errors, multiple sets of uniaxial compression tests can be conducted, and the average value of the uniaxial compressive strength of the rock is taken as the intact rock strength.

[0017] Compared with existing technologies, this invention has the following advantages: Unlike the traditional empirical method that uses a safety factor defined from the perspective of normal stress, this invention combines a new safety factor defined from the perspective of shear stress with numerical simulation methods. For specific engineering cases, numerical simulation is used to plot a new safety factor curve for narrow rock columns applicable to the specific project, used to evaluate the stability of the rock column. This invention can accurately evaluate the stability of narrow rock columns in underground caverns, helping to optimize the design of narrow rock column thickness, and has guiding application value for the rational layout and design of underground cavern groups. Attached Figure Description

[0018] Figure 1 A comparative analysis of the new safety factor and the traditional safety factor;

[0019] Figure 2 This is a flowchart of the numerical simulation method for evaluating the stability of narrow rock columns in underground caverns according to the present invention;

[0020] Figure 3 This is a schematic diagram of the numerical model of the underground cavern established in the embodiment;

[0021] Figure 4 The new safety factor curve for the narrow rock column is plotted in the example. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. These embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0023] The numerical simulation method for evaluating the stability of narrow rock columns in underground caverns, as described in the embodiment, is as follows: Figure 2 As shown, it includes the following steps;

[0024] S1. For a narrow rock column with an aspect ratio of 1, an underground cavern numerical model is established using RS2 numerical simulation software (i.e., RS2 finite element numerical simulation software from Rocscience for geotechnical engineering analysis and design). The boundary conditions of this underground cavern numerical model are set to fixed displacement boundaries on all four sides to facilitate adjustment of the in-situ stress values, ensuring that the average value of the new safety factor for the narrow rock column reaches the target value. In this case, the in-situ stress is directly applied to the boundary of the numerical model, thus the numerical model does not need to consider the actual burial depth of the cavern, making it suitable for both shallow and deep caverns. A schematic diagram of the established underground cavern numerical model is shown below. Figure 3 As shown, the cavern is 20 meters deep, 15 meters wide, and 8 meters high (5 meters for the vertical sidewalls). The rock pillar is 8 meters wide, therefore the width-to-height ratio of the rock pillar is 1. The parameters of this numerical model are as follows: the specific gravity of the rock mass is 24 kN / m³. 3 The uniaxial compressive strength of the rock is 25 MPa. Using the generalized Hawke-Brown failure criterion and ideal elastoplastic stress analysis, the Hawke-Brown parameter m... bThe parameters are: σ = 0, s = 0.02, a = 0.502, deformation modulus = 2 GPa, Poisson's ratio = 0.25, and lateral compression coefficient Ko = 1.5. The uniaxial compressive strength of the rock was obtained by sampling the rock mass in the area of ​​the underground cavern and conducting uniaxial compression tests according to standard ASTM D7012-23. To reduce errors, multiple sets of uniaxial compression tests were conducted, and the average uniaxial compressive strength was taken as the intact rock strength. In this embodiment, a total of 24 cavern rock samples were obtained, divided into 4 groups of 6 samples each, and uniaxial compression tests were conducted. The average uniaxial compressive strength of the rock was 25 MPa, which is the intact rock strength.

[0025] S2. Apply geostress to the boundary of the numerical model based on the rock mass specific gravity and lateral pressure coefficient.

[0026] S3. Complete the underground cavern excavation process in the numerical model, conduct elastoplastic stress analysis and calculation, retrieve the new safety factor cloud map in the numerical model, and obtain the average value of the new safety factor of the narrow rock column defined from the perspective of shear stress in the numerical model. If the average value of the new safety factor of the narrow rock column reaches the preset target value, obtain the average stress value of the narrow rock column; if the average value of the new safety factor of the narrow rock column does not reach the preset target value, keep the lateral pressure coefficient unchanged in the numerical model, adjust the in-situ stress value, so that the average value of the new safety factor of the narrow rock column reaches the preset target value, and obtain the average stress value of the narrow rock column. The average value of the new safety factor of the narrow rock column is the average value of the new safety factor at 5 points evenly distributed within the width of the rock column at half the height of the narrow rock column, and the average stress value of the narrow rock column is the average value of the stress values ​​at these 5 points. The preset target value of the new safety factor of the narrow rock column is determined according to known engineering design specifications and in combination with specific engineering geological conditions. In this embodiment, the preset target value of the new safety factor of the narrow rock column is 1.5.

[0027] S4. For different narrow rock columns with an aspect ratio of less than 1 (0.75, 0.5 and 0.25 in this example), repeat steps S1-S3 above to establish a numerical model of the underground cavern and obtain the average stress value of the narrow rock column.

[0028] S5. Based on the average stress values ​​of the narrow rock columns obtained under the four narrow rock column aspect ratio conditions, and combined with the intact rock strength obtained in step S2, four different data points are determined. These four data points are then connected to plot the results. Figure 4 The new safety factor curve for the narrow rock column shown is FS' = 1.5, where the horizontal axis represents the width-to-height ratio of the narrow rock column, and the vertical axis represents the ratio of the average stress value of the narrow rock column to the corresponding strength of intact rock. Similarly, when the target value of the new safety factor for the narrow rock column is set to 1.0, the corresponding new safety factor curve for the narrow rock column FS' = 1.0 can be plotted.

[0029] S6. Obtain the average stress value of the narrow rock column after excavation of the underground cavern to be evaluated, which is 2 MPa. Combined with the intact rock strength of the underground cavern to be evaluated, which is 25 MPa, calculate the ratio of the average stress value of the narrow rock column after excavation to its intact rock strength, which is 0.08. Considering the width-to-height ratio of the narrow rock column in the underground cavern to be evaluated, which is 0.8 (6.4 / 8), determine the data point as (0.8, 0.08) based on the calculation results. Compare this with the plotted new safety factor curve for the narrow rock column. Figure 4 As shown, the data point (0.8, 0.08) represented by the pentagram is located below the curve FS' = 1.5, indicating that the new safety factor of the narrow rock column in the underground cavern is greater than 1.5. Therefore, the narrow rock column with a width-to-height ratio of 0.8 in the underground cavern is stable after excavation.

Claims

1. A numerical simulation method for evaluating the stability of narrow rock columns in underground caverns, characterized in that, Includes the following steps: S1. For a narrow rock column with a width-to-height ratio of 1, an underground cavern numerical model is established using RS2 numerical simulation software; S2. Obtain the rock mass specific gravity, lateral pressure coefficient, and intact rock strength of the area where the underground cavern is located through geological exploration. Apply in-situ stress to the boundary of the numerical model based on the rock mass specific gravity and lateral pressure coefficient. S3. Complete the underground cavern excavation process in the numerical model, conduct elastoplastic stress analysis and calculation, and obtain the average value of the new safety factor of the narrow rock column defined from the perspective of shear stress in the numerical model. If the average value of the new safety factor of the narrow rock column reaches the preset target value, obtain the average stress value of the narrow rock column; if the average value of the new safety factor of the narrow rock column does not reach the preset target value, keep the lateral pressure coefficient unchanged in the numerical model, adjust the geostress value, so that the average value of the new safety factor of the narrow rock column reaches the preset target value, and obtain the average stress value of the narrow rock column. S4. For different narrow rock columns with a width-to-height ratio of less than 1, repeat the above steps S1-S3 respectively to establish the numerical model of the underground cavern and obtain the average stress value of the narrow rock column. S5. Based on the average stress value of the narrow rock column obtained under different width-to-height ratios, and combined with the intact rock strength obtained in step S2, plot the new safety factor curve of the narrow rock column. The horizontal axis is the width-to-height ratio of the narrow rock column, and the vertical axis is the ratio of the average stress value of the narrow rock column to the corresponding intact rock strength. S6. Obtain the average stress value of the narrow rock column after excavation of the underground cavern to be evaluated. Combined with the intact rock strength of the underground cavern to be evaluated, calculate the ratio of the average stress value of the narrow rock column after excavation to its intact rock strength. Combined with the width-to-height ratio of the narrow rock column of the underground cavern to be evaluated, determine the data point and compare it with the plotted new safety factor curve of the narrow rock column to evaluate the stability of the narrow rock column of the underground cavern. The evaluation criteria are: if the data point is below the new safety factor curve of the narrow rock column, the narrow rock column is evaluated as stable; otherwise, the narrow rock column is evaluated as unstable.

2. The numerical simulation method for evaluating the stability of narrow rock columns in underground caverns according to claim 1, characterized in that, In step S1, the boundary conditions of the underground cavern numerical model are set to fixed displacement boundaries around the perimeter.

3. The numerical simulation method for evaluating the stability of narrow rock columns in underground caverns according to claim 1, characterized in that, In step S3, the average value of the new safety factor of the narrow rock column is the average value of the new safety factor at several points at half the height of the narrow rock column, and the average stress value of the narrow rock column is the average value of the stress values ​​at those several points.

4. The numerical simulation method for evaluating the stability of narrow rock columns in underground caverns according to claim 1, characterized in that, In step S3, the preset target value of the new safety factor for the narrow rock column is determined based on known engineering design specifications and in combination with specific engineering geological conditions.

5. The numerical simulation method for evaluating the stability of narrow rock columns in underground caverns according to claim 1, characterized in that, In step S3, the preset target value for the new safety factor of the narrow rock column is 1.3 to 1.

5.

6. The numerical simulation method for evaluating the stability of narrow rock columns in underground caverns according to claim 1, characterized in that, In step S1, the obtained complete rock strength is the uniaxial compressive strength of the rock. The method for obtaining the uniaxial compressive strength of the rock is as follows: after sampling the rock mass in the area where the underground cavern is located, a uniaxial compression test of the rock is carried out according to the standard ASTM D7012-23.

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