Method for determining energy consumption limit value of surrounding rock of high-ground-stress deeply-buried soft rock tunnel

Abstract

The invention provides a method for determining the energy consumption limit value of surrounding rock of a high-ground-stress deeply-buried soft rock tunnel, and belongs to the technical field of tunnel engineering. Comprising the following steps: testing ground stress of a tunnel site area to obtain components of the ground stress in a large principal stress direction, a middle principal stress direction and a small principal stress direction; manufacturing a rock test piece; carrying out a true triaxial loading and unloading test on the test piece to obtain stress-strain of the test piece in a large principal stress direction, a middle principal stress direction and a small principal stress direction; calculating the elastic strain energy and the plastic dissipation energy of the test piece based on the elastic modulus and the Poisson ratio of the test piece; calculating the energy dissipation rate of the test piece; and taking the corresponding plastic dissipation energy when the energy dissipation rate of the test piece reaches the maximum value as the energy dissipation limit value of the surrounding rock. According to the method, the energy consumption limit value is used as the bearing capacity evaluation index of the surrounding rock of the high-crustal-stress deeply-buried soft rock tunnel, and the nature of instability failure of the surrounding rock of the high-crustal-stress deeply-buried soft rock tunnel is reflected.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel engineering and relates to a method for determining the energy dissipation limit value of surrounding rock in a deep-buried soft rock tunnel under high in-situ stress. Background Technique

[0002] In the construction of railway tunnel projects, as the tunnel burial depth gradually increases, deep-buried soft rock tunnels under high in-situ stress often appear. The squeezing large deformation caused by high in-situ stress poses great challenges to the construction and operation safety of tunnels. The evaluation index of the bearing capacity of surrounding rock is the basis for judging the stability of high in-situ stress tunnels and guiding the design of support structures. From the perspective of energy, the bearing capacity of surrounding rock and the stability of tunnels can be effectively evaluated. The energy storage limit is the most commonly used energy index for evaluating the bearing capacity of rocks at present, which refers to the maximum elastic strain energy that can be accumulated before the peak of the rock, and is widely used in the evaluation of the stability of surrounding rock in deep hard rock tunnels and the prediction of rockburst disasters. In a high in-situ stress environment, when the elastic strain energy absorbed by hard rocks exceeds the energy storage limit, the rocks will undergo severe brittle failure, and the strength of the rocks after the peak will decrease sharply. The essence of rockburst disasters is the result of the instantaneous release of the elastic strain energy accumulated in hard surrounding rock exceeding the energy storage limit.

[0003] For deep soft rocks, the energy storage limit of the rocks is very limited, and the energy input into the rocks in a high in-situ stress environment is easily exceeded the limit value. However, the post-peak strain softening behavior of soft rocks under high stress is significant, and the rocks still have a certain bearing capacity after the peak. Existing theoretical research and field tests show that the surrounding rock of the vast majority of deep-buried soft rock tunnels is in the post-peak plastic service state. It can be seen that using the energy storage limit as the bearing capacity evaluation index is inapplicable and will underestimate the bearing capacity of the surrounding rock in deep-buried soft rock tunnels under high in-situ stress. In a high in-situ stress environment, after the tunnel is excavated, the strain energy is input from a distance of the surrounding rock in the form of radial stress doing work. Part of the energy input into the surrounding rock is converted into elastic strain energy and stored inside the surrounding rock, and the other part is converted into plastic dissipation energy, which causes plastic deformation and damage degradation of the surrounding rock. The deformation and failure process of deep soft surrounding rock is driven by plastic dissipation energy. Therefore, the plastic dissipation energy of the surrounding rock caused by tunnel excavation needs to be controlled within a limit value. Summary of the Invention

[0004] Based on the deficiencies in the prior art, the present application proposes a method for determining the energy dissipation limit value of the surrounding rock of a deep-buried soft rock tunnel under high in-situ stress, taking the energy dissipation limit as the evaluation index of the bearing capacity of the surrounding rock of the deep-buried soft rock tunnel under high in-situ stress, so as to provide a new solution idea for the design and construction problems of deep-buried soft rock tunnels under high in-situ stress.

[0005] The present invention provides a method for determining the energy dissipation limit value of the surrounding rock of a deep-buried soft rock tunnel under high in-situ stress, including the following steps: Step 1: Test the in-situ stress in the tunnel site area to obtain the components of the in-situ stress in the directions of the major principal stress, intermediate principal stress, and minor principal stress respectively; Make specimens from the rock mass at the engineering site in the tunnel site area; Step 2: Conduct a true triaxial loading and unloading test on the specimens to simulate the true stress path of the surrounding rock after the excavation of the deep-buried tunnel, so as to obtain the stress-strain of the specimens in the directions of the major principal stress, intermediate principal stress, and minor principal stress respectively; Step 3: Calculate the elastic strain energy of the specimens based on the stress-strain of the specimens in the directions of the major principal stress, intermediate principal stress, and minor principal stress, as well as the elastic modulus and Poisson's ratio of the specimens and the plastic dissipation energy ; Step 4: Calculate the energy dissipation rate of the specimens based on the elastic strain energy and the plastic dissipation energy of the specimens; ; Step 5: Take the plastic dissipation energy corresponding to the maximum value of the energy dissipation rate of the specimens as the energy dissipation limit value of the surrounding rock .

[0006] Furthermore, the specific process of obtaining the components of the specimens in the directions of the major principal stress, intermediate principal stress, and minor principal stress respectively is as follows: Record the component of the in-situ stress in the direction of the major principal stress as the major principal stress , record the component of the in-situ stress in the direction of the intermediate principal stress as the intermediate principal stress and record the component of the in-situ stress in the direction of the minor principal stress as the minor principal stress ; According to the in-situ stress test results, set the initial values to be applied to the stresses on the six faces of the specimens respectively to simulate the stress state of the surrounding rock before the tunnel excavation; among them, set the initial values of the upper and lower axial stress acting surfaces of the specimens as the major principal stress , set the initial values of the lateral stresses on two mutually parallel side faces of the specimens as the intermediate principal stress , and set the initial values of the lateral stresses on the other two mutually parallel side faces of the specimens as the minor principal stress ; Keep the intermediate principal stress unchanged, continuously increase the axial major principal stress at a constant loading rate by means of displacement loading, continuously unload the minor principal stress at a constant unloading rate by means of stress unloading, and when the minor principal stress When the unloading reaches zero, the test ends, and the stress-strain in the directions of the major principal stress , the intermediate principal stress , and the minor principal stress of the specimen at different time periods during the true triaxial loading and unloading process are obtained.

[0007] Furthermore, the different time periods during the true triaxial loading and unloading include the elastic deformation stage, the plastic yield stage, the post-peak strain softening stage, and the residual stage.

[0008] Furthermore, the expression of the elastic strain energy of the specimen is as follows: ; ; where is the elastic modulus of the specimen, is the Poisson's ratio of the specimen, is the elastic strain in the direction of the major principal stress, is the elastic strain in the direction of the intermediate principal stress, is the elastic strain in the direction of the minor principal stress.

[0009] Furthermore, the expression of the plastic dissipation energy of the rock is as follows: ; ; where is the total energy input into the rock, and its value is equal to the integral of the principal stress in each direction with respect to the strain; is the axial strain in the direction of the major principal stress, is the lateral strain in the direction of the intermediate principal stress, is the lateral strain in the direction of the minor principal stress.

[0010] Furthermore, the specific process of taking the plastic dissipation energy when the energy dissipation rate of the specimen reaches its maximum value as the energy consumption limit value of the surrounding rock is as follows: Assume that the slope in the evolution curve of the energy dissipation rate of the specimen is when the energy dissipation rate of the specimen reaches its maximum value ; that is: ; where: is the differential.

[0011] Compared with the prior art, the present invention has the following beneficial effects: (1) In the present invention, a true triaxial loading and unloading test is carried out on a specimen made of rock mass at the engineering site in the tunnel site area based on the in-situ stress test results in the tunnel site area, and stress-strain curves of the specimen in the directions of the major principal stress, the intermediate principal stress, and the minor principal stress are obtained; then, based on the above stress-strain curves and the elastic modulus and Poisson's ratio of the specimen, the energy dissipation rate of the specimen is calculated; and then, the plastic dissipation energy corresponding to the maximum value of the energy dissipation rate of the specimen is used as the energy consumption limit value of the surrounding rock. By using the energy consumption limit value as an evaluation index for the bearing capacity of the surrounding rock of a deep buried soft rock tunnel under high in-situ stress, the present invention reflects the essence of the instability and failure of the surrounding rock of a deep buried soft rock tunnel under high in-situ stress. The deformation and failure process of deep rock under construction disturbance is driven by energy, and its essence is the result of energy dissipation after the input energy exceeds the energy storage limit of the rock. Energy dissipation will cause plastic deformation and damage deterioration of the surrounding rock, and finally lead to loosening and failure of the surrounding rock. Therefore, during on-site construction, the plastic dissipation energy of the surrounding rock should be controlled within the limit value to ensure the stability of the surrounding rock after excavation and unloading of a deep buried soft rock tunnel under high in-situ stress.

[0012] (2) The present invention proposes to use the energy consumption limit as an evaluation index, which can give full play to the bearing capacity of the surrounding rock of a deep buried soft rock tunnel under high in-situ stress after the peak. The energy storage limit is the most commonly used energy index for evaluating the bearing capacity of rocks at present and is widely used in the evaluation of the stability of the surrounding rock of deep hard rock tunnels. When the elastic strain energy absorbed by hard rock exceeds the energy storage limit, the rock will undergo severe brittle failure. However, for deep soft rock, after the elastic strain energy absorbed by the rock exceeds the energy storage limit, it will not fail immediately, but shows the characteristic of strain softening after the peak and still has a certain bearing capacity. The essence of the instability and failure of deep soft surrounding rock under high in-situ stress is the result that the plastic dissipation energy exceeds the limit value. Therefore, using the energy consumption limit as an evaluation index can consider the bearing capacity of squeezing surrounding rock after the peak.

[0013] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The following will refer to the drawings for a further detailed description of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 is a schematic diagram of the stress-strain curve of rock under true triaxial loading and unloading conditions in an embodiment of the present invention; Figure 2 is the energy evolution curve of rock under true triaxial loading and unloading conditions in an embodiment of the present invention.

[0015] Wherein: ① is the axial major principal stress - axial major principal strain curve, ② is the elastic strain energy evolution curve, ③ is the plastic dissipation energy evolution curve, and ④ is the energy dissipation rate evolution curve. Specific implementation manners

[0016] To make the above objects, features, and advantages of the present invention more clearly understandable, the specific implementation manners of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the drawings of the present invention are all in simplified forms and use non-precise scales, only for conveniently and clearly assisting in explaining the implementation of the present invention; the several mentioned in the present invention are not limited to the specific quantities in the drawing examples; the orientation or positional relationships indicated by 'front','middle', 'back', 'left', 'right', 'up', 'down', 'top', 'bottom','middle', etc. in the present invention are all based on the orientation or positional relationships shown in the drawings of the present invention, and do not indicate or imply that the devices or components referred to must have a specific orientation, nor can it be understood as a limitation to the present invention.

[0017] A method for determining the energy dissipation limit value of the surrounding rock of a high in-situ stress and deeply buried soft rock tunnel provided by the present invention includes the following steps: Step 1: Adopt the stress relief method to test the in-situ stress in the tunnel face area, and respectively obtain the components of the in-situ stress in the major principal stress direction, intermediate principal stress direction, and minor principal stress direction, and record the component of the in-situ stress in the major principal stress direction as the major principal stress and record the component of the in-situ stress in the intermediate principal stress direction as the intermediate principal stress and record the component of the in-situ stress in the minor principal stress direction as the minor principal stress; Meanwhile, select a complete and relatively large rock mass from the engineering site of the tunnel site area, and process the rock mass into specimens with dimensions of 100mm×100mm×100mm, a flatness error of ±0.05mm, and a perpendicularity error of ±0.25°.

[0018] Step 2: Conduct a true triaxial loading and unloading test on the specimens to simulate the true stress path of the surrounding rock after the excavation of the deeply buried tunnel, so as to respectively obtain the stress-strain curves of the specimens in the major principal stress , intermediate principal stress and minor principal stress directions.

[0019] Furthermore, the specific process of conducting the true triaxial loading and unloading test on the specimens is as follows: According to the in-situ stress test results, set the initial values to be applied to the stresses on the six surfaces of the specimens respectively, so as to simulate the stress state of the surrounding rock before the tunnel excavation; among them, set the initial values of the upper and lower axial stress acting surfaces of the specimens to the major principal stress Set the initial value of the lateral stress on two mutually parallel sides of the specimen as the intermediate principal stress Set the initial value of the lateral stress on the other two mutually parallel sides of the specimen as the minor principal stress ; Keep the intermediate principal stress unchanged, and continuously increase the axial major principal stress at a constant loading rate by means of displacement loading Continuously unload the minor principal stress at a constant unloading rate by means of stress unloading When the minor principal stress is unloaded to zero, the test ends, and the stress-strain curves of the specimen in the major principal stress direction, intermediate principal stress direction, and minor principal stress direction at different time periods during the true triaxial loading and unloading process are obtained

[0020] Furthermore, the different time periods during the true triaxial loading and unloading include the elastic deformation stage, plastic yielding stage, post-peak strain softening stage, and residual stage

[0021] Step 3: Calculate the elastic strain energy of the specimen based on the stress-strain of the specimen in the major principal stress direction, intermediate principal stress direction, and minor principal stress direction, as well as the elastic modulus and Poisson's ratio of the specimen and plastic dissipation energy ; The expression of the elastic strain energy of the specimen is as follows ; ; where is the elastic modulus of the specimen is the Poisson's ratio of the specimen is the elastic strain in the major principal stress direction is the elastic strain in the intermediate principal stress direction is the elastic strain in the minor principal stress direction

[0022] The expression of the plastic dissipation energy of the rock is as follows ; ; where is the total energy input to the rock, and its value is equal to the integral of the principal stress in each direction with respect to the strain is the total strain in the major principal stress direction is the total strain in the intermediate principal stress direction is the total strain in the minor principal stress direction; specifically , and Obtained by measuring with LVDT displacement sensors installed in the true triaxial test equipment.

[0023] Step 4: Based on the elastic strain energy and plastic dissipation energy of the specimen, calculate the energy dissipation rate of the specimen.

[0024] The expression of the energy dissipation rate of the specimen is as follows: .

[0025] Step 5: Take the plastic dissipation energy corresponding to when the energy dissipation rate of the specimen reaches its maximum value as the energy consumption limit value of the surrounding rock, and take the energy consumption limit value of the surrounding rock as the evaluation index for the bearing capacity of the surrounding rock of the deep-buried soft rock tunnel under high in-situ stress.

[0026] Specifically, assume that the slope in the evolution curve of the energy dissipation rate of the specimen is when the energy dissipation rate of the specimen reaches its maximum value ; that is: . Example:

[0027] Taking the minimum principal stress of 10 MPa, the intermediate principal stress of 15 MPa, and the maximum principal stress of 20 MPa obtained from the in-situ stress test of a certain tunnel site as an example, the determination process of the energy consumption limit of its tunnel surrounding rock is as follows: Step 1: Take intact red bed rock mass from the engineering site, cut and process it into standard cubic specimens of 100 mm × 100 mm × 100 mm, and ensure that the surface flatness error of the specimens is ±0.05 mm and the perpendicularity error is ±0.25°.

[0028] Step 2: Adopt the stress control method to apply the stresses on the six surfaces of the specimen to their initial values at a rate of 1.0 , where the upper and lower axial stress acting surfaces of the specimen are loaded to the major principal stress , the lateral stresses on two mutually parallel side surfaces of the specimen are loaded to the intermediate principal stress , and the lateral stresses on the other two mutually parallel side surfaces of the specimen are loaded to the minor principal stress , so as to simulate the stress state of the surrounding rock before tunnel excavation; Keep the intermediate principal stress Remain unchanged. Apply axial stress to the upper and lower surfaces of the specimen at a constant displacement rate of 0.1 mm / min in the form of displacement loading, while keeping the intermediate principal stress unchanged. Unload the minor principal stress at a rate of 0.5 in the form of stress unloading to simulate the true stress evolution path of the surrounding rock after tunnel excavation. When the minor principal stress is unloaded to zero, the test ends, and the stress-strain curves in the directions of the principal stresses of the rock during the true triaxial loading and unloading process are obtained. Specifically, the axial major principal strain curve in the direction of the axial major principal stress is shown in Figure 1 as follows.

[0029] Preferably, the different time periods in the true triaxial loading and unloading include the elastic deformation stage, the plastic yield stage, the post-peak strain softening stage, and the residual stage.

[0030] Step 3: Based on the stress-strain curves of the specimens in different time periods during the true triaxial loading and unloading process in the directions of the major principal stress , the intermediate principal stress , and the minor principal stress , as well as the calculation formulas for the energy components of the specimens, obtain the elastic strain energy and the plastic dissipation energy of the specimens; specifically, the evolution curves of the elastic strain energy and the plastic dissipation energy of the specimens with the axial strain are shown in .

[0031] Step 4: Obtain the evolution curve of the energy dissipation rate of the specimens. Based on the evolution curve of the plastic dissipation energy of the specimens, let the slope of the plastic dissipation energy evolution curve be the energy dissipation rate of the specimens, and thus obtain the evolution curve of the energy dissipation rate of the specimens with the axial strain, as shown in Figure 2 .

[0032] Step 5: Take the plastic dissipation energy corresponding to the maximum value of the energy dissipation rate of the specimens as the energy dissipation limit of the specimens. When the slope of the energy dissipation rate evolution curve is , the energy dissipation rate of the specimens reaches its maximum value . The test results of a certain deep-buried red-bed soft rock tunnel sampled on-site show that under the true triaxial loading and unloading conditions, when the initial unloading minor principal stress , the intermediate principal stress When, the maximum value of the energy dissipation rate of red sandstone is 1766.0 , and the corresponding plastic dissipation energy is 381.7 . It shows that the energy consumption limit value of the surrounding rock of the high in-situ stress and deep-buried soft rock tunnel is 381.7 .

[0033] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for determining the energy consumption limit value of surrounding rock of a deep-buried soft rock tunnel with high geostress, characterized in that: The following steps are involved: Step 1: Test the geostress in the tunnel site area to obtain the components of the geostress in the direction of the major principal stress, the direction of the medium principal stress, and the direction of the minor principal stress; Test specimens were made based on the rock mass at the engineering site of the tunnel area; Step 2: Conduct true triaxial loading and unloading tests on the specimens to simulate the actual stress path of the surrounding rock after deep tunnel excavation, so as to obtain the stress and strain of the specimens in the directions of major principal stress, medium principal stress and minor principal stress respectively; Step 3: Calculate the elastic strain energy of the specimen based on the stress and strain of the specimen in the direction of major principal stress, medium principal stress and minor principal stress, as well as the elastic modulus and Poisson's ratio of the specimen. and plastic dissipation energy ; Step 4: Elastic strain energy based on the specimen and plastic dissipation energy , calculate the energy dissipation rate of the specimen ; Step 5: Energy dissipation rate of the specimen reaches its maximum value The corresponding plastic dissipated energy is Energy consumption limit value of surrounding rock .

2. The method for determining the energy consumption limit value of surrounding rock of a deep-buried soft rock tunnel with high geostress according to claim 1 is characterized in that: The specific process of obtaining the components of the specimen in the direction of major principal stress, medium principal stress and minor principal stress is as follows: The component of the ground stress in the direction of the major principal stress is recorded as the major principal stress , the component of the ground stress in the direction of the intermediate principal stress is recorded as the intermediate principal stress And the component of the ground stress in the direction of the minor principal stress is recorded as the minor principal stress ; According to the ground stress test results, the initial values ​​required for the stresses on the six surfaces of the specimen are set to simulate the stress state of the surrounding rock before tunnel excavation; among them, the initial values ​​of the upper and lower axial stress action surfaces of the specimen are set as the major principal stress The initial values ​​of the lateral stress on two parallel sides of the specimen are set as the intermediate principal stress The initial values ​​of the lateral stresses on the other two parallel sides of the specimen are set as the minor principal stress ; Maintaining the intermediate principal stress The displacement loading method is used to continuously increase the axial principal stress at a constant loading rate. , using stress unloading to continuously unload the minor principal stress at a constant unloading rate , when the minor principal stress When the unloading reaches zero, the test ends, and the specimens at different time periods during the true triaxial loading and unloading process are , intermediate principal stress and minor principal stress Stress and strain in the direction.

3. The method for determining the energy consumption limit value of surrounding rock of a deep-buried soft rock tunnel with high geostress according to claim 2 is characterized in that: The different time periods in the true triaxial loading and unloading include the elastic deformation stage, the plastic yield stage, the post-peak strain softening stage and the residual stage.

4. The method for determining the energy consumption limit value of surrounding rock of a deep-buried soft rock tunnel with high geostress according to claim 3 is characterized in that: In calculating the elastic strain energy of the specimen and plastic dissipation energy When , only the stress and strain in the elastic deformation stage of true triaxial loading and unloading are applied.

5. The method for determining the energy consumption limit value of surrounding rock of a deep-buried soft rock tunnel with high geostress according to claim 4 is characterized in that: Elastic strain energy of the specimen The expression is as follows: ； ； in, is the elastic modulus of the specimen, is the Poisson’s ratio of the specimen, is the elastic strain in the direction of the major principal stress, is the elastic strain in the direction of the central principal stress, is the elastic strain in the direction of the minor principal stress.

6. The method for determining the energy consumption limit value of surrounding rock of a deep-buried soft rock tunnel with high geostress according to claim 5 is characterized in that: Plastic dissipation energy of rock The expression is as follows: ； ； in, is the total energy input into the rock, which is equal to the integral of the principal stress in all directions with respect to the strain; is the axial strain in the direction of the major principal stress, is the lateral strain in the direction of the central principal stress, is the lateral strain in the direction of the minor principal stress.

7. The method for determining the energy consumption limit value of surrounding rock of a deep-buried soft rock tunnel with high geostress according to claim 6 is characterized in that: The energy dissipation rate of the specimen reaches its maximum value The corresponding plastic dissipated energy is Energy consumption limit value of surrounding rock The specific process is as follows: Assume that the energy dissipation rate of the specimen is The slope of the evolution curve When , it is the energy dissipation rate of the specimen reaches its maximum value ;Right now: ； ； in: is a differential.

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