A method for determining the energy dissipation limit of surrounding rock in deep-buried soft rock tunnels with high ground stress

Abstract

The present invention provides a method for determining the energy dissipation limit of the surrounding rock of a high-in-situ stress deep-buried soft rock tunnel, belonging to the field of tunnel engineering technology; the method comprises: testing 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, the intermediate principal stress, and the minor principal stress; preparing a rock specimen; conducting true triaxial loading and unloading tests on the specimen to obtain the stress and strain of the specimen in the directions of the major principal stress, the intermediate principal stress, and the minor principal stress; calculating the elastic strain energy and plastic dissipation energy of the specimen based on the elastic modulus and Poisson's ratio of the specimen; calculating the energy dissipation rate of the specimen; and using the plastic dissipation energy corresponding to the maximum value of the energy dissipation rate of the specimen as the energy dissipation limit of the surrounding rock. The present invention reflects the nature of the instability and failure of the surrounding rock of a high-in-situ stress deep-buried soft rock tunnel by using the energy dissipation limit as an evaluation index for the bearing capacity of the surrounding rock of the high-in-situ stress deep-buried soft rock tunnel.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel engineering and relates to a method for determining the energy consumption limit value of the surrounding rock of a deep-buried soft rock tunnel with high ground stress. Background Art

[0002] During railway tunnel construction, as tunnel depth gradually increases, deep-buried soft rock tunnels with high geostress often appear. The large compression deformation caused by high geostress poses a great challenge to the construction and operational safety of tunnels. The bearing capacity evaluation index of surrounding rock is the basis for judging the stability of high geostress tunnels and guiding the design of support structures. It can effectively evaluate the bearing capacity of surrounding rock and the stability of tunnels from an energy perspective. The energy storage limit is currently the most commonly used energy index for evaluating rock bearing capacity. It refers to the maximum elastic strain energy that can be accumulated before the rock peak. It is widely used to evaluate the stability of surrounding rock in deep hard rock tunnels and predict rockburst disasters. Under high geostress conditions, when the elastic strain energy absorbed by hard rock exceeds the energy storage limit, the rock will undergo severe brittle failure, and the rock strength after the peak will drop sharply. The essence of rockburst disasters is the result of the instantaneous release of the elastic strain energy accumulated in the hard surrounding rock after exceeding the energy storage limit.

[0003] For deep soft rock, however, the energy storage limit is very limited, and the energy input to the rock under high in-situ stress environments can easily exceed this limit. However, weak rock exhibits significant post-peak strain softening behavior under high stress, and the rock still possesses a certain bearing capacity after the peak. Existing theoretical research and field tests indicate that the surrounding rock of most deep soft rock tunnels is in a post-peak plastic service state. Therefore, using the energy storage limit as a bearing capacity evaluation metric is inappropriate and tends to underestimate the bearing capacity of the surrounding rock of deep soft rock tunnels under high in-situ stress. Under high in-situ stress environments, strain energy is input from the surrounding rock in the form of radial stress work after tunnel excavation. Part of this energy is converted into elastic strain energy and stored within the surrounding rock, while the remaining part is converted into plastic dissipation energy, triggering plastic deformation and damage degradation of the surrounding rock. The deformation and failure process of deep soft rock is driven by plastic dissipation energy. Therefore, the plastic dissipation energy of the surrounding rock caused by tunnel excavation must be controlled within a certain limit. Summary of the Invention

[0004] Based on the deficiencies in the existing technology, this application proposes a method for determining the energy consumption limit of the surrounding rock of high-ground stress deep-buried soft rock tunnels, using the energy consumption limit as an evaluation indicator of the bearing capacity of the surrounding rock of high-ground stress deep-buried soft rock tunnels, to provide a new solution to the design and construction problems of high-ground stress deep-buried soft rock tunnels.

[0005] The present invention provides a method for determining the energy consumption limit value of the surrounding rock of a deep-buried soft rock tunnel with high ground stress, comprising the following steps:

[0006] Step 1: Test the in-situ stress in the tunnel area to obtain the components of the in-situ stress in the direction of the major principal stress, the direction of the intermediate principal stress, and the direction of the minor principal stress;

[0007] Test specimens were made based on the rock mass at the tunnel site;

[0008] Step 2: Conduct true triaxial loading and unloading tests on the specimen to simulate the actual stress path of the surrounding rock after deep tunnel excavation, so as to obtain the stress and strain of the specimen in the direction of major principal stress, intermediate principal stress, and minor principal stress.

[0009] 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, intermediate principal stress and minor principal stress, as well as the elastic modulus and Poisson's ratio of the specimen. and plastic dissipated energy ;

[0010] Step 4: Elastic strain energy based on the specimen and plastic dissipated energy , calculate the energy dissipation rate of the specimen ;

[0011] Step 5: Use the energy dissipation rate of the specimen Reach its maximum value The corresponding plastic dissipated energy Energy consumption limit of surrounding rock .

[0012] Furthermore, the specific process of obtaining the components of the specimen in the direction of major principal stress, intermediate principal stress and minor principal stress is as follows:

[0013] 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 ;

[0014] According to the ground stress test results, the initial values ​​of the stress 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 ;

[0015] Maintaining the intermediate principal stress The displacement loading method is used to continuously increase the axial major 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 respectively , intermediate principal stress and minor principal stress Stress and strain in the direction.

[0016] Furthermore, 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.

[0017] Furthermore, the elastic strain energy of the specimen The expression is as follows:

[0018] ;

[0019] ;

[0020] 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.

[0021] Furthermore, the plastic dissipation energy of rock The expression is as follows:

[0022] ;

[0023] ;

[0024] 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.

[0025] Furthermore, the energy dissipation rate of the specimen Reach its maximum value The corresponding plastic dissipated energy Energy consumption limit of surrounding rock The specific process is as follows:

[0026] 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 Reach its maximum value ;Right now:

[0027] ;

[0028] ;

[0029] in: is the differential.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention conducts true triaxial loading and unloading tests on specimens made from rock mass at the engineering site of the tunnel site based on the in-situ stress test results of the tunnel site, and obtains the stress-strain curves of the specimens in the directions of major principal stress, intermediate principal stress, and minor principal stress. The energy dissipation rate of the specimens is then calculated based on the above stress-strain curves and the elastic modulus and Poisson's ratio of the specimens. The plastic dissipation energy corresponding to the maximum value of the energy dissipation rate of the specimens is then used as the energy dissipation limit of the surrounding rock. The present invention uses the energy dissipation limit as an evaluation index for the bearing capacity of the surrounding rock of a deep-buried soft rock tunnel with high in-situ stress, reflecting the nature of the instability and failure of the surrounding rock of a deep-buried soft rock tunnel with 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 eventually lead to loosening and failure of the surrounding rock. Therefore, the plastic dissipation energy of the surrounding rock should be controlled within the limit value during on-site construction to ensure the stability of the surrounding rock after excavation and unloading of deep-buried soft rock tunnels with high ground stress.

[0032] (2) The present invention proposes to use the energy dissipation limit as an evaluation index, which can give full play to the post-peak bearing capacity of the surrounding rock of deep-buried soft rock tunnels under high ground stress. The energy storage limit is currently the most commonly used energy index for evaluating rock bearing capacity 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 the hard rock exceeds the energy storage limit, the rock will undergo severe brittle failure. However, for deep soft rock, the rock will not be destroyed immediately after the elastic strain energy absorbed by the rock exceeds the energy storage limit, but will show post-peak strain softening characteristics and still have a certain bearing capacity. The essence of the instability and failure of deep-buried soft surrounding rock under high ground stress environment is the result of plastic dissipation energy exceeding the limit value. Therefore, using the energy dissipation limit as an evaluation index can consider the post-peak bearing capacity of the extrusive surrounding rock.

[0033] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0035] Figure 1 Schematic diagram of stress-strain curve of rock under true triaxial loading and unloading conditions in an embodiment of the present invention;

[0036] Figure 2 It is the energy evolution curve of rock under true triaxial loading and unloading conditions in the embodiment of the present invention.

[0037] in:

[0038] ① is the major axial principal stress - Large axial 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. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned purposes, features and advantages of the present invention more clear and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be noted that the drawings of the present invention are all simplified and non-precisely scaled, and are only used to conveniently and clearly assist in explaining the implementation of the present invention; the "numbers" mentioned in the present invention are not limited to the specific quantities in the examples in the accompanying drawings; the directions or positional relationships indicated by "front", "middle", "back", "left", "right", "up", "down", "top", "bottom", "middle", etc. mentioned in the present invention are based on the directions 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 direction, nor can they be understood as limitations on the present invention.

[0040] The present invention provides a method for determining the energy consumption limit of surrounding rock of a high-in-situ stress deep-buried soft rock tunnel, comprising the following steps:

[0041] Step 1: Use the stress relief method to test the ground stress in the tunnel area near the tunnel face, and obtain the components of the ground stress in the direction of the major principal stress, the direction of the intermediate principal stress, and the direction of the minor principal stress. 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 ground stress is the minimum principal stress The component in the direction is recorded as the minor principal stress;

[0042] At the same time, a complete and large rock mass was selected from the engineering site of the tunnel area and processed into test pieces with a size of 100mm×100mm×100mm, a flatness error of ±0.05mm, and a verticality error of ±0.25°.

[0043] Step 2: Carry out 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 major principal stress of the specimens. , intermediate principal stress and minor principal stress Stress-strain curve in the direction.

[0044] Furthermore, the specific process of conducting true triaxial loading and unloading tests on the specimen is as follows:

[0045] According to the results of the ground stress test, the initial values ​​of the stress 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 ;

[0046] Maintaining the intermediate principal stress The displacement loading method is used to continuously increase the axial major 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 The test ends when unloading reaches zero, and the stress-strain curves of the specimens in the directions of major principal stress, intermediate principal stress, and minor principal stress at different time periods during the true triaxial loading and unloading process are obtained.

[0047] Furthermore, 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.

[0048] 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, intermediate principal stress and minor principal stress, as well as the elastic modulus and Poisson's ratio of the specimen. and plastic dissipated energy ;

[0049] Elastic strain energy of the specimen The expression is as follows:

[0050] ;

[0051] ;

[0052] 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.

[0053] Plastic dissipation energy of rock The expression is as follows:

[0054] ;

[0055] ;

[0056] 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 total strain in the direction of the major principal stress, is the total strain in the direction of the central principal stress, is the total strain in the direction of the minor principal stress; specifically, 、 and The displacement is measured using an LVDT displacement sensor installed in a true triaxial testing device.

[0057] Step 4: Elastic strain energy based on the specimen and plastic dissipated energy , calculate the energy dissipation rate of the specimen .

[0058] Energy dissipation rate of the specimen The expression is as follows:

[0059] .

[0060] Step 5: Use the energy dissipation rate of the specimen Reach its maximum value The corresponding plastic dissipation energy is taken as the energy dissipation limit of the surrounding rock. , based on the energy consumption limit of the surrounding rock As an evaluation index of the bearing capacity of the surrounding rock of deep-buried soft rock tunnels with high ground stress.

[0061] Specifically, let the energy dissipation rate of the specimen be The slope of the evolution curve When , it is the energy dissipation rate of the specimen Reach its maximum value ;Right now:

[0062] ;

[0063] .

[0064] Example:

[0065] Taking the in-situ stress test results of a tunnel site as an example, where the minimum principal stress is 10 MPa, the intermediate principal stress is 15 MPa, and the maximum principal stress is 20 MPa, the energy dissipation limit of the tunnel surrounding rock is determined as follows:

[0066] Step 1: Take the complete red bed rock from the project site and cut it into a standard cubic specimen of 100 mm × 100 mm × 100 mm, and ensure that the surface flatness error of the specimen is ±0.05 mm and the verticality error is ±0.25°.

[0067] Step 2: Use stress control method to 1.0 The stresses on the six surfaces of the specimen are applied to their initial values ​​at a rate of The lateral stress of two parallel sides of the specimen is loaded to the intermediate principal stress The lateral stresses of the other two parallel sides of the specimen are loaded to the minimum principal stress , thereby simulating the stress state of the surrounding rock before tunnel excavation;

[0068] Maintaining the intermediate principal stress The axial stress is continuously applied to the upper and lower surfaces of the specimen at a constant displacement rate of 0.1 mm / min by displacement loading, while maintaining the central principal stress Unchanged, stress unloading is adopted with 0.5 Unloading of minor principal stress at a rate , simulating the actual stress evolution path of the surrounding rock after tunnel excavation. When the unloading reaches zero, the test ends and the stress-strain curves of the rock in each principal stress direction during the true triaxial loading and unloading process are obtained. Axial principal strain in the direction Curve see Figure 1 shown.

[0069] Preferably, the different time periods in the true triaxial loading and unloading include an elastic deformation stage, a plastic yield stage, a post-peak strain softening stage and a residual stage.

[0070] Step 3: Based on the true triaxial loading and unloading process, the specimens at different time periods are respectively subjected to the maximum principal stress. , intermediate principal stress and minor principal stress The stress-strain curve in the direction and the calculation formula of each energy component of the specimen are used to obtain the elastic strain energy of the specimen. and plastic dissipated energy ; Specifically, the elastic strain energy of the specimen and plastic dissipated energy Evolution curve with axial strain .

[0071] Step 4: Obtain the evolution curve of the energy dissipation rate of the specimen. Based on the evolution curve of the plastic dissipation energy of the specimen, let the slope of the plastic dissipation energy evolution curve be the energy dissipation rate of the specimen. , and the energy dissipation rate of the specimen is obtained The evolution curve with axial strain can be found in Figure 2 shown.

[0072] Step 5: Use the energy dissipation rate of the specimen Reach its maximum value The corresponding plastic dissipation energy is taken as the energy dissipation limit of the specimen. When the slope of the energy dissipation rate evolution curve is When the energy dissipation rate of the specimen is Reach its maximum value The test results of a deep red soft rock tunnel on site show that under true triaxial loading and unloading conditions, when the initial small principal stress , intermediate principal stress , unloading rate When the energy dissipation rate of red sandstone reaches 1766.0 , the corresponding plastic dissipation energy is 381.7 The energy consumption limit of the surrounding rock of the deep-buried soft rock tunnel with high ground stress is shown in Figure 2. 381.7 .

[0073] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

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

2. The method for determining the energy consumption limit of surrounding rock in a deep-buried soft rock tunnel with high ground stress according to claim 1, characterized in that: The specific process of obtaining the components of the specimen in the direction of major principal stress, intermediate 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 ​​of the stress 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 major 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 respectively , intermediate principal stress and minor principal stress Stress and strain in the direction.

3. The method for determining the energy consumption limit of surrounding rock in a deep-buried soft rock tunnel with high ground stress according to claim 2, 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 of surrounding rock in a deep-buried soft rock tunnel with high ground stress according to claim 3 is characterized in that: In calculating the elastic strain energy of the specimen and plastic dissipated 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 of surrounding rock in a deep-buried soft rock tunnel with high ground stress according to claim 4, 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 of surrounding rock in a deep-buried soft rock tunnel with high ground stress according to claim 5, 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 of surrounding rock in a deep-buried soft rock tunnel with high ground stress according to claim 6, characterized in that: The energy dissipation rate of the specimen Reach its maximum value The corresponding plastic dissipated energy Energy consumption limit 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 Reach its maximum value ;Right now: ； ； in: is the differential.

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