Method and device for testing sliding friction coefficient of rock under true triaxial stress condition

Abstract

The invention discloses a method and device for testing the sliding friction coefficient of rock under the true triaxial stress condition, and belongs to the field of rock parameter tests.The method comprises the steps that a rock cube to be tested is cut into two parts along the diagonal line, and rock powder of the same texture is smeared on the diagonal planes of the two cut rocks; the two parts of rocks coated with the rock powder are attached together along the diagonal planes of the rocks, and confining pressure is applied to the two opposite directions of the attached to-be-measured rock cube respectively till the confining pressure reaches the corresponding preset value; applying an axial pressure to the attached to-be-tested rock cube at a constant loading speed until the change of the axial pressure tends to zero; and calculating the sliding friction coefficient of the rock cube to be measured according to the final stable value of the axial pressure. The method can test and simulate the rock friction coefficient of a real stratum under the three-dimensional ground stress condition, and the accuracy of a test result is improved.

Description

Technical Field

[0001] The invention belongs to the field of rock parameter testing, and more specifically, relates to a method and a device for testing the sliding friction coefficient of rocks under true triaxial stress conditions. Background Art

[0002] The rock sliding friction coefficient is an important parameter to characterize rock performance, and its accurate measurement is of great research significance. The existing methods for measuring the rock sliding friction coefficient are mainly divided into the following three methods: direct shear method, torsion method, and pseudo-triaxial measurement method of pre-set crack surface. The corresponding measurement methods are as follows: Figure 1 , Figure 2 , Figure 3 shown.

[0003] The direct shear method places the rock sample in a shear box, applies vertical and horizontal forces, measures the shear force and normal force, and then calculates the friction coefficient. The torsion method applies shear force to the rock surface by rotation and measures the relationship between friction and normal force. The pseudo-triaxial measurement method of the pre-set fracture surface applies confining pressure and axial pressure to measure the deformation and failure of the rock under pseudo-triaxial stress conditions, and then calculates the friction coefficient.

[0004] The existing methods are mainly based on measuring the friction coefficient of rock under simulated stress conditions in two directions, and the properties of the prefabricated fault surface are quite different from the actual situation, which leads to low accuracy in the measurement results of the rock sliding friction coefficient. Summary of the invention

[0005] In view of the defects of the prior art and the need for improvement, the present invention provides a method and device for testing the rock sliding friction coefficient under true triaxial stress conditions, which aims to solve the problems of the existing rock sliding friction coefficient testing method that the fault surface characteristics are not realistic enough and the test results are not accurate enough.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present invention, a method for testing the sliding friction coefficient of rocks under true triaxial stress conditions is provided, comprising: cutting a rock cube to be tested into two parts along a diagonal line, and applying rock powder of the same texture on the two oblique cut surfaces of the cut rock; fitting the two parts of rock coated with rock powder together along their oblique cut surfaces, and applying confining pressure in two relative directions of the fitted rock cube to be tested respectively and reaching corresponding preset values; applying axial pressure to the fitted rock cube to be tested at a constant loading speed until the change in the axial pressure approaches zero; and calculating the sliding friction coefficient of the rock cube to be tested based on the final stable value of the axial pressure.

[0007] Furthermore, the applying of confining pressures on two relative directions of the fitted rock cube to be tested specifically includes: placing the fitted rock cube to be tested into a pressure chamber, and applying confining pressures on two relative directions of the fitted rock cube to be tested by a manual hydraulic pump.

[0008] Furthermore, during the process of applying confining pressure, the two corresponding preset values ​​are: making the normal stress on the oblique surface of the rock cube to be tested reach the confining pressure value of the target normal stress; and making the lateral pressure on the oblique surface of the rock cube to be tested reach the confining pressure value of the target lateral pressure.

[0009] Furthermore, the target normal stress ranges from 8 to 32 MPa.

[0010] Furthermore, the target lateral pressure ranges from 8 to 32 MPa.

[0011] Furthermore, applying axial pressure on the assembled rock cube to be tested at a constant loading speed specifically includes: applying axial pressure on the assembled rock cube to be tested at a constant loading speed using a direct shear device.

[0012] Furthermore, the sliding friction coefficient is equal to the ratio between the shear stress on the oblique cut surface of the rock cube to be tested and the final stable value of the axial pressure.

[0013] According to another aspect of the present invention, a testing device for the sliding friction coefficient of rocks under true triaxial stress conditions is provided, which is used to execute the method described above, and the device comprises: a cutting and applying module, which is used to cut the rock cube to be tested into two parts along the diagonal line, and apply rock powder of the same texture on the two inclined surfaces of the cut rock; a confining pressure applying module, which is used to fit the two parts of rock coated with rock powder together along their inclined surfaces, and apply confining pressure in two relative directions of the fitted rock cube to be tested respectively and reach the corresponding preset value; an axial pressure applying module, which is used to apply axial pressure on the fitted rock cube to be tested at a constant loading speed until the change in axial pressure tends to zero; and a calculation module, which is used to calculate the sliding friction coefficient of the rock cube to be tested according to the final stable value of the axial pressure.

[0014] According to another aspect of the present invention, there is provided an electronic device, comprising: a processor; a memory storing a computer executable program, wherein when the program is executed by the processor, the processor executes the test method for the rock sliding friction coefficient under true triaxial stress conditions as described above.

[0015] According to another aspect of the present invention, there is provided a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for testing the rock sliding friction coefficient under true triaxial stress conditions as described above.

[0016] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0017] (1) A method for testing the sliding friction coefficient of rocks under true triaxial stress conditions is provided. On the one hand, the rock cube to be tested is cut into two parts along the diagonal line, and rock powder of the same texture is applied to the two rock oblique cut surfaces after cutting, which solves the problem that the properties of the preset fault surface are inconsistent with the actual situation, truly reflects the actual situation, is more objective and efficient, and can test the sliding friction coefficient of rocks under the conditions of three-dimensional ground stress of simulated real formations, thereby improving the test accuracy of the sliding friction coefficient of rocks;

[0018] On the other hand, confining pressure is applied to the two relative directions of the fitted rock cube. This technical feature takes into account the influence of the lateral pressure on the sliding friction coefficient and has been verified in the experimental test. It overcomes the problem of low accuracy in measuring the sliding friction coefficient of rocks based on the existing stress conditions in two directions, and further improves the test accuracy of the sliding friction coefficient of rocks.

[0019] (2) This method can be implemented by modifying the commonly used direct shear friction coefficient testing equipment, thus saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 , Figure 2 , Figure 3 Schematic diagram of measuring rock sliding friction coefficient using the traditional direct shear method, torsion method, and pseudo-triaxial method with pre-set crack surface;

[0021] Figure 4 A flow chart of a method for testing the rock sliding friction coefficient under true triaxial stress conditions provided by an embodiment of the present invention;

[0022] Figure 5 A measurement schematic diagram of a method for testing the rock sliding friction coefficient under true triaxial stress conditions provided by an embodiment of the present invention;

[0023] Figure 6 A block diagram of a testing device for rock sliding friction coefficient under true triaxial stress conditions provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0026] Embodiment 1

[0027] A test method for the sliding friction coefficient of rock under true triaxial stress conditions, see Figure 4-Figure 5 , which explains this method in detail. Figure 4 , the testing method of rock sliding friction coefficient under true triaxial stress conditions includes operation S1-operation S4.

[0028] Operation S1, cutting the rock cube to be tested into two parts along the diagonal line, and applying rock powder of the same texture on the two oblique cut surfaces of the cut rock.

[0029] The rock to be tested is designed into a cube shape. Since the cube has three opposite faces, it can more realistically simulate the three-dimensional ground stress in the actual stratum, thereby improving the accuracy of subsequent sliding friction coefficient testing. The rock cube to be tested is cut into two parts along the diagonal line, such as Figure 5 The same rock texture is made into powder and applied to the two cut surfaces of the rock.

[0030] Operation S2, the two parts of rock coated with rock powder are attached together along their oblique cut surfaces, and confining pressure is applied to two relative directions of the attached rock cube to be tested respectively and reaches corresponding preset values.

[0031] According to an embodiment of the present invention, applying confining pressures to two opposite directions of the assembled rock cube to be tested specifically includes: placing the assembled rock cube to be tested in a pressure chamber, and applying confining pressures to two opposite directions of the assembled rock cube to be tested by a manual hydraulic pump. The confining pressures applied in the two opposite directions are respectively Figure 5 σ1 and σ2 in .

[0032] During the process of applying confining pressure, the two corresponding preset values ​​are: making the normal stress on the oblique surface of the rock cube to be tested reach the confining pressure value of the target normal stress (i.e., the preset value corresponding to σ1); and making the lateral pressure on the oblique surface of the rock cube to be tested reach the confining pressure value of the target lateral pressure (i.e., the preset value corresponding to σ2).

[0033] Preferably, the target normal stress ranges from 8 to 32 MPa. The target lateral pressure ranges from 8 to 32 MPa.

[0034] Operation S3: applying axial pressure to the assembled rock cube at a constant loading speed until the change in the axial pressure approaches zero.

[0035] According to an embodiment of the present invention, applying axial pressure to the assembled rock cube at a constant loading speed specifically includes: applying axial pressure to the assembled rock cube at a constant loading speed using a direct shear device. The axial pressure is Figure 5 σ3 in .

[0036] The constant loading speed means that the axial pressure is loaded at a fixed speed. Due to the friction resistance of the oblique section of the rock cube to be tested, the actual size of the axial pressure in this case varies according to the stress of the rock. Considering this situation, the present embodiment is designed to terminate the test when the change value of the axial pressure approaches zero, so that the sliding friction coefficient calculated is more consistent with the actual situation, thereby improving the test accuracy of the rock sliding friction coefficient.

[0037] Operation S4, calculating the sliding friction coefficient of the rock cube to be tested according to the final stable value of the axial pressure.

[0038] Specifically, the test data is analyzed, the final stable value of the axial pressure is taken, and the sliding friction coefficient of the rock cube to be tested is calculated. The sliding friction coefficient is equal to the ratio between the shear stress on the inclined section of the rock cube to be tested and the final stable value of the axial pressure.

[0039] In this embodiment, the rock sliding friction coefficient obtained by the experiment is shown in Table 1.

[0040] Table 1

[0041] Sample No. σ1 / MPa σ2 / MPa σ3 / MPa Sliding friction coefficient 1 8 8 5.18 0.648 2 16 8 9.98 0.624 3 24 8 14.69 0.612 4 32 8 18.85 0.589 5 8 16 5.22 0.653 6 8 24 5.37 0.671 7 8 32 5.48 0.685

[0042] Embodiment 2

[0043] A test device for the sliding friction coefficient of rocks under true triaxial stress conditions. Figure 6 The testing device 600 for the rock sliding friction coefficient under true triaxial stress conditions includes: a cutting and smearing module 610, a confining pressure applying module 620, an axial pressure applying module 630 and a calculation module 640.

[0044] The cutting and applying module 610, for example, performs operation S1, which is used to cut the rock cube to be tested into two parts along the diagonal line, and apply rock powder of the same texture on the two oblique cut surfaces of the cut rock.

[0045] The confining pressure applying module 620 performs operation S2, for example, to fit two parts of rock coated with rock powder together along their oblique cut surfaces, and to apply confining pressure in two relative directions of the fitted rock cube to reach corresponding preset values.

[0046] The axial pressure applying module 630 performs, for example, operation S3, for applying axial pressure on the assembled rock cube to be tested at a constant loading speed until the change in the axial pressure approaches zero.

[0047] The calculation module 640, for example, performs operation S4 to calculate the sliding friction coefficient of the rock cube to be tested according to the final stable value of the axial pressure.

[0048] The relevant technical solution is the same as that in Embodiment 1 and will not be described in detail here.

[0049] Embodiment 3

[0050] An electronic device includes: a processor; a memory storing a computer executable program, and when the program is executed by the processor, the processor executes the test method of the rock sliding friction coefficient under the true triaxial stress condition. The related technical solution is the same as the first embodiment, and will not be repeated here.

[0051] Embodiment 4

[0052] A computer readable storage medium stores a computer program, and when the program is executed by a processor, the test method of the rock sliding friction coefficient under the true triaxial stress condition is implemented. The related technical solution is the same as the first embodiment, and will not be repeated here.

[0053] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for testing the sliding friction coefficient of rock under true triaxial stress conditions, characterized in that: include: Cut the rock cube to be tested into two parts along the diagonal line, and apply rock powder of the same texture on the two oblique cut surfaces of the cut rock; The two parts of rock coated with rock powder are attached together along their oblique cut surfaces, and confining pressure is applied to the two opposite directions of the attached rock cube to reach the corresponding preset value; Apply axial pressure to the fitted rock cube at a constant loading speed until the change in axial pressure approaches zero; The sliding friction coefficient of the rock cube to be tested is calculated according to the final stable value of the axial pressure.

2. The method for testing the sliding friction coefficient of rock under true triaxial stress conditions as claimed in claim 1, characterized in that: The step of applying confining pressures on two opposite directions of the assembled rock cube to be tested specifically includes: The fitted rock cube to be tested is placed in a pressure chamber, and confining pressure is applied in two opposite directions of the fitted rock cube to be tested by a manual hydraulic pump.

3. The method for testing the sliding friction coefficient of rock under true triaxial stress conditions as claimed in claim 1 or 2, characterized in that: During the application of confining pressure, the two corresponding preset values ​​are: The normal stress on the oblique surface of the rock cube to be tested is set to reach the confining pressure value of the target normal stress; and the lateral pressure on the oblique surface of the rock cube to be tested is set to reach the confining pressure value of the target lateral pressure.

4. The method for testing the sliding friction coefficient of rock under true triaxial stress conditions as claimed in claim 3, characterized in that: The target normal stress ranges from 8 to 32 MPa.

5. The method for testing the sliding friction coefficient of rock under true triaxial stress conditions as claimed in claim 3, characterized in that: The target lateral pressure ranges from 8 to 32 MPa.

6. The method for testing the sliding friction coefficient of rock under true triaxial stress conditions as claimed in claim 1, characterized in that: The step of applying axial pressure on the fitted rock cube at a constant loading speed specifically includes: Using a direct shear device, an axial pressure is applied to the fitted rock cube at a constant loading rate.

7. The method for testing the sliding friction coefficient of rock under true triaxial stress conditions as claimed in claim 1, characterized in that: The sliding friction coefficient is equal to the ratio between the shear stress on the oblique cut surface of the rock cube to be tested and the final stable value of the axial pressure.

8. A testing device for rock sliding friction coefficient under true triaxial stress conditions, characterized in that: For executing the method according to any one of claims 1 to 7, the device comprises: The cutting and applying module is used to cut the rock cube to be tested into two parts along the diagonal line, and apply the rock powder of the same texture on the two oblique cut surfaces of the cut rock; The confining pressure applying module is used to fit two parts of rock coated with rock powder together along their oblique cut surfaces, and to apply confining pressure in two relative directions of the fitted rock cube to reach corresponding preset values; An axial pressure applying module is used to apply axial pressure on the fitted rock cube to be tested at a constant loading speed until the change of the axial pressure approaches zero; The calculation module is used to calculate the sliding friction coefficient of the rock cube to be tested according to the final stable value of the axial pressure.

9. An electronic device, characterized in that: include: processor; A memory storing a computer executable program, wherein when the program is executed by the processor, the processor executes the method for testing the rock sliding friction coefficient under true triaxial stress conditions as described in any one of claims 1-7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, a method for testing the rock sliding friction coefficient under true triaxial stress conditions as described in any one of claims 1 to 7 is implemented.

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