Unstability energy criterion and method suitable for deep high-stress rock

Abstract

The invention relates to the technical field of deep rock engineering, in particular to an instability energy criterion and method suitable for deep high-stress rocks. The criterion is obtained by the method. The method comprises the following steps: acquiring a stress-strain curve of rock; obtaining an evolution curve of rock elastic strain energy and an evolution curve of rock dissipated energy; obtaining an evolution curve of the rock energy dissipation rate; the maximum value of the rock energy dissipation rate is used as an energy criterion of deep high-stress rock instability, and the method is used for preventing deep rock engineering instability accidents. The criterion provided by the invention is suitable for the deep high-stress rock, and the problem that the bearing capacity of the deep high-stress rock is underestimated by a traditional strength criterion is solved.

Description

Technical Field

[0001] The invention relates to the technical field of deep rock engineering, and in particular to an instability energy criterion and method suitable for deep high-stress rocks. Background Art

[0002] It is of great significance to explore the mechanical properties of deep rocks for resource development and infrastructure construction. Deep rocks exist in a high stress field (referred to as high stress, with stress greater than 10MPa) environment. There are significant differences between the mechanical properties of rocks under high stress loading conditions and those under shallow low stress loading conditions. The strength of the rock increases significantly when high stress is loaded, and the rock will not be destroyed immediately after the stress reaches the peak point, but will enter a longer plastic deformation stage, showing obvious post-peak strain softening characteristics. This is because the cracks and pores inside the rock are compacted in a high stress environment, the friction and bite force between particles increase, and the high stress limits the expansion and penetration of the internal cracks after the rock peak. In contrast, the development of cracks and pores inside the rock is relatively free when low stress is loaded, and the cracks will rapidly expand and penetrate after the stress reaches the peak point, resulting in brittle failure of the rock, a shorter plastic deformation stage, and no obvious strain softening characteristics.

[0003] Instability criterion is the premise for evaluating the stability of engineering rock and carrying out rock engineering design. Strength criterion is currently the most widely used rock instability criterion. It takes the peak strength of the rock stress-strain curve as the critical state of rock instability, which is suitable for evaluating the stability of shallow low-stress rock. However, for deep high-stress rock, the rock still has a certain bearing capacity after the stress reaches the peak strength. Most deep underground engineering rock masses are in a service state of plastic deformation after being disturbed by construction. Traditional strength criterion will underestimate the bearing capacity of deep high-stress rock and is not suitable for judging the stability of deep high-stress rock.

[0004] In summary, it is necessary to develop an instability energy criterion and method suitable for deep high-stress rocks to solve the problem that traditional strength criterion underestimates the bearing capacity of deep high-stress rocks. Summary of the invention

[0005] The purpose of the present invention is to provide an instability energy criterion and method suitable for deep high-stress rock. The specific technical scheme is as follows: In a first aspect, the present invention provides a method for obtaining an instability energy criterion applicable to deep high-stress rocks, comprising: Step S1, selecting a complete engineering rock mass on site to prepare a standard specimen, conducting a conventional triaxial compression test under a target confining pressure, and obtaining a stress-strain curve of the rock; Step S2: According to the test results of the rock stress-strain curve and the rock elastic strain energy Calculation formula and rock dissipated energy The calculation formula is used to obtain the evolution curve of rock elastic strain energy and the evolution curve of rock dissipated energy; Step S3: According to the evolution curve of rock elastic strain energy and the evolution curve of rock dissipated energy, obtain the evolution curve of rock energy dissipation rate; Step S4: Take the maximum value of the rock energy dissipation rate as the energy criterion for the instability of deep high-stress rocks, and use it to prevent the occurrence of instability accidents in deep rock engineering.

[0006] Optionally, the target confining pressure is above 10 MPa.

[0007] Optionally, the stress-strain curve includes a compaction stage, an elastic deformation stage, a plastic yield stage, a post-peak strain softening stage, and a residual stage.

[0008] Optionally, the rock elastic strain energy The calculation formula is expressed as follows: ; Wherein, represents the elastic modulus of the rock, and the slope of the stress-strain curve in the elastic deformation stage is taken as the elastic modulus of the rock, represents the Poisson's ratio of the rock; represents the axial stress of the rock; represents the target confining pressure.

[0009] Optionally, the rock dissipated energy The calculation formula is expressed as follows: ; Wherein, represents the total energy input into the rock.

[0010] Optionally, the total energy of the input rock is expressed as follows: ; Wherein, the magnitude is equal to the sum of the integrals of the stress with respect to the strain in the principal stress direction of the rock; represents the axial strain of the rock; represents the lateral strain of the rock.

[0011] Optionally, let the slope of the evolution curve of the rock dissipated energy be the rock energy dissipation rate , that is .

[0012] Optionally, the energy criterion for the instability of deep high-stress rocks is as follows: ; ; When the energy dissipation rate of the rock does not reach the peak point , and the slope of the dissipation rate evolution curve , the rock has no risk of unstable failure; When the energy dissipation rate of the rock reaches the peak point , and the slope of the dissipation rate evolution curve , the rock is about to undergo unstable failure; When the slope of the energy dissipation rate evolution curve of the rock , the rock has undergone unstable failure.

[0013] Optionally, the standard specimen is a standard cylindrical specimen.

[0014] In a second aspect, the present invention provides an instability energy criterion applicable to deep high-stress rocks, which is obtained by using the method for obtaining the instability energy criterion applicable to deep high-stress rocks described above.

[0015] Applying the technical solution of the present invention has at least the following beneficial effects: The present invention provides a method for obtaining an instability energy criterion applicable to deep high-stress rocks, which can solve the problem that the traditional strength criterion underestimates the bearing capacity of deep high-stress rocks. Specifically, the instability energy criterion proposed by the present invention establishes an evaluation index from the perspective of energy, which can reflect the essence of the instability failure of deep rocks; the present invention uses the rock energy dissipation rate as the evaluation index for rock instability. Compared with the traditional strength criterion, it can effectively predict the failure precursor of deep high-stress rocks and prevent the occurrence of instability accidents in deep rock engineering. In addition, the instability energy criterion proposed by the present invention is applicable to deep high-stress rocks and can consider the bearing capacity of rocks after the peak under high stress; under high stress conditions, rocks do not immediately fail after the stress reaches the peak strength, but show the characteristics of strain softening after the peak and produce large plastic deformations; the rock instability energy criterion proposed by the present invention, compared with the traditional strength criterion, can fully consider the bearing capacity of deep rocks after the peak during engineering applications and is applicable to deep high-stress rocks.

[0016] 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 to further elaborate on the present invention in detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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 of the present invention. In the drawings: Figure 1 In the embodiment, a stress-strain curve of the rock is obtained through a conventional triaxial compression test on deep rock under the target confining pressure; Among them, curve ① is the stress-strain curve of the rock; on curve ①, the OA curve segment is the compaction stage, the AB curve segment is the elastic deformation stage, the BC curve segment is the plastic yield stage, the CD curve segment is the post-peak strain softening stage, and the DE curve segment is the residual stage; Figure 2 In the embodiment, an energy evolution curve of the rock is obtained through a conventional triaxial compression test on deep rock under the target confining pressure; Among them, curve ② is the evolution curve of the elastic strain energy of the rock ; curve ③ is the evolution curve of the dissipated energy of the rock ; curve ④ is the evolution curve of the energy dissipation rate of the rock. Specific implementation manners

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention. Embodiment

[0019] A method for obtaining an instability energy criterion applicable to deep high-stress rock includes: Step S1: Select a complete in-situ engineering rock mass to prepare a standard specimen, and conduct a conventional triaxial compression test on it under the target confining pressure to obtain the stress-strain curve of the rock, see Figure 1 ; Step S2: According to the test results of the stress-strain curve of the rock, the calculation formula of the elastic strain energy of the rock and the calculation formula of the dissipated energy of the rock , obtain the evolution curve of the elastic strain energy of the rock and the evolution curve of the dissipated energy of the rock, see Figure 2 ; Step S3: According to the evolution curve of the elastic strain energy of the rock and the evolution curve of the dissipated energy of the rock, obtain the evolution curve of the energy dissipation rate of the rock, see Figure 2 ; Step S4: Take the maximum value of the energy dissipation rate of the rock as the energy criterion for the instability of deep high-stress rock, and use it to prevent the occurrence of instability accidents in deep rock engineering.

[0020] The target confining pressure is above 10 MPa, such as 10 MPa is selected.

[0021] During the conventional triaxial compression test, first, the lateral stress is applied to the standard specimen at a loading rate of 0.05 MPa / s in a stress loading manner until the set value; then, the axial stress is applied to the standard specimen at a loading rate of 0.1 mm / min in a displacement loading manner. When the axial stress-axial strain curve enters the residual stage, the test ends.

[0022] See Figure 1 , the stress-strain curve includes a compaction stage, an elastic deformation stage, a plastic yield stage, a post-peak strain softening stage, and a residual stage.

[0023] The elastic strain energy of the rock is calculated by the following formula: ; where represents the elastic modulus of the rock, and the slope of the stress-strain curve in the elastic deformation stage is taken as the elastic modulus of the rock, represents the Poisson's ratio of the rock; represents the axial stress of the rock; represents the target confining pressure.

[0024] The dissipated energy of the rock is calculated by the following formula: ; where represents the total energy input into the rock.

[0025] The total energy input into the rock is expressed by the following formula: ; where the value is equal to the sum of the integrals of the stress with respect to the strain in the principal stress direction of the rock; represents the axial strain of the rock; represents the lateral strain of the rock.

[0026] Let the slope of the evolution curve of the dissipated energy of the rock be the energy dissipation rate of the rock , that is .

[0027] The energy criterion for the instability of deep high-stress rocks is as follows: ; ; See Figure 2 , when the energy dissipation rate of the rock has not reached the peak point , and the slope of the dissipation rate evolution curve At this time, there is no risk of rock instability failure; When the energy dissipation rate of the rock reaches the peak point and the slope of the dissipation rate evolution curve at this time, the rock is about to undergo instability failure; When the slope of the energy dissipation rate evolution curve of the rock at this time, the rock has undergone instability failure.

[0028] The standard specimen is a standard cylindrical specimen (such as selecting a complete and large-volume red sandstone rock mass on site and cutting and processing it into a standard cylindrical specimen with a diameter of 50 mm × a height of 100 mm).

[0029] See Figure 2 For the maximum value of the rock energy dissipation rate is and the occurrence time of the maximum energy dissipation rate is when the axial strain is 1.613%, that is, the instability time of the rock is = 1.613%. If the traditional strength criterion is adopted and the peak point of the stress-strain curve is used as the rock instability criterion, then the instability time of the rock = 1.256%. It can be seen that the instability time predicted by the instability energy criterion proposed in the present invention is significantly later than the result predicted by the traditional strength criterion, and the predicted result is more in line with the actual situation, considering the bearing capacity of the rock after the peak under high stress.

[0030] The above is only the preferred embodiment of the present invention and is 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 in the protection scope of the present invention.

Claims

1. A method for obtaining instability energy criterion applicable to deep high-stress rock, characterized in that: include: Step S1, selecting a complete engineering rock mass on site to prepare a standard specimen, conducting a conventional triaxial compression test under a target confining pressure, and obtaining a stress-strain curve of the rock; Step S2: According to the test results of the rock stress-strain curve and the rock elastic strain energy The calculation formula of rock dissipation energy The calculation formula is used to obtain the evolution curve of rock elastic strain energy and the evolution curve of rock dissipated energy; Step S3, obtaining an evolution curve of rock energy dissipation rate according to the evolution curve of rock elastic strain energy and the evolution curve of rock dissipation energy; Step S4: Taking the maximum value of the rock energy dissipation rate as the energy criterion for deep high-stress rock instability, so as to prevent the occurrence of deep rock engineering instability accidents.

2. The method for obtaining the instability energy criterion applicable to deep high-stress rock according to claim 1, characterized in that: The target confining pressure is above 10 MPa.

3. The method for obtaining the instability energy criterion applicable to deep high-stress rock according to claim 1, characterized in that: The stress-strain curve includes a compaction stage, an elastic deformation stage, a plastic yield stage, a post-peak strain softening stage and a residual stage.

4. The method for obtaining the instability energy criterion applicable to deep high-stress rock according to claim 3, characterized in that: The rock elastic strain energy The calculation formula is expressed as follows: ； in, represents the elastic modulus of the rock, and the slope of the stress-strain curve in the elastic deformation stage is taken as the elastic modulus of the rock, represents the Poisson's ratio of the rock; It represents the axial stress of rock; Indicates the target confining pressure.

5. The method for obtaining the instability energy criterion applicable to deep high-stress rock according to claim 4, characterized in that: The rock dissipates energy The calculation formula is expressed as follows: ； in, Represents the total energy input into the rock.

6. The method for obtaining the instability energy criterion applicable to deep high-stress rock according to claim 5, characterized in that: The total energy input into the rock It is expressed as follows: ； Among them, the The value is equal to the integral sum of stress in the direction of the principal stress of the rock with respect to strain; represents the axial strain of the rock; Represents the lateral strain of rock.

7. The method for obtaining the instability energy criterion applicable to deep high-stress rock according to claim 6, characterized in that: Let the slope of the evolution curve of rock dissipation energy be the rock energy dissipation rate , Right now .

8. The method for obtaining the instability energy criterion applicable to deep high-stress rock according to claim 7, characterized in that: The energy criterion for instability of deep high-stress rocks is as follows: ； ； When the energy dissipation rate of the rock Not reaching the peak , and the slope of the dissipation rate evolution curve When the rock is unstable, there is no risk of failure. When the energy dissipation rate of the rock Reaching the peak point , and the slope of the dissipation rate evolution curve =0, the rock is about to fail; When the slope of the rock energy dissipation rate evolution curve When <0, the rock has become unstable and damaged.

9. The method for obtaining instability energy criterion applicable to deep high-stress rock according to claim 1, characterized in that: The standard specimen is a standard cylindrical specimen.

10. An instability energy criterion applicable to deep high-stress rock, characterized in that: The method for obtaining the instability energy criterion applicable to deep high-stress rocks is used to obtain the instability energy criterion according to any one of claims 1 to 9.

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