CN115931606A - Method for calculating rock damage degree under action of cyclic loading and unloading test - Google Patents
Method for calculating rock damage degree under action of cyclic loading and unloading test Download PDFInfo
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- CN115931606A CN115931606A CN202211506352.5A CN202211506352A CN115931606A CN 115931606 A CN115931606 A CN 115931606A CN 202211506352 A CN202211506352 A CN 202211506352A CN 115931606 A CN115931606 A CN 115931606A
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Abstract
The invention discloses a method for calculating rock damage degree under the action of a cyclic loading and unloading test, which relates to the technical field of coal mine safety, wherein an indoor cyclic loading and unloading test is designed according to the relation between two important factors of 'mechanical property of a surrounding rock mass' and 'borne surrounding rock pressure' influencing the stability of the surrounding rock in the coal mining process, quantitative analysis is carried out from the energy perspective, damage degree data of the rock mass in the cyclic loading and unloading process is obtained through the test and theoretical calculation, whether the current supporting scheme is adjusted or not is judged through the calculation result so as to improve the stability of the surrounding rock of a roadway, the surrounding rock damage degree data obtained through the method is highly consistent with common knowledge, the method has higher reliability and good practical application value, a powerful theoretical method is provided for prejudging the stability of the surrounding rock in the roadway in the coal mining process, and effective guarantee is provided for maintaining the life and safety of people.
Description
Technical Field
The invention relates to the technical field of coal mine safety, in particular to a method for calculating rock damage degree under the action of a cyclic loading and unloading test.
Background
During engineering activities such as coal mining, in-tunnel support in a stepping circulating advancing mode, chamber excavation, tunnel tunneling and the like, surrounding rocks are always in a circulating loading and unloading state, and the mechanical properties of the surrounding rocks are degraded due to circulating load, so that secondary disasters are induced. The method is an effective means for preventing the rock mass in mining engineering from being influenced by the excavation process to generate irreversible damage, judging the damage degree of the rock and solving the problem in an indoor circulating loading and unloading test room.
Rock damage is a process of deterioration of a material or structure due to microscopic structural defects (such as microcracks, micro-voids, etc.) under external load and environmental effects, and is called damage. And energy is a driving force for driving the microscopic structural defects to develop, so that the rock deformation and cracking process is necessarily accompanied by energy conversion, and the analysis of the energy conversion characteristics of the rock deformation and cracking process to describe the rock damage degree is feasible.
At present, many scholars mainly evaluate the damage degree of rocks through macroscopic mechanical parameters such as uniaxial strength, triaxial strength, shear strength, elastic modulus, deformation modulus and the like of the rocks, the heterogeneity of the rocks enables the macroscopic mechanical parameters of the rocks to have larger discreteness, and the macroscopic mechanical parameters serving as indexes for evaluating the damage degree of the rocks have the defects of low accuracy and poor reliability. However, there are technical and theoretical difficulties in accurately evaluating damage degrees of different rocks, especially damage degrees of dense rocks, so there are few reports on quantitatively analyzing damage degrees of different rocks from the energy point of view.
Disclosure of Invention
In order to solve the existing technical problems, the invention provides a method for calculating the damage degree of the rock under the action of a cyclic loading and unloading test.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for calculating rock damage degree under the action of a cyclic loading and unloading test is realized by the following steps:
1) After large rock blocks are collected on site, processing the large rock blocks into a cubic standard sample of 70 multiplied by 70mm in a laboratory, wherein the planeness and the verticality of the processed sample can reach the standard of rock test specifications according to specific conditions;
2) Determining a classified cyclic load area according to the field condition, and judging the load size and the load frequency of the load area to determine the test cycle frequency and the cyclic loading stress size of each time;
3) Editing a rock test system according to a set control program, performing a cyclic loading and unloading test at the speed of 0.1Mpa/s by using a single-shaft compressor, and loading the last stage until a test piece is damaged;
4) Outputting data to obtain a rock sample cyclic loading and unloading total stress-strain curve, performing area calculation of each cycle by utilizing origin software integral calculation function, and respectively obtaining U of the corresponding area of each cycle d And U e ，U d For loading the dissipated energy of the process rock sample, U e The elastic strain energy of the rock sample in the loading process can be known according to the law of energy conservation,
U＝U e +U d (1)
wherein U is the work of the press machine on the rock, namely the strain energy converted into the rock sample,
then
In the formula: u (i) -cumulative total strain energy at cycle i
U d (i) -accumulating dissipated energy at cycle i;
5) Damage course of rockDegree is defined as the ratio of cumulative dissipated energy of the rock sample to cumulative total strain energy when the rock sample is loaded to the last stage of loading failure, i.e.
In the formula: d (i) -degree of rock damage upon loading to i-cycle
U d (i) Accumulated dissipated energy at i-th cycle
U (t) -cumulative total strain energy at last stage failure;
6) And calculating the damage degree of the rock sample at the end of each stage of circulation according to the formula, and adjusting the support scheme by using the damage degree data to achieve reasonable support.
According to the invention, an indoor circulating loading and unloading test is designed according to the relation between two important factors of 'mechanical property of a surrounding rock body' and 'surrounding rock pressure' influencing the stability of the surrounding rock in the coal mining process, quantitative analysis is carried out from the energy perspective, damage degree data of the rock body in the circulating loading and unloading process is obtained through the test and theoretical calculation, and whether the current supporting scheme is adjusted or not is judged through the calculation result so as to improve the stability of the surrounding rock of the roadway.
Drawings
FIG. 1 is a schematic diagram of the pressure application mode of the cyclic loading and unloading test of the invention (the compressive strength of a rock sample is 40%, and the slope k = +/-0.1 MPa/s);
FIG. 2 is a schematic diagram of a variation curve of energy dissipation curves during a cyclic loading and unloading test according to the present invention;
FIG. 3 is a schematic diagram of the energy variation curve of the elastic strain energy in the cyclic loading and unloading test process of the present invention.
Detailed Description
The invention is described in detail below with reference to the following figures and specific embodiments:
as shown in fig. 1 to 3, the method for calculating the degree of rock damage based on the cyclic loading and unloading test of the invention is realized by the following steps:
1) After large rock blocks are collected on site, processing the large rock blocks into a cubic standard sample of 70 multiplied by 70mm in a laboratory, wherein the flatness and the verticality of the processed sample can reach the standard of rock test specifications according to specific conditions;
2) Determining a classified cyclic load area according to the field condition, and judging the load size and the load frequency of the load area to determine the test cycle frequency and the cyclic loading stress size of each time;
3) Editing a rock test system according to a set control program, performing a cyclic loading and unloading test at the speed of 0.1Mpa/s by using a single-shaft compressor, and loading the last stage until a test piece is damaged;
4) Outputting data to obtain a rock sample cyclic loading and unloading total stress-strain curve, performing area calculation of each cycle by utilizing origin software integral calculation function, and respectively obtaining U of the corresponding area of each cycle d And U e ，U d For loading the dissipated energy of the process rock sample, U e The elastic strain energy of the rock sample in the loading process can be known according to the law of energy conservation,
U＝U e +U d (1)
wherein U is the work of the press machine on the rock, namely the strain energy converted into the rock sample,
then
In the formula: cumulative total strain energy at Ui (i) — i-th cycle
U d (i) -accumulating dissipated energy at cycle i;
5) The rock damage degree is defined as the ratio of the cumulative dissipated energy of the rock sample to the cumulative total strain energy when the rock sample is loaded to the last stage of loading damage, namely
In the formula: d (i) — degree of rock damage upon loading to the i cycle
U d (i) Accumulated dissipated energy at i-th cycle
U (t) -Total strain energy accumulated at last stage failure;
6) And calculating the damage degree of the rock sample at the end of each stage of circulation according to the formula, and adjusting the supporting scheme by using the damage degree data to achieve reasonable supporting.
In order to verify the accuracy of the calculation method, three rock samples of sandstone, mudstone and coal rock are selected indoors, and a cyclic loading and unloading test is carried out according to the steps as three specific embodiments.
Before the cyclic loading and unloading test, respectively carrying out a uniaxial compression test on each lithologic rock sample, in order to avoid the influence of contingency on test results, preferably selecting 3 samples for each group to carry out repeated tests, respectively obtaining the average compressive strength of different lithologicals, and respectively carrying out cyclic loading and unloading on 40% of the compressive strength of different lithologies. The uniaxial compression test control mode adopts an axial displacement method for loading, and the loading speed is 0.2mm/min. And the stress control mode is adopted for single-shaft cyclic loading and unloading, the cyclic loading and unloading rate is 0.1Mpa/s, the cyclic times are 4, and after the cyclic loading and unloading are finished, the loading is continued until the test piece reaches the fracture instability. The test process is completed in ROCK test system of ROCK600-50 according to set control program. The ROCK600-50 ROCK testing system used in the present invention is a product that is available and whose functions and testing procedures are not described herein, but are understood and applied by those skilled in the art.
The data for the specific three rock sample cyclic loading and unloading tests are shown in the following table:
TABLE 1 mechanical parameter table of different lithologies
TABLE 2 Change table of energy parameters of cyclic loading and unloading
The following conclusions can be drawn from the data study:
(1) the accumulated dissipation energy of the sandstone is the highest relative to other two lithologies, but after four cycles of loading and unloading, the damage degree is the lowest, namely only 3.9 percent of damage, and on the other hand, the fatigue resistance of the sandstone is the highest relative to that of the coal and the mudstone;
(2) the accumulated dissipation energy of the coal is inferior to that of sandstone, but the damage degree of the coal is the highest, and after four times of cyclic loading and unloading, the damage is 10.44%, which exactly verifies that the strength limit of the coal is most obviously reduced in the deformation characteristics, the reduction is 16.11MPa, which is the difference between the compressive strength obtained by loading the coal to a test piece after four times of cyclic loading and unloading and the average compressive strength obtained by three times of uniaxial compression, and the deformation characteristics, the energy and the damage degree are mutually verified, so that the test result can be proved to be reasonable;
(3) for the mudstone, the accumulated dissipation energy is relatively lowest after four cycles of loading and unloading, which is related to that the mudstone is strong in elastic deformation and high in proportion of the elastic deformation energy in the total strain energy, so that the dissipation energy is low;
(4) under different lithological cyclic loading modes, except mudstone, the sound is very big when the rock sample is destroyed, and along with the phenomenon that rock blocks or rock debris are ejected, sandstone absorbs most energy, the elastic strain energy finally stored is the most, and the rupture degree is larger than other lithologies.
In conclusion, the conclusion obtained by the method is highly consistent with the basic knowledge, so that the rationality and the accuracy of the method are also proved. The method is used for carrying out digital estimation on the damage condition of the loaded rock area, and providing or adjusting the supporting method according to the actual condition so as to achieve the purpose of reasonable supporting.
It is to be understood that the above description is not intended to limit the present invention, and the present invention is not limited to the above examples, and those skilled in the art may make various changes, modifications, additions and substitutions within the spirit and scope of the present invention.
Claims (1)
1. A method for calculating rock damage degree under the action of a cyclic loading and unloading test is characterized by comprising the following steps:
1) After large rock blocks are collected on site, processing the large rock blocks into a cubic standard sample of 70 multiplied by 70mm in a laboratory, wherein the flatness and the verticality of the processed sample can reach the standard of rock test specifications according to specific conditions;
2) Determining a classified cyclic load area according to the field condition, and judging the load size and the load frequency of the load area to determine the test cycle frequency and the cyclic loading stress size of each time;
3) Editing a rock test system according to a set control program, performing a cyclic loading and unloading test at the speed of 0.1Mpa/s by using a single-shaft compressor, and loading the last stage until a test piece is damaged;
4) Outputting data to obtain a rock sample cyclic loading and unloading total stress strain curve, and performing each cycle by utilizing origin software integral calculation functionCalculating the area of the ring to respectively obtain the U of the corresponding area of each circulation d And U e ,U d For loading the dissipated energy of the process rock sample, U e The elastic strain energy of the rock sample in the loading process can be known according to the law of energy conservation,
U＝U e +U d (1)
wherein U is the work of the press machine on the rock, namely the strain energy converted into the rock sample,
then
In the formula: u (i) -cumulative total strain energy at cycle i
U d (i) -accumulating dissipated energy at cycle i;
5) The rock damage degree is defined as the ratio of the cumulative dissipated energy of the rock sample to the cumulative total strain energy when the rock sample is loaded to the last stage of loading damage, namely
In the formula: d (i) — degree of rock damage upon loading to the i cycle
U d (i) Accumulated dissipated energy at i-th cycle
U (t) -Total strain energy accumulated at last stage failure;
6) And calculating the damage degree of the rock sample at the end of each stage of circulation according to the formula, and adjusting the support scheme by using the damage degree data to achieve reasonable support.
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| CN116879406A (en) * | 2023-09-07 | 2023-10-13 | 山东科技大学 | Tunnel surrounding rock stability evaluation method and control method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116879406A (en) * | 2023-09-07 | 2023-10-13 | 山东科技大学 | Tunnel surrounding rock stability evaluation method and control method |
| CN116879406B (en) * | 2023-09-07 | 2023-12-22 | 山东科技大学 | Tunnel surrounding rock stability evaluation method and control method |
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