CN107782620A - A kind of determination method for the Rock Failure critical strain for considering time effect - Google Patents
A kind of determination method for the Rock Failure critical strain for considering time effect Download PDFInfo
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- 238000011156 evaluation Methods 0.000 abstract description 2
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Abstract
The invention discloses a kind of determination method for the Rock Failure critical strain for considering time effect.Rock sample is prepared first；Triaxial stress relaxation laboratory test is carried out to rock sample using rheometer, obtains the stress relaxation curve of rock；Rock Failure critical strain section is determined by triaxial stress relaxation laboratory test；According to obtained rock stress relaxation curve, the stress relaxation model of rock sample is established, draws model parameter；According to the rock sample size and feature of preparation, the corresponding numerical model of rock sample is established；Obtained Rock Failure critical strain section is divided into several pieces, as the axial strain value for intending applying in numerical experimentation, triaxial stress relaxation numerical experimentation is carried out to rock sample, the unstability critical strain exact value of rock sample is obtained by triaxial stress relaxation numerical experimentation.The present invention can solve the problem that the problem of prior art evaluation method can not truly reflect the actual unstability feature of rock, error is big；Rock Failure critical strain can accurately be drawn.
Description
The technical field is as follows:
the invention relates to the field of geotechnical engineering, in particular to a method for determining rock instability critical strain by considering time effect.
Secondly, background art:
the rock is deformed under the action of external force, and the deformation of the rock is increased along with the continuous action of the external force, so that the rock is suddenly broken and unstable, and geological disasters such as collapse, landslide and rock burst are caused. As a key index for judging the rock fracture instability, the research on the rock instability critical strain has an important influence on the prediction and the prevention of geological disasters. Numerous engineering practices have shown that failure and instability of rock engineering, from initial deformation to final destabilization failure, is a time-dependent complex non-linear progressive process, and in many cases does not occur immediately. Therefore, the determination of the rock instability critical strain needs to consider the time effect of the rock, which has very important theoretical and practical significance for truly reflecting the actual characteristics of rock engineering and evaluating the long-term stability and safety of the engineering.
At present, the rock instability critical strain is determined by applying axial stress to a rock sample mainly according to a conventional mechanical test in a rock chamber, wherein the axial stress in the test is continuously increased at a certain rate until the sample is damaged. And taking the strain value corresponding to the peak intensity or the residual intensity in the obtained axial stress-strain curve of the sample as the instability critical strain of the rock. The time effect problem of rock fracture instability is not considered in the test. Actual rock engineering usually suffers from rheological failure under the long term action of constant stress or strain. And determining the instability critical strain of the rock by adopting a stress relaxation test under constant strain, and more truly and accurately reflecting the actual characteristics of the rock. Based on rock stress relaxation laboratory tests, the maximum strain before rheological failure of the rock, namely instability critical strain, is difficult to directly obtain at present, and usually an interval value or an approximate value of the instability critical strain is obtained. The constant strain value applied in the test is too small, so that the rock sample cannot be rheologically damaged; the applied constant strain value is too large, the rock sample can be damaged too fast, and the rock instability critical strain is difficult to directly and accurately obtain. Therefore, it is necessary to develop a method for determining the critical strain of rock instability by considering the time effect, which can overcome the above disadvantages.
Thirdly, the invention content:
the technical problem to be solved by the invention is as follows: in order to overcome the defects of the existing rock instability critical strain determining method, the invention provides the rock instability critical strain determining method considering the time effect. The determining method can solve the problems that the evaluation method in the prior art cannot truly reflect the actual instability characteristics of the rock and has large errors; the rock instability critical strain can be accurately obtained.
In order to solve the problems, the invention adopts the technical scheme that:
the invention provides a method for determining rock instability critical strain by considering time effect, which comprises the following steps:
a. preparing a rock sample;
b. performing a triaxial stress relaxation indoor test on the prepared rock sample by adopting a rheometer to obtain a stress relaxation curve of the rock;
c. determining a rock instability critical strain interval through a triaxial stress relaxation indoor test;
d. according to the obtained rock stress relaxation curve, establishing a stress relaxation model of the rock sample to obtain model parameters;
e. b, establishing a corresponding numerical model of the rock sample in numerical software according to the size and the characteristics of the rock sample prepared in the step a;
f. and d, equally dividing the rock instability critical strain interval obtained in the step c into a plurality of parts, taking the parts as axial strain values to be applied in the numerical test, carrying out a triaxial stress relaxation numerical test on the rock sample, and obtaining an accurate value of the instability critical strain of the rock sample through the triaxial stress relaxation numerical test.
According to the method for determining the rock destabilization critical strain considering the time effect, the preparation method of the rock sample in the step a comprises the following steps:
the rock mass is gathered on the scene, transports the laboratory, adopts the water drilling method to bore the core sample to the rock mass, cuts core both ends face with the sawing machine and levels, grinds on the stone mill, makes the ratio of height and diameter 2: 1, cylindrical rock sample; the unevenness deviation of the end face of the sample is controlled within +/-0.003 mm, and the verticality deviation of the end face to the axis of the sample is controlled within +/-0.25 degrees.
According to the method for determining the rock instability critical strain considering the time effect, the operation method of the triaxial stress relaxation indoor test in the step b comprises the following steps:
firstly, a conventional triaxial test is carried out on a rock sample to obtain strain corresponding to the peak intensity of the sample, namely peak strain epsilonc(ii) a Then carrying out triaxial stress relaxation indoor test on the rock sample; determining the test confining pressure sigma according to the lateral stress of the rock in the engineering3Applying a confining pressure σ to the sample3To a predetermined value, maintaining the confining pressure σ3The change is not changed; applying axial strain epsilon to the sample from low to high by adopting a respective loading mode; the peak strain epsilon of the sample obtained in the conventional triaxial testc10 to 15 percent of the strain is taken as the axial strain difference value to be applied in the stress relaxation test, namely the first-stage axial strain value is the peak strain epsilon of the samplec10% -15% of the strain value of the second-stage axial strain is the peak strain epsilon of the samplec20% -30% of the total weight of the product, and so on; after each stage of axial strain epsilon is applied, keeping the axial strain epsilon constant, and observing and recording the change characteristics of the axial stress sigma of the sample along with the time t; and when the increasing rate of the axial stress sigma is less than 0.001MPa/h, stopping applying the axial strain of the current stage, and applying the axial strain of the next stage until the sample is subjected to relaxation failure to obtain a stress relaxation curve of the sample.
According to the method for determining the rock instability critical strain considering the time effect, the method for determining the rock instability critical strain interval in the step c comprises the following steps:
the stress relaxation curve of the rock sample obtained in the step b is divided into three stages: a rapid relaxation, deceleration relaxation and acceleration relaxation phase; at a certain level of axial strain epsilonnUnder the action of the stress relaxation curve of the sample, only rapid relaxation and deceleration relaxation stages occur, and the axial strain epsilon of the next stage isn+1Under the action of (1), after a stress relaxation curve of a sample passes through a rapid relaxation stage and a deceleration relaxation stage, an acceleration relaxation stage is generated, so that the sample is subjected to relaxation failure, and the interval range of rock instability critical strain is as follows: epsilonn～εn+1。
According to the method for determining the rock instability critical strain considering the time effect, the operation method for establishing the stress relaxation model of the rock sample and obtaining the model parameters in the step d comprises the following steps:
b, analyzing the stress relaxation characteristic of the rock according to the stress relaxation curve of the rock sample obtained in the step b; considering the characteristics of the stress relaxation stage, establishing mechanical models of the rock in different stress relaxation stages; when the stress relaxation curves of the rock sample under all levels of axial strain are in rapid relaxation and deceleration relaxation stages, selecting a Hooke-Kelvin rheological model; the stress relaxation curve of the rock sample under the current several levels of axial strain is expressed as a rapid relaxation stage and a deceleration relaxation stage, and the stress relaxation curve of the rock sample under the last level of axial strain is expressed as a rapid relaxation stage, a deceleration relaxation stage and an acceleration relaxation stage, and then a nonlinear rheological model is selected; according to the established rock stress relaxation model, identifying test data by adopting a least square method, a regression analysis method or a particle swarm optimization algorithm; and continuously adjusting model parameters to enable a model fitting curve to be overlapped with a test curve as much as possible, wherein the fitting error is in a set range, and the optimal parameters obtained by fitting are used as rock stress relaxation model parameters.
The stress relaxation equation of the Hooke-Kelvin rheological model is as follows:
the stress relaxation equation for the nonlinear rheological model is:
wherein,
in the formula: σ is axial stress, ε is axial strain, εfTo a strain threshold, E1、E2、η1、η2B is the model parameter, t is the test time.
According to the method for determining the rock instability critical strain considering the time effect, the method for establishing the corresponding numerical model of the rock sample in the step e comprises the following steps:
according to the size of the rock sample prepared in the step a and the peak strain of the sample obtained in the conventional triaxial test in the step b, establishing a corresponding numerical model in numerical software, and carrying out mesh generation and unit assignment; the boundary conditions and the operation method of the numerical model are the same as those of the step b; and d, applying the rock stress relaxation model and the parameters obtained in the step d to a numerical model, so that the numerical model can accurately perform rock stress relaxation numerical tests.
According to the method for determining the rock instability critical strain considering the time effect, the specific method for acquiring the accurate value of the rock instability critical strain in the step f is as follows:
equally dividing the rock instability critical strain interval obtained in the step c into L parts as an axial strain value to be applied in a numerical test, namely epsilonn、…、εk、εk+1、…、εn+1(ii) a The L value is determined according to the set rock instability critical strain precision, and the higher the set instability critical strain precision is, the larger the L value is; applying the numerical model established in the step e, applying axial strain from low to high by adopting a respective loading mode, and performing a rock triaxial stress relaxation numerical test to obtain a change curve of the axial stress sigma of the sample along with the time t under each level of axial strain; when in the k-th order of axial strain εkUnder the action, the stress relaxation numerical test curve of the sample shows rapid relaxation and deceleration relaxation stages, and the axial strain epsilon is in the k +1 st levelk+1Under the action, after the test curve of the stress relaxation numerical value of the sample passes through the rapid relaxation stage and the deceleration relaxation stage, the accelerated relaxation stage appears, and when the rock sample is subjected to relaxation and damage, the axial strain epsilonkIs an accurate value of rock instability critical strain.
The method firstly determines the interval range of the rock instability critical strain according to the indoor test result, and then accurately obtains the rock instability critical strain based on the numerical test result.
The invention has the following positive beneficial effects:
1. the existing method for determining the critical strain of rock instability does not consider the time effect problem of the rock, and is difficult to truly reflect the actual instability characteristics of the rock; the invention introduces the time effect into the rock instability critical strain determination, overcomes the defects of the prior method, and can more truly and accurately reveal the instability characteristics of the rock.
2. The existing method for determining the rock instability critical strain cannot control and solve the obtained rock instability critical strain precision; the method can preset the rock instability critical strain precision to be solved, and can accurately obtain the rock instability critical strain considering the time effect; compared with the prior art, the method has the advantages that the calculation result is more objective and scientific, and a novel method with controllable precision is provided for determining the rock instability critical strain.
3. The rock stress relaxation indoor test has high cost and long period, can apply few strain levels, cannot directly obtain the maximum strain value before rock damage, namely the instability critical strain, and only can obtain the rock instability critical strain interval; the rock instability critical strain interval obtained by the indoor test is equally divided into a plurality of strain values according to the set precision, the numerical test which is low in cost, high in precision and capable of being repeated is adopted, a large amount of multi-level strain loading which cannot be achieved by the indoor test is accurately reproduced, the maximum strain value before rock damage is accurately obtained from the instability critical strain interval, and the rock instability critical strain can be accurately obtained.
4. The invention gives play to the advantages of numerical tests, makes up the defects of indoor tests, and is easy to popularize and apply in actual rock engineering.
Fourthly, explanation of the attached drawings:
FIG. 1 is a schematic flow chart of a method for determining rock instability critical strain by considering time effect;
FIG. 2 is a plot of stress relaxation room tests for silty mudstone;
FIG. 3 is a schematic diagram of a stress relaxation curve phase of a rock;
FIG. 4 is a graph showing the accurate value of critical strain for silty mudstone instability based on a numerical test curve;
FIG. 5 is a graph of a stress relaxation room test of carbonaceous slates;
FIG. 6 is a graph for determining an accurate value of critical strain for instability of the carbonaceous slate based on a numerical test curve.
The fifth embodiment is as follows:
the invention is further illustrated by the following examples, but the technical content of the invention is not limited thereto.
The operation flow diagram of the rock destabilization critical strain determination method considering the time effect is shown in the attached figure 1 in detail.
Example 1:
taking silty mudstone of a certain highway engineering in southwest of China as an example, determining the instability critical strain of the silty mudstone considering the time effect based on indoor tests and numerical tests, and specifically comprising the following operation steps:
a. collecting silty shale rock blocks on site, transporting to a laboratory, drilling cores by a water drilling method for sampling, cutting and flattening two end faces of the rock cores by a sawing stone cutting machine, and grinding on a stone grinding machine to prepare standard cylindrical samples with the diameter of 50mm and the height of 100 mm; the unevenness deviation of the end face of the sample is controlled within +/-0.003 mm, and the perpendicularity deviation of the end face to the axis of the sample is controlled within +/-0.25 ℃;
b. firstly, a rock pressure testing machine is adopted to carry out a conventional triaxial test on a silty mudstone sample, and the confining pressure sigma is determined according to the actual lateral stress of the rock in the engineering3Taking the strain as 1MPa, and obtaining the peak strain epsilon corresponding to the peak intensity of the silty shale sample in a conventional testc1.27%; then, carrying out a triaxial stress relaxation test on the sample by adopting a rheometer; and the confining pressure sigma in the conventional test3Same value, confining pressure σ applied to the test specimen in the stress relaxation test3Also 1MPa, maintaining confining pressure sigma3The change is not changed; applying axial strain epsilon in a separate loading mode, wherein the axial strain epsilon is respectively the peak strain epsilon of the sample in the conventional testc15%, 30%, 45%, 60%, 75% and 90%, i.e. 0.19%, 0.38%, 0.57%, 0.76%, 0.95% and 1.14%; after each stage of axial strain epsilon is applied, keeping the axial strain epsilon constant, and observing the change rule of the axial stress sigma of the sample along with the time t; when the increasing rate of the axial stress sigma is less than 0.001MPa/h, stopping applying the axial strain of the current stage, and applying the axial strain of the next stage until the sample is subjected to relaxation failure to obtain a stress relaxation curve of the silty shale sample (as shown in figure 2);
c. the stress relaxation curve of the silty mudstone obtained in the step b is divided into three stages: the fast relaxation, deceleration relaxation and acceleration relaxation phases (as shown in fig. 3); under the action of axial strain epsilon of 0.19%, 0.38%, 0.57%, 0.76% and 0.95%, respectively, a sample stress relaxation curve only has a rapid relaxation stage and a deceleration relaxation stage, and under the action of axial strain epsilon of 1.14%, after the sample stress relaxation curve passes through the rapid relaxation stage and the deceleration relaxation stage, an acceleration relaxation stage also occurs, and the sample is subjected to relaxation failure, so that the instability critical strain interval range of the silty shale sample is as follows: 0.95% -1.14%;
d. b, analyzing the stress relaxation characteristic of the rock according to the stress relaxation curve of the silty mudstone obtained in the step b; a nonlinear rheological model is selected to describe the rapid relaxation, deceleration relaxation and acceleration relaxation stages of the silty mudstone; identifying the test data by using a least square method, and setting a correlation coefficient square R of a fitting value of the model and the test value2And if the stress relaxation model parameter is more than 0.95, obtaining the stress relaxation model parameters of the silty mudstone under different axial strains, wherein the stress relaxation model parameters are shown in the table 1.
TABLE 1 stress relaxation model parameters of silty mudstone under different axial strains
| Axial strain ε/% | E1/MPa | E2/MPa | η1/(MPa·h) | η2/(MPa·h) | b | R2 |
| 0.19 | 27.510 | 102.285 | 901.965 | 23.915 | 0.99631 | |
| 0.38 | 28.755 | 51.143 | 450.933 | 11.950 | 0.99792 | |
| 0.57 | 29.170 | 34.095 | 300.647 | 7.970 | 0.99864 | |
| 0.76 | 24.376 | 25.571 | 225.494 | 5.979 | 0.99854 | |
| 0.95 | 21.502 | 20.457 | 180.393 | 4.783 | 0.99958 | |
| 1.14 | 23.631 | 20.237 | 135.295 | 6.626 | -31.348 | 0.98158 |
e. According to the size of the sample prepared in the step a and the peak strain epsilon of the sample obtained in the step bc1.27% in finite difference software FLAC3DEstablishing a corresponding silty mudstone sample numerical model, and carrying out mesh subdivision and cell assignment; d, carrying out secondary development on the nonlinear rheological model obtained in the step d and embedding the nonlinear rheological model into FLAC3DIn software, applying the model parameters obtained in the step d to a numerical model; to try outB, applying a fixed boundary condition to the bottom of the sample, applying confining pressure to the top and two sides of the sample, wherein the confining pressure is the same as that in the indoor test in the step b and is also 1MPa, and keeping the confining pressure constant; applying a set axial strain to the top of the sample, keeping the axial strain unchanged, and recording and outputting a change curve of the axial stress sigma of the sample along with time t by software; changing the applied axial strain value to ensure that the numerical model can accurately carry out triaxial stress relaxation numerical tests of silty mudstone under different axial strains;
f. setting the precision of the rock instability critical strain to be solved to be 0.01%, equally dividing the silt shale instability critical strain interval of 0.95% -1.14% obtained in the step c into 19 parts, wherein the axial strains to be applied in the numerical test are respectively 0.96%, 0.97%, 0.98%, … and 1.14%; applying the silty mudstone numerical model established in the step e, and gradually applying the axial strain value from low to high to perform a triaxial stress relaxation numerical test of the rock; when the axial strain is increased to 1.02%, the stress relaxation numerical test curve of the sample only has the rapid relaxation and deceleration relaxation stages, and does not have the acceleration relaxation stage, and under the action of the next-stage axial strain of 1.03%, the stress relaxation numerical test curve of the sample passes through the rapid relaxation and deceleration relaxation stages and has the acceleration relaxation stage (as shown in figure 4), and the instability critical strain of the silty shale sample is 1.02% according to the set precision.
Example 2:
taking a certain hydraulic engineering carbon slate in the western part of China as an example, determining the instability critical strain of the carbon slate considering the time effect based on indoor tests and numerical tests, and specifically operating the following steps:
a. collecting carbon slate rock blocks on site, transporting the carbon slate rock blocks to a laboratory, drilling cores by a water drilling method for sampling, cutting and flattening two end faces of the rock cores by a sawing stone cutting machine, and grinding the rock cores on a stone grinding machine to prepare standard cylindrical samples with the diameter of 50mm and the height of 100 mm; the unevenness deviation of the end face of the sample is controlled within +/-0.003 mm, and the perpendicularity deviation of the end face to the axis of the sample is controlled within +/-0.25 ℃;
b. firstly, a rock pressure testing machine is adopted to carry out a conventional triaxial test on a carbon slate sample, and the confining pressure sigma is determined according to the actual lateral stress of the rock in the engineering3Taking the strain as 0.5MPa, and obtaining the peak strain epsilon corresponding to the peak intensity of the carbonaceous slate sample in a conventional testc1.060%; then, carrying out a triaxial stress relaxation test on the sample by adopting a rheometer; and the confining pressure sigma in the conventional test3Same, confining pressure σ applied to the specimen in the stress relaxation test3The pressure is also 0.5MPa, and the confining pressure is kept unchanged; applying axial strain epsilon in a separate loading mode, wherein the axial strain epsilon is respectively the peak strain epsilon of the sample in the conventional testc10%, 20%, 30%, 40% and 50%, i.e. 0.106%, 0.212%, 0.318%, 0.424% and 0.530%; after each stage of axial strain epsilon is applied, keeping the axial strain epsilon constant, and observing the change rule of the axial stress sigma of the sample along with the time t; when the increasing rate of the axial stress sigma is less than 0.001MPa/h, stopping applying the axial strain of the current stage, and applying the axial strain of the next stage until the sample is subjected to relaxation failure to obtain a stress relaxation curve of the carbon slate sample (as shown in figure 5);
c. the stress relaxation curve of the carbonaceous slate obtained in the step b is divided into three stages: a rapid relaxation, deceleration relaxation and acceleration relaxation phase; under the action of axial strain epsilon of 0.106%, 0.212%, 0.318% and 0.424%, respectively, the stress relaxation curve of the sample only has a rapid relaxation stage and a deceleration relaxation stage, and under the action of axial strain epsilon of 0.530%, after the stress relaxation curve of the sample passes through the rapid relaxation stage and the deceleration relaxation stage, an acceleration relaxation stage also occurs, the sample is subjected to relaxation failure, and the interval range of the instability critical strain of the carbon slate sample is as follows: 0.424% -0.530%;
d. b, analyzing the stress relaxation characteristic of the rock according to the stress relaxation curve of the carbonaceous slate obtained in the step b; a nonlinear rheological model is selected to describe the rapid relaxation, deceleration relaxation and acceleration relaxation stages of the carbonaceous slates; identifying test data by least square method, and setting modelCorrelation coefficient squared R of fitting value and test value2And if the stress relaxation model parameter is more than 0.95, the stress relaxation model parameters of the carbon slates under different axial strains are obtained (shown in the table 2).
TABLE 2 stress relaxation model parameters of carbonaceous slates under different axial strains
| Axial strain ε/% | E1/MPa | E2/MPa | η1/(MPa·h) | η2/(MPa·h) | b | R2 |
| 0.106 | 22.976 | 88.726 | 4868.634 | 18.690 | 0.98700 | |
| 0.212 | 21.019 | 98.524 | 2023.061 | 13.234 | 0.99821 | |
| 0.318 | 20.157 | 107.546 | 2036.117 | 65.253 | 0.99612 | |
| 0.424 | 19.627 | 117.492 | 1603.014 | 59.611 | 0.99035 | |
| 0.530 | 19.330 | 843.298 | 139.686 | 22.532 | -75.189 | 0.99604 |
e. According to the size of the sample prepared in the step a and the peak strain epsilon of the sample obtained in the step bc1.060% in finite difference software FLAC3DEstablishing a corresponding carbon slate sample numerical model, and carrying out mesh subdivision and cell assignment; d, carrying out secondary development on the nonlinear rheological model obtained in the step d and embedding the nonlinear rheological model into FLAC3DIn software, applying the model parameters obtained in the step d to a numerical model; b, applying a fixed boundary condition to the bottom of the sample, and applying confining pressure to the top and two sides of the sample, wherein the magnitude of the confining pressure is equal to that of the indoor test in the step bMeanwhile, the pressure is also 0.5MPa, and the confining pressure is kept constant; applying a set axial strain to the top of the sample, keeping the axial strain unchanged, and recording and outputting a change curve of the axial stress sigma of the sample along with time t by software; changing the applied axial strain value to ensure that the numerical model can accurately carry out triaxial stress relaxation numerical tests of the carbonaceous slates under different axial strains;
f. setting the precision of the rock instability critical strain to be solved to be 0.001%, equally dividing the carbon slate instability critical strain interval of 0.424% -0.530% obtained in the step c into 106 parts, wherein the axial strains to be applied in the numerical test are respectively 0.425%, 0.426%, 0.427%, … and 0.530%, applying the carbon slate numerical model established in the step e, and applying the axial strain values step by step from low to high to perform the rock triaxial stress relaxation numerical test; when the axial strain is increased to 0.461%, the test curve of the sample stress relaxation number still only has the rapid relaxation and deceleration relaxation stages, and does not have the acceleration relaxation stage, and under the action of the next stage of axial strain of 0.462%, the test curve of the sample stress relaxation number passes through the rapid relaxation and deceleration relaxation stages, and has the acceleration relaxation stage (as shown in figure 6), and the instability critical strain of the carbon slate sample is 0.461% according to the set precision.
Claims (7)
1. A method for determining a critical strain for rock destabilization considering time effects, the method comprising the steps of:
a. preparing a rock sample;
b. performing a triaxial stress relaxation indoor test on the prepared rock sample by adopting a rheometer to obtain a stress relaxation curve of the rock;
c. determining a rock instability critical strain interval through a triaxial stress relaxation indoor test;
d. according to the obtained rock stress relaxation curve, establishing a stress relaxation model of the rock sample to obtain model parameters;
e. b, establishing a corresponding numerical model of the rock sample in numerical software according to the size and the characteristics of the rock sample prepared in the step a;
f. and d, equally dividing the rock instability critical strain interval obtained in the step c into a plurality of parts, taking the parts as axial strain values to be applied in the numerical test, carrying out a triaxial stress relaxation numerical test on the rock sample, and obtaining an accurate value of the instability critical strain of the rock sample through the triaxial stress relaxation numerical test.
2. The method for determining the rock destabilization critical strain considering the time effect according to claim 1, wherein the rock sample in the step a is prepared by the following steps:
the rock mass is gathered on the scene, transports the laboratory, adopts the water drilling method to bore the core sample to the rock mass, cuts core both ends face with the sawing machine and levels, grinds on the stone mill, makes the ratio of height and diameter 2: 1, cylindrical rock sample; the unevenness deviation of the end face of the sample is controlled within +/-0.003 mm, and the verticality deviation of the end face to the axis of the sample is controlled within +/-0.25 degrees.
3. The method for determining the critical strain for rock destabilization considering time effect according to claim 1, wherein the operation method of the triaxial stress relaxation laboratory test in the step b is as follows:
firstly, a conventional triaxial test is carried out on a rock sample to obtain strain corresponding to the peak intensity of the sample, namely peak strain epsilonc(ii) a Then carrying out triaxial stress relaxation indoor test on the rock sample; determining the test confining pressure sigma according to the lateral stress of the rock in the engineering3Applying a confining pressure σ to the sample3To a predetermined value, maintaining the confining pressure σ3The change is not changed; applying axial strain epsilon to the sample from low to high by adopting a respective loading mode; the peak strain epsilon of the sample obtained in the conventional triaxial testc10 to 15 percent of the strain is taken as the axial strain difference value to be applied in the stress relaxation test, namely the first-stage axial strain value is the peak strain epsilon of the samplec10% -15% of the strain value of the second-stage axial strain is the peak strain epsilon of the samplec20% -30% of the total weight of the product, and so on; after each stage of axial strain epsilon is applied, keeping the axial strain epsilon constant, and observing and recording the change characteristics of the axial stress sigma of the sample along with the time t; and when the increasing rate of the axial stress sigma is less than 0.001MPa/h, stopping applying the axial strain of the current stage, and applying the axial strain of the next stage until the sample is subjected to relaxation failure to obtain a stress relaxation curve of the sample.
4. The method for determining the rock destabilizing critical strain considering the time effect according to the claim 1, characterized in that the method for determining the rock destabilizing critical strain interval in the step c comprises the following steps:
the stress relaxation curve of the rock sample obtained in the step b is divided into three stages: a rapid relaxation, deceleration relaxation and acceleration relaxation phase; at a certain level of axial strain epsilonnUnder the action of the stress relaxation curve of the sample, only rapid relaxation and deceleration relaxation stages occur, and the axial strain epsilon of the next stage isn+1Under the action of (1), after a stress relaxation curve of a sample passes through a rapid relaxation stage and a deceleration relaxation stage, an acceleration relaxation stage is generated, so that the sample is subjected to relaxation failure, and the interval range of rock instability critical strain is as follows: epsilonn～εn+1。
5. The method for determining the critical strain for rock destabilization considering time effect according to claim 1, wherein the operation method for establishing the stress relaxation model of the rock sample and obtaining the model parameters in the step d comprises the following steps:
b, analyzing the stress relaxation characteristic of the rock according to the stress relaxation curve of the rock sample obtained in the step b; considering the characteristics of the stress relaxation stage, establishing mechanical models of the rock in different stress relaxation stages; when the stress relaxation curves of the rock sample under all levels of axial strain are in rapid relaxation and deceleration relaxation stages, selecting a Hooke-Kelvin rheological model; the stress relaxation curve of the rock sample under the current several levels of axial strain is expressed as a rapid relaxation stage and a deceleration relaxation stage, and the stress relaxation curve of the rock sample under the last level of axial strain is expressed as a rapid relaxation stage, a deceleration relaxation stage and an acceleration relaxation stage, and then a nonlinear rheological model is selected; according to the established rock stress relaxation model, identifying test data by adopting a least square method, a regression analysis method or a particle swarm optimization algorithm; and continuously adjusting model parameters to enable a model fitting curve to be overlapped with a test curve as much as possible, wherein the fitting error is in a set range, and the optimal parameters obtained by fitting are used as rock stress relaxation model parameters.
6. The method for determining the critical strain for rock destabilization considering time effect according to claim 1, wherein the corresponding numerical model establishing method of the rock sample in the step e comprises the following steps:
according to the size of the rock sample prepared in the step a and the peak strain of the sample obtained in the conventional triaxial test in the step b, establishing a corresponding numerical model in numerical software, and carrying out mesh generation and unit assignment; the boundary conditions and the operation method of the numerical model are the same as those of the step b; and d, applying the rock stress relaxation model and the parameters obtained in the step d to a numerical model, so that the numerical model can accurately perform rock stress relaxation numerical tests.
7. The method for determining the rock destabilizing critical strain considering the time effect according to claim 1, wherein the specific method for obtaining the accurate value of the rock destabilizing critical strain in the step f is as follows:
equally dividing the rock instability critical strain interval obtained in the step c into L parts as an axial strain value to be applied in a numerical test, namely epsilonn、…、εk、εk+1、…、εn+1(ii) a The L value is determined according to the set rock instability critical strain precision, and the higher the set instability critical strain precision is, the larger the L value is; applying the numerical model established in the step e, applying axial strain from low to high by adopting a respective loading mode, and performing a rock triaxial stress relaxation numerical test to obtain a change curve of the axial stress sigma of the sample along with the time t under each level of axial strain; when in the k-th order of axial strain εkUnder the action, the stress relaxation numerical test curve of the sample shows rapid relaxation and deceleration relaxation stages, and the axial strain epsilon is in the k +1 st levelk+1Under the action, after the test curve of the stress relaxation numerical value of the sample passes through the rapid relaxation stage and the deceleration relaxation stage, the accelerated relaxation stage appears, and when the rock sample is subjected to relaxation and damage, the axial strain epsilonkIs an accurate value of rock instability critical strain.
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