CN109991097B - Rock loading and unloading response ratio change point judging method based on damage strength - Google Patents
Rock loading and unloading response ratio change point judging method based on damage strength Download PDFInfo
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Abstract
The invention discloses a rock loading and unloading response ratio change point judging method based on damage strengthc(ii) a Taking a sample with the same specification, and using sigmacCarrying out uniaxial compression grading loading and unloading tests on the strain to obtain axial strain and lateral strain; drawing an axial stress-axial strain curve, determining loading and unloading peak points of each level of loading and unloading tests, calculating loading and unloading response ratios of each level of loading and unloading tests according to the loading and unloading peak points, and drawing a loading and unloading response ratio-axial strain curve; and summing the axial strain and the lateral strain corresponding to the same axial stress to obtain volume strain, drawing an axial stress-volume strain curve and determining an inflection point of the curve, wherein the axial stress corresponding to the inflection point is the damage strength, and then determining a loading and unloading response comparison change point by utilizing the damage strength. The problem of rock unipolar compression onset point discernment inaccurate and cause the incident is solved.
Description
The present application claims priority of a chinese patent application entitled "a method for discriminating rock load/unload response versus change point based on damage strength" filed by the chinese patent office on 2/2019 and having application number 201910108065.0, the entire contents of which are incorporated herein by reference.
Technical Field
The invention belongs to the technical field of rock damage judgment, and particularly relates to a rock loading and unloading response ratio change point judgment method based on damage strength.
Background
The Load-Unload Response Ratio (LURR) theory is a theory for researching the nonlinear failure precursor and failure forecast of the rock or rock mass. At present, the loading-unloading response ratio theory has made a series of progress in the instability prediction of non-linear systems such as earthquake, landslide and the like. For the problem of the rock sample compression damage, along with the improvement of the loading force, when the rock sample is loaded to the later stage (the loading force is greater than 60% of peak strength), the sample can be converted from the elastic deformation stage to the fracture generation and expansion stage, and when the internal damage of the rock sample is accumulated to a certain degree, the rock sample enters the fracture unstable development until the fracture stage. When the rock sample is in an elastic deformation stage, reversibility is a basic characteristic of elastic deformation, the deformation modulus of a loading section and the deformation modulus of an unloading section are the same, after the rock sample enters a fracture and is unstably developed until a fracture stage, the deformation of the rock sample has irreversibility, the deformation modulus of the loading section is smaller than that of the rock sample in the unloading process, the difference shows a trend that the mechanical property of the rock begins to deteriorate, the trend can be very regularly reflected on the numerical value of a rock loading and unloading response ratio, specifically, the loading and unloading response ratio can be gradually increased along with the increase of loading force, and how to judge the starting point of the increasing trend becomes the most critical problem.
And defining the initial point of the gradual increase of the loading and unloading response ratio as the change point of the loading and unloading response ratio, wherein after the rock reaches the fracture unstable development until the destruction stage, the internal fracture of the rock starts to be communicated, and the phenomenon that the loading and unloading response ratio starts to gradually increase at the moment. The loading and unloading response ratio change point is the starting point of the fracture instability development stage, at the moment, the opening crack in the sample along the main stress direction is gradually communicated, and a macroscopic fracture surface is about to be generated in the rock sample, so that the integral instability of the rock sample is predicted. Compared with a judgment method of a change point, the method for determining the loading and unloading response can more accurately analyze the damage evolution process of the rock in the loading and unloading process, and can predict the integral instability of the rock.
Disclosure of Invention
The invention aims to provide a rock load and unload response ratio change point judging method based on damage strength, which aims to solve the problems of accurately identifying rock uniaxial compression change points in determining rock damage strength and safety accidents caused by inaccurate identification of the rock uniaxial compression change points.
The invention adopts the technical scheme that a rock loading and unloading response comparison change point judging method based on damage strength comprises the following specific steps:
step S1, sampling on site, and processing the obtained rock blocks into a plurality of cylindrical samples;
step S2, carrying out uniaxial compression test, loading a cylindrical sample until the rock sample is destroyed, measuring the axial stress peak value of the rock sample, and taking the axial stress peak value as the uniaxial compressive strength sigma of the rock samplec；
Step S3, taking a cylindrical sample with the same specification, and utilizing the uniaxial compressive strength sigmacCarrying out uniaxial compression grading loading and unloading tests on the rock sample to obtain axial strain and lateral strain of the rock sample;
s4, drawing an axial stress-axial strain curve of the rock sample, and determining loading and unloading peak points of each stage of loading and unloading tests;
step S5, calculating the loading and unloading response ratio of each level of loading and unloading tests according to the loading and unloading peak points of each level of loading and unloading tests, and drawing a loading and unloading response ratio-axial strain curve;
step S6, summing the axial strain and the lateral strain corresponding to the same axial stress to obtain the volume strain of the rock sample, and drawing an axial stress-volume strain curve of the rock sample;
step S7, determining an inflection point of an axial stress-volume strain curve, wherein the axial stress corresponding to the inflection point of the axial stress-volume strain curve is the damage strength of the rock;
and step S8, determining the loading and unloading response change point by using the rock damage strength.
Further, the uniaxial compression step loading and unloading test of step S3 is first carried out until the uniaxial compression strength σ is obtainedc4% of the total weight and then unloaded to 0 as a class 1 load; then loaded to uniaxial compressive strength σc8% of (C), unload to uniaxial compressive strength σc4% of the total load as class 2 load; each stage of loading strength is increased by uniaxial compressive strength sigma compared with the previous stagecAnd 4% of the total weight of the rock sample, wherein the unloading strength of each stage is the loading strength of the previous stage, and the loading and unloading are carried out step by step until the rock sample is damaged.
Further, the loading and unloading peak points of the loading and unloading tests at each stage in the step S4 are the axial stress peak points of the loading and unloading tests at each stage in the axial stress-axial strain curve of the rock sample.
Further, the loading-unloading response ratio of each stage of loading-unloading test is calculated in step S5, where each stage of loading-unloading peak point is taken as an upper limit, data points with a certain length are respectively taken in a loading section before and an unloading section after each stage of loading-unloading peak point, then a slope of the loading section data points and a slope of the unloading section data points of each stage of loading-unloading test are fitted by using a least square fitting method, and a ratio of the slope of the unloading section data points of each stage of loading-unloading test to the slope of the loading section data points thereof is the loading-unloading response ratio of each stage of loading-unloading test.
Further, the inflection point of the axial stress-volume strain curve of step S7 is a volume strain peak point in a volume strain curve in the axial stress-volume strain curve of the rock sample.
Further, the specific process of step S8 is as follows: firstly, determining the axial strain corresponding to the damage strength in the axial stress-axial strain curve of the rock sample according to the rock damage strength, wherein the axial strain corresponding to the damage strength in the axial stress-axial strain curve of the rock sample is the damage strength, and the loading and unloading response ratio point corresponding to the loading and unloading response ratio-axial strain curve is the loading and unloading response ratio starting point of the rock sample.
Further, the uniaxial compression test in the step S2 and the uniaxial compression step loading and unloading test in the step S3 are both performed on an electrohydraulic servo material testing machine, and the loading rate is 12 KN/min.
Further, the diameter of the cylindrical sample in the step S1 is 48-52mm, and the length is 1.8-2.2 times of the diameter
The rock stress-volume strain inflection point early warning method has the advantages that firstly, the damage strength of the rock is determined through the rock axial stress-volume strain inflection point, the loading and unloading response variation strength is determined through the damage strength, the loading and unloading point corresponding to the loading and unloading response variation strength is the loading and unloading response variation point, in the rock loading process, the occurrence of the loading and unloading response variation point indicates that a rock sample is about to have instability damage, the rock loading and unloading response variation point can be accurately judged through the method, further early warning is carried out on rock damage, safety of personnel and test equipment in the test process is protected, and the problems that the rock uniaxial compression variation point is accurately identified in the rock damage strength determination and safety accidents are caused by inaccurate rock uniaxial compression variation point identification are effectively solved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic flow diagram of the process of the present invention;
FIG. 2 is a perspective view of a cylindrical test piece;
FIG. 3 is a schematic view of a rock sample staged loading and unloading scheme;
FIG. 4 is a schematic diagram of a least squares fit of load-unload response ratios;
FIG. 5 is a plot of loading and unloading response ratio as a function of axial strain calculated according to a least squares fit;
FIG. 6 is a graph for determining the loading and unloading response ratio change point of a rock according to the inflection point of an axial stress-volume strain curve;
FIG. 7 is a graph showing the relationship between the intensity of a lesion and the variation intensity determined by the difference method.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
And (3) carrying out a rock uniaxial compression grading loading and unloading test on the MTS815 electrohydraulic servo material testing machine, and judging the loading and unloading response comparison change point of the rock.
As shown in fig. 1, the method for discriminating the change point of the rock load and unload response ratio based on the damage strength specifically comprises the following steps:
(1) and (3) sampling on site, processing the obtained rock mass into a cylindrical sample, wherein the diameter D is 48-52mm, and the length L of the sample is 1.8-2.2 times of the diameter, as shown in figure 2. The test should be carried out as follows:
(2) according to rock mechanics uniaxial compression test regulations, 1 cylindrical rock sample is placed on a rigid electrohydraulic servo material control testing machine, loading is carried out at a force control loading rate of 12KN/min until the rock sample is destroyed, a stress-strain curve is obtained, and the peak value of the axial stress of the rock sample is used as the uniaxial compressive strength sigma of the rock samplec。
(3) 1 cylindrical rock sample with the same specification is taken again, the rock is subjected to graded loading and unloading test at the same force control loading rate, the loading and unloading scheme is shown in figure 3, and the test sample is firstly loaded to the uniaxial compressive strength sigmac4% of the total weight of the load, then unloading to 0, taking the load as the 1 st level load, then loading to 8% of the uniaxial compressive strength again, unloading to 4% of the load as the 2 nd level load; and then loading to 12 percent, unloading to 8 percent, taking the load as the 3 rd-level load, and repeating the steps until the rock sample is destroyed, thereby obtaining the axial strain and the lateral strain of the rock sample.
(4) And after a graded loading and unloading stress-strain curve of the rock sample is obtained, respectively taking 1MPa data downwards from the stress of the peak point on the axial stress of the loading section and the unloading section before and after each loading and unloading peak point, and calculating the loading and unloading response ratio by using a least square fitting method. The specific operation is that each stage of loading and unloading peak point is taken as an upper limit, 1MPa data is respectively taken in a loading section and an unloading section, and the slope of the loading section and the slope of the unloading section are respectively fitted according to a least square fitting method, as shown in FIG. 4, the response rates of the loading and unloading sections are the inverses of the slopes, and the loading and unloading response ratio of each stage is the ratio of the response rates of the loading section and the unloading section.
(5) And calculating the loading and unloading response ratio of the rock sample at each loading and unloading point to obtain a change curve of the loading and unloading response ratio along with the axial strain, and obtaining the volume strain of the rock through the sum of the axial strain and the lateral strain, referring to fig. 5.
(6) As shown in fig. 6, an axial stress-volume strain curve of the rock and an axial stress-axial strain curve of the rock are made, the inflection point position of the axial stress-volume strain curve is the damage strength of the rock, the loading and unloading response variation strength is the same as the damage strength of the rock, and the loading and unloading point at the current stage corresponding to the loading and unloading response variation strength is the loading and unloading response variation point.
Example 1:
taking the green sandstone as an example, firstly calculating the volume strain of the rock, then determining the damage strength according to the axial stress-volume strain inflection point, and then judging the loading and unloading response ratio change point of the green sandstone according to the damage strength, wherein the specific steps are as follows:
step 1: processing a rock block retrieved from an engineering site into a cylindrical rock sample with the diameter of 50mm and the length of 100mm, taking 1 rock sample with the same specification, carrying out a uniaxial compression test in an MTS815 electrohydraulic servo material testing machine, loading in a force control loading mode with the loading rate of 12KN/min, wherein the peak value of the axial stress of the rock sample is 80.1MPa, so that the uniaxial compressive strength sigma of the green sandstone sample isc＝80.10MPa。
step 2: uniaxial compressive strength σ according to step1cThe first-level load is determined to be 3.2MPa, the second-level and third-level loads are determined to be 6.4MPa and 9.6MPa, and the load ratio of each level is the last oneAnd the step load is increased by 3.2MPa, and the step load are gradually increased and unloaded until the rock sample is damaged.
step 3: taking 1 rock sample with the same specification, named green sandstone K1, performing uniaxial compression grading loading and unloading test on green sandstone K1, loading the test sample to rock damage at a force control loading rate of 12KN/min, loading the test sample to uniaxial compressive strength sigma as shown in figure 3 in a loading and unloading modec4% of the total weight of the load, then unloading to 0, taking the load as the 1 st level load, then loading to 8% of the uniaxial compressive strength again, unloading to 4% of the load as the 2 nd level load; and then loading to 12 percent, unloading to 8 percent, taking the load as the 3 rd-level load, and repeating the steps until the rock sample is destroyed, thereby obtaining the axial strain and the lateral strain of the rock sample.
step 4: and analyzing the axial stress-strain curve obtained in step3 to determine the position of each loading and unloading peak point, and respectively taking 1MPa data from the stress of the peak point downwards on the axial stresses of the loading section and the unloading section before and after each loading and unloading peak point to calculate the loading and unloading response ratio by using a least square fitting method. The specific operation is that each stage of loading and unloading peak points are taken as upper limits, 1MPa data is respectively taken in a loading section and an unloading section, and the slope of the loading section and the slope of the unloading section are respectively fitted according to a least square fitting method.
step 5: and step4, obtaining the slopes of the loading section and the unloading section, wherein the response rate of each level of loading section and unloading section is the reciprocal of the slope of the loading section and the unloading section, and the loading and unloading response ratio of each level of loading and unloading peak point is calculated by the ratio of the response rate of the loading section to the response rate of the unloading section.
Step 6: determining a loading and unloading response ratio change point according to the damage intensity: the volume strain of the rock is obtained through the sum of the axial strain and the lateral strain, an axial stress-volume strain curve of a rock sample is analyzed, the axial stress corresponding to the inflection point of the axial stress-volume strain curve is the damage strength of the rock, the axial stress corresponding to the loading and unloading response ratio inflection point is the attack strength of the rock, the volume strain is taken as a horizontal axis, the axial stress is taken as a vertical axis, the coordinate of the inflection point of the axial stress-volume strain curve of the green sandstone K1 is (0.0029, 66.66), the damage strength of the green sandstone K1 is 66.66MPa, the attack strength and the damage strength of the rock are the same, the loading and unloading response ratio attack strength is determined by utilizing the damage strength of the rock, and then the loading and unloading point corresponding to the loading and unloading response ratio attack strength at the current stage is the loading and unloading response ratio attack point. The strain strength of the green sandstone K1 determined according to the damage strength is 66.66MPa, and the loading and unloading stage number corresponding to the loading and unloading response ratio change point is 21.
TABLE 1 Strength of Change determined by Damage Strength method and Difference method
| Rock sample numbering | Strain strength/MPa determined from the damage strength | Loading and unloading response versus loading and unloading stage number corresponding to change point |
| K1 | 66.66 | 21 |
In addition, the change point of the loading and unloading response ratio is defined as the starting point of the gradual rise of the loading and unloading response ratio, and the method for determining the change point according to the definition comprises the following steps: recording the difference value of the loading and unloading response ratio of two adjacent stages as delta LURR and delta LURRι＝LURRι-LURRι-1(iota is not less than 2) wherein Δ LURRιFor the difference value of the loading-unloading response ratio, LURR, corresponding to the i-th loading-unloading testιFor i-th stage load-unload response ratio, LURRι-1The i-1 st loading/unloading response ratio. And (3) inspecting the corresponding delta LURR values after the 60% peak intensity of the rock sample, and if three continuous delta LURR values are positive, namely the rock loading and unloading response ratio is shown to be increased step by step, determining the peak value point of the previous stage loading and unloading test corresponding to the first delta LURR in the three continuous delta LURRFor the onset point, this method of determining the load/unload response ratio change point by definition is the load/unload response ratio difference method.
TABLE 2 variation strength of ten rocks determined according to damage strength and difference method
According to the damage strength method and the difference value method, the strain-starting points and the strain-starting strengths of 10 rock materials of Shaoyang twist granite, fine granite, yellow rust granite, red sandstone, black sandstone, green sandstone, limestone, Leishui Yang white marble, macrocrystalline marble and Guangxi white marble are calculated. As shown in Table 2, the stress-strain-response-to-load-versus-load-variation strengths determined by the damage strength and difference method are listed for 10 rock materials, and three rock samples are taken for each rock material to be tested according to the method for verifying the accuracy of the stress-strain-response-to-load-versus-variation point judgment method. FIG. 7 is a graph showing the point-change fit relationship of the loading/unloading response ratio determined by the two methods, wherein the horizontal axis P is2The vertical axis P is the change point of the loading and unloading response ratio determined by the loading and unloading response ratio difference method1The variable intensity fitting curve function of the loading and unloading response ratio determined by the two methods is P1＝0.99P2+0.31, indicating that the strain strength determined by the two methods is consistent, and also indicating that the stress-strain response of the rock is more accurate and feasible than the strain point by using the damage strength of the rock.
The loading and unloading response ratio change point determined by the loading and unloading response ratio difference method is consistent with the loading and unloading response ratio change point determined by the rock damage strength, three continuous change points are determined to be positive according to the loading and unloading response ratio change point determination method determined by the difference method, and the loading and unloading response ratio change point can be determined by only detecting the inflection point of the axial stress-volume strain curve of the rock sample by the damage strength-based loading and unloading response ratio change point determination method, so that the loading and unloading response ratio change point is more rapid and accurate.
The above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (1)
1. The method for judging the change point of the loading and unloading response ratio of the rock based on the damage strength is characterized by comprising the following specific steps of:
step S1, sampling on site, and processing the obtained rock blocks into a plurality of cylindrical samples;
step S2, carrying out uniaxial compression test, loading a cylindrical sample until the rock sample is destroyed, measuring the axial stress peak value of the rock sample, and taking the axial stress peak value as the uniaxial compressive strength sigma of the rock samplec；
Step S3, taking a cylindrical sample with the same specification, and utilizing the uniaxial compressive strength sigmacCarrying out uniaxial compression grading loading and unloading tests on the rock sample to obtain axial strain and lateral strain of the rock sample;
s4, drawing an axial stress-axial strain curve of the rock sample, and determining loading and unloading peak points of each stage of loading and unloading tests;
step S5, calculating the loading and unloading response ratio of each level of loading and unloading tests according to the loading and unloading peak points of each level of loading and unloading tests, and drawing a loading and unloading response ratio-axial strain curve;
step S6, summing the axial strain and the lateral strain corresponding to the same axial stress to obtain the volume strain of the rock sample, and drawing an axial stress-volume strain curve of the rock sample;
step S7, determining an inflection point of an axial stress-volume strain curve, wherein the axial stress corresponding to the inflection point of the axial stress-volume strain curve is the damage strength of the rock;
step S8, determining a loading and unloading response comparison change point by using the rock damage strength;
the single-shaft compression step loading and unloading test of the step S3 is carried out by firstly addingCompressive strength σ of load to uniaxialc4% of the total weight and then unloaded to 0 as a class 1 load; then loaded to uniaxial compressive strength σc8% of (C), unload to uniaxial compressive strength σc4% of the total load as class 2 load; each stage of loading strength is increased by uniaxial compressive strength sigma compared with the previous stagec4% of the total weight of the rock sample, wherein the unloading strength of each stage is the loading strength of the previous stage, and the loading and unloading are carried out step by step until the rock sample is damaged;
the loading and unloading peak points of the loading and unloading tests of each stage in the step S4 are the axial stress peak points of the loading and unloading tests of each stage in the axial stress-axial strain curve of the rock sample;
calculating the loading-unloading response ratio of each stage of loading-unloading tests in step S5, by taking each stage of loading-unloading peak point as an upper limit, respectively taking data points with a certain length in a loading section before and an unloading section after each stage of loading-unloading peak point, and then fitting the slope of the data points of the loading section and the slope of the data points of the unloading section of each stage of loading-unloading tests by using a least square fitting method, wherein the ratio of the slope of the data points of the unloading section of each stage of loading-unloading tests to the slope of the data points of the loading section is the loading-unloading response ratio of each stage of loading-unloading tests;
the inflection point of the axial stress-volume strain curve of the step S7 is the volume strain peak point in the volume strain curve in the axial stress-volume strain curve of the rock sample;
the specific process of step S8 is as follows: firstly, determining the axial strain corresponding to the damage strength in an axial stress-axial strain curve of a rock sample according to the rock damage strength, wherein the axial strain corresponding to the damage strength in the axial stress-axial strain curve of the rock sample is the damage strength, and a loading and unloading response ratio point corresponding to the loading and unloading response ratio-axial strain curve is the loading and unloading response ratio starting point of the rock sample;
the uniaxial compression test in the step S2 and the uniaxial compression graded loading and unloading test in the step S3 are both carried out on an electro-hydraulic servo material testing machine, and the loading rate is 12 KN/min;
the diameter of the cylindrical sample in the step S1 is 48-52mm, and the length of the cylindrical sample is 1.8-2.2 times of the diameter.
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| CN109781540A (en) | 2019-05-21 |
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