CN103994928A - Mechanics-acoustics combined testing method in orientated rock extrusion fracture process - Google Patents

Abstract

The invention discloses a mechanics-acoustics combined testing method in orientated rock extrusion fracture process, belonging to the technical field of physical mechanical behavior research in the rock fracture process. The method comprises the following steps: preparing a rock test sample, dividing a stress applying area, pasting a strain gage, fixing an ultrasonic wave probe and an acoustic emission sensor, putting the rock test sample into a pressure machine, additionally arranging a partial loading pressing block between the rock test sample and a pressing head, centering and aligning the partial loading pressing block to the stress applying area, starting the pressure machine for applying the stress in a gradient manner, acquiring data signals through the acoustic emission sensor, the ultrasonic wave probe and the strain gage, stopping stress applying till the rock test sample has orientated macro cracks, and extracting the testing data for data analysis. By adopting a partial orientated applying mode, the formation of a macro crack side is manually controlled, the phenomena of the generation of multiple macro crack sides and intersected combination of macro cracks are effectively avoided, and further, the study on the physical mechanical behavior in the rock extrusion fracture process is possible.

Description

A Mechano-Acoustic Combined Testing Method for Rock Directional Compression Fracture Process

technical field

The invention belongs to the technical field of physical and mechanical behavior research of rock fracture process, and in particular relates to a mechanical-acoustic joint test method of rock directional extrusion fracture process.

Background technique

The study of the physical and mechanical behavior of the rock fracture process plays a very important role in the prediction of earthquakes, the study of the mechanism of earthquakes, and the inversion of the stress field of rock formations.

At this stage, carrying out physical and mechanical experiments of rock extrusion fracture in the laboratory environment is a means for relevant technicians to study the physical and mechanical behavior of rock fracture process.

Relevant technicians have carried out stress-strain mechanical tests of rock compression fractures under uniaxial and triaxial conditions, but there will always be multiple groups of macro-crack surfaces and macro-cracks in the experimental process. It was a great inconvenience, and it was impossible to explain the phenomenon of rock extrusion and fracture well.

Because rocks are often accompanied by acoustic emission phenomena in the process of extrusion and fracture, studies have shown that the acoustic signals emitted during rock extrusion and fracture can well explain the physical and mechanical behavior of rock fractures, so related technicians have identified two The main acoustic testing methods include acoustic emission testing and ultrasonic testing. Acoustic emission testing can be used to understand the damage evolution process of rocks, and ultrasonic testing can well characterize the internal changes and damage degrees of rocks.

However, there is currently no effective method that can combine mechanical testing and acoustic testing for simultaneous testing, and avoid the appearance of multiple groups of macroscopic crack surfaces and the occurrence of macroscopic crack cross-combination during the testing process. I want to study further For the physical and mechanical behavior of rock during extrusion and fracture, the existing testing technology cannot meet this goal for the time being.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a combined mechanical-acoustic testing method for the directional extrusion fracture process of rocks. By means of local directional loading, the formation of macro-crack surfaces is manually controlled, effectively avoiding the generation of multiple sets of macro-crack surfaces. The phenomenon of cross-combination with macroscopic cracks occurs; while the mechanical test is carried out, the acoustic test is simultaneously realized, which provides the possibility for further research on the physical and mechanical behavior of the rock extrusion fracture process.

In order to achieve the above object, the present invention adopts the following technical scheme: a mechanical-acoustic joint testing method for rock directional extrusion fracture process, comprising the following steps:

Step 1: Prepare a rock sample, the ratio of length, height and width of the rock sample is 3:2:1;

Step 2: Delineate the stress loading area on the two long × wide end faces of the rock sample respectively, and the stress loading area is located at the center of the long × wide end face;

Step 3: Paste strain gauges on one long × high-end surface of the rock sample;

Step 4: Fix the ultrasonic probes on the two high × wide end faces of the rock sample, including the ultrasonic transmitting probe and the ultrasonic receiving probe. The ultrasonic transmitting probe is located at the center of one high × wide end face, and the ultrasonic receiving probe is located at the center of the other high × wide end face. ;

Step five: fixing the acoustic emission sensor on the long × high-end surface of the rock sample;

Step 6: Place the rock sample between the upper indenter and the lower indenter of the rock press, add a local loading block at the upper end between the rock sample and the upper indenter, and place the rock sample and the lower indenter Install the lower end partial loading press block between them, the upper end partial loading press block and the lower end partial loading press block are aligned with the stress loading area of the long × wide end face of the rock sample at the same time;

Step 7: Start the rock press, and carry out stepwise stress loading on the rock sample; at the same time, continuously and real-time collect the acoustic emission signal through the acoustic emission sensor, collect the ultrasonic signal through the ultrasonic probe, and collect the strain signal through the strain gauge until the rock test Oriented macroscopic cracks appear, and the loading stops;

Step 8: Extract test data and analyze the acquired test data.

The ultrasonic transmitting probe, the ultrasonic receiving probe and the rock sample are coupled through a coupling agent.

The upper and lower partial loading press blocks are both rigid pads, the length of which is half the length of the rock sample, and the width is equal to that of the rock sample.

A friction reducer is added between the rock sample and the locally loaded compact at the upper end, and the locally loaded compact at the lower end. The friction reducer is polytetrafluoroethylene film or stearic acid synthetic friction reducer.

A balance ball head is installed between the local loading pressure block at the upper end and the upper pressure head.

Acquisition of ultrasonic signals by the ultrasonic probe needs to be performed at the stress loading step, that is, an ultrasonic test is performed every time the stress loading increases by one level.

Beneficial effects of the present invention:

The present invention can artificially control the formation of macro-crack surfaces by means of local directional loading, effectively avoiding the generation of multiple sets of macro-crack surfaces and the occurrence of cross-combination phenomena of macro-cracks; while performing mechanical tests, the simultaneous realization of acoustic tests provides further research The physical and mechanical behavior in the process of rock extrusion and fracture provides the possibility.

Description of drawings

Fig. 1 is the installation state schematic diagram before rock sample test among the embodiment;

Fig. 2 is a rock sample stress loading curve figure in the embodiment;

Fig. 3 is the graph of relationship between strain and stress, ultrasonic wave velocity, and acoustic emission pulse number in the embodiment;

In the figure, 1—rock sample, 2—short grid strain gauge, 3—long grid strain gauge, 4—partially loaded pressure block at the upper end, 5—locally loaded pressure block at the lower end, 6—balance ball head, 7—ultrasonic transmitting probe , 8—ultrasonic receiving probe, 9—acoustic emission sensor, 10—upper pressure head, 11—lower pressure head.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

The mechanical-acoustic combined testing method of the rock directional extrusion fracture process comprises the following steps:

Step 1: Prepare the rock sample 1, the size ratio of its length, height, and width is 3:2:1. In this embodiment, the length, height, and width of the rock sample 1 are 200mm, 100mm, and 50mm. Each end face of sample 1 needs to be ground and flattened so that the parallel error of each two parallel end faces does not exceed 0.02mm;

Step 2: Delineate stress loading areas on the two length x width (200mm x 50mm) end faces of the rock sample 1 respectively, and the stress loading area is located at the center of the length x width (200mm x 50mm) end faces;

Step 3: Paste strain gauges on a long × high (200mm × 100mm) end surface of the rock sample 1. The strain gauges include short-grid strain gauge 2 and long-grid strain gauge 3, and the short-grid strain gauge 2 is used to measure the rock sample The local strain at one point, the long grid strain gauge 3 is used to measure the average strain of the rock sample 1 as a whole;

Step 4: Fix the ultrasonic probes on the two high × wide (100mm × 50mm) end faces of the rock sample 1, including the ultrasonic transmitting probe 7 and the ultrasonic receiving probe 8, and the ultrasonic transmitting probe 7 is located on a height × width (100mm × 50mm) At the center of the end face, the ultrasonic receiving probe 8 is located at the center of another end face with height×width (100mm×50mm);

Step 5: fixing the acoustic emission sensor 9 on the end face of the length × height (200mm × 100mm) of the rock sample 1;

Step 6: Place the rock sample 1 between the upper indenter 10 and the lower indenter 11 of the rock press, and install an upper-end partial loading briquetting block 4 between the rock sample 1 and the upper indenter 10. Between the sample 1 and the lower indenter 11, add the lower end partial loading press block 5, the upper end partial loading press block 4, and the lower end partial loading press block 5 simultaneously with the stress loading of the end face of the length × width (200mm × 50mm) of the rock sample 1. The area is centered, as shown in Figure 1;

Step 7: Start the rock press, and perform stepwise stress loading on the rock sample 1 with a loading gradient of 20KN and a loading rate of 1KN/s, as shown in Figure 2; at the same time, the acoustic emission signal is continuously monitored through the acoustic emission sensor 9 Real-time collection, collecting ultrasonic signals through ultrasonic probes, and collecting strain signals through strain gauges, until directional macroscopic cracks appear in rock sample 1, and the loading stops;

Step 8: Extract the test data, analyze the obtained test data, draw the relationship curve between strain and stress, ultrasonic wave velocity, and acoustic emission pulse number through the test data, as shown in Figure 3.

In order to reduce test errors and improve test accuracy, the ultrasonic transmitting probe 7, the ultrasonic receiving probe 8 and the rock sample 1 are coupled through a coupling agent.

The upper locally loaded briquetting block 4 and the lower end locally loaded briquetting block 5 are both rigid pads whose length is half the length of the rock sample 1 and whose width is equal to that of the rock sample 1, and their function is to control the formation of macroscopic cracks.

In order to reduce the friction between the rock sample 1 and the local loading briquetting block 4 at the upper end and the local loading briquetting block 5 at the lower end, and reduce the interference of friction on the acoustic emission signal, the rock sample 1 and the local loading briquetting block 4 at the upper end, A friction reducer is added between the local loading briquetting blocks 5 at the lower end, and the friction reducer adopts polytetrafluoroethylene film or stearic acid synthetic friction reducer.

In order to ensure the force balance of the rock sample 1 , a balance ball head 6 is installed between the local loading briquetting block 4 at the upper end and the upper pressing head 10 .

In order to prevent the mutual interference between the acoustic emission signal and the ultrasonic signal, the ultrasonic signal collection by the ultrasonic probe needs to be carried out at the stress loading step, that is, an ultrasonic test is performed every time the stress loading increases by one level.

The solutions in the embodiments are not intended to limit the scope of patent protection of the present invention, and all equivalent implementations or changes that do not deviate from the present invention are included in the patent scope of this case.

Claims (6)

1. a mechanical-acoustic joint testing method of rock directional extrusion fracture process, is characterized in that comprising the steps: Step 1: Prepare a rock sample, the ratio of length, height and width of the rock sample is 3:2:1; Step 2: Delineate the stress loading area on the two long × wide end faces of the rock sample respectively, and the stress loading area is located at the center of the long × wide end face; Step 3: Paste strain gauges on one long × high-end surface of the rock sample; Step 4: Fix the ultrasonic probes on the two high × wide end faces of the rock sample, including the ultrasonic transmitting probe and the ultrasonic receiving probe. The ultrasonic transmitting probe is located at the center of one high × wide end face, and the ultrasonic receiving probe is located at the center of the other high × wide end face. ; Step five: fixing the acoustic emission sensor on the long × high-end surface of the rock sample; Step 6: Place the rock sample between the upper indenter and the lower indenter of the rock press, add a local loading block at the upper end between the rock sample and the upper indenter, and place the rock sample and the lower indenter Install the lower end partial loading press block between them, the upper end partial loading press block and the lower end partial loading press block are aligned with the stress loading area of the long × wide end face of the rock sample at the same time; Step 7: Start the rock press, and carry out stepwise stress loading on the rock sample; at the same time, continuously and real-time collect the acoustic emission signal through the acoustic emission sensor, collect the ultrasonic signal through the ultrasonic probe, and collect the strain signal through the strain gauge until the rock test Oriented macroscopic cracks appear, and the loading stops; Step 8: Extract test data and analyze the acquired test data. 2. A combined mechanical-acoustic testing method for rock directional extrusion fracture process according to claim 1, characterized in that: the ultrasonic transmitting probe, the ultrasonic receiving probe and the rock sample are coupled through a coupling agent. 3. the mechanical-acoustic joint testing method of a kind of rock directional extrusion fracture process according to claim 1, is characterized in that: described upper end local loading briquetting block, lower end local loading briquetting block are all rigid pads, and its length is Half the length of the rock sample, its width is equal to the rock sample. 4. The mechanical-acoustic joint testing method of a kind of rock directional extrusion fracture process according to claim 1, characterized in that: between the rock sample and the local loading briquetting block at the upper end, and the local loading briquetting block at the lower end, all add The antifriction agent is used, and the antifriction agent adopts polytetrafluoroethylene film or stearic acid synthetic antifriction agent. 5. A combined mechanical-acoustic testing method for rock directional extrusion fracture process according to claim 1, characterized in that: a balance ball head is installed between the local loading pressure block at the upper end and the upper pressure head. 6. The mechanical-acoustic joint testing method of a rock directional extrusion fracture process according to claim 1, characterized in that: collecting ultrasonic signals through the ultrasonic probe needs to be carried out at the stress loading step, that is, every increase in stress loading At level one, an ultrasonic test is performed.