CN106442174A - True triaxial test method for simulating shearing type rock burst - Google Patents

Abstract

The invention discloses a true triaxial test method for simulating shear-type rockburst. The method adopts a true triaxial loading path and boundary conditions with one face empty and five faces stressed. By taking a larger-sized test piece and applying a certain The three-dimensional load and the loading rate in one direction are controlled, and the special mechanical behavior of the representative rock unit of the surrounding rock in the field during the process of tangential stress concentration is simulated by using a cuboid rock sample in a one-sided hollow and three-dimensional compressive stress state. Using this method, the whole process of gestation and occurrence of shear rockburst can be reproduced in the laboratory. The invention solves the problem that the traditional indoor test method cannot reasonably simulate the shear-type rockburst under complex stress conditions, and has important practical significance and academic value for promoting the mechanism and prediction research of this type of rockburst.

Description

A true triaxial test method for simulating shear rockburst

technical field

The invention belongs to the field of rock mechanics test research, in particular to a true triaxial test method for simulating shear-type rockburst.

Background technique

In recent years, the rapid development of mining, water conservancy, transportation, nuclear waste treatment and other fields has led to the continuous expansion of the depth and scale of underground engineering excavation, and the increasing ground stress has induced frequent rockburst disasters in surrounding rocks near the excavation boundary. Rockburst refers to the release of radial (perpendicular to the excavation boundary) stress and continuous concentration of tangential (parallel to the excavation boundary and perpendicular to the hole axis) stress during the excavation of deep underground engineering. The ejection failure phenomenon of brittle surrounding rock. Due to the sudden occurrence and limited underground engineering space, rockbursts often cause casualties, equipment damage and serious damage to the excavation surface. For example, on November 28, 2009, an extremely strong rockburst occurred in the construction drainage tunnel of the diversion tunnel of the Jinping II Hydropower Station. The depth of the blast pit was 8-9m, the vertical range was about 30m, the total volume of the explosion was nearly 1,000 cubic meters, and the support system was completely damaged. , The TBM equipment was buried, the main beam broke, 7 workers were killed and 1 was injured. Due to the complex internal and external conditions of gestation, the mechanism of rockburst is still not very clear, which has become an urgent problem to be solved in the field of rock mechanics and engineering, and it is urgent to carry out systematic laboratory simulation test research.

According to the mechanical mechanism of rockburst crater formation, rockburst can be divided into tension type and shear type rockburst. Different from the tensional rockburst caused by the sudden breakage of the rock slab after the rock slab splits in the surface surrounding rock (the rockburst crater is mostly "shallow pit type", and the rockburst debris is mainly in the shape of a plate), the shear type rockburst Explosions are often accompanied by shearing and slipping in the depths. Huge rock fragments are ejected and thrown out. Most of the burst craters are in the shape of "V" or "deep pit". . Shear rockburst refers to that after the excavation of relatively complete hard and brittle rock mass in deep underground engineering, the stress redistribution makes the tangential compressive stress of the local surrounding rock gradually increase, and the surface surrounding rock is compressed due to the loss of stress in the direction of the tunnel diameter. Under tension, the deep surrounding rock is subject to three-dimensional compression due to the stress in the direction of the tunnel diameter. When the tangential compressive stress exceeds the ultimate bearing capacity of the deep rock mass, the high-stress rock mass suddenly shears and slips, resulting in a large amount of rock mass. The strong dynamic geological disaster phenomenon thrown out by the ejection of blocks.

At present, in engineering practice, it is difficult to reasonably predict shear-type rockburst, and the prediction level cannot meet the requirements of engineering practice. The fundamental reason is that shear-type rockburst has many influencing factors and its occurrence mechanism is highly complex.

Indoor rockburst test is an important means of rockburst mechanism research. Most of the current rockburst test studies only focus on the instability and failure of the surrounding rock at the excavation boundary of the cavern, and simulate the stress state of the rockburst by means of uniaxial, biaxial, conventional triaxial and true triaxial loading and unloading tests. A large number of on-site investigations and theoretical analysis show that shear rockbursts mostly occur within a certain depth range near the excavation boundary, accompanied by shear slippage at depth, and often lag behind excavation significantly, and occur at the time of radial stress unloading. Later, during the process of continuous concentration of tangential stress, it belongs to the category of loading rockburst. After the cavern is excavated, the rock mass within a certain depth range near the excavation boundary is subjected to multiple stresses such as tangential normal stress, tunnel axial normal stress, radial normal stress, and surface shear stress. , Special true triaxial stress state of five-face force. At the same time, under high ground stress conditions, especially when the difference between the large and small principal stresses is large, the radial stress at the excavation boundary is zero, and the radial stress rises sharply away from the excavation boundary, and the radial stress in a certain depth near the excavation boundary is Clear gradient distribution. Therefore, the special true triaxial method of carrying out the loading test with one plane in the air and five planes under force, and considering the gradient distribution of radial stress, can truly simulate the on-site shear-type rockburst breeding environment.

The traditional true triaxial rockburst test does not consider the influence of the radial stress of the gradient distribution, the thickness direction of the specimen (the radial direction of the simulated tunnel) is small, and it is difficult for the test to simulate the stress of the rock mass within a certain depth range near the excavation boundary on site conditions, especially the gradient distribution of radial stress. At the same time, the ejection failure of small-sized specimens is difficult to present the shear-type rockburst failure in a certain depth range on site, and it is not easy to observe and record. The use of larger-sized specimens can better simulate the stress and boundary conditions of the surrounding rock within a certain depth range near the excavation boundary, and present the different fracture failure timing and modes of the rock mass along the radial direction, so as to reveal the breeding of shear-type rockbursts The mechanism.

To sum up, there is no reference method for the indoor test simulation of shear rockburst within a certain depth range near the excavation boundary. The present invention proposes a true triaxial test method for simulating shear-type rockbursts. The process of shearing rockbursts caused by the concentration of tangential compressive stress in caverns is reproduced indoors by loading larger-sized rock samples. Explosion mechanism research provides a practical and effective technical means.

Contents of the invention

The purpose of the present invention is to provide a true triaxial test method for simulating shear type rockburst.

The technical scheme that the present invention solves the problems of the technologies described above is as follows:

A true triaxial test method for simulating a shear-type rockburst, comprising the steps of:

Step 1: Determine the geometric dimensions of the test piece according to the loading conditions of the testing machine, the environment of the simulated object, and the strength properties of the rock to be used, and make a rock test piece that meets the accuracy requirements.

Step 2: Refer to the stress and boundary conditions of the surrounding rock on site, adopt a special true triaxial loading method with one face empty and five faces stressed, and consider the test results to select the confining pressure level, loading rate and control method.

Step 3: Simultaneously apply loads to the vertical and horizontal axes of the specimen to simulate the hoop stress of the tunnel and the stress in the direction of the longitudinal axis of the tunnel respectively, keep one side free in the horizontal radial direction, and then apply loads to the other side to simulate the excavation of the tunnel The free boundary formed and the radial stress distributed along the radial gradient.

Step 4: Stop loading after the specified load is reached in the horizontal axial direction and horizontal radial direction (single surface), and keep the load constant, and continue loading in the vertical direction with a force or displacement control method at an appropriate loading rate, and stop loading until the specimen is damaged load.

Step 5: During the vertical loading process, the deformation, stress, acoustic emission and other measuring instruments are used to monitor and record the test process, and a high-speed camera is used to monitor the damage phenomenon of the free surface of the rock sample.

Step 6: Collation and analysis of test data.

The test piece in the above step 1 is a representative unit of hard and brittle surrounding rock with good integrity. Specifically, cuboid rock blocks with a size of 200×100×100mm or larger, such as granite, marble, etc., are processed in strict accordance with the international rock Society of Mechanics Standards.

The special true triaxial loading in the above step 2, which is one-sided empty and five-sided loaded, is mainly realized by the friction or shear stress existing between the specimen and the fixture, which belongs to the loading of non-principal stress space, and can truly simulate a certain The force and restraint of rock mass in the depth range.

The horizontal axial stress and horizontal radial stress (gradient) of the above steps 3 and 4 are relatively large, especially the horizontal radial stress (gradient); the continuous loading of the vertical stress adopts displacement control or stress with a higher strain rate. control. Specifically, for a 200×100×100mm specimen, the stress loading rate should be controlled above 0.5MPa/s, or when loading with displacement control, the loading rate should be set above 0.1mm/min.

The horizontal axial stress and the horizontal radial stress (gradient) in the above step 3 are relatively large, especially the horizontal radial stress (gradient); the continuous loading of the vertical stress adopts displacement control or stress control with a higher strain rate. Specifically, for a 200×100×100mm specimen, the stress loading rate should be controlled above 0.5MPa/s, or when loading with displacement control, the loading rate should be set above 0.1mm/min.

The monitoring and recording of the test process in the above step 5 uses the testing machine control and acquisition system to record the stress-strain characteristics of the specimen, uses acoustic emission, recording pen, and decibel meter to record the physical signals during the test process, uses video recorders to record the test process images, and uses high-speed cameras Record the ejection process of fragments near the free surface of the specimen at the moment of rockburst, and take photos of the specimen in all directions after the test.

The test data collation and analysis of the above step 6, using the information of stress and deformation, crack development, dynamic ejection and other information of the rock monitored and recorded during the test, combined with the shape of the sample and the broken rock block, etc., to analyze the shear rockburst During the occurrence process, the deformation characteristics, fracture damage development, failure mode and kinetic energy release law of the rock were comprehensively analyzed. In particular, the use of professional image analysis software to track the flight trajectory of the ejected rock blocks in high-speed cameras, and further measure the ejection speed, can finally statistically estimate the kinetic energy of rock burst ejection damage.

Advantage and positive effect of the present invention:

1. The failure process of shear-type rockburst can be reproduced indoors, which provides a powerful test method for the study of the mechanism and prediction of shear-type rockburst.

2. It can truly simulate the environment for the occurrence of shear rockbursts. The method of the present invention carries out the loading rockburst test under the special true triaxial stress state where one face is empty and five faces are stressed, and the surrounding rock mass in a certain depth range near the tunnel excavation boundary is truly simulated by the excavation, and the radial stress is released. The force and constraint conditions of continuous concentration of tangential stress, and the obvious increase of radial stress in the depth. The failure phenomenon of the shearing rockburst test implemented by the method of the invention is basically the same as that of the on-site shearing rockburst failure phenomenon, and the failure characteristics and modes of the test pieces are more consistent with the on-site conditions.

3. It can reveal the failure characteristics and modes of surrounding rock at different depths near the excavation boundary. The method of the present invention adopts a relatively large-sized rock specimen, especially with a relatively large radial thickness. The test can simulate the failure characteristics and modes of the surrounding rock at different radial depths on the site, and can more realistically reproduce the cracking failure of the surface surrounding rock. On-site rockburst process of shear failure in deep surrounding rock.

4. It can realize the fine analysis of the failure process of shear rockburst. The method of the invention monitors and records in detail information or phenomena such as stress and deformation, crack development, and dynamic ejection of the rock during the rockburst process, and can obtain rock deformation characteristics, fracture damage development, and kinetic energy release laws.

The true triaxial test method for simulating shear rockburst of the present invention is obviously different from traditional uniaxial compression, conventional triaxial compression and true triaxial compression and other material mechanics test methods based on small-sized rock samples in the principal stress space, which overcomes the The above method cannot reasonably simulate the shear rockburst and its ejection process limitations under the three-dimensional stress condition, and provides strong support for the experimental research on the mechanism of the shear rockburst, which has important scientific and practical implications for scientific research and engineering practice. Engineering significance.

Description of drawings

Fig. 1 is a schematic diagram of the stress state of the rock mass within a certain depth range near the excavation boundary of the cavern according to the present invention.

Fig. 2 is a schematic diagram of the special true triaxial loading of the present invention in which one face is empty and five faces are stressed.

Fig. 3 is a test loading path diagram of the present invention.

Fig. 4 is the failure process diagram of the shear type rockburst test specimen of the present invention.

Fig. 5 is a crater morphological diagram of a shear rockburst according to the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments described here are for illustration only and do not limit the invention.

After the excavation of the deep underground cavern, the stress state of the rock mass within a certain depth range near the boundary is shown in Figure 1. The present invention adopts a true three-axis loading method in which one face is empty and five faces are loaded to simulate the above stress state, as shown in FIG. 2 . Among them, the vertical stress σ _z simulates the site tangential stress σ _θ , the horizontal stress σ _x simulates the site axial stress σ _a , and the horizontal stress σ _y simulates the site radial stress (distribution) σ _r . Referring to the stress redistribution process under site excavation disturbance, the test loading path shown in Fig. 3 was formulated and adopted. The hard and brittle rock specimens with good integrity, such as granite and marble, are selected as the representative units of the surrounding rock, and the length is 200 (height, along the vertical z)×100 (width, along the horizontal x)×100 ( Thick, cuboid rock specimens of y) mm or larger in the horizontal direction.

The present invention uses a true triaxial rockburst test system to carry out shear-type rockburst simulation, and the system includes a rockburst tester, a hydraulic power system, a control system, a high-speed camera, an acoustic emission instrument, a decibel meter, a digital video recorder, and the like. Among them, the rockburst testing machine is a high-pressure servo dynamic true three-axis press (patent number: ZL 2014 20227384.6). The main machine adopts an overall frame structure. Less than 5000kN/mm; the testing machine can independently add static loads in the x-direction and z-direction, and independently add static loads in the y-direction in two directions. The maximum loading static pressure is 5000kN, and the maximum loading static pressure in x direction and y direction is 3000kN. With the help of the loading fixture to provide clamping and friction, the testing machine can realize the special true triaxial stress state loading in the air on one side and the force on five sides.

The specific implementation steps of the true triaxial test method for simulating shear rockburst:

Step 1: Make rock specimens. Cut a cuboid specimen slightly larger than the standard size (exceeding 1~2mm) from the complete large rock body, and perform fine-tuning according to the fact that the unevenness of each surface is not greater than ±0.02mm, and the verticality deviation of two adjacent surfaces is not greater than ±0.25°. polished. Measure the physical and mechanical parameters such as the quality of the test piece and the ultrasonic wave velocity.

Step 2: Install the specimen and loading fixture. Assemble the specimen and the five-sided loading fixture (Figure 2), and install it to the corresponding loading position of the true triaxial testing machine, adjust and ensure the centering of the loading in all directions, and then arrange the acoustic emission probe and LVDT deformation gauge around the fixture.

Step 3: Experiment with preloading. First fit the vertical z-direction loading push head to the loading fixture, and load σ _z to 2MPa (ie 20kN), at a rate of 2mm/min; then fit the horizontal x-direction loading push head to the loading fixture, and load σ _x to 0.5MPa (ie 10kN), also at a rate of 2mm/min; finally, attach the horizontal y-direction loading push head (single side) to the loading fixture.

Step 4: Test loading. Load according to the stress path shown in Figure 3. First, stress control is used to load σ _z and σ _x at 0.5~1.0MPa/s; then stress control is used to load σy (single surface) at 0.1~ _0.5MPa /s; finally σ _x and _σy reach the specified load Stop loading and keep the load constant, and continue to load _σz at a higher strain rate until rockburst failure of the specimen occurs, and the test ends. Specifically, for a 200×100×100mm specimen, the subsequent loading rate of σ _z should be controlled above 0.5MPa/s, or when loading with displacement control, the loading rate should be set above 0.1mm/min.

Step 5: Test monitoring and recording. During the test, use the testing machine control and acquisition system to record the stress-strain characteristics of the specimen, use acoustic emission, recording pen, and decibel meter to record the physical signals during the test, use video recorders to record the images of the test process, and use high-speed cameras to record the moment of rockburst The ejection process of fragments near the free surface of the test piece, and all-round photographs of the test piece after the end of the test.

Step 6: Collation and analysis of test data. Using the rock stress and deformation, crack development, dynamic ejection and other information monitored and recorded during the test, combined with the sample and the shape of the broken rock block, etc., the deformation characteristics and fracture damage of the rock during the shear rockburst Comprehensive analysis of growth, failure mode and kinetic energy release. In particular, the use of professional image analysis software to track the flight trajectory of the ejected rock blocks in high-speed cameras, and further measure the ejection speed, can finally statistically estimate the kinetic energy of rock burst ejection damage.

Typical test case. A relatively complete marble rock block was recovered from the 2500m burial site of the diversion tunnel of the Jinping II Hydropower Station in Sichuan Province, and a cuboid marble specimen with a geometric size of 200×100×100mm was produced; the stress in the x direction was set to 40MPa, and the y direction The (single-sided) stress is 10MPa; correctly install the specimen and loading fixture, and complete the preloading; adopt stress control 0.5MPa/s, load σ _z and σ _x , and then adopt stress control 0.2MPa/s, load σ _y ( After σ _x reaches 40MPa and _σy reaches 10MPa, the loading is stopped and the load is maintained, and the loading of σ _z is continued, controlled by stress, at a rate of 1MPa/s; particle ejection and splitting into Plates, cut into blocks, and block pieces ejected, and the test is over. Organize and analyze test data including stress-strain data, acoustic emission data, high-speed images, etc. The rockburst failure process recorded by the high-speed camera is shown in Figure 4, and the fracture and failure form of the specimen after the rockburst is shown in Figure 5. It can be seen that the V-shaped surface explosion crater and the deep shear slip zone.

It can be seen that the technical scheme of the present invention realizes reasonable indoor test simulation of shear rockburst.

The technical solution described in the present invention is only a better and typical specific implementation of the present invention, but the protection scope of the present invention is not limited thereto, and any changes and replacements based on the present invention should be covered by the protection scope of the present invention within. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (6)

1. a kind of simulation shearing-type rock burst true triaxial test method it is characterised in that：Comprise the following steps：

Step 1：Test specimen is determined according to the loading environment of testing machine, the intensity property that environment, plan rock occur of simulated object Physical dimension, and make the rock sample meeting required precision；

Step 2：Stress according to country rock live after the underground cavern excavation of deep and boundary condition, face sky using one side, five faces are subject to The special true triaxial load mode of power, and consider test effect, selected confined pressure level, using suitable loading speed and controlling party Formula；

Step 3：Vertically it is further applied load with horizontal axis to test specimen, the tangential and hole axial stress of simulated field, protects respectively simultaneously Hold horizontal radial one side freely, and be further applied load then to another side, simulated field excavates the free boundary being formed and radially The radial stress of Gradient distribution；

Step 4：Horizontal axis and horizontal radial one side stop loading and keeping load constant after reaching specified load, vertically take The speed of design and control mode continue to load up to test specimen destruction；

Step 5：Process of the test is monitored record using deformation, stress, acoustic emission, high-speed camera measuring instrument；

Step 6：Test data arranges and analysis.

2. according to claim 1 simulation shearing-type rock burst true triaxial test method it is characterised in that：Described step 1 Rock sample be the hard fragility country rock with good integrity Representative Volume Element, specifically adopt 200 × 100 × 100mm or Larger sized cuboid sillar, such as granite, griotte etc., machining accuracy strictly presses International Rock mechanics association criterion.

3. according to claim 1 simulation shearing-type rock burst true triaxial test method it is characterised in that：Described step 2 One side face sky, the special true triaxial of five face stress loads and realizes by the friction of preservation between test specimen and fixture or shear stress, belong to In the loading of the non-principal stress space, can the truly excavation simulation border stress of rock mass and constraint in the range of certain depth nearby.

4. according to claim 1 simulation shearing-type rock burst true triaxial test method it is characterised in that：Described step 3, The horizontal axis stress of step 4 and horizontal radial stress gradient choose relatively large value, particularly horizontal radial stress gradient；Vertically The continuation of stress loads Bit andits control or Stress Control using improved strain rate.

5. according to claim 1 simulation shearing-type rock burst true triaxial test method it is characterised in that：Described step 5 Process of the test monitoring record adopt testing machine control and acquisition system record test specimen stress-strain characteristic, using acoustic emission, record Physical signalling in sound pen, decibel instrument record process of the test, using digital VTR record process of the test image, is taken the photograph using high speed Fragment ejection process near the camera record rock burst moment test specimen scope of freedom, and after off-test, comprehensive bat is carried out to test specimen According to.

6. according to claim 1 simulation shearing-type rock burst true triaxial test method it is characterised in that：Described step 6 Test data arrange with analysis, using in process of the test monitoring with record rock stress with deformation, crackle develop, power Information such as ejection, and combine the form of sample and broken sillar, to deformation spy's characteristic of rock in shearing-type rock burst generating process, Fracture damage growth, failure mode and kinetic energy release rule etc. are analyzed comprehensively.Wherein special, using professional image analysing computers The flight path launching sillar in high-speed camera followed the trail of by software, and a pacing of going forward side by side is calculated its ejection speed, can finally statistical estimation be gone out The kinetic energy that rock burst ejection destroys.