A method for predicting stability of mine goaf

Abstract

The present invention relates to a method for predicting the stability of a mined - out area in a mine, which is characterized by the following steps: 1) Sampling and preparing rock specimens; 2) Testing to obtain the maximum shear stress of the rock specimens and the peak stress σ of rock failure under different confining pressures w c ; 3) Establishing a relationship model between σ c and w; 4) Arranging microseismic monitoring points for the surrounding rock of the mined - out area and obtaining monitoring information; 5) Establishing a safety evaluation index S for the stability of the mined - out area; 6) Conducting a preliminary safety classification evaluation of the mined - out area. The advantages of the present invention are as follows: By testing, the maximum shear stress of the rock specimens in the mined - out area and the peak stress of rock failure under different confining pressure conditions are obtained. A relationship model between the peak stress of rock failure and the confining pressure is established through test data, and considering the influence of the number of monitored microseismic events on the stability of the mined - out area, a safety evaluation index for the stability of the mined - out area is established, so as to realize the early prediction of the rock stability in the mined - out area.

Description

Technical Field

[0001] The invention belongs to the technical field of mining engineering safety evaluation, and in particular relates to a method for predicting the stability of a mine goaf. Background Art

[0002] As one of the major safety risks in mines, goaf instability is characterized by suddenness, latency and large-scale destructiveness, which seriously threatens the safe production of mines and the lives of personnel. In particular, frequent mining blasting in the vicinity is more likely to cause cumulative damage to the surrounding rock of the goaf, which in turn leads to instability phenomena such as rock bursts in the goaf. However, these damages are often caused by a series of micro-destructions such as the initiation, development and penetration of tiny fractures. A large number of mining areas, chambers and tunnels left over from underground mining have not been dealt with in a timely manner, forming goafs with complex structures. Moreover, with the increase in mining depth, the hidden dangers of goaf collapse gradually increase. At present, the methods for dealing with goafs are extremely limited, and there are many hidden dangers. Therefore, it is very necessary to predict the stability and safety status of goafs that have not yet been dealt with based on monitoring instruments with different means, so as to make early judgments on potential dangers in goafs and take measures to prevent them before they happen. Microseismic monitoring technology is one of the most widely used means of monitoring deep rock changes in engineering. It can monitor the movement of cracks inside the rock mass in real time. It has the characteristics of remote monitoring, all-round detection, and high precision. According to the number and energy of microseismic events, it can identify precursor information of rock instability. Summary of the invention

[0003] The purpose of the present invention is to provide a method for predicting the stability of mine goafs. The method obtains the maximum shear stress of rock samples in the goaf and the peak stress of rock failure under different confining pressure conditions through experiments, establishes a relationship model between the peak stress of rock failure and the confining pressure through experimental data, and establishes a safety evaluation index for the stability of the goaf in combination with the influence of the number of monitored microseismic events on the stability of the goaf, thereby achieving early prediction of the stability of the rock in the goaf.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] A method for predicting the stability of a mine goaf area of ​​the present invention is characterized by comprising the following steps:

[0006] Step 1, sampling different types of rocks in the goaf of the tunnel to prepare rock samples;

[0007] Step 2: Experimentally obtain the maximum shear stress of the rock in the goaf of the tunnel; Experimentally obtain the rock failure peak stress σ under different confining pressures w of the rock in the goaf of the tunnel c ;

[0008] Step 3: Establish rock failure peak stress σ cRelationship model with confining pressure w;

[0009] Step 4: Arrange microseismic monitoring points of surrounding rock in goaf areas of tunnels and obtain monitoring information;

[0010] Step 5, establish the safety evaluation index S of the tunnel stability in the goaf area;

[0011] Step 6: Conduct preliminary safety classification assessment of tunnel goaf areas.

[0012] In step 2, the maximum shear stress of the rock in the goaf of the tunnel is obtained by conducting a triaxial compression test on the rock sample, that is, a Hopkinson test with a confining pressure device is performed on the rock sample to obtain the rock failure peak stress σ at which the rock sample is destroyed under different confining pressure conditions. c Experimental data.

[0013] In step 3, the rock failure peak stress σ at which the rock sample fails under different confining pressure conditions is calculated. c Test data, establish rock failure peak stress σ c The relationship between the confining pressure w, σ c =aw 2 +bw+q, and through σ c The fitting constants a, b, q are obtained by fitting the experimental data of and w;

[0014] In step 4, a section is taken every 5 m in the length direction of the goaf area of ​​the roadway, five microseismic monitoring points are evenly arranged on the surrounding rock of each section, microseismic sensors and confining pressure measurement sensors are buried, and the surrounding rock of the goaf area of ​​the roadway is continuously monitored for 24 hours to obtain monitoring information, including the confining pressure w and the number of microseismic events per unit time ΔA;

[0015] In step 5, according to the confining pressure w and the number of microseismic events per unit time ΔA monitored in step 4, the safety evaluation index S of the tunnel stability in the goaf area is established as follows:

[0016]

[0017] ΔA is the number of microseismic events within the test unit period, and k is the shear strength, which is the ratio of the maximum shear stress of rock to the peak stress of rock failure.

[0018] In step 6, according to the roadway goaf area roadway stability safety evaluation index S, the roadway goaf area safety classification pre-evaluation standard is determined as follows:

[0019]

[0020] The safety classification pre-evaluation standards are used in conjunction with the early warning system, and different prevention and control plans are adopted according to the evaluation level.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention obtains the maximum shear stress of rock samples in tunnel goaf areas and the peak stress of rock failure under different confining pressure conditions through experiments, establishes a relationship model between the peak stress of rock failure and the confining pressure through experimental data, and establishes a stability safety evaluation index for tunnel goaf areas by combining the influence of the number of monitored microseismic events on the stability of tunnel goaf areas. The peak strength and the number of microseismic events of the surrounding rock under different confining pressure conditions can be predicted, so as to achieve early warning of deformation, instability and failure, and make early predictions on the stability of rocks in tunnel goaf areas. Different prevention and control plans can be taken in advance according to the evaluation level to improve the overall safety of tunnel goaf areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of the safety pre-evaluation method for tunnel goaf areas;

[0024] Figure 2 This is a schematic diagram of the arrangement of measuring points along the goaf of the roadway;

[0025] Figure 3 This is a schematic diagram of the arrangement of measuring points in the tunnel section of the goaf area. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0027] Embodiment 1:

[0028] The goaf area 1 of an underground mine tunnel is buried at a depth of -300m and the surrounding rock is granite. However, due to the cumulative damage to the surrounding rock of goaf area 1 caused by mining blasting, a large number of cracks penetrate the tunnel. Therefore, it is necessary to monitor the microseismic and confining pressure of goaf area 1 in order to predict the risk of rock burst and collapse in advance.

[0029] like Figure 1-Figure 3 As shown, a method for predicting stability of a mine tunnel goaf area of ​​the present invention is characterized by comprising the following steps:

[0030] Step 1, sampling different types of rocks in the goaf 1 of the tunnel to prepare rock samples;

[0031] Step 2: Obtain the maximum shear stress of the rock in the goaf 1 of the tunnel; obtain the rock failure peak stress σ of the rock in the goaf 1 of the tunnel c ;

[0032] Step 3: Establish the rock failure peak stress σ c Relationship model with confining pressure w;

[0033] Step 4, arrange surrounding rock microseismic monitoring points 3 in the goaf 1 of the tunnel and obtain microseismic monitoring information;

[0034] Step 5, establishing a roadway stability safety evaluation index S for the roadway goaf 1;

[0035] Step 6, conduct preliminary safety classification assessment of tunnel goaf area 1.

[0036] In step 2, the maximum shear stress of the rock in the goaf of the tunnel is obtained by conducting a triaxial compression test on the rock sample, that is, a Hopkinson test with a confining pressure device is performed on the rock sample to obtain the rock failure peak stress σ at which the rock sample is destroyed under different confining pressure conditions. c Experimental data.

[0037] In step 3, the rock failure peak stress σ at which the rock sample fails under different confining pressure conditions is calculated. c Test data, establish rock failure peak stress σ c The relationship between the confining pressure w, σ c =aw 2 +bw+q, and through σ c The fitting constants a, b, q are obtained by fitting the experimental data of and w;

[0038] In step 4, a section 2 is taken every 5 m in the length direction of the goaf 1 of the tunnel, five microseismic monitoring points 3 are evenly arranged on the surrounding rock of each section 2, microseismic sensors and confining pressure measurement sensors are buried, and the surrounding rock of the goaf 1 of the tunnel is continuously monitored for 24 hours to obtain monitoring information, including the confining pressure w and the number of microseismic events per unit time ΔA;

[0039] In step 5, according to the confining pressure monitored in step 4 and the number of microseismic events per unit time, the safety evaluation index S of the tunnel stability of the goaf 1 is established as follows:

[0040]

[0041] ΔA is the number of microseismic events within the test unit period, w is the confining pressure, a, b, and q are fitting constants, and k is the shear strength, that is, the ratio of the maximum shear stress of rock to the peak stress of rock failure.

[0042] In step 6, according to the tunnel stability safety evaluation index S of tunnel goaf area 1 established in step 5, a safety classification pre-evaluation of tunnel goaf area 1 is performed to achieve the purpose of stability prediction of tunnel goaf area 1. The closer S is to 1, the more likely it is to be damaged. The specific pre-evaluation standards are as follows:

[0043]

[0044] In this embodiment, according to mechanical tests, the peak stress of granite under different confining pressure conditions is obtained, as shown in Table 1:

[0045] Table 1 Peak stress of granite failure under different confining pressures

[0046]

[0047] After fitting the test data, we get a=-0.0181, b=8.476, q=170, and the number of microseismic events monitored is 210. The maximum shear stress of granite under a confining pressure of 50 MPa is measured to be 329.13 MPa. Under this condition, the peak stress of granite when it is destroyed is 548.55 MPa, and the peak strength k is 60%. According to the evaluation index, S=1.14 is obtained. The prediction result is that rock burst is very likely to occur, and the on-site personnel and equipment in the goaf of the tunnel should be evacuated urgently.

[0048] Embodiment 2:

[0049] According to indoor test measurements, the surrounding rock of tunnel goaf 1 is granite, and the rock mass above tunnel goaf 1 is large, which exerts great pressure on tunnel goaf 1. Without performing other treatment on tunnel goaf 1, it is necessary to monitor its stability to prevent instantaneous energy release of the rock, which may cause accidents such as ground collapse.

[0050] The implementation steps of this embodiment are the same as those of Embodiment 1.

[0051] The test data, monitoring calculation and prediction results of this embodiment are as follows:

[0052] The number of microseismic events monitored by microseismic monitoring is 130. The test shows that the maximum shear stress of granite under a confining pressure of 30 MPa is 203.99 MPa. The granite a=-0.0181, b=8.476, q=170. Under these conditions, the peak stress of granite when it is destroyed is 407.99 MPa, and the peak strength k is 50%. According to the evaluation indicators, S=0.79, which belongs to the process of rock damage incubation. The surrounding rock is in a metastable state and requires safety reminders. There are large deformations or cracks in the surrounding rock.

[0053] Embodiment 3:

[0054] The surrounding rock of tunnel goaf 1 is mainly limestone. The tunnel is 120m long, the average confining pressure is 30MPa, and the tunnel is shallow. Since other mining and blasting links are carried out 200m near tunnel goaf 1, it is necessary to monitor and predict the stability of its surrounding rock to prevent blasting from causing cumulative damage to tunnel goaf 1.

[0055] The implementation steps of this embodiment are the same as those of Embodiment 1.

[0056] The test data, monitoring calculation and prediction results of this embodiment are as follows:

[0057] In this embodiment, according to mechanical tests, the peak stress of limestone under different confining pressure conditions is obtained, as shown in Table 2:

[0058] Table 2 Peak stress of limestone failure under different confining pressures

[0059]

[0060] The number of microseismic events monitored by microseismic monitoring is 20. The test shows that the maximum shear stress of limestone under the condition of confining pressure of 30Mpa is 69.86Mpa, the limestone a=0.0464, b=1.069, q=42.6. Under this condition, the peak stress of limestone when it is destroyed is 116.43Mpa, and the peak strength k is 60%. According to the evaluation index, S=0.51 can be obtained. The surrounding rock is in a stable state and no safety warning is required.

[0061] Embodiment 4:

[0062] The surrounding rock of tunnel goaf area 1 is marble, the tunnel shape is a three-center arch, and the burial depth is 200m. The supporting capacity of the surrounding rock of tunnel goaf area 1 is weak. In order to prevent the occurrence of danger, it is necessary to monitor and predict the stability of the surrounding rock.

[0063] The implementation steps of this embodiment are the same as those of Embodiment 1.

[0064] The test data, monitoring calculation and prediction results of this embodiment are as follows:

[0065] In this embodiment, according to mechanical tests, the peak stress of marble under different confining pressure conditions is obtained, as shown in Table 3:

[0066] Table 3 Peak stress of marble failure under different confining pressures

[0067]

[0068] The number of microseismic events monitored by microseismic monitoring is 70. The test shows that the maximum shear stress of marble under the condition of confining pressure of 30Mpa is 205.42Mpa, marble a=-0.0435, b=6.767, q=129.6. Under this condition, the peak stress of marble when it is destroyed is 293.46Mpa, and the peak strength k is 70%. According to the evaluation indicators, S=0.83. The surrounding rock is in a metastable state and belongs to the intensive active period. Support work should be done well during construction.

Claims

1. A method for predicting the stability of a mine goaf, characterized in that: The steps include: Step 1, sampling different types of rocks in the goaf of the tunnel to prepare rock samples; Step 2: Experimentally obtain the maximum shear stress of the rock in the goaf of the tunnel; Experimentally obtain the rock failure peak stress σ under different confining pressures w of the rock in the goaf of the tunnel c ; Step 3: Establish rock failure peak stress σ c Relationship model with confining pressure w; In step 3, the rock failure peak stress σ at which the rock sample fails under different confining pressure conditions is calculated. c Test data, establish rock failure peak stress σ c The relationship between the confining pressure w, σ c =aw 2 +bw+q, and through σ c The fitting constants a, b, and q are obtained by fitting the data of and w; Step 4: Arrange microseismic monitoring points of surrounding rock in goaf areas of tunnels and obtain monitoring information; Step 5, establish the safety evaluation index S of the tunnel stability in the goaf area; In step 5, according to the confining pressure w and the number of microseismic events per unit time ΔA monitored in step 4, the safety evaluation index S of the tunnel stability in the goaf area is established as follows: ΔA is the number of microseismic events in the test unit period, k is the shear strength, that is, the ratio of the maximum shear stress of rock to the peak stress of rock failure; Step 6: Conduct preliminary safety classification assessment of tunnel goaf areas.

2. A method for predicting goaf stability according to claim 1, characterized in that: In step 2, the maximum shear stress of the rock in the goaf of the tunnel is obtained by conducting a triaxial compression test on the rock sample, that is, a Hopkinson test with a confining pressure device is performed on the rock sample to obtain the rock failure peak stress σ at which the rock sample is destroyed under different confining pressure conditions. c Experimental data.

3. A method for predicting goaf stability according to claim 1, characterized in that: In step 4, a section is taken every 5 m in the length direction of the goaf area of ​​the roadway, five surrounding rock microseismic monitoring points of the goaf area of ​​the roadway are set on each section, and monitoring information is obtained, including the confining pressure w and the number of microseismic events per unit time ΔA.

4. A method for predicting goaf stability according to claim 1, characterized in that: In step 6, according to the roadway goaf area roadway stability safety evaluation index S, the roadway goaf area safety classification pre-evaluation standard is determined as follows: The safety classification pre-evaluation standard is used in conjunction with the early warning system, and different prevention and control plans are adopted according to the evaluation level.

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