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Physical simulation of rock burst induced by stress waves
JOURNAL OF CHINA UNIVERSITY OF
MINING & TECHNOLOGY J China Univ Mining & Technol 18 (2008) 0401–0405 www.elsevier.com/locate/jcumt
Physical simulation of rock burst induced by stress waves LU Ai-hong, MAO Xian-biao, LIU Hai-shun School of Sciences, China University of Mining & Technology, Xuzhou, Jiangsu 221008, China
Abstract: The behavior of stress wave propagation in rock walls and the process of rock bursts were simulated by application tests of material similar to rock. Results show that 1) the attenuation characteristics of stress waves were related to the material properties, stress waves attenuate more quickly in soft material and 2) when the explosion load was applied at the top of the roadway, the number and the length of the cracks increased with a decrease in the distance between the explosive point and roof of the roadway. When the distance was 280 mm, only some chips appeared near the source, when the distance was 210 mm, some small cracks started to appear near the road-rib and when the distance was reduced to 140 mm, larger cracks appeared at the road-rib. It can be concluded that, under a given stress the number of cracks is closely related to the intensity of stress waves. The cracks in the surrounding rock can be reduced by controlling the intensity of the stress waves and rock bursts can be avoided to some extent by preventing the formation of layered crack structures. A new experimental approach has been provided for studying rock bursts by using physical simulation. Key words: similar material; stress wave; physical simulation; rock burst
1
Introduction
With the increase in mining depth, the frequency and intensity of rock bursts increase continually, seriously threatening the safety in coal mine production. Controlling the mechanism of rock bursts has attracted much attention of scientists who have proposed a series of theories on the mechanism of the origin of rock bursts and some countermeasures for preventing them from taking place. Classic theories includes: intensity theory, energy theory, impact tendency theory, three guideline theory and others[1–5]. However, there is not one accepted theory about the mechanism of rock burst formation because it has a rather complex dynamic instability. It is therefore urgent to study the mechanism of the formation of dynamic hazards such as rock bursts. It is well known that the main reason for rock bursts lies in the deformation energy in hard rocks and the mechanical processes involved in rock bursts are generally regarded as static (or quasi-static)[4–9]. However, static load theory cannot explain all the mechanisms about rock bursts. The accumulation of strain energy is a necessary condition for rock bursts but not a necessary and sufficient condition. Therefore, an external disturbance is necessary for a rock
burst. Moreover, stress waves may be produced by driving, blasting, roof breaking, weighting of the working face, and seismic waves in mining processes, i.e., external disturbances are often introduced before the occurrence of a rock burst. It is necessary to study the effect of stress waves in rock burst. Meanwhile, simulation is an important means in the study of rock bursts because it can simulate the rock burst process and provide some important information about the mechanism of its incidence, failure spots and the methods of failure. Liu studied the effect of rock failure caused by a superimposed sine wave, concluding that the disturbance of stress wave decreases the strength of rocks[10]. The relationship between the disturbance and rock burst needs to be further investigated. Xi simulated the effect of static load on the propagation of known cracks and their unstable failure by using a precrack in the rock and thus obtaining the distribution of its speed of propagation[11]. However, the propagation of cracks under a dynamic load has not been investigated. In our investigation, the incidence and development of rock bursts were simulated with material similar to rock and the mechanism of splitting type rock bursts was studied.
Received 14 February 2008; accepted 28 May 2008 Projects 50490270 and 50634050 supported by the National Natural Science Foundation of China, 2007CB209400 by the National Basic Research Program of China and 2006A039 by the Youth Scientific Research Foundation of China University of Mining & Technology Corresponding author. Tel: +86-516-83885757; E-mail address: [email protected]
402
Journal of China University of Mining & Technology
2 Similar material and simulation experiment 2.1 Similar material In geotechnical engineering, selection and experiments with similar material are relatively mature for static problems within an elastic stage. However, few investigations have been carried out on the characteristics of this material beyond the elastic stage, espeTable 1
2.2
Vol.18 No.3
cially those of dynamic unstable failures. In our experiment, sand, gypsum, calcium carbonate, cement, borax and water were used to prepare material similar to rocks according to the proportions listed in Table 1 and the mechanical properties of this material were determined. For the measurement of mechanical properties, standard specimens with φ˙50 mm in diameter and l = 100 mm in height were prepared, followed by drying and then tested by using the MTS Electro-hydraulic Servo test system.
Parameters and mechanical properties of similar material
Number
Sand
Gypsum
Calcium carbonate
Water
Borax
σ c (MPa)
E (GPa)
1
22.5
3.6
2.0
5.4
0.0004
2.13
1.16
2
18.0
3.2
1.8
4.6
0.0004
1.92
1.10
3
22.5
3.2
1.8
4.6
0.0004
1.62
1.00
4
18.0
5.4
1.8
6.0
0.0004
0.81
2.85
5
18.0
4.6
2.4
4.5
0.0004
0.74
2.12
6
18.0
9.9
2.4
1.8
0.0004
1.46
7
18.0
2.9
2.0
4.3
0.0004
0.45
8
18.0
2.0
2.0
3.2
0.0004
0.04
Physical model
70
70
40
h
400
Material used in the simulation were prepared according to the proportions of the material numbered 1–8. The dimensions of the mould were 520 mm × 400 mm × 70 mm, producing a physical model of the same size as the mould. A module with dimensions 50 mm×40 mm×70 mm was placed into the mould to simulate the rectangle roadway in making the physical model and a cylindrical module with a hole of 15 mm diameter for an explosion (Fig. 1). After the initial set of our simulated material, the module of roadway and the cylinder of the explosion hole were drawn out to form the roadway and the explosion hole in the physical model. The explosion point in the model was arranged vertically above the roadway. The distance between the explosion point and the roof of the roadway is h (Fig. 1).
Fig. 1
Schematic diagram of experimental model
The physical model was placed in the test rack and the load of the overlying strata was applied using a lever with a load proportional to the weight of the overlying strata. The loading and constraints were in a plane stress state. The loading device is shown in
Fig. 2 and the disturbance load was applied at the explosion point (Fig. 1).
Fig. 2
Longitudinal load-application device
2.3 Arrangement of equipment To analyze the effect of material properties and charge location on the roadway structure, three experiments with the proportions of #1~#3 material were carried out (Table 1). The surface of the physical model was painted white to make the results more visible (Fig. 3). The arrangement of measurement points is shown in Fig. 4. The vertical distance between the measurement points is 40 mm and the signal of acceleration was picked up by the accelerometer attached to a piece of iron based in the physical model (Fig. 4). The vertical acceleration of the piece of iron and that of the physical model can be approximately regarded as identical, since the acceleration transducer was attached to the piece of iron. The output signal of the acceleration transducer was amplified by using an integrated amplifier, recorded and analyzed by a dynamic virtual analyzer (QLV) and relevant software developed by Chongqing University. The wave form is shown on the computer monitor (Fig. 5b).
LU Ai-hong et al
Physical simulation of rock burst induced by stress waves
Fig. 3
Constraint device of the model
Fig. 4
Arrangement of the measurement points
(a) Integrated amplifier (CA-3)
Fig. 5 Explosion source
(b) Monitor
Acceleration recording equipment
Accelerometer
Integral amplifier
Virtual signal analyzer
Measurement point
Fig. 6
3
Diagram of experimental test
Results and analysis
3.1 Amplitude characteristic of explosion stress wave for different materials Table 2 shows the peak displacement, peak velocity and peak acceleration at each measurement point. From the fitted curves in the peak displacement, peak velocity, and peak acceleration, as functions of distance x (mm) (Fig. 7), the attenuation indices of the maximum peak displacement are 0.0073, 0.0083 and Table 2
2
3
0.0104, that of the maximum peak velocity 0.0064, 0.0092 and 0.0125 and that of the maximum peak acceleration 0.0174, 0.0183 and 0.0275 for the #1 to #3 material, respectively (Table 3). In addition, from the three fitted curves, the maximum acceleration attenuates most rapidly, which is correlated with the material properties. There is a specially big difference between the acceleration for the #1 and #3 materials. The variation in vertical acceleration as a function of distance in the surrounding rock can be explained by stress-strain behavior of the material. The ultimate stress of elastic deformation is low for soft material and when the wave propagates, partial energy is absorbed and dissipated by the local plastic deformation when the stress exceeds the ultimate stress. When the wave propagates in the #1 material, because the material is harder and the ultimate stress is relatively high, the stress range before elastic ultimate stress becomes relatively small, corresponding to soft material. Therefore, the energy absorbed and dissipated is relatively small and the wave amplitude relatively large when the wave propagates in hard material.
Peak characteristics of different materials
Peak displacement (mm)
Peak velocity (cm/s)
Peak acceleration (cm/s2)
Measurement point 1
0.789
0.510
337.16
Measurement point 2
0.473
0.472
310.3
Measurement point 3
0.382
0.338
59.3
Measurement point 1
0.702
0.505
217
Measurement point 2
0.436
0.384
201
Measurement point 3
0.306
0.272
54.7
Measurement point 1
0.679
0.490
215
Measurement point 2
0.373
0.302
151
Measurement point 3
0.292
0.163
13.7
Material number
1
403
Journal of China University of Mining & Technology
(a) Peak displacement
Fig. 7
Table 3
(b) Peak velocity
Peak displacement, peak velocity and peak acceleration index/distance Displacement
Velocity
Acceleration
#1
0.0073
0.0064
0.0174
#2
0.0083
0.0092
0.0183
#3
0.0104
0.0125
0.0275
Breakage course of surrounding rock of roadway under stress wave
Fig. 8 shows the breakage of the surrounding rock under explosive stress waves and the same charge to
(a) t = 0
(b) t = 0.0005 s
Fig. 8
4
Effect of explosion source on roadway damage
(a) h = 280 mm
(b) h = 210 mm
Fig. 9
time (t) for the #1 material. It can be seen from Fig. 8 that the cracks appear in the upper boundary surrounding the rock of the road-rib where the stress was concentrated and they propagated deeply in the boundary area parallel to the road-rib. Due to the initial stress field (i.e., weight of overlying strata), many cracks were formed, parallel to the road-rib. These cracks propagated, resulting in macroscopic cracks along the direction of the principal stress under the stress waves.
(c) t = 0.001 s
(d) t =0.002 s
Development of cracks and local failure in surrounding rock under stress wave
There were four test models in our experiment, the source of the explosion was in the upright top position of the roadway and the intensity of stress was simulated by different distances from the explosion. The damage of the surrounding rock near the roadway is shown in Fig. 9. It can be seen from Fig. 9 that
5
(c) Peak acceleration
Peak displacement, velocity and acceleration in surrounding rock as a function of distance for different materials
Material properties
3.3
Vol.18 No.3
a (cm/s2)
u (mm)
v (cm/s)
404
there are no cracks near the roadway when h=280 mm, however some minute cracks appeared near the road-rib when h=210 mm along the roadway and large cracks appeared at the road-rib when h=140 mm along the roadway. The cracks of the surrounding rock increase gradually with a decrease in the distance between the explosion source and the roof of the roadway h.
(c) h = 140 mm
(d) h = 70 mm
Layer-crack failure in surrounding rock under different intensity of stress wave
Conclusions
1) Although a certain amount of difference exists between our similar material and actual rock, the
process and phenomenon of instability of rock can be accurately simulated when suitable material and their proportions are selected. 2) The attenuation characteristics of stress waves
LU Ai-hong et al
Physical simulation of rock burst induced by stress waves
are related to material properties. The stress waves attenuated more quickly for the softer material. 3) For the explosion load applied at the top of the roadway, the number and length of cracks increase with a decrease in the distance between the source of the explosion and the roadway, When distance h=280 mm from the roof of roadway there were no cracks near the roadway. However, when distance h=210 mm along the roadway, some minute cracks appeared near the road-rib and when distance h=140 mm, larger cracks appeared. Under a given amount of pressure, the appearance of cracks is related to the intensity of the stress wave. The intensity of the stress wave can be controlled in order to decrease the appearance of cracks in the surrounding rock and prevent the formation of a layered crack structure.
References [1]
[2]
[3]
Morrison R G K. Theory and the practical problem of rock bursts. Engineering and Mining Journal, 1948, 149(3): 66–72. Brady B T. Anomalous seismicity prior to rock bursts: implications for earthquake prediction. Pure and Applied Geophysics, 1977, 115(1–2): 357–374. Mueller W. Numerical simulation of rock bursts. Mining
405
Science & Technology, 1991, 12(1): 27–42. Casten U, Fajklewicz Z. Induced gravity anomalies and rock-burst risk in coal mines: a case history. Geophysical Prospecting, 1993, 41(1): 1–13. [5] Zhao B J, Ten X J. The Rock Burst and Its Prevention and Treatment. Beijing: Coal Industry Publishing House, 1995. (In Chinese) [6] Wang X N, Huang R Q. Analysis of the influence of the dynamic disturbance on rock burst. Mountain Research, 1998, 16(3): 188–192. (In Chinese) [7] Mansurov V A. Prediction of rock bursts by analysis of induced seismicity data. International Journal of Rock Mechanics and Mining Sciences, 2001, 38(6): 893–901. [8] Qi C Z, Qian Q H. Physical mechanism of dependence of material strength on strain rate for rock-like material. Chinese Journal of Rock Mechanics and Engineering, 2003, 22(2): 177–181. (In Chinese) [9] Gao M S, Dou L M, Zhang N, et al. Simulation of the relationship between roadway dynamic destruction and hypocenter parameters. Journal of China University of Mining & Technology, 2008, 18(1): 93–97. [10] Liu X M. Damage Mechanics Experimental Study for Brittle Rock and Rock Burst Analysis on Underground Powerhouse of LAXIWA [Ph.D dissertation]. Wuhan: Wuhan University of Hydraulic and Electrical Engineering, 1995. (In Chinese) [11] Xi D Y, Zhong S J, Huang L X. Study of growth speed of rock crack and inquiry of earthquake process. Rock and Soil Methanics, 1994, 15(3): 51–58. (In Chinese) [4]
MINING & TECHNOLOGY J China Univ Mining & Technol 18 (2008) 0401–0405 www.elsevier.com/locate/jcumt
Physical simulation of rock burst induced by stress waves LU Ai-hong, MAO Xian-biao, LIU Hai-shun School of Sciences, China University of Mining & Technology, Xuzhou, Jiangsu 221008, China
Abstract: The behavior of stress wave propagation in rock walls and the process of rock bursts were simulated by application tests of material similar to rock. Results show that 1) the attenuation characteristics of stress waves were related to the material properties, stress waves attenuate more quickly in soft material and 2) when the explosion load was applied at the top of the roadway, the number and the length of the cracks increased with a decrease in the distance between the explosive point and roof of the roadway. When the distance was 280 mm, only some chips appeared near the source, when the distance was 210 mm, some small cracks started to appear near the road-rib and when the distance was reduced to 140 mm, larger cracks appeared at the road-rib. It can be concluded that, under a given stress the number of cracks is closely related to the intensity of stress waves. The cracks in the surrounding rock can be reduced by controlling the intensity of the stress waves and rock bursts can be avoided to some extent by preventing the formation of layered crack structures. A new experimental approach has been provided for studying rock bursts by using physical simulation. Key words: similar material; stress wave; physical simulation; rock burst
1
Introduction
With the increase in mining depth, the frequency and intensity of rock bursts increase continually, seriously threatening the safety in coal mine production. Controlling the mechanism of rock bursts has attracted much attention of scientists who have proposed a series of theories on the mechanism of the origin of rock bursts and some countermeasures for preventing them from taking place. Classic theories includes: intensity theory, energy theory, impact tendency theory, three guideline theory and others[1–5]. However, there is not one accepted theory about the mechanism of rock burst formation because it has a rather complex dynamic instability. It is therefore urgent to study the mechanism of the formation of dynamic hazards such as rock bursts. It is well known that the main reason for rock bursts lies in the deformation energy in hard rocks and the mechanical processes involved in rock bursts are generally regarded as static (or quasi-static)[4–9]. However, static load theory cannot explain all the mechanisms about rock bursts. The accumulation of strain energy is a necessary condition for rock bursts but not a necessary and sufficient condition. Therefore, an external disturbance is necessary for a rock
burst. Moreover, stress waves may be produced by driving, blasting, roof breaking, weighting of the working face, and seismic waves in mining processes, i.e., external disturbances are often introduced before the occurrence of a rock burst. It is necessary to study the effect of stress waves in rock burst. Meanwhile, simulation is an important means in the study of rock bursts because it can simulate the rock burst process and provide some important information about the mechanism of its incidence, failure spots and the methods of failure. Liu studied the effect of rock failure caused by a superimposed sine wave, concluding that the disturbance of stress wave decreases the strength of rocks[10]. The relationship between the disturbance and rock burst needs to be further investigated. Xi simulated the effect of static load on the propagation of known cracks and their unstable failure by using a precrack in the rock and thus obtaining the distribution of its speed of propagation[11]. However, the propagation of cracks under a dynamic load has not been investigated. In our investigation, the incidence and development of rock bursts were simulated with material similar to rock and the mechanism of splitting type rock bursts was studied.
Received 14 February 2008; accepted 28 May 2008 Projects 50490270 and 50634050 supported by the National Natural Science Foundation of China, 2007CB209400 by the National Basic Research Program of China and 2006A039 by the Youth Scientific Research Foundation of China University of Mining & Technology Corresponding author. Tel: +86-516-83885757; E-mail address: [email protected]
402
Journal of China University of Mining & Technology
2 Similar material and simulation experiment 2.1 Similar material In geotechnical engineering, selection and experiments with similar material are relatively mature for static problems within an elastic stage. However, few investigations have been carried out on the characteristics of this material beyond the elastic stage, espeTable 1
2.2
Vol.18 No.3
cially those of dynamic unstable failures. In our experiment, sand, gypsum, calcium carbonate, cement, borax and water were used to prepare material similar to rocks according to the proportions listed in Table 1 and the mechanical properties of this material were determined. For the measurement of mechanical properties, standard specimens with φ˙50 mm in diameter and l = 100 mm in height were prepared, followed by drying and then tested by using the MTS Electro-hydraulic Servo test system.
Parameters and mechanical properties of similar material
Number
Sand
Gypsum
Calcium carbonate
Water
Borax
σ c (MPa)
E (GPa)
1
22.5
3.6
2.0
5.4
0.0004
2.13
1.16
2
18.0
3.2
1.8
4.6
0.0004
1.92
1.10
3
22.5
3.2
1.8
4.6
0.0004
1.62
1.00
4
18.0
5.4
1.8
6.0
0.0004
0.81
2.85
5
18.0
4.6
2.4
4.5
0.0004
0.74
2.12
6
18.0
9.9
2.4
1.8
0.0004
1.46
7
18.0
2.9
2.0
4.3
0.0004
0.45
8
18.0
2.0
2.0
3.2
0.0004
0.04
Physical model
70
70
40
h
400
Material used in the simulation were prepared according to the proportions of the material numbered 1–8. The dimensions of the mould were 520 mm × 400 mm × 70 mm, producing a physical model of the same size as the mould. A module with dimensions 50 mm×40 mm×70 mm was placed into the mould to simulate the rectangle roadway in making the physical model and a cylindrical module with a hole of 15 mm diameter for an explosion (Fig. 1). After the initial set of our simulated material, the module of roadway and the cylinder of the explosion hole were drawn out to form the roadway and the explosion hole in the physical model. The explosion point in the model was arranged vertically above the roadway. The distance between the explosion point and the roof of the roadway is h (Fig. 1).
Fig. 1
Schematic diagram of experimental model
The physical model was placed in the test rack and the load of the overlying strata was applied using a lever with a load proportional to the weight of the overlying strata. The loading and constraints were in a plane stress state. The loading device is shown in
Fig. 2 and the disturbance load was applied at the explosion point (Fig. 1).
Fig. 2
Longitudinal load-application device
2.3 Arrangement of equipment To analyze the effect of material properties and charge location on the roadway structure, three experiments with the proportions of #1~#3 material were carried out (Table 1). The surface of the physical model was painted white to make the results more visible (Fig. 3). The arrangement of measurement points is shown in Fig. 4. The vertical distance between the measurement points is 40 mm and the signal of acceleration was picked up by the accelerometer attached to a piece of iron based in the physical model (Fig. 4). The vertical acceleration of the piece of iron and that of the physical model can be approximately regarded as identical, since the acceleration transducer was attached to the piece of iron. The output signal of the acceleration transducer was amplified by using an integrated amplifier, recorded and analyzed by a dynamic virtual analyzer (QLV) and relevant software developed by Chongqing University. The wave form is shown on the computer monitor (Fig. 5b).
LU Ai-hong et al
Physical simulation of rock burst induced by stress waves
Fig. 3
Constraint device of the model
Fig. 4
Arrangement of the measurement points
(a) Integrated amplifier (CA-3)
Fig. 5 Explosion source
(b) Monitor
Acceleration recording equipment
Accelerometer
Integral amplifier
Virtual signal analyzer
Measurement point
Fig. 6
3
Diagram of experimental test
Results and analysis
3.1 Amplitude characteristic of explosion stress wave for different materials Table 2 shows the peak displacement, peak velocity and peak acceleration at each measurement point. From the fitted curves in the peak displacement, peak velocity, and peak acceleration, as functions of distance x (mm) (Fig. 7), the attenuation indices of the maximum peak displacement are 0.0073, 0.0083 and Table 2
2
3
0.0104, that of the maximum peak velocity 0.0064, 0.0092 and 0.0125 and that of the maximum peak acceleration 0.0174, 0.0183 and 0.0275 for the #1 to #3 material, respectively (Table 3). In addition, from the three fitted curves, the maximum acceleration attenuates most rapidly, which is correlated with the material properties. There is a specially big difference between the acceleration for the #1 and #3 materials. The variation in vertical acceleration as a function of distance in the surrounding rock can be explained by stress-strain behavior of the material. The ultimate stress of elastic deformation is low for soft material and when the wave propagates, partial energy is absorbed and dissipated by the local plastic deformation when the stress exceeds the ultimate stress. When the wave propagates in the #1 material, because the material is harder and the ultimate stress is relatively high, the stress range before elastic ultimate stress becomes relatively small, corresponding to soft material. Therefore, the energy absorbed and dissipated is relatively small and the wave amplitude relatively large when the wave propagates in hard material.
Peak characteristics of different materials
Peak displacement (mm)
Peak velocity (cm/s)
Peak acceleration (cm/s2)
Measurement point 1
0.789
0.510
337.16
Measurement point 2
0.473
0.472
310.3
Measurement point 3
0.382
0.338
59.3
Measurement point 1
0.702
0.505
217
Measurement point 2
0.436
0.384
201
Measurement point 3
0.306
0.272
54.7
Measurement point 1
0.679
0.490
215
Measurement point 2
0.373
0.302
151
Measurement point 3
0.292
0.163
13.7
Material number
1
403
Journal of China University of Mining & Technology
(a) Peak displacement
Fig. 7
Table 3
(b) Peak velocity
Peak displacement, peak velocity and peak acceleration index/distance Displacement
Velocity
Acceleration
#1
0.0073
0.0064
0.0174
#2
0.0083
0.0092
0.0183
#3
0.0104
0.0125
0.0275
Breakage course of surrounding rock of roadway under stress wave
Fig. 8 shows the breakage of the surrounding rock under explosive stress waves and the same charge to
(a) t = 0
(b) t = 0.0005 s
Fig. 8
4
Effect of explosion source on roadway damage
(a) h = 280 mm
(b) h = 210 mm
Fig. 9
time (t) for the #1 material. It can be seen from Fig. 8 that the cracks appear in the upper boundary surrounding the rock of the road-rib where the stress was concentrated and they propagated deeply in the boundary area parallel to the road-rib. Due to the initial stress field (i.e., weight of overlying strata), many cracks were formed, parallel to the road-rib. These cracks propagated, resulting in macroscopic cracks along the direction of the principal stress under the stress waves.
(c) t = 0.001 s
(d) t =0.002 s
Development of cracks and local failure in surrounding rock under stress wave
There were four test models in our experiment, the source of the explosion was in the upright top position of the roadway and the intensity of stress was simulated by different distances from the explosion. The damage of the surrounding rock near the roadway is shown in Fig. 9. It can be seen from Fig. 9 that
5
(c) Peak acceleration
Peak displacement, velocity and acceleration in surrounding rock as a function of distance for different materials
Material properties
3.3
Vol.18 No.3
a (cm/s2)
u (mm)
v (cm/s)
404
there are no cracks near the roadway when h=280 mm, however some minute cracks appeared near the road-rib when h=210 mm along the roadway and large cracks appeared at the road-rib when h=140 mm along the roadway. The cracks of the surrounding rock increase gradually with a decrease in the distance between the explosion source and the roof of the roadway h.
(c) h = 140 mm
(d) h = 70 mm
Layer-crack failure in surrounding rock under different intensity of stress wave
Conclusions
1) Although a certain amount of difference exists between our similar material and actual rock, the
process and phenomenon of instability of rock can be accurately simulated when suitable material and their proportions are selected. 2) The attenuation characteristics of stress waves
LU Ai-hong et al
Physical simulation of rock burst induced by stress waves
are related to material properties. The stress waves attenuated more quickly for the softer material. 3) For the explosion load applied at the top of the roadway, the number and length of cracks increase with a decrease in the distance between the source of the explosion and the roadway, When distance h=280 mm from the roof of roadway there were no cracks near the roadway. However, when distance h=210 mm along the roadway, some minute cracks appeared near the road-rib and when distance h=140 mm, larger cracks appeared. Under a given amount of pressure, the appearance of cracks is related to the intensity of the stress wave. The intensity of the stress wave can be controlled in order to decrease the appearance of cracks in the surrounding rock and prevent the formation of a layered crack structure.
References [1]
[2]
[3]
Morrison R G K. Theory and the practical problem of rock bursts. Engineering and Mining Journal, 1948, 149(3): 66–72. Brady B T. Anomalous seismicity prior to rock bursts: implications for earthquake prediction. Pure and Applied Geophysics, 1977, 115(1–2): 357–374. Mueller W. Numerical simulation of rock bursts. Mining
405
Science & Technology, 1991, 12(1): 27–42. Casten U, Fajklewicz Z. Induced gravity anomalies and rock-burst risk in coal mines: a case history. Geophysical Prospecting, 1993, 41(1): 1–13. [5] Zhao B J, Ten X J. The Rock Burst and Its Prevention and Treatment. Beijing: Coal Industry Publishing House, 1995. (In Chinese) [6] Wang X N, Huang R Q. Analysis of the influence of the dynamic disturbance on rock burst. Mountain Research, 1998, 16(3): 188–192. (In Chinese) [7] Mansurov V A. Prediction of rock bursts by analysis of induced seismicity data. International Journal of Rock Mechanics and Mining Sciences, 2001, 38(6): 893–901. [8] Qi C Z, Qian Q H. Physical mechanism of dependence of material strength on strain rate for rock-like material. Chinese Journal of Rock Mechanics and Engineering, 2003, 22(2): 177–181. (In Chinese) [9] Gao M S, Dou L M, Zhang N, et al. Simulation of the relationship between roadway dynamic destruction and hypocenter parameters. Journal of China University of Mining & Technology, 2008, 18(1): 93–97. [10] Liu X M. Damage Mechanics Experimental Study for Brittle Rock and Rock Burst Analysis on Underground Powerhouse of LAXIWA [Ph.D dissertation]. Wuhan: Wuhan University of Hydraulic and Electrical Engineering, 1995. (In Chinese) [11] Xi D Y, Zhong S J, Huang L X. Study of growth speed of rock crack and inquiry of earthquake process. Rock and Soil Methanics, 1994, 15(3): 51–58. (In Chinese) [4]