Abstract
In order to effectively describe the whole creep process of fractured rock mass, triaxial unloading creep tests were carried out on prefractured coal samples using constant axial pressure and graded unloading confining pressure, and the axial and lateral creep laws of fractured coal samples with different dip angles were studied. Combined with the characteristics of creep curve and based on Kachanov’s creep damage theory, the damage variable is introduced into the constitutive relation and creep equation, and the evolution equation of damage variable with time in the whole creep process is derived. At the same time, a new method to calculate the initial damage is proposed. The elastoplastic body with damage variable is connected with the Burgers model in series. Meanwhile, lade criterion and switch element are introduced into the creep model to establish a new fracture damage creep model. The one-dimensional and three-dimensional damage creep equations are derived. The damage creep equation is obtained according to the superposition principle. A simple and feasible method for parameter identification of the model is given based on the characteristics of creep curve. The applicability of the model is verified by comparing the creep test curve of fractured coal sample with the theoretical curve. The results show that the two models are in good agreement. The model can not only accurately reflect the nonlinear characteristics of creep curves in the attenuation and isokinetic stages but also describe the accelerated creep characteristics of fractured rocks.
Highlights
Rock burst refers to the local high stress concentration in coal caused by the mining of working face and the tunneling of roadway, which makes the local elastic energy in coal accumulate stably in time and transfer to weak surface through easy propagation path, resulting in continuous generation of weak structure in coal and rock, causing local fracture, damage, instability, and sliding of coal. e phenomenon that the elastic potential energy stored in coal is released instantaneously after some external disturbance [1–5]. is phenomenon can only last for a few seconds to tens of seconds, which will produce severe vibration, accompanied by a large number of coal thrown out, seriously threatening the safety of coal production [6–8]
Rock burst will occur under the condition of no disturbance. e sudden release of this type of energy is because of creep-type rock burst [9–11]. erefore, it is of great significance for the prevention and control of coal body impact disaster that the creep-type impact risk can be predicted by quickly judging the creep deformation of coal body on-site. e existing prevention and control methods of rock burst mainly include the following: (1) energy releasing drilling method; (2) high-pressure water injection in coal seam; (3) deep hole controlled blasting; and (4) hydraulic slotting pressure relief method [12–15]
Because of the mining depth, creep-type rock burst occurs frequently, and the number of coal mines and coal seams is increasing. is kind of rock burst disaster has seriously restricted the safety production of coal mines in China. e prediction and prevention of this kind of rock burst is different from the conventional type
Summary
Rock burst refers to the local high stress concentration in coal (rock) caused by the mining of working face and the tunneling of roadway, which makes the local elastic energy in coal (rock) accumulate stably in time and transfer to weak surface through easy propagation path, resulting in continuous generation of weak structure in coal and rock, causing local fracture, damage, instability, and sliding of coal (rock). e phenomenon that the elastic potential energy stored in coal (rock) is released instantaneously after some external disturbance [1–5]. is phenomenon can only last for a few seconds to tens of seconds, which will produce severe vibration, accompanied by a large number of coal (rock) thrown out, seriously threatening the safety of coal production [6–8]. E existing prevention and control methods of rock burst mainly include the following: (1) energy releasing drilling method; (2) high-pressure water injection in coal seam; (3) deep hole controlled blasting; and (4) hydraulic slotting pressure relief method [12–15]. Li Chao et al used the method of cutting coal body with high-pressure water jet to prevent rock burst and monitored the test results with KBD5 electromagnetic radiation monitor. It shows that the effect of cutting on stress unloading of shallow coal is the best, and the stress is redistributed around the seam, so that the. Under the coupling effect of engineering disturbance and rock damage fracture penetration and fusion, roof falling, rock burst, and other disasters are likely to occur
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