A Numerical Study Of The Failure Characteristics And Mechanism Of Rock During Instantaneous Unloading

With continuous enhancement of modern science and technology and the rapid development of national economy, in order to make full and reasonable use of natural space resources, mining and other underground engineering field gradually develop to the deeper direction. However, deep rock mass exist in a complex mechanical environment of "three highs and one disturbance" over a long period time. The high in-situ stress is one of the "three highs", and high stress means high energy storage. Rock suddenly unloading can cause engineering disasters such as the rock breaking even rock burst. The engineering disasters have the characteristics of sudden and violent, and that will threat the personal safety of construction personnel and the property. So it is necessary to study the dynamic failure process of rock under high unloading rate and the propagation and reflection characteristics of the stress wave.This paper uses nonlinear finite element software ANSYS/LS-DYNA to establish the solid model and simulate the failure process of instantaneous unloading rock sample under different initial stress. The propagation rules of stress in rock mass and the influences of initial stress and unloading rate on the rock sample failure are discussed, and the influences of initial stress and unloading rate on rock mass energy change are studied.The results show that the unloading stress wave generating during the instantaneous unloading rock mass produce the tensile wave after the reflection of the fixed end, and the tensile wave make the rock damage in the direction of perpendicular to unloading. In a certain range, when the initial stress is same, the longer the unloading time is, the bigger the covering range of stress wave in rock mass is, the bigger the stress response in rock mass is, and the greater the damage degree of rock mass is. When the unloading time is same and the initial stress is different, the propagation process of stress in rock mass and the covering range of is basically same, but the damage degree of rock mass is different. The bigger the initial stress is, the bigger the damage degree of rock mass is. The strain rate changes are obvious in any position before the failure of rock. After the stress wave pass the position, the strain rate change slowly. But strain rate has a sudden change when the rock mass failure, the strain rate gradually flatten out again after that. When the unloading time is longer, the initial stress is greater, the strain energy stored in rock mass is greater, and the internal energy at the time of damage of rock mass is bigger too. The internal energy decreases rapidly after the damage of rock mass, and the speed of the internal energy decreases is greater than the speed of internal energy increases before the failure of rock mass.