动静组合作用下刀具破岩机制数值分析

Numerical simulation of rock fracture mechanism induced by a drill bit under combined dynamic and static loading

基于细观损伤有限元方法,模拟分析了刀具在单一动载、动静联合荷载、静态围压条件下动静联合荷载3种情况下岩体破碎的全过程。模型采用黏弹性人工边界剔除了边界应力波反射对模拟结果准确性的影响。数值模拟结果表明:在弹性情况下,静压的存在对岩体内部最小主应力值影响不大,却显著提高了材料内部最大主应力水平,增大了剪应力的大小,导致剪切破坏可能性增加;当有围压存在时,岩体内部受拉区域减少,岩体强度有所提高。单一动载和动静联合荷载破岩时,岩体内部除刀头附近呈现少量压破坏外,破坏均以拉破坏为主;而围压条件下,岩体破碎面积相对减小,裂纹在围压的作用下向两侧自由面延伸,岩体内部破坏形式则趋于多样化,压破坏比重明显增大,整体表现为拉压复合作用。模拟结果还表明,刀头侵入量主要受动载力大小影响,在相同幅值增量下,动载力增加导致的刀头侵入量远大于静压增加所导致的侵入量。相对单一动载和静压作用下的岩石破碎机制来说,动静组合加载破岩的研究还需更为深入的探讨。研究结果可望对岩体破坏机制以及地下工程作业等实际应用提供一定的参考。

Based on the meso-scopic damage mechanics and the finite element method, a numerical code of rock fragmentation process analysis （RFPA） is used to simulate fragmentation process under three different loading conditions, i.e. single dynamic, combined dynamic and static loading, and the combined dynamic loading under the confining pressure. In the analysis model, the visco-elastic boundary is considered to eliminate the influence of the reflected stress waves from the boundary. Numerical simulation results show that the presence of static pressure has little effect on the value of the minimum principal stress within the rock mass, but significantly improve the level of the maximum principal stress; so the value of the shear stress is increased, as well as the possibility of the shear failure. While in the confining pressure condition, the tensile zone in the rock reduces and rock mass strength increases on the other hand. In according to the property of the rock which preformed strong in resist pressure but weak in the resist tensile, the capability of the rock increased within the certain range of the confining pressure. The cracks extend towards both side of the free surface and the failure in the rock becomes more complex under the influence of the confining pressure. The proportion of the pressure failure increases obviously while almost all the damage is tensile failure occurred in the single dynamic loading and combined dynamic and static loading model. The research results will be helpful for understanding the mechanism of rock failure under the dynamic-static loading and underground engineering construction.