含张开/闭合裂隙的巴西圆盘裂纹扩展过程

Fracture growth of Brazilian disk with open/closed cracks

大量的岩体失稳与节理、裂隙的起裂、扩展和贯通密切相关,裂纹扩展机理及分析方法研究具有重要的科学和工程意义。数值模拟作为一种有效的岩石破裂分析方法备受研究者青睐,但目前的模拟方法在分析压剪闭合等复杂裂隙的力学行为时,还存在诸如扩展路径锯齿化、网格依赖、扩展步长受限等问题。基于此,以巴西圆盘为基本研究对象,开展了不同初始裂隙类型(张开、闭合、填充)、接触摩擦、裂隙倾角等物理力学参数对裂纹扩展特性的影响及破裂机理的研究。首先,基于岩石断裂力学理论和裂纹尖端应力场,运用最大周向应力准则(MTS)研究了张开、闭合等初始裂纹扩展过程,分析了产生锯齿状扩展路径的内在原因,以及传统方法在快速、有效的裂纹扩展路径模拟方面存在的问题。在此基础上,建立了准脆性材料破裂局部化理论的岩体断裂模拟方法,避免了断裂参数计算不准的难题,显著提高了计算的易操作性和精度。此外,通过裂纹尖端区域的局部网格自动重划分,单步的扩展长度并不受网格大小的限制,解决了裂纹扩展的网格依赖问题。最后,通过对裂纹扩展过程力学特性以及起裂角度、扩展路径等分析,获得了整个破裂过程中裂隙面的接触、分离及再闭合等状态以及裂纹扩展的力学机理。该研究提高了岩石破裂过程模拟的效率和准确性,弥补了目前有关压剪应力状态下闭合裂纹扩展研究的不足,实现了破裂路径的精细模拟。

Many rock mass hazards and instabilities are tightly associated with the initiation,propagation and penetration of joints and faults.The study of crack propagation mechanism and analytical methods have profound meanings for the prevention of catastrophes.Numerical simulation is favored by researchers,as an effective rock failure analysis method.However,current simulation methods will encounter the unrealistic issues of zigzag propagation path,grid dependence,and limited propagation length when analyzing complex fracturing such as the compression-shear closed.To solve this,the present study explores the effects of various fault types(open,closed,filled),contact friction,fault inclination and other physical and mechanical parameters on both the fracture propagation characteristics and the fracture mechanism by taking Brazilian disc as the basic research object.First,based on the theory of rock fracture mechanics and the stress field at the crack tip,the maximum tangential stress criterion(MTS)is used to study the propagation process of open and closed faluts,and the potential reasons why zigzag propagation path occurs are analyzed.And the issues of traditional methods are discussed in fast and effective simulation of fracture propagation path.Second,a fracture simulation method of rock mass based on fracture localization theory for quasi-brittle material is established,which avoids inaccurate calculation of fracture parameters and significantly improves the operability and accuracy of calculation.In addition,the fracture propagation length is not limited by the grid size by an automatic re-meshing method in the fracture tip,which addresses the grid dependence.Finally,the contact status of the contact surface in the whole fracture process and the mechanical mechanism of fracture propagation are obtained by analyzing the mechanical properties,fracture initiation angle and fracture propagation path.The proposed method boosts the efficiency and accuracy of rock failure process simulation,remedies the insufficient studies on closed crack propagations under compression and shear stress,thereby achieving detailed simulation of fracturing path.