自由边界形状与近边界裂纹相互作用模型研究

Research on interaction model of free boundary shape on crack propagation

大量的研究表明,岩爆发生条件与岩石的力学性能有关。岩体中微裂纹的形成、扩展和汇合对岩体的力学性能产生显著影响,可以导致材料的逐渐劣化直至破坏。对于单轴压缩的岩石试件,其破坏型式主要是微裂纹的摩擦滑移、自相似平面扩展和弯折扩展。基于断裂力学机制,对单轴压缩荷载下3种不同边界形状,即直边、凸形、凹形情况下近边界原生斜裂纹的扩展进行了理论研究,并运用FLAC数值模拟技术,建立了基于Interface界面单元的裂纹扩展数值模型。近直边界及凸形边界情况的裂纹扩展使用梁渐近模型来解析薄片岩层的屈曲断裂问题,对于近凹形边界情况给予简化,提出了裂纹-圆-椭圆相互作用的修正模型并进行理论分析。研究结果表明,基于Interface界面单元的裂纹扩展的数值模型正确,解析解与数值解吻合较好,相应的梁渐近模型及裂纹-圆-椭圆模型可以合理地分析应力调整过程中裂纹的扩展和裂纹与不同洞室表面形状的相互作用问题,为岩爆工程及理论研究提出了新的理论依据。

A great many researches show that the rockburst is related to the mechanical properties of rock. The microcracks in rock mass are formed, expanded and converged which have remarkable influences on the mechanical properties of rock, It may bring about material inferiority and failure. For rock samples under uniaxial compression test, its failure forms include friction slippage, self-similar propagation and crankle expansion of microcracks. Based on the fracture mechanism, these mechanisms of crack propagation situated close to the boundary are studied by theoretical methods with considering three different boundary shapes, i.e. straight, convex and concave. Based on ＂Interface＂ element of FLAC simulation technology, the direct numerical simulations of crack propagation are proposed and analyzed. When the crack is situated close to the straight and convex boundary, the beam asymptotic model can be employed to find the crack-free surface interaction. A crack-hole-ellipse interaction model is proposed when crack propagation is near a concave boundary using some simplified methods. The expressions for crack propagation near different boundaries are all derived. The results show good agreement between the numerical and theoretical results. The proposed model can analyze the propagating, interaction of crack with free boundary due to stress distributing of surrounding rock, which can provide new basis for rockburst and theoretical research.