异形孔在膨胀荷载作用下的定向致裂机制

Directional Cracking Mechanism of Special-shaped Holes under Expansion Load

基于室内相似材料应变试验,对带有尖角的异形孔如正三角孔、等腰直角三角孔、120°顶角的等腰三角孔在膨胀压力作用下的裂岩机理展开讨论.在此基础上,使用颗粒流模拟进一步研究了单向致裂效果的最佳角度、双孔的最佳作用间距以及岩石强度对压裂效果的影响.结果表明,异形孔作用下试样的起裂和破碎时间均短于圆形孔,并且其裂纹的发展是可控的,总是沿着尖角角平分线延长线方向进行.根据应变的变化,可将试验分为三个阶段.平稳发展阶段,各个方向的应变增长速率几乎没有差别;快速增长阶段,新的破裂面广泛形成且具备一定的方向性;衰弱阶段,断裂不断出现导致能量消散,应变急剧下降.数值模拟结果表明,双正三角孔间距为7倍正三角形边长时定向效果最佳,岩石强度和致裂效果呈乘幂关系.

Based on the strain tests of similar materials in laboratory,this research focus on crushing mecha⁃nism under expansion pressure of special-shaped holes with sharp angles,such as regular triangle hole,isosceles right triangle hole and 120°top angle isosceles triangle hole.On this basis,particle flow simulation is employed to find out the optimum angle of directional cracking effect,the optimum spacing of double holes and the influence of rock strength on fracturing effect.The results show that the crack initiation and fracture time of the sample under pressure of special-shaped holes are shorter than that of round holes,and the crack development is controllable since it is always along the extension line of sharp Angle bisector.According to the change of strain,the test can be divided into three development stages.In the steady development stage,the strain growth rate in each direction has nearly no difference.In the rapid increasing stage,new fracture surfaces are formed widely and show certain directiv⁃ity.In the weak stage,recurring fractures result in energy dissipation and a sharp drop in strain.The numerical simu⁃lation shows that the best orientation effect occurs when the angular spacing is 7 times the length of the equilateral tri⁃angle side,and the rock strength has a exponential relationship with the cracking effect.