三点弯曲条件下薄层状岩体单层厚度对裂纹扩展路径的影响

EFFECT OF LAYER THICKNESS OF FLAGGY ROCK ON CRACK PROPAGATION PATH SUBJECTED TO THREE-POINT BENDING

为了揭示薄层状岩体单层厚度对裂纹扩展路径的影响,利用ABAQUS软件进行数值模拟,对含预制裂纹的不同单层厚度的层状岩体进行三点弯曲数值试验,岩体试样长度和宽度一定(512 mm×128 mm),分5种不同的单层厚度建模,单层厚度分别为:64 mm、32 mm、16 mm、8 mm、4 mm。提取破裂过程中的声发射信息及主裂纹路径参数,对比分析不同层理厚度时,岩体的峰值载荷、声发射事件数、累计声发射事件数、主裂纹长度等对单层厚度的变化规律。研究结果表明:(1)薄层状岩体的强度与单层厚度有一定关系,单层厚度越大,岩体的抗弯强度越小,并且这种变化是非线性的。(2)在不同层厚条件下,层理面均表现出了阻止裂纹向上扩展的效果。同时,裂纹在层状岩体中的扩展是不连续的,裂尖沿层理面发生了水平迁移,整体呈现阶梯状。(3)在三点弯曲条件下,随着单层厚度的减小,岩体破裂时的裂纹总长度先增大后减小。(4)裂纹在岩体层面扩展时破裂类型多为滑移与拉张破裂的组合,而在非层理面的岩体内部扩展时,以拉张破裂为主。(5)薄层状岩体在三点弯曲条件下,声发射事件在岩体的压密阶段几乎没有出现,直至接近峰值载荷时才大量涌现。到了载荷快速下降时,单位时间的声发射事件数也达到最大。研究结果将对预测层状岩石的裂缝演化提供依据。

In order to reveal the influence of single layer thickness on crack propagation path of flaggy rock,we used ABAQUS for numerical simulation.We carried out three-point bending tests of layered rock with specimens length and width constant(512mm×128mm).There were 5 layer thicknesses.They were respectively 64mm,32mm,16mm,8mm,and 4mm.Information of acoustic emission and main crack path were extracted.We summarized the regulation of peak load and acoustic emission data.The results of the study show that:(1)The strength of flaggy rock is relevant to single layer s thickness.The larger the monolayer thickness is,the smaller the bending strength of rock mass is,meanwhile this change is nonlinear.(2)Although with different thickness,the bedding surface consistently shows the effect of preventing crack propagating upward.(3)With monolayer s thickness decreasing,the total crack length of rock mass first increases and then decreases.(4)When the cracks expand along the weak surface,the fracture type is a combination of slip and tensile fracture.In contrast,when they expand inside the rock mass,tensile fractures dominate.(5)Acoustic emission event will not occur instantly.In the contrary,they increase sharply just when the peak intensity approaching.Accompanied by the stress plunging,the number of acoustic emission events reaches the maximum.The research results will provide a basis for predicting the fracture process of layered rocks.