细观结构的非均质性对花岗岩蠕变特性影响的离散元模拟研究

Discrete element simulation study on the influence of microstructure heterogeneity on the creep characteristics of granite

基于颗粒离散元方法,通过将等效晶质模型和应力腐蚀模型相结合,建立考虑晶体粒径分布的非均质性蠕变颗粒流模型。通过室内试验和数值模拟计算结果的对比分析,验证该方法在花岗岩蠕变力学特性研究中的适用性和可靠性,表明晶体粒径分布所造成的非均质性对花岗岩蠕变失效时间、稳态蠕变速率、裂纹数量和长期强度等性质都具有很大的影响。主要研究结论如下:(1)当非均质性因子越小时,岩石越均质,单轴抗压强度和长期强度越高,岩石的长期强度和单轴抗压强度的比值在0.70左右;(2)岩石在同一应力下,当非均质性因子越大时,蠕变失效时间越小;在同一驱动应力比下,随着非均质性因子的增加,岩石稳态蠕变速率降低,蠕变失效破坏时间更长;(3)微裂纹的发展大致分为3个阶段:缓慢扩展阶段、等速扩展阶段和加速扩展阶段,从微裂纹数量上,呈现出晶间拉裂纹、晶内拉裂纹、晶间剪裂纹数量递减的规律,晶间裂纹在总裂纹数量中占主导地位;(4)岩石的细观结构对破坏模式起着控制性作用,当模型较为均质时,破坏模式呈现出劈裂破坏;当非均质性增加时,破坏模式转变为剪切破坏。微裂纹在扩展过程中会优先选择晶体边界扩展,并且出现了明显的'绕核'现象,即粒径较大的长石对裂纹扩展和破坏模式影响明显,当岩石非均质性越大时,该现象越明显。

Based on discrete element method,a heterogeneous model considering the crystal size distribution was established by combining the grain-based model and parallel-bonded stress corrosion model.Through the comparative analysis of laboratory test and numerical simulation results,the applicability and reliability of the method of creep mechanical properties of granite were verified,and it is revealed that the heterogeneity caused by the crystal size distribution has significant influence on creep failure time,steady creep rate,number of microcracks and long-term strength.The main research conclusions are as follows:(1)The smaller the heterogeneity index,the more homogeneous the rock is,and the higher the uniaxial compressive strength and long-term strength are.The ratio of the long-term strength to the uniaxial compressive strength is about 0.70.(2)Under the same stress,the larger the heterogeneity index,the smaller the creep failure time is.Under the same driving stress ratio,the creep rate of the rock decreases and the creep failure time increases with increasing the heterogeneity index.(3)The development of microcracks is roughly divided into three stages including slow expansion,constant velocity expansion and accelerated expansion.The number of intergranular tensile microcracks is most and then intragranular tensile microcracks,followed by intergranular shear microcrack.(4)The microstructure of rock plays a controlling role in failure mode,and microcracks are preferred in the process of expansion.When the model is homogeneous,the failure mode exhibits cleft breakage.when the heterogeneity increases,the failure mode transforms to shear failure.The expansion of microcracks originates from crystal grain boundary with an obvious'bypassing core'phenomenon,that is,the feldspar with larger grain size has obvious influence on microcrack propagation and failure mode.The larger the rock heterogeneity,the more obvious the phenomenon is.