基于矿物晶体模型非均质岩石单轴压缩力学特性研究

Research on mechanical properties of heterogeneous rocks using grain-based model under uniaxial compression

为研究岩石微观结构非均质性对宏观力学特性及裂纹扩展规律的影响,结合花岗岩室内单轴试验及矿物晶体模型(Grain-based model, GBM)对岩石的微观矿物结构进行离散元建模,研究了非均质岩石宏观应力-应变曲线、声发射及晶体尺度裂纹扩展规律。通过改变岩石微观结构进一步研究了不同矿物组成条件下岩石宏观力学特性及其变化原因。结果表明:GBM可在考虑岩石微结构及强度非均质的条件下,有效模拟岩石加载过程中宏观及微观力学特性;加载初期,岩石内部晶体尺度裂纹首先以晶间裂纹为主,随后转变为以晶内裂纹为主,且裂纹破坏主要为拉伸破坏,岩石破坏时拉伸裂纹及晶内裂纹与总裂纹占比分别约为93.87%,60.95%;加载过程中,岩石微裂纹首先随机分布在岩石内部,后开始聚集并造成宏观破裂面的出现,且宏观破裂面的形成主要与矿物晶体内裂纹的扩展及聚合有关;随岩石内长石矿物含量的增加,岩石峰值应力与损伤应力整体呈增加的变化趋势,且该变化规律可能与长石矿物内裂纹数增加及云母矿物内裂纹数减小有关;通过矿物晶体模型对岩石微观结构进行模拟并对非均质性所造成的力学特性变化进行微观尺度解释,有利于更好理解岩石非均质性与宏观力学特性的关系。

In order to investigate the influences of structural heterogeneity on the mechanical properties and crack growth of rocks, the microstructure of granite is modelled by using grain-based model(GBM). In comparison with the results of laboratory experiments, the properties of stress-strain curves, acoustic emission and grain-scale crack growth of rocks with different mineralogies are investigated. The results show that GBM can be used to efficiently study the macro-and micro-mechanical properties of rocks when the mineral components have different structures and strengths. The grain-scale cracks in rocks are mainly intergranular cracks at the onset of loading, then the intragranular cracks become predominant inversely, and the failure pattern of cracks is always dominated by tensile cracks. When the model fails, the ratios of intergranular and intragranular cracks to total cracks are about 93.87% and 60.95%, respectively. During the whole loading, the locations of microcracks are first located randomly, then the clustering of microcracks leads to the appearance of macroscopic failure surface, and the formation of failure surface is related to the propagation and coalescence of intragranular cracks. When the feldspar mineral in rocks increases, the corresponding peak stress and damage stress increase due to the increase of intragranular cracks formed in feldspar mineral and the decrease of intragranular cracks formed in biotite mineral. In this study, the modelling of micro-structure based on GBM and the reason why heterogeneous rocks behave different mechanical properties may promote our understanding of the influences of rock heterogeneity on the mechanical properties.