华南风化花岗岩劈拉断裂行为的试验与细观模拟研究

EXPERIMENTAL AND MESO-SCALE NUMERICAL MODELING OF SPLITTING TENSILE BEHAVIOR OF WEATHERED GRANITES FROM SOUTH CHINA

为研究不同风化程度花岗岩在劈拉受载下的破损行为,该文对广东从化地区新鲜、微风化、中风化三种风化程度的花岗岩进行微观特征测量及巴西圆盘试验研究。分别基于考虑空间相关特征的随机模型和数字图像技术两种方法实现对岩样细观结构的表征,结合细观参数反演技术,建立反映岩石细观非均质组构特性的颗粒离散元模型,对花岗岩劈拉试验进行数值仿真试验研究。结果表明,随着风化级别的提高,花岗岩中粘结力较强的长石等矿物向粘土矿物转化,结晶强度降低,微孔隙等软弱结构增多,岩石宏观力学性能不断劣化,劈拉破坏由单一裂纹主导转为多条分叉状裂纹,岩样脆性也逐渐减弱。基于两种方法建立的细观随机力学模型仿真结果均表明岩样的劈拉强度随风化级别的提高逐渐降低,与试验结果变化趋势相符,分析得到不同风化花岗岩的劈拉破裂响应特征与试验结果一致,且从细观层面对花岗岩样受劈拉作用的渐进破裂响应提供了深入认识。

This paper presents an investigation into the splitting tensile damage and fracture behavior of granite rocks from South China showing various levels of weathering. The rock samples were selected from Conghua, Guangdong Province, and can be sub-divided into three series, namely, fresh, slightly weathered and moderately weathered granite rocks. Mineral composition tests and Brazilian tension tests were conducted to study the difference in mineral compositions and its effect on the fracture failure patterns. Two types of pre-processing approaches were adopted to represent the meso-scale structure of weathered granites, one using a statistical method considering spatial correlation character and the other using digital image processing technique. Comprehensive numerical analyses of the Brazilian tests were then carried out using bonded-particle discrete element method. The test results show that the feldspar minerals in granite will progressively change into clay minerals with the increasing weathering levels, which leads to a decrease of the strength of crystallization, an increase of void defects, and in turn the degradation of the macro-scale mechanical properties of granites. It is also found that the single crack failure pattern is dominant in fresh granites whilst the moderately weathered granite samples present multiple crack branching, and that the brittleness of granite rocks decreases with the weathering levels. The numerical results from the two types of meso-scale numerical models both compare well with the test observation that the tensile strength decreases with the weathering levels, and similar fracture failure patterns are also given. Moreover, the present numerical study can provide an in-depth investigation into the meso-scale cracking mechanism in the granite rocks with respect to the weathering induced internal deterioration.