花岗岩高温高压损伤破裂细观机制模拟研究

Meso-fracture mechanism of granite specimens under high temperature and confining pressure by numerical simulation

为了探究花岗岩高温高压损伤破裂细观机制,使用颗粒流程序(PFC)中的晶粒模型(GBM)单元开展高温作用后花岗岩常规三轴压缩模拟,分析应力-应变曲线、强度特征及破裂模式随围压及温度演化,研究其破裂过程,研究结果表明:GBM模型可以反映晶粒间的嵌锁效应,较好地模拟花岗岩劈裂、三轴压缩过程以及真实的花岗岩拉压比和强度随围压非线性特征,一定程度上克服了圆形颗粒嵌锁力不足的问题。不同围压下试样峰值强度随温度升高总体呈现先基本不变后迅速下降的趋势,450℃为阈值温度。莫尔–库仑准则回归得到的内摩擦角及黏聚力随温度总体呈先增高后降低趋势,且花岗岩强度参数的变化与其受力结构密切相关。当石英发生α-β相变后(573℃),花岗岩内产生大量穿晶裂纹及晶粒边界裂纹。单轴压缩下,试样的破裂特征受到热裂纹控制,峰后呈延性破坏;而高围压下,剪切带穿过晶粒,导致试样峰后产生脆性破坏。

To explore the mesoscopic fracture mechanism of granite under high temperature and confining pressure,GBM in PFC was adopted to simulate the triaxial tests of granite specimens after thermal treatment,and then the strain-strain curve,strength,failure modes and the fracture process were investigated. Based on the above analysis,the following conclusions can be obtained:GBM can reflect the interlock between grains and the nonlinear variation characteristic of the peak strength with confining pressure,and it also can overcome the problem that the circular particles is insufficient locking force. The peak strength of granite under different confining pressures is almost constant first and then decreases rapidly with increasing temperature,and 450 ℃ is the threshold temperature. The internal friction angle and cohesion first increase and then decrease with temperature,and the variation of the mechanical parameters is closely related to the mechanical structure of granite. After quartz underwent α-β phase transition(573 ℃),a large number of intra-granular cracks and inter-granular cracks occur in granite specimen.Under uniaxial compression,the fracture process of the specimen is controlled by thermal cracks,and the specimen exhibits ductile failure after the peak strength. Under high confining pressure,the shear band passes through the grain,loading to the brittle failure after the peak strength.