北山深部花岗岩弹塑性损伤模型研究

ELASTOPLASTIC DAMAGE MODEL OF BEISHAN DEEP GRANITE

基于力学特性试验和三维声发射监测技术,研究北山花岗岩在压应力条件下的力学行为特征和损伤演化机制,并构建岩石的力学损伤模型。试验结果表明,在低围压条件下岩石主要发生的是脆性破坏;随围压增大,岩石力学行为逐渐向延性转化,表现出剪胀、塑性变形等非线性行为。结合微裂隙产生和扩展规律,对岩石在外力作用下的损伤演化过程和破坏机制进行分析,认为北山花岗岩的破坏及非线性行为是损伤和塑性变形共同作用的结果。基于这一认识,在热动力学框架下提出北山花岗岩准唯象弹塑性损伤模型。模型引入非关联的塑性流动方程,以反映岩石在压应力作用下体积变形从压缩到膨胀的转化过程。基于已有的损伤理论建立损伤演化方程,并通过在塑性屈服面中引入独立损伤变量,建立塑性和损伤发展的耦合关系。数值模拟和试验数据的对比表明,模型可以很好地描述北山花岗岩在不同应力水平下的损伤演化规律和力学行为,特别是随围压增大岩石力学行为从脆性到延性的转化过程以及岩石峰前塑性硬化和峰后应力软化等行为特征。

Based on the mechanical investigation, a coupled elastoplastic damage model is proposed to simulate the mechanical behaviour and damage evolution process of the intact deep granite in Beishan area. The experimental results revealed that Beishan granite exhibits typical brittle failure mode under low confining pressure. With the increase of confining pressure, the brittle-ductile transition of the mechanical behaviour took place; and significant plastic deformation and volumetric dilatation are noticed. The damage evolution process is also analyzed according to the initiation and propagation characteristics of the stress-induced microcracks. It is indicated that the failure and nonlinear mechanical behaviour of Beishan granite are essentially related to the coupling effect between the damage and plastic deformation. Based on this acknowledgement, a coupled elastoplastic damage model is proposed. In the model, a non-associated plastic flow rule is used to describe the compression-dilatation transition of the volumetric deformation. The coupling between the damage and plastic deformation is realised by introducing the independent damage variable in the plastic yield surface. The comparison between the predictive result and experimental data suggests that the proposed model is capable to reproduce the main mechanical performances of Beishan granite under compressive stress condition, especially the brittle-ductile transition of mechanical behaviour with the increase of confining pressure.