基于损伤控制方法的大理岩非线性剪胀特性试验研究

Experimental study of nonlinear dilatancy characteristics based on the damage-controlled method

剪胀角是描述岩石体积膨胀扩容的常用参数,在非关联流动法则中,连续介质理论通常假设剪胀角为0;在关联流动法则中,其值恒定且等于内摩擦角。岩石三轴压缩全过程体应变曲线表明,其体积剪胀性依赖于围压和塑性参量,破坏过程中不仅其特征强度随围压和塑性参量呈非线性变化,而且剪胀特性也表现出非线性特征。基于塑性力学理论,针对锦屏大理岩损伤控制的全过程三轴加、卸载试验,采用双参数非线性函数拟合方法建立了能同时考虑围压效应和塑性参量的非线性剪胀角模型。结果表明,对于大理岩、中硬岩,在破坏过程中扩容行为强烈依赖围压和岩石塑性参量,均表现出先快速增加至峰值后,随着塑性变形增加逐渐减小的非线性演化规律。提出的双参数非线性剪胀角模型很好地描述了岩石破坏过程中的体积扩容特性,其结果对于研究地下工程围岩应力变化诱发的围岩剪胀破坏机制、体积扩容膨胀区范围预测和围岩支护的合理设计均具有一定的理论和工程应用价值。

Dilatancy angle is commonly used to describe the expansion behaviours of rock. Continuum theory generally assumes that the value of dilatancy angle is 0° for the materials obeying the non-associated flow rule, but for those materials obeying the associated flow rule the dilatancy angle is a constant value equal to internal friction angle. The full volumetric curves of triaxial compression show that volumetric dilatancy is highly dependent on the confining pressure and plastic parameters. In a full failure process, not only the characteristic strength but also characteristics of dilatancy properties behave in a nonlinear manner with change of confining pressure and plastic parameters,. Employing plasticity theory and the nonlinear fitting method, a double parameters’ dilatancy angle model is developed, based on damage control triaxial loading and unloading cycle test data of Jinping marble, to take into account the effects of the confining pressure and plastic parameters. The model reveals that the dilatancy behaviors of marble as well as similar hard rocks are mainly governed by the confining pressure and plastic parameters during a failure process, which shows significant nonlinearity,and the dilatancy angle rapidly increases to the peak and then decreases gradually with increasing plastic deformation. The proposed double-parameters nonlinear dilatancy angle model can be used to describe the volumetric dilatancy properties, helping understand the mechanism of surrounding rock failure around underground openings and predict the range of expansion volume. In addition, the proposed model has theoretical and practical bearings on the design of supporting structures in underground rock engineering.