围岩瞬态卸荷应力及塑性区分布的有限元分析

深部地下工程围岩卸荷导致的拉伸破坏是一个常见但没有得到充分研究的科学现象.将卸荷视为动态力学过程，基于连续介质弹塑性力学理论，运用有限元软件COMSOLMultiphysics对围岩瞬态卸荷破坏成因进行初步探究，建立了围岩瞬态卸荷塑性力学模型.研究结果表明:开挖将在围岩中激起强烈的卸载扰动，应力场的重新分布是由动力响应过渡到静力作用的动态过程.瞬态卸荷将导致开挖自由面附近产生拉应力.尽管拉应力时间短、幅值低、范围小，但由于岩石抗压不抗拉的特性，在高地应力条件下，拉应力可导致围岩产生拉伸破坏.分析表明横向惯性作用可能是导致这一现象的原因之一.

Finite Element Analysis of Transient Unloading and Plastic Zone Distribution in Surrounding Rock

Up to now， the tensile failure in highly stressed rock after excavation， resulted from unloading， is a common phenomenon， but not well theoretically explained yet. Taking the unloading as a dynamic process， a plasticity model for transient unloading was developed to study the failure mechanism in the surrounding rock based on the theory of continuum elasto plasticity using the finite element analysis (FEA) with a commercial software COMSOL Multiphysics. The results show that excavation can trigger strong disturbance in surrounding rock due to the transient release of in situ stress. The stress redistribution is a dynamic process transiting from dynamic stress response to quasi static stress condition. The transient unloading can cause tensile stress near the excavation surface. Although the duration of transient tensile stress is short， its amplitude is small and the affected domain is limited， the tensile stress may result in tensile failure because the uniaxial tensile strength of rock is far lower than its compressive strength. It is also denoted that the lateral inertia effect may be one reason for this phenomenon.