卸荷条件下横观各向同性岩体扩容与能量特性分析

Dilatancy and energy characteristics analysis of transverse-isotropic rock mass under triaxial unloading condition

丹巴水电站引水隧洞围岩主要为石英云母片岩,位于高应力区,层状特征显著,属于典型的横观各向同性岩体,其扩容和能量特性问题突出。针对平行片理和垂直片理方向的试件,基于MTS815岩石力学试验平台,研究三轴卸荷条件下石英云母片岩的扩容特性及能量变化规律。研究表明:(1)平行组与垂直组试件的特征应力均随围压的增大而增大,两者间具有良好的线性关系;(2)平行组试件裂纹闭合应力、损伤扩容应力及峰值应力均大于垂直组,起裂应力低于垂直组;(3)平行组试件扩容参数(扩容指标及剪胀角)大于垂直组,且随着围压的增大,两组试件扩容特征相继减弱,试件扩容指标与围压呈良好的指数型分布,特征剪胀角与偏应力比呈良好的线性分布;(4)平行组与垂直组试件峰值点和残余点处能量值均随围压增加而增大,且与围压呈良好指数型分布,相同围压下,平行组试件峰值点处能量特征值及残余可释放应变能均大于垂直组,残余耗散能低于垂直组;(5)无论是峰值点还是残余点处,两组试件耗散能量值与剪胀角以及能量特征值与扩容指标间均呈现良好指数型关系。

The surrounding rock of diversion tunnel in Danba Hydropower Station is mainly composed of quartz mica schist at the high-stress zone, which is typical transversely isotropic rock mass and has distinct layered characteristics with apparent dilatancy and high energy. Based on the MTS815 system, triaxial unloading tests were conducted to ifivestigate the characteristics of dilatancy and energy change, and the loading direction was parallel and perpendicular to the schistosity of rock samples, respectively. The results demonstrate that the characteristic stress of both groups increased with confining pressure, which exhibited a good linear relationship with confining pressure. The crack closing stress, damage and expansion stress and peak stress of the parallel group were superior to those of the vertical group, whereas the crack stress was inferior to that of the vertical group. The dilataney parameters of the parallel group were higher than vertical group. However, expansion characteristics of these two groups were weakened with the increase of confining pressure. Moreover, the index of expansion showed great agreement with confining pressure by an exponential distribution, and dilataney angles had a linear relationship with the partial stress ratio. At the peak point and the residual point, the energy values of these two groups enhanced with confining pressure, and the energy values revealed good exponential distribution with confining pressure. Furthermore, under the same confining pressure, the energy characteristic value at the peak point and the residual released energy of the parallel group were greater than those of the vertical group. However, the residual dissipated energy of the parallel group was lower than that of the vertical group. For both groups, the relationship between the dissipated energy value and the dilatancy angle, together with the energy characteristic value and the dilatancy index, demonstrated good exponential distribution,which fit at the peak point as well as the residual point.