深部软弱地层TBM掘进围岩变形破坏特性室内试验研究

LABORATORY STUDY OF DEFORMATION AND FAILURE OF SOFT ROCK FOR DEEP GROUND TUNNELLING WITH TBM

为了揭示深部软弱地层TBM开挖卸荷围岩变形破坏特性,分析深埋隧道TBM机械开挖卸荷的本质特征为高初始围压下的缓慢准静态卸荷,开展不同卸荷速率下砂质泥岩三轴卸围压试验,研究卸荷速率效应,获取TBM缓慢准静态卸荷围岩变形破坏特性:(1)缓慢卸荷条件下的峰前应力–应变曲线与常规三轴压缩时较接近,卸荷屈服阶段,岩石产生损伤扩容,侧向变形加速增长,从体积压缩开始转向扩容;(2)达到峰值强度后,岩石首先沿已贯通的破裂面滑移,发生1~2级规模较小的脆性跌落,随着围压继续缓慢卸除,岩石沿一条斜率较小的近似斜直线发生线性应变软化,且线性应变软化过程中伴随多级微破裂;(3)岩石变形全过程经历弹性变形、峰前卸荷损伤扩容、峰后脆性跌落、含有多级微破裂的线性应变软化以及残余强度阶段;(4)缓慢卸荷破坏过程中,岩石发生宏观张剪复合破坏,伴有轴向劈裂裂纹,破裂断面为由许多劈裂裂纹相互贯通形成具有一定宽度的剪切带,剪切带内劈裂的岩片在轴向挤压力和沿剪切面的剪切力共同作用下被挤压和摩擦成许多细颗粒和岩粉。

The TBM excavation in deep stratum is a process of smooth and quasi-static unloading of high initial confining pressure. In order to reveal the deformation and failure characteristics of soft rock at deep ground under the condition of TBM tunnelling,triaxial unloading tests on sandy mudstone with different unloading rates were carried out. The pre-peak stress-strain curves under the condition of smooth and quasi-static unloading of confining pressure were found close to the ones obtained from the conventional triaxial compression test. At the yielding stage upon unloading , the specimens exhibit damage dilatation , the lateral deformation grows accelerated,resulting in a turning of the volumetric strain from shrinkage into dilatation. After the peak strength, the specimens slide along the fracture surface already formed to display the modest brittle drop of strength once or twice. Then a linear strain softening stage accompanied by multistage micro fractures occurs on the stress-strain curve with a line segment of a small slope as the confining pressure is continuously and slowly unloaded. The complete deformation process of unloading is composed of the elastic deformation,the damage dilation,the post-peak brittle drop,the linear strain softening and the residual stress period. The specimens display composite shear-tension failure macroscopically accompanied with axial splitting cracks during the process of smooth unloading. Many split cracks link and cross each other to form a shear band of a certain width. The rock in the shear band is squeezed and wears into the fine particles and the powder as a result of the interaction of axial extrusion and the shear stress along the shear plane.