TBM掘进圆形隧洞底鼓机理FDEM数值模拟研究

FDEM numerical simulation study on the floor heave mechanism of the circular tunnel excavated by TBM

采用耦合的有限元-离散元法(finite-discrete element method, FDEM)研究了圆形隧洞底板大变形灾变机制,并研究了地应力量值、侧压系数、底板位置和隧洞形状对底鼓灾害的影响。结果表明:1)在静水压力状态下,圆形隧洞底板大变形灾变力学机制为隧洞开挖造成围岩径向应力降低和切向应力升高,当超过岩体强度后产生共轭剪切破裂,并伴随拉伸断裂;浅部破裂岩块在深部围岩弹性变形恢复和剪胀效应下发生向隧洞内的翻转大运动,进而引发底板大变形灾害;2)随着地应力量值、侧压系数和底板位置的变化,围岩破坏率、损伤破裂区半径和隧洞表面围岩最大位移量等也发生变化,但仍为破裂碎胀性的大变形;3)传统的滑移线场理论难以解释直墙拱形底板围岩的共轭剪切破裂和深部岩体破裂,采用FDEM和双轴压缩力学模型可成功解释上述现象,为隧洞底鼓大变形灾变机制提供新的研究思路。

The combined finite-discrete element method(FDEM)is used to study the floor large deformation mechanism of a circular tunnel,and the influences of in-situ stress value,lateral pressure coefficient,location of the floor and tunnel shape on the floor heave disaster mechanism are also studied.The results indicate that:1)under hydrostatic pressure,the mechanical mechanism of large deformation of the circular tunnel floor is that the radial stress of the surrounding rock decreases and the tangential stress increases due to the excavation.Therefore,when the strength of the rock mass exceeds,conjugate shear fractures occur,and are accompanied by tensile fractures.Under the action of elastic deformation recovery and dilatancy effect of the deep surrounding rock mass,the shallow fractured rock has a large overturning movement into the tunnel,which then produces a large deformation disaster of the floor.2)With the changes of in-situ stress value,lateral pressure coefficient and floor position,the failure degree of surrounding rock mass,the radius of damage-fracture zone and the maximum displacement of the surrounding rock mass on the surface of the tunnel also change,but it is still a fracturing expansion and squeezing deformation.3)For the traditional slip-line field theory,it is difficult to explain the conjugate shear fracture of the surrounding rock mass of the straight-wall-top-arch tunnel floor and the fracture of the deep rock mass.The FDEM numerical method and the biaxial compression mechanics model in this paper can successfully explain the above phenomenon,which provides a new idea for the catastrophic mechanism of the large deformation of the tunnel floor heave.