不同侧压系数条件下圆形巷道岩爆过程模拟

Numerical simulation of rockburst processes of a circular tunnel at different lateral pressure coefficients

利用FLAC模拟了水平及垂直方向围压不同(非静水压力)条件下的圆形巷道的岩爆过程。为了模拟巷道开挖,利用编写的FISH函数删除巷道内部的单元。岩石服从摩尔-库仑剪破坏与拉破坏复合的破坏准则,破坏之后呈现应变软化-理想塑性行为。模拟分为3步:首先,将两个方向压力施加在模型上,直到达到静力平衡状态;然后,利用FISH函数开挖巷道;最后,计算重新开始,直到达到静力平衡状态或者塑性流动状态。模拟结果表明,当水平与垂直方向压力差较小时(或侧压系数较小时),围岩中出现了"狗耳"形的V型坑,岩爆之后围岩能保持稳定。当侧压系数适中时,可以相继观察到V型坑和U型坑(或"平底锅"形坑),岩爆之后围岩仍然是稳定的;当侧压系数较大时,围岩中先产生V型坑,然后是U型坑,之后由于剪切带相互贯通,形成了"鱼鳞"形的破坏区域,它们位于巷道顶部之上和底部之下,这将造成围岩的失稳。然而,在巷道两侧未观察到破坏现象。

Rockburst processes of a tunnel at different lateral pressure coefficients are modeled by use of FLAC. To model excavation,a FISH function is written and used to delete the elements in the tunnel. For rock elements exhibiting linear strain-softening behavior beyond the occurrence of failure and then ideal plastic behavior,the failure criterion obeys composite Mohr-Coulomb criterion with tension cut-off. The present calculation is divided into three steps. Firstly,the pressures in the horizontal and vertical directions are applied to the plane strain model until a static equilibrium state is reached. Secondly,the tunnel is excavated using the written FISH function. Thirdly,the calculation renews to achieve a new equilibrium state or a plastic flow state. Results show that at lower lateral pressure coefficients,dog-ear or V-shaped notches are generated in the surrounding rock that is stable after rockbursts. At moderate lateral pressure coefficients,V-shaped and U-shaped （panlike） notches are observed one after the other and the surrounding rock is still stable after rockbursts. When the lateral pressure coefficients are higher,the V-shaped notches are firstly generated and then the U-shaped notches are formed; afterwards,shear bands intersect and scalelike failed zones are formed above the roof and below the floor,leading to the unstable failure of the surrounding rock. However,no failed zones are formed at the two sides of the tunnel.