深埋圆形隧洞板裂化弧形岩板凹曲变形的论证

以锦屏二级水电站TBM开挖的圆形断面施工排水洞为例，首先根据围岩实际破坏特性明确指出围岩劈裂后产生弧形岩板的客观存在性，然后提出其存在发生凹曲变形（指其发生弯曲方向指向隧洞外部、半径减小即曲率增大的弯曲变形）的可能性，最后从力学分析与数值试验两个方面对弧形岩板发生凹曲变形的可能性进行了论证。论证显示：对处于垂直地应力与水平地应力不相等条件下的深埋圆形隧洞，弧形岩板可以发生凹曲变形，发生的控制因素是两向应力差对圆形隧洞产生的垂直方向压缩、水平方向拉伸的压扁作用。弧形岩板凹曲变形的论证对今后深入认识深埋圆形隧洞完整或较完整硬岩动力破坏的发生机制提供了一条新思路。

Demonstration of concave deformation of arc-shaped rock slabs in deep circular tunnels

Slabbing is a failure phenomenon that the surrounding rock mass is separated into parallel slabs because of splitting effect in underground excavation. It always occurs in intact or relatively intact, hard, brittle and deep buried surrounding rock mass. The slabs are always arc-shaped in circular tunnels. When an arc-shaped slab experiences a bending deformation, which directs to the external of a tunnel, decreases the radius of the slab and increases its curvature, this kind of bending deformation can be named as concave deformation. In the case of the drainage tunnel excavated by TBM in Jinping Ⅱ Hydropower Station, the existence of arc-shaped slabs owing to splitting in the circular tunnel is definitely pointed out according to the in-situ characteristics of the surrounding rock mass, and the possibility of the concave deformation of the arc-shaped slab is put forward as well. Then the possibility of the concave deformation is demonstrated by means of mechanical analyses and numerical tests respectively. The demonstration reveals that the occurrence of the concave deformation is dominated by the stress difference between vertical and horizontal geostresses which press the circular tunnel into an approximatively elliptical one. The demonstration of the concave deformation for the arc-shaped slab will play an important role in intensive studies on mechanism of dynamic failure of deep and intact rock mass in circular tunnels.