基于强度折减和上限有限元的椭圆形毛洞隧道围岩稳定性分析

将强度折减法引入刚体平动运动单元上限有限元并编制计算程序，针对椭圆形毛洞隧道围岩稳定性和破坏模式开展计算分析，获得了围岩抗剪强度参数、隧道埋深、跨度等与安全系数的关系曲线，并探讨了围岩强度折减极限状态对应的刚性块体破坏模式的形态特征.结果表明：强度折减法可方便嵌入运动单元上限有限元非线性规划模型；围岩安全系数与其围岩强度参数正相关，与埋深比和跨度比负相关；隧道跨度对安全系数的影响较为明显，当隧道跨度与高度比(B/D)由0.5增加到2.0时，安全系数降低幅度处于27%~46%之间；强度折减极限状态下刚体平动运动单元上限有限元所得围岩破坏模式形态鲜明，其主要滑动破坏面由隧道底部或边墙处延伸至地表，错动的滑移线集中于隧道拱部和边墙上方，而水平破坏区域延伸范围均小于1.5倍隧道高度.
To study the unlined elliptical tunnel stability, strength reduction method was introduced into the finite element upper bound method. The relations between safety factor and influence factors such as shear strength parameters, buried depth and span were studied with self-made program. Meanwhile, the failure modes were also explored for limit states derived from strength reduction method. The results show that strength reduction method can be easily embedded into finite element upper bound method. The relation curves have shown a positive correlation between rock safety factors and shear strength parameters, while rock safety factors have negative correlations with buried depth and span. The influence of the tunnel span on the safety factor is obvious, and the reduction in rock safety factors has been found to vary approximately in a range of 27%~46% when the ratio of tunnel span and height (B/D) increases from 0.5 to 2.0. The failure modes with distinct characteristics reveal that the main slip surface starts from the bottom or the side wall of the tunnels and then extends up to the ground surface. The slip lines are mainly focused on the top of the tunnel arch and side wall. Meanwhile, horizontal extents of the damage area are less than 1.5 times of tunnel height.