高原多年冻土区隧道暗挖法安全稳定性三维数值分析

青藏铁路风火山隧道以其高海拔、常年冻土环境而给施工带来了新的挑战 ,为了防止土体冻融产生的冻胀力对隧道结构造成的破坏 ,施工中必须强调衬砌结构的快速封闭。虽然全断面法和微台阶法均能较快地实现衬砌的封闭 ,但在洞口段岩体较为破碎的条件下 ,到底哪种方法能够满足既安全又快速的施工要求 ,是摆在施工者面前的难题。笔者采用三维数值模拟的方法 ,对风火山隧道出口端的开挖方法和支护方式的安全稳定性进行了研究 ,其结果认为 ,全断面开挖难以控制工作面的稳定 ,会因过大沉降和结构开裂而危及施工安全 ,而同等条件下 ,采用微台阶法施工 ,则可以将拱顶沉降和结构应力控制在允许范围内。经分析对照 ,证明数值分析预测结果正确 ,与施工实践有很好的一致性。

3D-digital Simulation of Security and Stability of Tunneling in Permanent Frozen Stratum on Plateau

New challenges of high altitude and permanent frozen environment were met during the construction of tunnel at Mt. Fenghuo on Qin-Zang railway. In order to prevent the damage caused by freezing expansion, fast closing of the tunnel lining was emphasized. Though both entire section method and micro-bench method could realize fast closing of tunnel lining, it was hard to decide which one would be more suitable in the broken district of tunnel portal. A 3-D finite element method was used to study the security and stability of excavating and timbering mode of tunneling at the tunnel portal of Mt. Fenghuo. Simulation showed that the entire section method was thought inaccessible to stable the tunnel face and would endanger safety in construction because of much too settlement and split of structure. However, under the same condition the micro-bench method was able to control the settlement and stress within the allowable range. By comparison, the prediction proved to be agreeable to the measurements of construction.