铁路隧道初期支护结构随机有限元及可靠度分析

Stochastic Finite Element and Reliability Analysis of Primary Support for Railway Tunneling

将围岩与支护结构视为一起受力的整体不确定体系,假设原始应力为围岩自重应力,用弹塑性平面有限元程序和按蒙特卡罗-随机有限元法分析初期支护作用效应的统计特征,应用"分位值"法对现行单线电化铁路隧道复合式衬砌通用图的初期支护按连续介质模型计算其可靠指标。计算结果表明,各级围岩随着埋深的增加,可靠指标不断减少,Ⅳ级围岩超过200 m、Ⅲ级围岩超过300 m后可靠指标都很低,这一结果与实际情况不符,说明完全按埋深来确定围岩原始应力是不合适的。而对于同样埋深,围岩愈松软,可靠指标愈小,特别是松软的Ⅴ级围岩,抗开裂可靠指标不能满足要求,抗压的可靠指标也很低,说明Ⅴ级围岩的初期支护要加强,一定要加钢筋格栅或型钢拱,以防大面积裂损。

Surrounding-rock and primary support structure are considered as an uncertain system, the stress due to rock weight is assumed as initial stress, Monte-Carlo elastoplastic random FEM is used to calculate the statistical character of effects of support actions, ＂fractile method＂ is used to analyses the reliability index of primary support of single-track electrification railway tunnel complex lining. The calculation indicates that the reliability index reduces with the depth of the tunnel, the reliability index is very low when the depth of tunnel in grade Ⅲ rock exceeds 300 m and 400 m. in grade Ⅳ rock. This result is different from the truth, which indicates that initial stress of surrounding rock can not be determined only according to the depth. The softer surrounding rock is, the lower reliability index is, and especially, grade Ⅴ rock has very low reliability index of crack resistance and compressive resistance, so that primary support in the condition of grave Ⅴ surrounding rock must be strengthened, such as using lattice girder or steel arch to protect surrounding rock from cracking in a large area.