大跨度隧道环形开挖上台阶合理高度探讨

Reasonable Height of Annular Excavation Up-Step with Large Span Tunnel

减小上台阶高度是大跨度隧道环形开挖时提高围岩和支护结构稳定性的经验做法。通过建立上台阶拱圈的简化力学模型,对比不同高度拱圈结构在拱顶发生相同沉降和相同比例沉降时的弯矩值。结果表明,台阶高度越大,支护结构弯矩极大值越小,"拱效应"越明显,因此上台阶高度宜取较大值。

Reducing up-step height is the experience approach to improve stability of surrounding rock and supporting structure of annular excavation with large span tunnel. Through establishing the simplified mechanical model of up-step arch, the author compares the bending moment value of different height arch structure in the same vault settlement and the same percentage settlement. The results show that more bigger the step height is, more smaller the maximum bending moment of supporting structure is and more obvious the ＂arching＂ is, so the up-step height should take larger values.