Abstract: The closely spaced tunnels with large cross － section have large excavation span，low flat rates and significant effect of two holes. The mechanical behavior and stress mechanism of closely spaced tunnels with large cross-section are more complicated than those of normal tunnels in construction. Based on the engineering project of Chaoyangsi tunnel which underpasses the Yu-Ling expressway，the deformation characteristics of supporting structure and the rock surrounding tunnel are obtained. Then the concept of close proximity to yielding degree is adopted to make an evaluation of the mechanical characteristics in supporting structure and the rock surrounding tunnel. Finally，the changing rule of the closely spaced tunnels with large cross-section during excavating is discussed. The research results show that the reasonable distance between two tunnels should be 1D ～ 1. 2D. Their deformation and mechanical characteristics of the surrounding rock in the naked tunnels are obtained by the strength reduction method. These calculated results are in accordance with the foregoing results. So a new reasonable distance of the closely spaced tunnels with large cross-section is proposed. The research findings would provide some references for the design and construction of similar tunnels.

Key words: closely spaced tunnel, tunnel with large cross-section, construction characteristics, distance optimization; close proximity to yielding degree

摘要： 小净距大断面隧道开挖跨度大，扁平率低，双洞相互影响显著，在施工过程中其施工力学性态及受力机理较 普通隧道更为复杂。依托朝阳寺隧道下穿渝邻高速段工程，分析了围岩及支护结构的变形特性，引入屈服接近度 概念对其受力进行评价，探讨了隧道不同近接施工力学变化规律，结果表明其较为合理的净距为1D～1.2D。通过 强度折减法计算对比研究，结论与前述一致，由此提出一种新的适用于小净距大断面隧道净距选取原则。研究成 果可为类似隧道设计及施工提供经验参考。

关键词: 小净距隧道, 大断面隧道, 施工特性, 净距优化, 屈服接近度