基于单元安全系数法的浅埋隧道三台阶法开挖进尺优化

Optimization of Excavation Footage of Three-step Method of Shallow Tunnels Based on Element Safety Coefficient Method

为进一步研究浅埋隧道三台阶法开挖进尺问题,以鹅岭隧道为工程背景,采用FLAC_(3D)有限差分法数值模拟软件建立了隧道三维稳定性分析模型,模拟了4种开挖方案,并引入单元安全系数法,计算了隧道围岩各区域的安全系数,分析了隧道围岩潜在的破坏形式,确定了三台阶法合理的开挖参数。通过对比分析围岩的安全系数、位移、应力、塑性区可得,上台阶开挖长度越长,中、下台阶开挖以及前方土体对隧道工作面的挤压越小,越有利于隧道开挖面的稳定性;而台阶越长,支护间隔越长,支护效果就越差,安全系数就越小,隧道围岩的失稳风险就越大。在施工过程中,隧道最危险的部位为拱脚与拱底处,建议采取方案一进行开挖,各台阶之间为不同步开挖,且预留核心土,上台阶开挖长度宜为5~10 m,开挖进尺宜为0.5~0.6 m。

In order to further study the problem of excavation footage of three-step method of shallow tunnels,based on the engineering background of Eling tunnel,the three-dimensional stability analysis model of tunnel was established by the FLAC_(3D) finite difference method numerical simulation software,the four excavation schemes were simulated.The element safety factor method was introduced,the safety factor of each area of tunnel surrounding rock was calculated,the potential failure form of tunnel surrounding rock was analyzed,and the reasonable excavation parameters of three-step method were determined.And the safety factor,displacement,stress and plastic zone of surrounding rock were compared and analyzed.The longer the excavation length of the upper step was,the smaller the extrusion of the middle and lower step excavation and the soil ahead on the tunnel face was,which was more conducive to the stability of the tunnel face.However,the longer the steps and the longer the support interval,the worse the support effect,the smaller the safety factor,and the greater the risk of instability of tunnel surrounding rock.During the construction process,the most dangerous parts of the tunnel were the arch toe and the arch bottom.It was suggested that the first scheme should be adopted for excavation.The excavation between the steps was asynchronous,and the core soil was reserved.The excavation length of the upper step should be controlled in the range of 5 m to 10 m,and the excavation footage should be controlled in the range of 0.5 m to 0.6 m.