振动荷载作用下导洞临空面土体的稳定性分析与研究

Stability Analysis and Research on Soil at Free Face of Pilot Tunnel under Vibration Loads

摘要: 新建地铁隧道近距离下穿既有运营地铁线路时，既有线列车循环振动荷载会造成新建隧道掌子面低围压临空土体发生强度软化，诱发土体疲劳破坏失稳，是暗挖施工的重大安全风险。以北京地铁17号线东大桥站–工人体育馆站区间下穿既有6号线工程为研究背景，采用FLAC2D有限差分软件开展数值模拟，采用强度折减法和拟静力分析方法计算不同工况下导洞临空面土体安全系数。计算结果表明，由于土体在循环荷载作用下的强度软化效应，若不进行注浆加固，导洞临空面土体在列车振动荷载作用下将会发生疲劳破坏，以致土体结构失稳破坏，注浆加固后，不同位置处的导洞临空面土体在振动荷载作用下的安全系数均在1.5左右，土体结构处于相对稳定的状态。

Abstract: When a newly built metro tunnel passes underneath an existing operating metro line at a short distance, cyclic vibration loads induced by trains on the existing line may cause strength softening of the soil at the tunnel face with low confining pressure of the new tunnel, triggering fatigue failure and instability of the soil. This constitutes a major safety risk for mined tunnelling construction. Taking the undercrossing project of the interval between Dongdaqiao Station and Workers’ Stadium Station of Beijing Metro Line 17 beneath the existing Line 6 as the research background, FLAC2D finite difference software is adopted for numerical simulation. The strength reduction method and pseudo-static analysis are used to calculate the safety factor of soil at the free face of the pilot tunnel under various working cases. The calculation results show that due to the strength softening effect of soil under cyclic loads, fatigue failure and subsequent instability of the soil mass will occur at the free face of the pilot tunnel under train vibration loads without grouting reinforcement. After grouting reinforcement, the safety factors of soil at the free face of the pilot tunnel at different positions under vibration loads are all approximately 1.5, and the soil mass remains relatively stable.