Abstract:
[Objective] Due to the special construction method of overlapping tunnels, the formation of land subsidence troughs and the increase in stratum loss rate may affect the surrounding environment and buildings. Therefore, it is necessary to study the influence law of land subsidence in overlapping tunnel construction. [Method] Taking the completely overlapping tunnel section of Qinghe Xiaoyingqiao Sta.–Xuezhiyuan Sta. Interval on Beijing Subway Changping Line as example, combining numerical analysis and on-site monitoring data, a systematic study of land subsidence and stratum loss during shield overlapping tunnel construction is conducted. The impact of the construction sequence of the upper and lower line tunnels on the morphology of land subsidence troughs, the maximum subsidence values, and stratum loss rates is analyzed. [Result & Conclusion] There is a significant superposition effect in shield overlapping tunnel construction. The construction of upper line tunnel causes some amount of stratum loss and leads to an increase in the maximum land subsidence value. Under overlapping construction conditions, the stratum loss caused by the excavation of upper line tunnel is less than that caused by the separate construction of upper line tunnel without involving the overlapping construction situation. The stratum loss rate during overlapping tunnel construction is not affected by changes in tunnel buried depth, and there is little difference in stratum loss rate between single-line excavation and overlapping excavation. In similar geological conditions to this engineering, the stratum loss rate can be roughly estimated at 0.25%.