Construction Mechanical Characteristics and Monitoring Analysis of the Existing Subway over the Newly Built Long Foundation Pit

Abstract

In view of the safety of the construction of the long foundation pit of the new upper span to the existing subway under urban complex environment conditions, combined with the construction of the intersection section of the first line of the existing subway across the north–south Expressway in Shenyang, the mechanical properties during construction were studied by means of numerical simulation and on-site monitoring. The results showed that the general deformation characteristic of the existing metro tunnel was “uplift first, then restrain”. The local deformation characteristic was an unloading rebound in the cross region, and a compression deformation occurs outside the cross region. The index could be controlled in the range of the control value of the existing line protection by adopting the measures consisting of an uplift pile + capping beam balance, reinforcing the surrounding soil, the excavation of the foundation pit in sections, and the comprehensive construction.