Stability Analysis on Rectangular Transition Section Tunneling in Beiwan Horsehead Region of No. 7 Subway

Abstract

The settlement of ground and vault by tunneling has important effect on construction safety and normal operation of urban transport system. The soils around reserved shaft of Beiwan region in No.1 section of Beijing Metro Line No.7 are backfilled and complex. In order to tunnel safely and keep surrounding structures safe, the stability of rectangular transition section by tunneling of Beiwan horsehead region is analyzed. Based on the data of surface survey, drilling, prediction detection of the strata and engineering design, the software of 3D FLAC is used to study the vault and ground settlements during the excavation of six pilot tunnels of rectangular transition section, and the results are also compared with the results of in-situ monitoring. The research shows that the results of numerical simulation and in-situ monitoring are matched very well, the ultimate ground settlement will be 17 mm when the transition tunnel is excavated by non-shrinkage (WSS) pre-grouting method and CRD method, and meets with the requirements of standard specification. Therefore, the six-pilot-tunneling method is good for keeping the transition tunnel stable.