STUDY ON SUPPORT AND EXCAVATION OF HORSEHEAD IN THE RESERVED SHAFT OF A TUNNELL

During tunneling construction in subways, the settlement in arch crown and ground will greatly impact on the construction safety, engineering function and normal operation of urban roads. The soil around the reserved shaft in Beiwan region of No.1 section, No.7 Subway of Beijing is backfilled and complex. In order to ensure the safety of tunneling construction and structures, it's necessary to do schematic studies on the removal and excavation of horsehead in backfill soils. Based on the data of surface survey drilling and prediction detection of the strata and the engineering design data, the software FLAC^3D is used to study the two reinforcement schematics when the horsehead of the reserved shaft is exploded, also, the arch crown and ground settlements resulted from the construction of six pilot tunnels in the rectangular transient cross-section are simulated and compared with the monitoring results of pilot tunnels' excavation. The research showed that when the horsehead is removed, the settlement using non-shrinkage grouting of deep hole method was one third to a half of that using advanced small pipe support method.