Research of Advance Support Construction Technology for Water-rich Weak Surrounding Rock Bias Tunnel

Advance support construction technology for water-rich weak surrounding rock bias tunnel is studied. Taking the national One Belt and One Road key project, Majiazhai Tunnel on the Linxiang-Qingshuihe Expressway in Lincang of Yunnan province as the engineering background, a finite element model of tunnel excavation was established with or without advance support by finite element software MIDAS GTS NX. In addition, the variation of surrounding rock stability, primary support stress and plastic zone of surrounding rock under the condition of advanced support without long-term support and long pipe shed were analyzed. The results show that, with the excavation of tunnel, the settlement of vault becomes larger and larger. The maximum arch settlement after the completion of tunnel excavation without pre-supporting conditions is 9.56 mm. The arch settlement of the long pipe shed was reduced by 44.9% under the condition of advanced support. For the deformation of surrounding rock, the maximum vertical deformation of surrounding rock decreased by 48.0% under the condition of advanced support of long pipe shed, the maximum Y direction deformation is reduced by 50.4%. In the absence of advanced support conditions, the maximum compressive stress of the primary support exceeds the allowable value of 13.5 MPa. The maximum primary support compressive stress of the long pipe shed under the advanced support condition is 11.47 MPa. Long tube shed advanced support can effectively control the surrounding rock deformation of the biased section of the water-rich weak surrounding rock tunnel, improve structural stress state, and ensure the safty of tunnel construction.