Abstract: Two different soil layers are deposited at a tunnel of Shangbai Passenger Rail for DatongXian Line. The upper dry silty fine sand soil is at the arch portion of the tunnel, and the underlying soil is classified as loess. The silty fine sand soil is characterized as low moisture content, uniform in grain size and it has a poor selfstability. The conventional permeating grout often results in a poor cementation outcome. Further, the grouting operation can often lead to the sand flow and even collapse incidents and a safe construction of the tunnel is jeopardized. After feasibility studies of several prelining mitigation methods, the horizontal jet grout methods followed by the threebench excavation were selected. The tunnel excavation process was also simulated with the three dimensional numerical method. Both the construction monitoring and the simulation results indicated that the adopted mitigation method of horizontal jet grout is a viable solution.

Key words: Dry Silty Fine Sand, Large Section Tunnels, Horizontal Jet Grout Prelining, 3D Finite Element Methods, ThreeBench Excavation Method