Effect of mortar injection on over-cutting area using slurry pipe-jacking

Recently, small-diameter shallow tunnels are often being built by using slurry pipe-jacking. This is the sewage tunnel drivage method. This system involves the pushing or thrusting of a drivage machine through concrete pipes ahead of jacks. The mortar injection into the over-cutting area is carried out after the drivage and pushing processes are finished. The purpose of the mortar injection is to maintain a permanent stability of the surrounding soil and the over-cutting area. The injection amount of the mortar is obtained as the value, which multiply 40 % of the cross section area of the over-cutting area and pushing length. However, the behavior of the mortar around the pipes and the optimum injection amount is not clearly understood. From these points of view, this paper discusses the performance of the mortar around the concrete pipes and the evaluation of the present and an improved mortar injection system, which is developed, by means of 2-D Eulerian-Lagragian seepage analysis.