Construction of double track subway tunnel in the alluvial soils with shallow overburden

Abstract

One of the most difficult tunnel construction case in the second phase of the Seoul Subway Expansion Project is presented in this paper. The constructed tunnel passed through shallow sedimentary sandy gravel alluvium with a high groundwater table. Heavy traffic including the foundation of the elevated highway over the tunnel made the cut and cover method inapplicable. Several ground improvement techniques and intensive monitoring programs were applied to limit the ground deformation. A comprehensive finite element analysis was performed before the construction to estimate the ground movement. SGR (Space Grouting Rocket System), LW (Labile Wasser Glass) and Urethane grouting were performed for the ground improvement and prevention of groundwater inflow. Pipe roof and fore-poling techniques were also applied as auxiliary measures. The ground settlement was limited to less than 30 mm and the coefficient of permeability of the ground was reduced to approximately 1% of the untreated ground, thus successfully preventing the water inflow. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.