Behavior of Soft Ground Tunnel Under Strip Footing: Fid-Bau Portal

Behavior of Soft Ground Tunnel Under Strip Footing

Jao, M. / Wang, M. C.

There are cases that soft-ground tunnels are overlain by footings. The tunnel and footing may interact so that they may mutually influence the individual's stability adversely. Presently, there is no widely accepted analysis or design methodology available to ensure the stability of such footing/soft ground tunnel systems. As a step toward the development of such a methodology, this study was undertaken to investigate-the interaction between the soft-ground tunnel and the overlying strip footing. In this study, a two-dimensional plane-strain elasto-plastic finite element computer program was utilized to analyze the behavior of the tunnel for a wide range of soil type and tunnel conditions. Based on the results of the analysis, the mechanistic behavior of the footing/tunnel system was evaluated. It was concluded that the presence of the underground tunnels causes stress transfer from the tunnel crown to the spring line. The degree of stress redistribution depends on soil properties, tunnel location, tunnel size, and lining thickness. It was also concluded that for a given footing and tunnel condition, different lining thicknesses may be required for different soil types. Along a concrete lining, critical locations which required special attention in the lining design are in the intrados between crown and shoulder as well as between haunch and invert. This paper presents the results of the study and their practical applications.