Parameters and Considerations in Soft Ground Tunneling   Wooi Leong Tan School of Civil & Environmental Engineering Nanyang Technological University, Singapore and Pathegama Gamage Ranjith Department of Civil Engineering Monash University, Melbourne, Australia e-mail: ranjith.pg@eng.monash.edu.au
			ABSTRACT

Construction of urban tunnels in soft soil or weak rocks requires meticulous considerations in terms of geotechnical site investigations, construction methods, types of tunnel boring machines, tunnel support systems, instrumentation and monitoring of surface subsidence and the subsequent impact on nearby buildings and services. Among the considerations, the most important aspect is the control of surface subsidence to minimize any disturbance to nearby buildings and services. The study of surface subsidence is limited to mainly empirical solutions based on field studies, and very few analytical studies have been carried out. The available analytical solutions are not sufficient to include complex ground conditions and hence a comprehensive analytical solution coupled with numerical modeling is necessary to model the effect of surface subsidence due to soft ground tunneling. This paper discusses a variety of parameters and considerations that are required to formulate a theoretical solution to predict surface, sub surface and lateral settlement due to tunneling induced ground movement. Moreover, the importance of considering the tunnel support system as a parameter in determining the settlements is often neglected or excluded and thus is highlighted in the paper. A number of empirical solutions to predict the settlements are also compared to differentiate their effectiveness in various soil conditions.

Keywords: soft ground tunneling; soft soil; weak rocks; subsidence; tunnel support system.

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