Subway tunnel design using a ground surface settlement profile to characterize an acceptable configuration

Tunneling induced settlement is often a controlling factor in the design of a subway or underground facility due to the impact on adjacent or overhead infrastructure. A method is proposed that uses an acceptable ground surface settlement profile to generate a tunnel system configuration that reproduces the acceptable/tolerable settlement profile. A brief discussion of existing methods of tunnel settlement analysis and two (2) case studies illustrating the proposed method are presented. The chosen case studies are urban subgrade rail tunnels (subways) constructed in Istanbul, Turkey and Bangkok, Thailand. Each case study is used to illustrate the use of the bifurcated static back calculation – iterative finite element model prediction/solution method.The initial settlement profiles used for both case histories were measured settlement profiles obtained from the literature (Ercelbi et al., 2005 and Suwansawat, 2002). These settlement profiles were assumed to be the tolerable settlement profiles for the subway systems. For each case history, the iterative static back calculation – finite element model ingested the individual literature obtained design settlement profile to identify an optimum tunnel configuration (depth and size) that will reproduce the design settlement profile. Comparisons were made between the as-built tunnel configuration and the tunnel configuration predicted using the proposed method.