The northern section of the bored tunnels of Contract C706 of the Singapore MRT North East Line is located in varying soil conditions ranging from cemented Old Alluvium to very soft marine clay. The bored tunnels will run along Race Course Road, underneath a residential area underpassing several religious temples. The tubes will be constructed by earth pressure balanced shield machines. The paper is presenting the key approaches adopted for the design of the tunnel lining, the assessment of ground movements under the particular circumstances as well as the basic design considerations for the intersection of MRT tunnels with the future tunnels of the Singapore Underground Road System (SURS). In this context, the effect of water pressures in terms of sectional lining forces was studied in detail. A design chart has been developed to determine the sectional forces due to the water pressure loadand in relation to the subgrade reaction modulus. An approach to consider the influence of the second tunnel has been developed and is presented in this paper.
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By Georg Atzl and Oskar Sigl