Recent large-diameter tunnel construction in Singapore using sprayed concrete linnings

Sprayed Concrete Lining (SCL) or the New Austrian Tunnelling Method (NATM) has had limited exposure in Singapore. Previously this has been restricted to excavations of less than 6 metres inside diameter in the boulder clay an d decomposed granite. For the North East Line Project (NELP) a section of S CL tunnel was constructed as part of the tunnelling works on Contract 710. This paper describes the design, planning, and construction issues of twin 8.4-metre inside diameter crossover tunnels spaced less than one diameter a part constructed in the Jurong Formation. In addition, the construction of a SCL tunnel in the OldAlluvium is also described. This tunnel is an advanc e tunnel for the future Deep Tunnel Sewage Scheme (DTSS) and is being const ructed as part of the NELP Contract 705 Works. Details of the Jurong Format ion and Old Alluvium are given together with their geotechnical characteris tics, which played a major role in the selection of temporary support metho ds used and the behaviour of the ground during tunnelling. The planning and design issues concentrate on aspects to ensure overall integrity and stabi lity of both SCL projects. The success of various construction techniques u tilised to construct the tunnels safely is discussed and a summary of the g round movements is presented. (C) 2000 Published by Elsevier Science Ltd. A ll rights reserved.