doi:10.3850/978-981-08-6396-8_P074

ABSTRACT

This paper is about a non-conventional approach to underpin a pier for an operational LRT line. The steel-pile foundation for the pier is above the base of the excavation for a cut-and-cover tunnel construction. Owing to space constraint and difficult ground condition, the conventional method of using new replacement piles for the pier not only poses construction difficulties, the risk of excessive pier movement on the LRT operation is high. A posttensioned transfer beam spanning across the excavation provides an effective solution to the problem. It has the added advantage of providing the option of “load balancing” to control the pier movement and also an unobstructed space beneath the pier during the tunnel construction. When the permanent support for the pier is eventually provided by the new tunnel structure, the transfer beam is no longer needed. Instrumentations are installed to monitor the movements and to also facilitate the load balancing process. This unconventional method not only reduces risks, it also saves considerable construction time and cost.

Keywords: Underpin, Transfer beam, Prestressing, Cut-and-cover, Tunnel, Excavation.

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