ABSTRACT:

An excavation, 3.5m deep into soft marine clay, was required for the construction of a four-storey building with one basement at Changi Road in Singapore. The proposed building was to be constructed in a heavily built-up area. An adjacent four-storey building with two basements was on the boundary and the existing basement wall would be exposed during the excavation works. The soil investigation indicated that the site was on a soft ground with a substantial layer of marine clay. The difficult site and ground conditions made the project very challenging to the design and construction engineers. A temporary sheetpile wall system was proposed for the excavation works. The wall was supported by one level of struts at the top and a jet grout improved layer below the excavation level. Instrumentation was provided to monitor the ground and wall movements and the effect of the construction work on the adjacent building. A jet grout trial was carried out prior to the installation of the working jet grout piles (JGP) to confirm the operation parameters, the achievable pile size and the strength and elastic modulus of the JGP. The triple fluid system was found to be effective in improve the marine clay. The retaining wall system functioned successfully during the excavation and construction works. The results from the JGP trial and instrumentation monitoring are presented and discussed in the paper.

INTRODUCTION

The Changi area of Singapore is generally underlain by a Kallang formation member according to the local geological classification. This formation is dominated by substantial thick layers of soft marine clay. The site of the development was located in the Changi area, with its southern boundary adjacent to Changi Road. It was situated within a heavily built-up area with exiting residential and office buildings next to the site boundaries.

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