Performance of Rapid-Jet system for soil improvement works in soft marine clay

This paper reports a case study of using the Rapid-Jet system for installation of jet grout piles (JGP) in soft marine clay of up to 44.8 m. The use of JGP is part of the ground improvement works for the construction for one of the tunnelling project that are constructed by China Railway First Group Co. Ltd. Singapore Branch in Singapore. The tunnel went through a soft marine clay layer which needed to be grouted from below the tunnel to the Old Alluvium (OA) layer. At the project site, there was a 1.8 m outer diameter storm water pipe crossing the tunnel alignment at 8m below ground level. The pipe obstructed the installation of JPG piles in marine clay. The Rapid-Jet method was adopted. The nominal diameter of the JGPs was 3.0 m which was verified by the sound detector during jet grouting and excavation after installation. 24 samples were taken for unconfined compression tests. The total coring recovery (TCR) for each core were also recorded. Based on the JGP trial panel testing results, the working parameters were proven to be suitable for the formation of 1.5, 2.0, 2.5 and 3.0 m diameter grouting column for the JGP works. The TBM tunnelling works were completed successfully without causing ground settlement exceeding the limit.