A Case Study of Effectiveness of Large Diameter Jet Grout for Soil Improvement Works in Soft Marine Clay

Abstract

This paper reports a case study of using the Rapid-Jet system jet grouting for installation of jet grout piles (JGP) in soft marine clay. The use of JGP is part of the ground improvement works for the construction for one of the tunnelling projects that is constructed by China Railway First Group Co. Ltd. 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 stormwater pipe crossing the tunnel alignment at 8 m below ground level. The pipe obstructed the installation of JGP piles in marine clay. The Rapid-Jet method was adopted. A field trial programme is conducted to verify the application of the adopted jet grouting parameters. Five trial jet grout columns with sound pipes were carried out. Each panel consisted of a 3 m diameter JGP column to a depth of about 46.6 m in soft marine clay. The nominal diameter of the JGPs was 3.0 m which was verified by the sound detector during jet grouting and excavation after installation. Four coring points were used to obtain cores through the full depth of the grouted block. Nineteen SPT tests also carried out in grout block, 24 samples were taken for unconfined compression tests. The total coring recovery (TCR) for each core were also recorded. The settlements monitored during JGP were consistent and did not breach the alert level. The working parameters were proven to be suitable for the actual JGP works.