Case Studies with Innovative Technology

   doi:10.3850/978-981-07-0188-8_P035

ABSTRACT

A 14 m deep and 20 m wide excavation for an underground expressway project in Singapore was back-analyzed in this study. The excavation is located in a thick reclamation fill underlain by thick deposit of soft marine clay and fluvial sand and clay layers locally known as Kallang Formation. The retaining wall structure adopted is tubular steel pipe pile wall with three levels of struts. In order to control the deflection of the earth retaining wall, ground improvement was implemented using the Deep Cement Mixing (DCM) method. The thickness of the ground improvement layer was 5 m which was located just below the formation level. Geotechnical instruments were installed to monitor the performance of the DCM during the excavation. The readings from inclinometers were used to back analyze the fill parameters and DCM stiffness. Results show that it is important to adopt a modulus that increases with depth in a thick sand fill instead of using a constant modulus for the entire layer. The back-analyzed DCM stiffness is much higher than the design value. The high DCM stiffness resulted in a higher the bending moment in the wall.

© 2012 by Geotechnical Society of Singapore (GeoSS)