Stabilisation of soft clay by deep cement mixing (DCM) method – A case study

Soft ground under the sea often presents challenges for supporting seawall or reclamation without treatment if no dredging is implemented. Ground treatment is often required to improve the engineering properties of weak soils to enhance bearing capacity for supporting the intended structures. Deep soil mixing with addition of binder is one of the ground treatment methods that has been widely used in Asia and worldwide. This method was recently adopted by the authors for a practical ground improvement project in Hong Kong. This paper presents the characteristics of cement-soil mixture in the laboratory environment as well as performance of the field mixed soil using the same binder material. A detailed test programme was developed to evaluate the strength and other properties of the cement-soil mixtures by using various amounts of binder and water to binder ratios. A series of unconfined compressive strength (UCS) of the laboratory mixture were performed. The relationship of strength of the cement-soil mixture with binder dosages is developed. Test results of laboratory mixed soils were compared with those of field mixed soils. The relationship of strength between laboratory mixed soils and field mixed soils was derived. Field installation of deep mixing for the project is discussed.