Geotechnical Challenges in Reclamation of a Soft Soil Site

This paper highlights the geotechnical challenges faced during reclamation of a soft soil site for an international container shipping terminal in Southern Vietnam. The terminal incorporates a pile-supported wharf with a barge quay and a 60-hectare (150-acre) upland development for container storage. This paper focuses on the settlement and slope stability challenges associated with reclamation of the upland portion of the terminal. Prior to development, the site comprised an intertidal salt marsh with ground surface elevation ranging from about -1 to +3.5 meters (-3.5 to +11.5 feet). Geotechnical exploration and testing indicated that the site was underlain by up to about 45 meters (150 feet) of very soft to stiff, highly compressible clay soils overlying medium dense to very dense sand deposits. In order to accommodate the design tidal range, development plans called for raising site grades to an average elevation of +6 meters (+19.5 feet). Settlement analyses indicated that consolidation settlement in excess of 3 meters (10 feet) could occur in the area of the container yard when site grades were raised and working loads applied. In order to reduce post-construction settlement, a preloading program using closely spaced prefabricated vertical drains was undertaken. Slope stability analyses indicated that placing fill over the weak clay soils would destabilize the waterside slope. Through a series of iterations of geotechnical design and collaboration between the civil/structural and geotechnical engineers, a buttressing system using a thickened section of blanket stone and armor stone was constructed to maintain the stability of the slope.