Effect of capping on the consolidation of hydraulic fills

Department of Civil and Environmental Engineering, Politecnico di Milano, Milano, Italy

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Abstract

In land reclamation projects, dredged clay, typically deposited in a highly saturated and very soft state, remains inaccessible for construction or instrumentation for a long period of time. Capping has become a practical approach to enable early site access and accelerate ground improvement. Placing an unsaturated clay layer above the reclaimed fill, usually obtained from onshore excavation works and commonly referred to as a cap, allows the restoration of accessibility at an earlier stage when dealing with hydraulically dredged clay. This study investigates the effect of the unsaturated cap on the consolidation behaviour of the underlying saturated dredged clay when subjected to sand surcharge preloading. The presence of an unsaturated cap influences the rate of consolidation, depending on its permeability, thickness, retention characteristics, and atmospheric conditions, affecting pore-pressure dissipation, surface drainage, and suction equalisation between the cap and the dredged clay. Using coupled hydro-mechanical numerical modelling, an insight into the influence of the unsaturated state on the long-term response of the reclamation is given. The results indicate that the degree of saturation of the cap can significantly influence the consolidation behaviour and long-term response of the reclamation. Partially saturated caps can delay pore-pressure dissipation by modifying drainage conditions and increasing storage within the system.