Consolidation of Lumpy Clay Fills

The rapid economic growth of Singapore and shortage of land for housing, transportation, commercial and industrial needs make it necessary to reclaim land from the sea. In the past, hill-cut materials and seabed sand were used as fill materials. Since the above two are virtual exhausted in Singapore, dredged sand is imported from neighbouring countries as fill materials. This requires a huge amount of sands to be imported in the future. Since the seabed is made of mostly stiff clay in the area, there is a significant advantage to use dredged stiff clay as fill material for reclamation from the economical point of view. However, stiff clay is grabbed in lump from seabed in grabbed-dredging to form reclaimed land fill made of clay lumps and a conventional formulations can not be used to predict the consolidation of such fill. A new consolidation theory of lumpy clay soil is formulated treating the soil as porous lumps containing voids in lump structure. The porewater flow is governed by the boundary conditions of the fill as a whole with introducing porewater exchanged between the pores in both lumps and lump structure in a gross manner. A similar approach was used previously in analysing the porewater in rock mass and stiff clay with fissures also. The new formulations can take into account the following quantities in both lump and lump structure: porosity, permeability, compressibility and excess porewater pressure. In one-dimensional condition, the formulations form two coupled differential equations of porwater pressures in lump and lump structure. An efficient numerical method is developed for inhomogeneous lumpy fill to solve the differential equations for given boundary conditions at the top and bottom of the fill. The developed formulation is used to predict the centrifuge test results on consolidation behaviour of lumpy clay fill to verify the new consolidation theory and formulation. The parametric studies are conducted to understand characteristics of consolidation behaviour of lumpy clay fill.