One-dimensional self-weight consolidation of a lumpy clay fill

Abstract

The need to use a large amount of dredged and excavated materials as fill for land reclamation necessitates an examination of the consolidation of a lumpy fill. Experimental results have shown the existence of two systems of voids in such a fill: inter-lump voids and intra-lump voids. The consolidation of this fill is highly complicated, and a simple box-spring model analogy is used to provide a better interpretation of the consolidation of this fill. To model this consolidation, the dualporosity model developed for fissured clay is used to model the consolidation of the lumpy fill; the primary motivation is the similarity between fissured clay and a lumpy fill with inter-lump voids. In the paper, this theory is re-derived using a two-phase flow analogy. Self-weight is explicitly included in the derivation: this is considered to be more relevant than the case of surcharge only, as the fill is often left to stand for a long period before sand fill is placed on top. A previously derived analytical solution is now modified to include self-weight. Using the analytical solution, salient features of the consolidation are demonstrated. In a lumpy fill, owing to the large inter-lump voids, the permeability of the inter-lump system is much larger than that of the intra-lump system. Parametric analyses using the analytical solution show that the inter-lump permeability dominates the overall consolidation behaviour in two ways. First, it will cause a rapid dissipation of the pore pressure in the inter-lump voids, and this in turn will cause a greater difference between the pore pressure in the inter-lump and intra-lump systems, thereby accelerating the fluid transfer from the intra-lump voids to the inter-lump voids.