Consolidation of lightly OC clays with PVDs as a phase change process

Many natural clays are lightly overconsolidated with overconsolidation ratio ranging between 1.0 and 4.0 because of cementation, glaciation, isostatic uplift, creep, erosion, etc. Under an applied load, the soil passes initially through a reloading stage for effective stresses less than the pre-consolidation stress and then on to the virgin compression state at later times. The conventional theory of radial consolidation used often for the analysis of clays treated with PVDs is applicable only for normally consolidated soil.

This paper presents a consolidation theory for radial flow in lightly overconsolidated clays as a phase change process. The void ratio - effective stress relation is considered to be bilinear with m_vo and m_vn being the slopes for the recompression and virgin compression ranges respectively but with the respective coefficients of consolidation to be constant in each state. The governing equation of consolidation is solved numerically by the finite difference method and parametric study carried out. The variations of degree of dissipation of pore pressure and of degree of settlement with time factor are found to be different from each other unlike in the case of normally consolidated soils and very sensitive to the overconsolidation ratio of the soil. Lightly overconsolidated soils exhibit faster rates of pore pressure dissipation and degree of settlement compared to those for normally consolidated soils.