CONSOLIDATION ANALYSIS OF SOFT CLAY CONSIDERING THE THRESHOLD HYDRAULIC GRADIENT AND A CONTINUOUS DRAINAGE BOUNDARY

The logical problem in Terzaghi's one-dimensional consolidation theory between boundary conditions and initial conditions and the phenomenon that the velocity of water in soft clay can be negligible under low hydraulic gradient have been gradually recognized. However, under a continuous drainage boundary condition, the one-dimensional consolidation theory considering both the continuous drainage boundary condition and the threshold hydraulic gradient, especially the analytical solution for this model of consolidation, is rarely reported in the literature. It introduces a continuous drainage boundary and develops a single-sided drainage consolidation model of homogeneous soil layers considering the threshold hydraulic gradient in clay soil. The finite Fourier transform method was adopted to obtain solutions for excessive pore pressure, average degree of consolidation and settlement. Furthermore, the influence of continuous drainage boundary condition and initial hydraulic gradient on the consolidation behavior is analyzed when a constant load is applied to a soil layer. The results show that the effect of the continuous drainage interface parameter b on the consolidation behavior of soil with initial hydraulic gradient is the same as that with Darcy's law. The larger the b, the better the permeability of the drainage surface, and the faster the dissipation rate of the pore pressure, and the shorter the consolidation time. On the contrary, the smaller the b, the worse the permeability of the drainage surface, the less the dissipation rate of the excess pore pressure, and the longer the consolidation completion time. When the continuous drainage condition is considered, the influences of the dimensionless variable R (the product of initial hydraulic gradient, specific weight of water and the thickness of the soil layer divided by external load) on the consolidation behavior considering the continuous drainage boundary are not significantly different from that with a fully permeable boundary. The larger the R, the longer the time for the seepage front to reach the bottom of the soil layer. The larger the R, the greater the residual value of the excess pore water pressure in the soil layer when the consolidation is completed. The larger the R, the smaller the average consolidation degree defined by the pore pressure, and the smaller the final settlement.