Free-strain solutions for two-dimensional consolidation with sand blankets

To analyze the consolidation with horizontal sand drainage blankets, the partial differential equation for two-dimensional free-strain consolidation under plane strain conditions is solved. Two cases are considered. One is with sand blankets on both the top and the bottom surfaces of the consolidating soil, and the other is with a single sand blanket on the top surface of the consolidating soil. By using the method of separation of variables, explicitly expressed analytical solutions are obtained for calculating the excess pore-water pressure and the overall average degree of consolidation. Their validity is verified by comparing the calculated results obtained from the proposed solutions with those from finite element analyses. The effects of the hydraulic conductivity and thickness of sand blanket on consolidation are investigated for the consolidating soil with various hydraulic conductivities, widths and thicknesses. It is shown that the key parameter for the design of sand blanket is the ratio of the hydraulic conductivity of sand blanket to that of consolidating soil. For the sand blanket close to or reaching a fully drained boundary condition, this ratio is required to be within 10⁴~10⁵, with higher values for the consolidating soil with larger width or lower hydraulic conductivity.