Influence of Drain Installation-Induced Stress on the Consolidation of a Natural Soft Foundation

Sand drain wells or prefabricated drain boards are widely used in natural soft ground improvement. The soil surrounding a drain can be highly disturbed during the installation process, which can result in two impacts on the soil in the smear zone. (1) The soil structure is totally destroyed, and the permeability of the smeared zone is reduced. (2) An increase in excess pore water pressure (u_ex-i) is induced by the shear of the soil due to drain installation. However, research on consolidation behavior due to the dissipation of installation-induced u_ex-i has not yet been reported. In this study, first, a structured soil was made by a large-scale one-dimensional consolidation test to simulate natural soft ground, and the soil parameters were back-analyzed. Second, a drain installation test was performed, and the radial consolidation after drain installation was investigated. The effect of drain installation on the consolidation behavior was equivalent to an additional load. Finally, the effect of installation stress on the consolidation rate under surcharge preloading was studied theoretically. The results showed that the installation of drains can induce an increase in excess pore water pressure, resulting in a decrease in permeability and a delay in the consolidation time during the surcharge stage, which should be well considered in engineering design.