Recent advances in the use of prefabricated vertical drains in soft soils

Buddhima Indraratna

Abstract

A system of prefabricated vertical drains with surcharge load to accelerate consolidation by shortening the drainage path is one of the most popular methods of soft ground improvement. An analytical solution is proposed based on radial (lateral) soil permeability while considering variations in vacuum pressure. The predicted smear zone and effects of drain unsaturation are compared with laboratory data obtained from large-scale radial consolidation tests. When a higher load is required to meet the desired rate of settlement and the cost of raising a surcharge embankment is also significant, the application of vacuum pressure with a reduced surcharge load can be used. In this method, the vacuum creates a suction head that increases the effective stress. Analytical and numerical analyses were conducted for several case histories using the equivalent plane strain solution for Darcian and non-Darcian flows. The effectiveness of vertical drains on cyclic loading was also investigated based on a laboratory study. . This paper shows that vertical drains can dissipate the built up excess pore pressure under repeated loading and that short drains can be sufficient in certain cases rather than driving the drains to cover the entire depth of soft clay deposits. The research findings verify that the effects of soil disturbance and vacuum pressure can affect soil consolidation considerably, which means that these aspects need to be modelled correctly in any numerical approaches.