Consolidation of ground with prefabricated vertical drains combined with time-depending surcharge loading in Membrane system
The system of vertical drains combined with vacuum pressure and/or surcharge preloading is widely used to accelerate the consolidation of soft clay, in order to decrease the long-term settlements and curtail lateral displacement. This study presents a solution of soil consolidation subjected to vacuum preloading for a membrane system, which is comprised of an airtight membrane laid over the drainage layer, under time-dependent surcharge preloading. Both vertical and horizontal drainage were considered in this analysis to reflect realistic in-situ conditions. The model was verified using the measured settlement and excess pore water pressure obtained from various sites at Ballina Bypass, Australia. In the paper, the solutions improve the accuracy of predicting the dissipation of pore water pressure and the associated settlement. The effect of the permeability of the sand blanket in the membrane system and the possible loss of vacuum are also discussed. Finally, design charts have been developed, for the convenience of practicing engineers.
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