Liquefaction and Drainage in Stratified Soil

Remediation schemes for the treatment of liquefiable ground, such as vertical drains, have evolved over the last $30\text{years}$ largely as a result of consideration of uniform sand beds. However, many liquefiable sites also contain thin layers of silts and clays which will act as an obstacle to fluid dissipating from liquefying sands, such that the performance and requirements of a remediation scheme will be different. In particular, water films may be produced. This paper presents results from a series of dynamic centrifuge experiments on vertical drains in level liquefiable sand deposits. Centrifuge tests were conducted both with and without surface fine layers. The drains prevented sand boiling, and the thin surface fine layers did not significantly affect excess pore pressure response. A further centrifuge test on a thin layer of low-permeability fines separating two liquefiable sandy layers, showed evidence suggesting that material boiled from the lower sand to the upper sand in the absence of a drain through the fines. All of the experiments suggest that the presence of unblocked vertical drains prevent water film formation.