Centrifuge modeling of prefabricated vertical drains for liquefaction remediation

Drainage methods for liquefaction remediation have been in use since the 1970s and have traditionally included stone columns, gravel drains, and more recently prefabricated vertical drains. This paper presents the results from a dynamic centrifuge test designed to evaluate the performance of a liquefiable site treated with prefabricated vertical drains. The centrifuge model consisted of gently sloping, untreated and treated liquefiable soil deposits overlain by a clay crust. The model was subjected to multiple shaking events that included both recorded earthquake acceleration-time histories and sinusoidal input motions. Comparisons of deformations and excess pore water pressures in the untreated and treated areas showed that drains were effective in expediting the dissipation of excess pore water pressures and reducing deformations. However, depending on the characteristics of the input ground motion, the peak excess pore pressures in the treated area were not always substantially smaller than in the untreated area. Nevertheless, the deformations in the treated area were consistently smaller, which illustrates that the peak excess pore pressure ratio may not be a good indicator of overall performance. On the basis of the data from the centrifuge test, a better indicator of overall performance may be the time spent at elevated excess pore water pressures, which related better to the magnitude of the resulting deformations.