Class A prediction of the behavior of soft estuarine soil foundation stabilized by short vertical drains beneath a rail track
Abstract: In Australia, very few rail tracks have been constructed directly on deep estuarine deposits. In recent years, Kooragang Island has become a major export terminal and most coal trains need to cross the main lines at Sandgate to enter Kooragang Island. In this study, a rail track built on up to 30 m of thick soft estuarine soil was stabilized with relatively short vertical drains to consolidate the soil just beneath the track, and no additional preloading surcharge was provided, except the weight from the trains. The initial soil compression was caused by the passage of trains with a speed restricted at 40 km/h. From this study, it is shown that prefabricated vertical drains significantly decrease the buildup of excess pore-water pressure during cyclic loading, and also continue to dissipate excess pore-water pressure during the rest period. A preliminary finite-element analysis was employed to examine the performance of vertical drains, and a Class A prediction was obtained in terms of lateral and vertical displacements. The monitored settlement and lateral displacement results are presented and discussed. The study shows that relatively short vertical drains are sufficient for providing stability for rail tracks, without the need for driving deep vertical drains through the entire soft soil depth.