Cyclic behaviour of PVD-soft soil subgrade for improvement of railway tracks

The behaviour of saturated soft clays subjected to cyclic Loading is of considerable importance in the design of railway subgrades. Soft clays can be extensively found in many coastal regions of Australia up to significant depths, including the coastal belt and the central part of NSW. These soft clay deposits are characterized by very tow bearing capacity and excessive settlement. The increase in generated excess pore pressures due to heavy freight trains significantly reduces the bearing capacity and causes serious damage to the rail infrastructure such as clay pumping underneath tracks and excessive subsidence. The use of prefabricated vertical drains (PVDs) is one of the popular methods for soft ground improvement. In this paper, the behaviour of soft clay subjected to cyclic toads is investigated using large-scale triaxial tests. Cyclic triaxial tests on rebounded soft clay samples with vertical drains have been carried out using a large-scale triaxial apparatus designed and built at the University of Wollongong. The improvement gained by drained compression using PVDS is presented and discussed in terms of the pore pressure ratio. An attempt is also made to modes such behaviour numerically in CRISP finite element code.