Application of geosynthetic vertical drains under cyclic loads for track stabilization
Large scale cyclic triaxial tests were conducted using reconstituted Kaolin specimens (300mm diameter and 600mmheight).To allow for radial drainage during and after the cyclic tests, a single Prefabricated Vertical Drain (PVD) was installed in the centre of the soil cylinder. The effectiveness of radial drainage in dissipating the excess pore pressure was examined. It was found that with an increased cyclic stress ratio, the radial drainage decelerated the rate of excess pore pressure build up to its critical value, so the soil could undergo more loading cycles prior to failure. The test results also suggested that for newly constructed railway lines, a train with a lower speed is preferred initially, until the track becomes stable for the next loading stage. A radial consolidation model under cyclic loading is proposed to capture the behavior of soft clays subjected to cyclic loading when radial drainage is allowed during the loading and rest periods. This was achieved by combining the theory of radial consolidation with an undrained cyclic loading model. The effects of the stress history and dissipation of excess pore pressure on the generation of excess pore pressure were considered in the proposed model, which was verified using the large scale cyclic triaxial tests. Analysis was also carried out to investigate the effects of rest period and the cyclic stress ratio.