Innovative thermal technique for enhancing the performance of prefabricated vertical drain during the preloading process

This paper examines the effect of raising the temperature of soft Bangkok clay, up to 90 °C, on the performance of the prefabricated vertical drain (PVD) during the preloading process. The effect of temperature on the engineering behavior of soft Bangkok clay was first investigated using a modified triaxial test apparatus and flexible wall permeameter which can handle temperatures up to 100 °C. The results of the triaxial tests on clay specimens demonstrate that raising the soil temperature increases its shear strength, under drained heating condition, as well as its hydraulic conductivity. In addition, large oedometer tests were performed to investigate the performance of PVD at elevated temperatures. The response of the soil sample with PVD for the thermal consolidation path which involved increasing the soil temperature at constant vertical effective stress condition and the thermo-mechanical path which involved increasing simultaneously both the soil temperature and the vertical effective stress were investigated. The consequent results indicated that the thermo-mechanical path shows promising results regarding the consolidation rate. For both reconstituted and undisturbed specimens, higher consolidation rate was observed for the soil specimen with PVD loaded under elevated temperature. This behavior can be attributed to the increase in the soil hydraulic conductivity as the soil temperature increases. Therefore, raising the soil temperature during the preloading period can enhance the performance of the PVD, particularly, by reducing the drainage retardation effects due to the smear zone around PVD.