Preloading using either vacuum or fill surcharge is an effective method for the treatment of very soft saturated clay. The preloading will reduce the water content and increase the shear strength of soil. However, when the soil to be treated is very soft, it is difficult to take soil samples for lab tests or carry out in-situ tests to determine the soil properties including shear strength. Therefore, there is a need to develop an analytical method to estimate the shear strength during preloading. In this paper, a simple correlation among settlement, water content and undrained shear strength using critical state theory is proposed for saturated soil under one-dimensional loading condition to allow the undrained shear strength variation of the soil to be estimated during preloading without testing. Laboratory model test and field monitoring data are used to verify the validity of this method and the proposed correlation is effective to be used as rough estimations on the undrained shear strength of soft clay.
来源平台：PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-GROUND IMPROVEMENT
