Engineering properties of soft Bangkok clay improved using PVD with surcharge and vacuum preloading

This paper describes a case study performed on deposit of soft Bangkok clay in which prefabricated vertical drain (PVD) was installed with surcharge and vacuum preloading in order to promote consolidation when subjected to pre-loading imposed by a full-scale test embankment. The profile of undrained shear strength, S-u, with depth was measured before and after the ground improvement by mean of in-situ and laboratory tests. The results of field vane as well as laboratory compression tests show that S-u of the subsoil with the surcharge increased by the factor of 1.5 to 2 down to the depth of 8 m and 1.1 to 1.5 for the depths 8 to 12 m over a short period of five months. It is also shown that flat dilatometer test (DMT) was a useful tool for evaluating the shear strength increase associated with consolidation in the soft clay deposit. Predicted undrained sheer strength as applying SHANSEP method showed a good agreement with the measured data for the depths blow 6 m, where aging effects were small.