Vacuum-PVD Improvement: a Case Study of the Second Improvement of Soft Bangkok Clay on the Subsiding Ground

This paper describes a case study of the second improvement of soft Bangkok clay utilizing a vacuum-PVD combined with embankment preloading. Airtight membranes, horizontal prefabricated drains, and field-distributed air–water separation vacuum systems were applied in this case study. Surface settlement plates, pore pressure piezometers, and inclinometers were installed in the soft clay layer. The settlement and consolidation degree predictions employing one-dimensional consolidation, the Asaoka observational method, and pore water pressure data were analyzed. Back-calculation of flow parameters, comparison of soil properties before and after the first improvement were performed. The ground cracks and lateral movements induced by vacuum consolidation were also reported. After the first improvement, the properties of very soft clay were improved due to increased undrained shear strength and maximum pressure. In contrast, water content, void ratio, and compression index were reduced. The results illustrated that the vacuum-PVD improvement with an innovative field-distributed air–water separation system is effective for the second improvement of soft Bangkok clay.