During the investigation period by the official investigation team, significant attention and effort was placed on the quality of the sand blanket, and sand samples were collected from the excavated pits and tested by independent authorities. It should be noted that from the technical point of view, if the quality of the sand blanket was poor with high percentage of fines, then the sand would not function as a drainage layer in the PVD method. The poor sand quality would lead to slow rate of settlement, but there was no evidence of slow settlement rate in the construction. Technical evaluation reports on the ground improvement works were prepared by the construction supervision consultants and submitted to AOT after the completion of the improvement work, but it appeared that the investigation team had failed to obtain a copy during the investigation period.