Construction projects have often encountered very soft soil deposits, which can pose headache problems of stability and/or excessive settlement. To solve these problems, many varieties of ground improvement techniques have been developed and put into practice so far. Sand Compaction Pile Method (SCP) was developed and put into practice in Japan in the 1960s. Numerous research efforts have been paid to investigate the properties of sand piles, behavior of SCP improved ground under static and dynamic conditions, design method, and execution techniques.
　The current Design Procedure on SCP method for clay ground application is based on the slip circle analysis for the stability calculation. The Design Procedure was revised twice in 1989 and 1999. Ministry of Land, Infrastructure and Transport (former Ministry of Transport) has a plan to modify the current Design Procedure and to introduce a reliability based design for marine construction works in 2007, in which the Design Procedure on SCP improved ground will also be modified to the reliability based. In the new Design Procedure, the average and variation of soil
parameters and external loads are incorporated by partial safety factors to investigate the stability of improved ground. The authors have been studied the design procedure and magnitude of partial safety factors. In this article, the studies on reliability based design of the method are described to provide detail information on the Design Procedure for practical and research engineers as well as academina.