For the structure foundation under the soft clay layer conditions, the design charts are first presented for the evaluation of both bearing capacity and total settlement in the raft alone foundation system. Loadsettlement relationship curves are used to evaluate the ultimate soilbearing capacity. The total settlement is evaluated by applying various traditional safety factors of the uniformly distributed loads. Then, the parametric studies are carried out for the piled raft foundation system. In the numerical analyses, elasto-plastic finite elements models are used to present the foundation response and the design charts, which enable the determination of the raft size and pile length and spacing if piles are available.
As Korean government has proposed a plan of new land development in the Nakdong river deltaic plane near the Busan, second largest city in Korea, infrastructures such as industrial and commercial facilities have being constructed since the early 1990's. In this area, the soft clay layer about 20 to 30m thickness have been deposited over the sandy soil or directly on the undulated bedrock surface. On the top of the soft clay layer, typically about 5 to 10m's of sand layer is placed. Figure 1 shows the typical results of laboratory tests on samples of Busan clay. The insitu groundwater table is around 0.5 to 0.8m below the ground surface. For the structure foundation under the soft clay condition in this area, piles are costumery used to transmit the structural loads to the bedrock. So far, the designer of the raft or the piled raft foundations in this area has very little information available for the evaluation of both bearing capacity and settlement in the preliminary design stage. The early work for the piled raft foundation design was carried out by Prakoso and Kulhawy (2001).
