Abstract: Model tests were conducted to investigate the installation behavior of modified suction caisson (MSC) and regular suction caisson (RSC) in layered soil (sand, clay, sand over clay and clay over sand). It was found that the MSC can penetrate the layered soil to the desired depth. The final penetration depths for MSC in sand, clay, sand over clay and clay over sand increase approximately 10.0%, 2.3%, 3.0% and 9.6%, compared with the RSC. In addition, the maximum required suctions for MSC in sand, clay, sand over clay and clay over sand increase approximately 0.9%, 14.4%, 66.2% and 92.2%, compared with the RSC. It was found that the installation behavior of MSC in layered soil is strongly influenced by the position and the thickness of the clay layer. When the MSC penetrates clay over sand, the maximum value of suction is achieved when the suction caisson tip contacts the interface between sand and clay. The maximum applied suction increases with increasing the soil distribution coefficient t (ratio of upper soil thickness to the total soil thickness). However, the final penetration depth was found to decrease with increasing the t value. When the MSC penetrates sand over clay, the maximum applied suction was obtained at the final penetration depth. The maximum applied suction decreases with increasing the t value. The soil distribution coefficient has little effect on the final penetration depth for MSC in sand over clay. In addition, the installation way effectively influences the final penetration depth. The final penetration depths for MSC in sand, clay, clay over sand ( 0.4) and sand over clay ( 0.4) under the installation way of simultaneously pumping out water in the internal compartment and external structure increase about 13.8%, 3.4%, 16.4% and 4.6%, compared with those under the installation way of only pumping out water in the internal compartment. This study results can guide the design and construction of the suction caisson in layered soil.

Key words: modified suction caisson (MSC), layered soil, model test, installation way, suction variations, soil plug height