In this study the seismic behavior of caisson-type foundation in the clayey grounds is investigated by using centrifuge shaking model test. The tested ground is composed of a reclaimed liquefiable sand layer, underlain by an Holocene clay layer, a Pleistocene clay layer, and a Pleistocene gravel layer as bottom layer. As the results, it is found that the excess pore pressure ratio in the clayey ground (especially in Pleistocene clay ground) increases to about 0.1–0.2 during shaking, and that the shear strain of the clayey ground is increased to about 0.5% – 2.0% for Holocene and increased to about 0.2% – 0.5% for Pleistocene. As for the displacement of the caisson-type foundation during shaking, the sliding action in the bottom of caisson-type foundation is observed as well as the rocking action.
After the 1995 Hyogoken-Nanbu Earthquake, re-examinations have been made on the seismic performance of the foundation of many existing structure, which are located on liquefiable grounds. However, for those foundations located in the clayey grounds below liquefiable soil, there are not so many re-examinated cases. In this study, seismic behavior of the caissontype foundation in the clayey ground is investigated by using centrifuge shaking model test. Fig. 1 shows the cross section of the prototype ground in this study. The model ground is consist of a liquefiable sand layer, underlain by an Holocene clay layer, a Pleistocene clay layer and a Pleistocene gravel layer as bottom.
The model ground materials are as follows : Pleistocene and Holocene clay : Kobe marine clay Pleistocene gravel sand : Silica sand #3 Liquefiable sand : Toyoura sand. In this study, Holocene clay was modeled as normally consolidated and Pleistocene clay is over-consolidated with OCR = 1.5–20.
