Centrifuge model tests on spudcan penetration and extraction in sand-clay mixed soil

Abstract

Jack-up vessels have been used for the construction of offshore wind turbines, and various studies have been conducted on the ground behavior during the penetration and extraction of their spudcans. In this study, the ground behavior of sand-clay mixed soil was investigated. Specifically, a series of actual operations, such as penetration, repeated loading, extraction, and repenetration, were reproduced by centrifuge model tests using sand and clay, as well as their mixtures with different fine-grain contents. Several elemental tests were also conducted prior to the model tests. In addition, the bearing capacity of the spudcan was discussed using estimation equations. The results of the elemental tests showed that in the soils used, the effect of partial drainage became more pronounced when the fine-grain content exceeded 20%, and the permeability, consolidation coefficient, and shear properties changed. These results were close to those of clay when the fine-grain content exceeded 50%. In the centrifuge model tests, the deformation characteristics of the ground changed, and the penetration resistance decreased as the fine-grain content increased. The influence of consolidation and drainage conditions was suggested. The estimation equations of the bearing capacity showed that, in the case of mixed soil, the bearing capacity obtained by the estimation equation under drained or undrained conditions differed significantly from the test results, and the estimation equation that considered the effect of partial drainage could be used to calculate the bearing capacity.