Centrifuge modelling of lateral cyclic behaviour of a tetrapod piled jacket in soft clay

This paper describes a series of centrifuge tests on the cyclic lateral behaviour of a tetrapod piled jacket foundation (TPJ) in Malaysian kaolin clay. The dimensions and axial and bending stiffness of the model foundation were determined in accordance with a prototype TPJ foundation built in the Guishan offshore wind farm in Guangdong Province of China. Both one- and two-way cyclic loadings with differing load magnitudes were applied. The rotational, lateral and vertical displacements of the TPJ and the corner piles, the distribution of internal forces along piles and the lateral pile–soil interactions were scrutinised. It was shown that settlement of the model foundation is dominant during both one- and two-way loading, and even the upwind piles that are expected to be pulled up exhibit considerable downward displacement except for the very first few cycles of loading. In addition, a two-way loading that is applied after one-way loading could generate considerable reversal accumulative displacements, both rotationally and laterally, on the TPJ foundation, provided that the load magnitudes are comparable. The reduction in lateral pile–soil resistance with the number of loading cycles is quantified by means of a degradation factor, which appears to be significantly higher than that in sand.