ABSTRACT

The soft clay surrounding the laterally-loaded offshore piles experiences remolding and softening under cyclic laterally loading. The spatial distribution of damage of soft clays is essential for the degradation of cyclic ultimate bearing capacity of the pile foundation. In this work, the spatial distribution of damage of soft clays around the laterally loaded pile was investigated using a plane strain finite element model in ABAQUS. Based on our findings, we propose an improved spatial distribution of damage function for disturbed soft clays under small cyclic amplitudes.

INTRODUCTION

Offshore pile foundations undergo lateral cyclic loadings from the ocean wave during operation, which causes remolding and softening of the surrounding seabed soil (Andersen et al., 1980; Zhang et al., 2011). The spatial distribution of damage of soft clays is essential for the degradation of cyclic ultimate bearing capacity of offshore pile foundation. Therefore, the lateral bearing capacity, especially the degradation of the capacity under lateral cyclic load, must be considered in the design of offshore single pile (Randolph et al., 2005). Einav and Randolph (2005) deduced the degradation relationship between soil strength and soil shear strain based on large amplitude cyclic T-bar penetration test in clay. The damage influence zone represents an idealization of the full two-dimensional flow process (Martin and Randolph, 2006; Einav and Randolph, 2005; Zhou and Randolph, 2009). Wang et al. (2016) proposed a soil strength degradation relationship characterized by cumulative plastic displacement. A triangle probability damage function has been proposed by Hodder et al. (2010) for cyclic degradation of soft clays based on large cycle amplitudes, which is not applicable to small cyclic amplitudes for pile foundations. The cyclic movement of pile foundation in deep embedment is with small amplitude (Jeanjean et al., 2009), and the degradation of ultimate bearing capacity of pile and soil caused by small amplitude circulation cannot be ignored. Therefore, it is necessary to obtain accurate distribution and expansion of soil damage influence zone, and propose corresponding calculation method of cumulative plastic displacement. In this paper, the spatial distribution of damage of soft clays for cyclic laterally loaded piles was investigated with a plane strain finite element model in ABAQUS. Based on the results, an improved spatial distribution of ‘damage influence zone’ for disturbed soft clays under small cyclic amplitude is proposed with Wendland kernel function (quadric smooth spline kernel function), and the extent size of ‘damage influence zone’ is obtained by fitting simulation results.

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