Influence of spatial variability of soil strength on load and resistance factors calibration for the design of breakwater foundation

Many studies have recognized that spatial variability of soil (SVS) has significant influences on the reliability analysis of geotechnical engineering problems. However, the influence of SVS on the load and resistance factors (LRFs) calibrated for the limit state design of breakwater foundations has received limited attention and has become questionable. This study aims to investigate the effects of SVS on the LRFs calibrated based on a probabilistic approach. Accordingly, two breakwater foundations of the tanφ and c-tanφ forms with various scales of fluctuation and coefficients of variation of soil strength were considered. The results reveal that the SVS significantly reduces the variance of resistance and increases the positive correlation between load and resistance. These important effects of SVS strongly influence the load and resistance factors calibrated. Ignoring the SVS results in lower values of normalized resistance factor and thus a more conservative design for breakwater foundation stability outcomes. Specifically, considering SVS increases the normalized resistance factor by approximately 7%–23% for the commonly reported values of the scale of fluctuation and the coefficients of variation of soil strength. Thus, the SVS should be considered in the LRFs calibration to provide a more rational and economical design of breakwater foundations.