Bearing capacity of skirted footings on bedrock under large eccentric loads: Deterministic and probabilistic approaches

Skirted foundations, commonly used in offshore engineering, are subjected to vertical and large moment (VM) loads. Their ultimate capacity is often evaluated using VM failure envelopes from numerical methods that neglect the spatial variability of seabed soils. This study examines the probabilistic undrained capacity of skirted foundations with varying embedment ratios in spatially variable soils, using lower and upper bound random finite element limit analysis with both stationary and non-stationary random fields. The study presents two key novel contributions. First, it proposes new bearing capacity factors and normalized failure envelope equations that account for foundation embedment, load eccentricity, and soil heterogeneity, enabling more reliable design. Second, it quantifies the effect of a rigid layer beneath the foundation, showing that a shallower rigid base can nearly double the vertical capacity, though this advantage reduces under large eccentric loads. The research also highlights the significant roles of soil heterogeneity, embedment depth, strength variability, and spatial correlation in determining foundation bearing capacity. The advantages of using probabilistic approach in relation to deterministic one are presented, underscoring the importance of accounting for soil variability and uncertainty in foundation engineering.