Reliability analysis of pile group in spatially variable unsaturated expansive soil based on load transfer method

Accurate assessment of pile group's performance in spatially variable unsaturated expansive soil has long been a challenge in geotechnical engineering. This paper presents a methodology to perform reliability analysis for vertically loaded pile group, where the modified load transfer method (LTM) is utilised to investigate the load–displacement response considering the pile–pile interaction and the non-linear relationship of the pile–soil interface under the influence of matric suction reduction and the swelling of expansive soil; the Karhunen–Loève (KL) expansion method is adopted to simulate the spatial variability of soil parameters; the first–order reliability method (FORM) is utilised to perform reliability analysis of each pile in the pile group; and the reliability analysis of pile group is then performed using the sequential compounding method (SCM) by considering the pile group as a parallel system. By applying the proposed methodology to a 3 × 3 pile group under different vertical loads and infiltration times, the relative magnitudes of reliability indices for different piles in the pile group and the pile group system under two failure modes of uplifting and sinking are identified. The effects of soil's spatial variability and pile spacing on the reliability of pile group are also analysed.