Experimental Investigation of Suction Installation Behavior of Caissons in Loose Saturated Sands

With the continuous expansion of global offshore wind power, suction caissons are increasingly becoming a significant foundation form due to their advantages such as low installation noise, convenient construction, and reusability. However, localized seepage induced soil disturbance and strength changes during their installation remain underexplored, leading to uncertainties in their capacity assessment. This paper presents a series of experimental investigations in loose saturated sand, comparing suction and embedded installations for caissons with varying length-to-diameter (L/D) ratios coupled with Cone Penetration Tests (CPT) to evaluate soil strength changes inside and outside the caissons. For both installations, the results reveal similar lateral load-bearing capacities (0.12 kN) for shorter caissons (L = 120 mm), whereas for longer suction installed caissons (L = 240 mm), the capacity was reduced by approximately 80%, due to internal soil weakening and an upward shift of the rotation centre. CPT data further revealed compaction enhancement outside and seepage-induced reduction in soil strength inside the caisson, jointly affecting failure behavior. Based on these findings, the conventional bearing capacity formula for fully embedded caissons was modified to account for partial embedment and external-internal soil strength differences, and a novel mechanically-derived failure criterion was proposed, accurately capturing non-linear load responses and improving prediction of suction caisson capacity for various load eccentricities and L/D ratios, thus supporting optimized offshore foundation design.