Offshore foundations usually experience long-term cyclic loading, where the weakly bound water at the soil-structure interface can be transformed into free water. The free water enriched at the soil-structure interface would influence the mechanical characteristics of the soil near the interface, weakening the interface strength and posing a significant threat to the safety and stability of offshore foundations. This study proposed a novel concept, i.e. the characteristic water film thickness, to quantify the enrichment degree of water film at the soil-structure interface under cyclic loading. A series of cyclic shearing tests were carried out by using self-developed cyclic loading equipment combined with a small constant temperature centrifuge. The influence of different clay and salt contents on the characteristic water film thickness was investigated and analyzed. It was found that both the kaolin and salt contents significantly impacted the characteristic water film thickness, where it was positively correlated with the kaolin content while negatively correlated with the salt content. The research outcome enriched the understanding of the weakening mechanism underlying the load and deformation transfer between soil-structure interface.

Civil excavation projects frequently yield substantial excess spoil, posing challenges to sustainable construction. This study explores repurposing such spoil for creating controlled low strength material (CLSM), emphasizing the novel use of polycarboxylate superplasticizer (PCE) to reduce the water requirement. The work also distinctively utilizes water film thickness (WFT) theory to elucidate the effects of PCE dosage and WFT on material properties, thereby advancing CLSM mix design. First, using an experimental approach, a series of fresh CLSM samples are prepared, with varying the water-to-solid ratio (W/S) and PCE dosage, to evaluate their packing density, WFT, flowability, and bleeding rate. It is demonstrated that both packing density and WFT experienced a non-linear increase with rising PCE dosage. Regression analysis of the experimental data reveals that the flowability and bleeding rate linearly increase with the rising WFT, and the enhancements are more pronounced at higher PCE dosage. Notably, at a given WFT, the impact of PCE dosage on flowability and bleeding rate reduce as WFT decreases. Additionally, the research identifies specific WFT thresholds correlating with maximum flowability and a 5% bleeding rate. These thresholds mark the critical point at which WFT ceases to influence flowability and delineate the maximum WFT that satisfies the bleeding rate requirements, respectively. These insights are important for optimizing the design of CLSM with PCE in terms of flowability and bleeding rate.