To examine the coral reef limestone–concrete shear failure characteristics, we conducted large-scale direct shear tests to study five types of interfaces: planar, sloped, arc shaped, stepped, and triangular. Furthermore, the shear failure characteristics and shear strength variations were examined under three interface connection types: smooth, mud filled, and cemented. The results show that the shear phenomena at the smooth and mud-filled interfaces between the coral reef limestone and concrete were characterized by the interface slip failure mode. The mud at the interface acted as a good lubricant and greatly reduced the shear strength. For the cemented connection between the coral reef limestone and concrete, the shear strength increased rapidly with the shear displacement. When the shear strength reached a certain value, it abruptly decreased and then tended to level off, and shear failure occurred at the coral reef limestone side of the interface. Among the studied specimens, the maximum shear strengths were in the following order from highest to lowest: stepped interface, triangular interface, arc-shaped interface, sloped interface, and planar interface, while the corresponding shear displacements increased in that order. The results of this study can serve as a reference for the construction of pile foundations on coral reef limestone strata.

The shear characteristics of the interfaces between soil and concrete structures are essential for the safety of the structures. In this study, a large-scale direct shear test apparatus was developed to measure the mechanical parameters of soil–concrete interfaces under conditions with different soil types, soil moisture contents, and interfacial filling materials. The results showed that the shear stress of the soil–concrete interface increased initially and then became stable with the increase in the shear displacement. The shear displacement of the sandy soil when the shear stress became stable was smaller than that of the clayey soil. The silty sand–concrete interface had a smaller friction angle than the interface with the medium-coarse sand. Moreover, with the increase in the soil moisture content, the friction angle of the clayey soil–concrete interface decreased rapidly, whereas the cohesion first increased and then decreased, and the peak cohesion was near the plastic limit of the soil. Under the same moisture content, the friction angle and cohesion of the clay–concrete interface was reduced by filling the interface with a thin layer of sandy soil, while filling the silty sand–concrete interface with a thin layer of silt reduced the friction angle and increased the interfacial cohesion. Nonetheless, the filling had little impact on the overall shear strength of the interface.

In this study, we investigated the rockfall motion characteristics for varying rock sizes and the structural responses of steel pipes with and without energy dissipation components. Specifically, we conducted rockfall tests under three conditions: (1) an inclined steel pipe, (2) an inclined pipe with a horizontal segment for energy dissipation, and (3) inclined and horizontal steel pipes combined with baffles. The results revealed that the velocity of the rocks of different sizes was similar in the steel pipes without energy dissipation components. The energy dissipation was primarily due to the friction between the rock and the steel pipe, and the friction coefficient was independent of the rock size. The use of horizontal steel pipes effectively dissipated the kinetic energy and reduced the rock velocities by an average of 72.23%. However, as the rock size increased, the velocity increased accordingly, resulting in reduction of the energy dissipation effect. The addition of baffles in the steel pipes increased the energy dissipation during the rockfall and decreased the rock velocity and the impact stress on the horizontal steel pipes. Compared to the single-baffle condition, the average impact stress on the horizontal steel pipes was reduced by 26.5% and 59.6% under the two-baffle and three-baffle conditions, respectively.

This study addresses the common challenges of complex soil behavior and the difficulties in achieving precise control during the construction of large open caissons. A centrifugal model test was conducted to investigate open caisson–fine sandy soil interaction, and the findings were further verified through field testing. Results indicated that during the sinking process, the open caisson–soil interface exhibited slip failure characteristics, while the soil at the cutting edge of the open caisson showed a tendency for inward shear slippage. The horizontal earth pressure along the open caisson sidewall was found to correspond to static earth pressure in the upper section and gradually approached active earth pressure in the lower section. The maximum earth pressure occurred at approximately three-quarters of the embedded depth of the open caisson wall. Furthermore, the friction angle at the soil-open caisson interface was approximately 0.63 times that of the soil friction angle. Based on the observed distribution patterns of earth pressure and skin friction, theoretical calculation formulas were developed. Their accuracy was confirmed through field tests, providing valuable references for the design and construction of large open caisson projects.