Measurement and prediction of the initial settlement of cube-type artificial reefs caused by free-fall installation using a laboratory-scale experiment, regression analysis, and numerical collision analysis

Abstract

Several studies have identified stability issues related to artificial reefs (ARs) installed on the seabed. However, initial AR settlement during free-fall installation has not been well examined. We performed a laboratory-scale experiment, regression analysis, and numerical simulation to evaluate the initial settlements of two cube-type AR models during free-fall installation into soft soil. Settlement tended to increase by impact velocity and AR mass but to decrease as soil density increased. The most significant parameter controlling settlement was soil density, followed by the impact velocity and the AR mass. Of the 56 cases examined, 76.79, 71.43, and 98.21% exhibited relative differences of ±20% as revealed experimentally, and by regression analysis and simulation. Given the terminal velocities of the two AR models, the corresponding settlement ranges were 2.12–5.36 mm and 4.56–11.56 mm, respectively. Thus, the effective useable volumes of the AR models fell by approximately 4–12% (depending on clay composition) if the models attained their terminal velocities during free-fall installation. These initial settlement data indicate that free-fall installation negatively affects both AR stability and functionality.