Submarine landslides are a geological hazard that may cause significant damage, and are among the most serious problems in offshore geotechnics. Understanding the mechanism of submarine landslide/offshore structure interaction is essential for risk assessment, but it is challenging due to its complexities. In this study, ten centrifuge tests were conducted to determine how offshore wind turbines founded on four piles respond to consecutive submarine landslides. The tests highlighted two mechanisms of soil deformation and foundation settlement associated with the landslide cycle: (1) deformations of the clay were associated with induced excess pore water pressure, and increased with the number of landslides; and (2) by contrast, foundation settlements largely depended on the dynamic impact of the first cycle and remained unchanged for the remaining events. The settlements were 0.5 m for the 10 m pile foundation and about 0.1 m for the 20 m pile foundation, both in clay and in sand. It was also found that increasing pile length reduces the excess pore water pressure, soil deformation and foundation settlement.

Current practice to model the occurrence of submarine landslides is based on methods that assess the potential of site-specific failures, all with the objective of providing elements to identify and quantify regional features associated to geohazards, before a project development takes place. Also, survey data to estimate parameters required to model submarine landslides show typically limited availability, mainly because of the cost associated to offshore surveying campaigns. In this paper, a probabilistic calibration approach is introduced using Bayesian statistical inference to maximize the use of available site investigation data, and to best estimate the occurrence of a marine landslide. For this purpose, a landslide model thought for its simplicity is used to illustrate the applicability and potential of the calibration methodology. The aim is to introduce a systematic approach to produce prior probability distributions of the model parameters, based on an actual integrated marine site investigation including geological, geophysical, and geomatics data, to then compare it with a posterior probability distribution of the same model parameters, but estimated after collecting in situ soil samples and testing them in the laboratory to produce the corresponding soil strength properties. This comparison allows to explore (a) the influence of the number of in situ samples, (b) the influence of a landslide factor of safety, and (c) the influence of the soil heterogeneity, into the likelihood of the occurrence of a marine landslide. The model parameters that are considered for calibration include the initial state of the submerged and saturated soil unit weight, the thickness of the soils' unit layers, the pseudo-static seismic coefficient, and the slope angle, while the soil undrained shear strength is considered as the reference parameter to conduct the calibration (i.e., to compare model predictions vs. actual observations). Results show the potential of the proposed methodology to produce landslide geohazard maps, which are needed for the planning and design of marine infrastructure.

Seismic-induced submarine landslides pose significant risks to offshore structures. To enhance our understanding of this phenomenon, we have developed a CFD-MPM capable of simulating complete mechanisms behind earthquake induced submarine landslide. Recent centrifuge tests have demonstrated that the permeability of marine sediment is a critical factor in determining the failure mechanism of submarine landslides. Specifically, a lower permeability increases the likelihood of a slope transitioning from failure to gravity debris flow. Our CFDMPM, validated with centrifuge tests, supports this conclusion. Moreover, we conducted a sensitivity analysis of seismic-induced submarine landslides using the CFD-MPM. In the case of contractive soil, a lower permeability leads to slower dissipation of excess pore water pressure, resulting in longer submarine debris flow runouts. Additionally, in the case of softening soil, a lower permeability increases the chances of spreads as a failure mechanism, while a higher permeability favours retrogressive flow slides. This study sheds light on the diverse effects of sediment permeability on submarine landslide mechanisms, offering crucial insights for hazard assessment and mitigation strategies in offshore engineering and coastal management.

Submarine landslides are common marine disasters that pose significant threats to human safety. However, there is no established method for monitoring submarine landslides. To effectively prevent and control such disasters, this study conducted a series of investigations based on the Zhujiajian Landslide. Based on optical fibre sensing and numerical simulation technology, this study proposed a sensor optimisation method for a submarine land-slide simulation experiment. Three types of fibre-optic sensors with high sensitivity and corrosion resistance were developed, and the designed sensors have broad application prospects for monitoring complex environments. A wavelength-division multiplexing sensor-networking method for submarine landslide simulation tests was pro-posed. A simulation test of a submarine landslide under wave action was conducted to verify the practicability of the optical fibre monitoring system, and experimental data were collected. The variation characteristics of the seepage pressure, displacement, and velocity fields were studied. The results showed that submarine landslides are the products of liquefaction and shear failures. Continuous wave action causes the accumulation of pore water pressure in the soil mass inside the slope, which leads to a decrease in the shear strength. The shearing action of waves is the driving force for submarine landslides. When a submarine landslide occurred, both displacement and pore water pressure showed a sudden change, but the sudden change in pore water pressure occurred approximately 5 s earlier than that of the sudden change in displacement. A 50:1 on-site prototype was obtained by converting the time similarity scale, and the on-site pore water pressure mutation time was approximately 30s earlier than the submarine landslide occurrence time. Therefore, when conducting on-site submarine landslide monitoring, pore water pressure can be prioritised as an evaluation index for the stability of submarine slopes. The research results provide effective technical support for the prevention and control of submarine landslides and have reference significance and application value for similar projects.