Abstract
Sand erosion and scouring caused by waves and marine currents result in gradual increase of local seabed inclination and formation of slopes around hydraulic structures and offshore foundations. During this process, shear stresses in the soil body increase monotonically which may lead to static liquefaction and damage of the adjacent offshore infrastructure. This paper presents the details of a newly developed static liquefaction triggering actuator to be used at an enhanced gravity condition in a geotechnical centrifuge. This actuator simulates the steeping process of submarine sand layers due to scouring and enables the investigation of failure mechanisms in submerged slopes. The details of the centrifuge test set-up designed and constructed to simulate the process of triggering static liquefaction in loose sand layers are presented. Furthermore, the performance of the novel integrated model preparation facility using sand fluidization is explained. The set-up was used to conduct several centrifuge tests at four different slope steepening rates to investigate the slope steepening rate effects. Moreover, the effect of viscosity of the submerging pore fluid on the behaviour of the slopes at the onset of failure is investigated. The Coriolis effect on loose saturated sand samples during increase of g-level is examined as well. Results show that the built-up of pore pressure due to local shear deformations can be detected and considered as one of the triggering mechanisms of this kind of submarine slope instabilities.
Highlights
The failure of natural or man-made slopes under water is one of the main threats to offshore assets
The stress state of the soil element in Fig. 1a is indicated as point A which lies on the K0 line, where K0 is the ratio of effective horizontal stress to effective vertical stress at rest
It is reasonable that the sample bottom layer is denser than the sand above, as the vertical effect stress increases with the sample depth
Summary
The failure of natural or man-made slopes under water is one of the main threats to offshore assets. Liquefied submerged slopes or embankments are often characterized by relatively small failure angle, sudden failure, a considerable amount of released soil mass and large influencing areas (Kvalstad et al 2001). These make static liquefaction to be one of the most catastrophic mechanisms of under-water slope failures. Askarinejad et al (2018) adopted the water pluviation method and successfully prepared saturated slopes with relative density of 15% This technique was reported to be extremely time consuming, i.e. approximately 8 h was required to construct a sample in a strongbox with dimensions of 270 mm × 150 mm × 135 mm
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