| Summary: | To protect pipelines in Arctic regions they are often buried in trenches, effectively preventing damage by ice gouging. When trenching is performed in Arctic soil, subsea permafrost may be encountered at water depths up to 100 m, mainlywhile excavating clay soil. Frozen clay is an anisotropic inhomogeneous material with a tensile strength and behavior comparable to soft rock. Previous observations of cutting experiments on submerged frozen clay indicated that the dominant failure mechanism is tensile brittle. With an increasing thickness of the layer cut, the increase of cutting forces seems to be less than proportional. An explanation for this trend is the size effect, which describes the probabilistic weakening of the material when the thickness of the layer cut increases. An optimal thickness of the layer cut could result in lower specific energy consumption, however this may lead to higher cutting forces. In order to excel in the design and construction of efficient subsea excavation equipment (e.g. subsea trenchers) thorough knowledge of physical characteristics of permafrost is mandatory. These characteristics include the failure mechanisms, the required cutting forces and power consumption. Due to the brittle behavior of the frozen clay the use of a vibration-impact mechanism has been investigated. A literature reviewidentified that the knowledge on vibration-impact cutting in permafrost is very limited. Therefore Royal IHC and Delft University of Technology joined forces to fill this knowledge gap. The main goal of this research is to identify the governing parameters in (vibration-impact) cutting of frozen clay. Knowledge of the effect of vibration-impact cutting leads to the ability to calculate cutting forces in similar conditions and to determine the parameters required for designing effective subsea excavation equipment. In this study a prediction model of the vibration-impact cutting tool and soil is developed. A specialized large scale vibration-impact cutting setup was designed and constructed. ...
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