Conductor casing jetting operations have become commonplace in deepwater environments and has become the preferred method of installation in most deepwater environments where seafloor sediments allow the technique to be utilized. Operators have found the technique to be faster than the historical method of drilling a borehole and cementing the casing in place. But very little literature has been published regarding jet excavation mechanism in cohesive soil. In particular, some empirical method ignores the hydrodynamic characteristics of the jet and soil properties.

As the submarine soil is a deformable body whose behavior falls between a linear elastic solid and viscous liquid, its behavior is governed by general theory of rheology. A simple linear model of visco-plasticity, the Bingham rheological model, can describe soil deformation under steady-state stress. The generalized observation was that flow of soil is initiated only when the stress exceeds the yield stress. Beyond this stress, soil flows in a manner similar to viscous fluids at a rate proportional to the stress in excess of the yield stress. On the other hand, the visco-plastic material behaves like solids when the applied shear stress is less than the yield stress.

This article is to clarify the excavation mechanism associated with jet cutting in a cohesive soil, based on computational ?uid dynamics approaches. To investigate the profile of the excavated hole and the ultimate cutting distance of the jet, taking into account both the hydrodynamic characteristics of the jet and the undrained shearing resistance of the cohesive soil. The simulation results using FLUENT reveal that ultimate cutting distance grows with increasing flow intensities and decreasing clay shear strength as well as the distance of jet-soil interface from the nozzle. Based on the research results, propose the expression for jet excavation depth with shear strength and the other factors, which provides an improved prediction tool that can be applied in industry.

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