A 3D Method to dynamically model the cutting of submerged rocks with evaluation of pore pressure effects

Rock cutting is often necessary for dredging and seabed installation processes, for example in pile drilling, trenching, offshore mining and capital dredging. Efficient rock cutting is still one of the main challenges that the dredging industry faces. The cutting forces and the excavation rate are determined by the design of and power supplied by the equipment. Often the design of this equipment is based on quasi-static analytical or semiempricial rock cutting models. However, these are often limited in their applicability for 3D processes. This paper will elaborate on an extension to 3D of previous work on 2D rock cutting simulations. While cutting, the rock matrix deforms and as a result local fluid pressure differences will occur. Near the tip of the tool, rock is crushed, giving rise to a local increase in fluid pressure. In the case that chips break loose from the rock, cracks occur, resulting in a local decrease of fluid pressure. The magnitude of these pressure differences, and thus its effect on the cutting process depends on the water depth and the cutting velocity. As a result of this, cutting forces and rock deformations are susceptible to both the cutting velocity and the water depth at which rock is excavated. The Discrete element Method (DEM) has already been successfully applied in 2D to model rock cutting processes for shallow water and deep sea applications. Unfortunately, the 2D models are not sufficient to model all relevant aspects, the required normal (penetration) force is underestimated, break out angles are not calculated. This paper will focus on the progress of the extension of the DEM model towards 3D. Qualitative results are based on linear cutting tests of a single pick point. The new method gives more insight in the physical processes that occur during cutting and it can help to improve the design and operational guidelines of the cutting equipment and cutting processes.