Inclusion of pore pressure effects in discrete element modeling of rock cutting

Many rock excavation processes occur in a marine environment, like in drilling for oil/gas, dredging, trenching and deep sea mining. The presence of a fluid in and surrounding the rock can have a significant influence on the cutting process, through differences in the ambient (confining) and pore pressure. The cutting motion deforms the rock matrix, and as a result, local fluid pressure differences will occur. The magnitude of these pressure differences, and thus its effect on the cutting process, increases with larger water depths and/or higher cutting velocities. The apparent strength of the rock matrix increases with higher confining pressures, resulting in a higher cutting force. The Discrete Element Method is used successfully to simulate the rock cutting process of dry rock for various applications. In this paper, the authors extend DEM with a fully coupled fluid pressure model to simulate the mechanics of saturated rock. This is done by solving a pore pressure diffusion equation with a Smoothed Particle (SP) method. By using the SP, it is possible to convert the discontinuum properties of the DEM to a continuum, in which the fluid pressure is modeled and applied as an additional force in the DEM. Qualitative results show that the model is able to capture the increase in cutting force with increasing confining pressure, as well as deformation rate effects applied on saturated rocks