Speed effects in cutting and ploughing

A significant speed effect occurs when blades and ploughs cut saturated soil. The cutting force increases dramatically with cutting speed, sometimes by a factor of five or more. In some soils, the effect occurs at very low speeds. It has significant practical implications, and has caused difficulties in several projects, The effect is explained by the intense reduction of pore pressure which occurs when a dilatant sand is forced to deform rapidly in an undrained or partially drained condition, The reduction in pore pressure increases the effective stress and increases the resistance to shear, The paper develops the equation that governs the pore pressure, which is the diffusion equation in a moving medium, It develops an analytical solution for the idealization of a vertical triangular concentrated shear zone ahead of the cutting blade. The results are compared with measurements in the laboratory and in the field. The implications for modelling are examined, and the cutting force in the cavitating condition is predicted.