Abstract
Breaching is a type of slope failure that generates sustained turbidity flow and delivers sand into deep sea. Breaching generally has very high failure angles and the erosion rate is slow and steady. Breaching can occur in a variety of sediment types including coarse silt, fine grained sand and poorly sorted medium sand. Breaching is caused by shear dilation of sand, which creates negative excess pore pressure and increases the strength of sand. The retrogressive erosion of sand triggers the shear dilation. Due to the organization of granular material the amount of dilation is much more near the failure surface, creating a negative excess pore pressure signal close to the water-sediment interface. The excess pore pressure signal creates pressure gradient which triggers pore pressure dissipation. The Dissipation of pore pressure transmits this signal away from the failure surface and its rate is controlled by the diffusivity of the sediment. The retrogressive erosion rate is proportional to the diffusivity of sand. This creates a pore pressure profile that is only a function of the relative strength of dilation and the distribution of stress in the sediment.