Micromechanics and Geomechanics on Scour

Abstract

At the Great East Japan Earthquake of 2011, coastal structures were weakened by ground scouring and the consequent loss of the wave resistance function led to large scale damage. As this could seriously affect the economy of a country, urgent measures need to be taken to minimize the damage. In addition, floods arising from frequent heavy rains cause water levels to rise and prolonged high water levels lead to riverbed fluctuations, erosion, and destruction of river levees, and erosion due to overflow. In studies on the scouring phenomenon, tractive force has been widely used for evaluation. Evaluation by tractive force is done from a microscopic viewpoint, focusing on the balance between the shear force generated by the fluid on the ground surface and the effective weight of a soil particle in the outermost ground layer. However, when we consider the scouring phenomena that occurs around structures and on account of overtopping, the scale of scouring is such that it cannot be explained merely from the viewpoint of tractive force. Moreover, it has been pointed out in recent studies that the effect of fluid force does not only to affect the ground surface, but also causes stress changes inside the ground, thereby promoting scouring. Therefore, besides the microscopic view, it is necessary to elucidate the phenomena regarding the meso-scale of soil elements and to consider a wide range of perspectives of the macro scale of structures. Therefore, this paper demonstrates some of the findings from our research on the scour phenomenon focusing on soil-fluid interaction in multiple scales.