DAMAGE TO GRASS COVERED SLOPES DUE TO OVERTOPPING

Abstract

Many dike failures have been ignited by damage due to erosion on the landward slopes. This paper investigates how grass covered slopes perform when being attacked by overtopping flow during storm surges. Based on observations during a number of simulator tests, damage is classified into three types 'head-cut', 'roll-up' and 'collapse' depending on the combination of grass, material components and corresponding layer thickness. To quantitatively predict the potential types, strength ratio and thickness ratio are proposed. Besides, erosion usually starts at weak spots so their spatial distributions are evaluated along dike stretches with various lengths. Finally, the overtopping resistance of a grass turf is presumably represented by critical velocities depending on soil cohesion and apparent cohesion induced by roots. The computed results are comparable to erosion on Bermuda and Carpet grass slopes tested with the simulator.