Effect of Rock Mass Diameter on Runout Distance and Velocity Attenuation of Dry Granular Avalanche

Abstract

In order to rationalise the existing methods for evaluating the runout distance of rock-slope failure debris, it is necessary to clarify the relationship between the runout distance of granular materials and the materials' flow behavior. In this study, a series of model tests were conducted to analyse the effect of several parameters, including slope angle, flow height, and granular diameter, on the runout distance and flow velocity of particles in dry granular avalanches. Our test results indicate a dependency between runout distance and the characteristics of the granular materials involved. Specifically, we show that when granular materials are present at the toe of a slope, subsequent materials of larger diameter can act to push these preceding materials further out, thereby increasing their effective runout distance. In contrast, we show that if the subsequent granular materials manage to overtake the granular materials already present, and if the velocity of granular materials goes to zero around the toe of the slope, the runout distance of the largest granular diameter may not be maximal. To investigate dry granular avalanche runout distance in cases of secondary slope failure, we conducted an additional series of model tests in which rock masses generated by primary slope failure were deposited at the toe of the slope. These test results indicated that, regardless of the particle size, maximum runout distances in cases of secondary slope failure and primary slope failure avalanches are identical.