Implications of sand grains’ mobility and inundating area to landslides at different slope angles

Abstract

The apparent friction coefficient, namely Heim’s ratio, is a prevalent dimensionless parameter to represent landslides’ mobility. Many empirical and theoretical models have been developed on the Heim’s ratio and landslides’ volume. However, studies on the ratio and their slope angles are lacking. Here, we performed a series of laboratory landslides at different slope angles to explore their mobility and motion characteristics. Our results show that the runout of the laboratory landslides decreases linearly with an increase in slope angles. A theoretical relationship between the apparent friction coefficient and slope angle is proposed, based on a hypothesis that the ratio of energy dissipation occurring when an object collides with a plane is power law to its impact angle. The relationship shows well approximation to our experimental data, and data from Crosta (IOP Conf. Ser. Earth Environ. Sci. 26:012004, 2015) and natural landslides. We also obtain that the coefficients of apparent friction and effective friction are almost identical at low slope angles. The dimensionless length and area of the laboratory landslides increase first and then decrease during their whole motion. The maximum area of them during their motion decreases with an increase in slope angles. The study will support studies on the morphological variation during the whole motion and mobility of landslides.