The effects of gravel cushion particle size and thickness on the coefficient of restitution in rockfall impacts

In: Natural hazards and earth system sciences: NHESS, Band 18, Heft 6, S. 1811-1823

Open Access

Abstract

Abstract. Gravel cushions are widely used to absorb the impact energy of falling rocks
in open-pit mines. A particularly important application is to enhance the
energy-absorbing capacity of rockfall sheds. In this paper, we study how
varying the thickness and particle size of a gravel cushion influences its
energy-consumption and buffering effects. We performed a series of laboratory
drop tests by dropping blocks from a fixed height onto cushions of different
thicknesses and particle sizes. The results indicate that, for a given impact
energy, the cushion thickness has a strong influence on the measured
coefficient of restitution (COR) and therefore impact pressure. Additional
tests were performed to study how the radius of the block and the height it
is dropped from affect the measured COR. This showed that as the movement
height of the block is increased the COR also increases, and blocks with
larger radii exhibit a larger variability in measured COR. Finally, we
investigated the influence of rockfall block radius, r, movement height,
H, cushion thickness, h, and particle size, d, on the COR and the
damage depth, L, of the cushion. The test results reveal that the cushion
thickness is the primary design parameter, controlling not only COR, but also
the stability of the cushion material. The results provide a theoretical and
practical basis for the design of gravel cushions for rockfall protection.