Impact force of a surge of water and sediments mixtures against slit check dams

Abstract

Slit check dams are widely used protection structures against debris flows. The role of these structures is to trap part of the debris in order to diminish the peak of the solid discharge. However, the high volume and velocity involved induce considerable impact forces. Correspondingly, an improved estimation of the impact force is fundamental to properly design the protection structures. In order to develop an analytical expression for the impact force of a debris flow surge against a slit check dam, we have adopted a rational criterion based on the principles of mass and momentum conservation. In our formulation we have introduced a proper coefficient to account for the horizontal contraction of the streamlines near the check dam slit. This coefficient is calibrated through a series of physical experiments. Furthermore, the paper addresses the influence of a debris flow breaker located within the opening of the slit check dam. The differences between the check dam with and without flow breaker are evaluated in terms of impact forces by comparing two check dams with the same slit width and the same net slit width. By comparing the force acting in the presence of the breaker or without it, we observed that the impact is more onerous in the first case, since the incoming flow is deviated from the flow breaker to the check dam wings.

Keywords: Debris flow breaker; Dynamic impact; Protection structures; Slit check dam.