Influence of deflector on the impact dynamics of debris flow against rigid barrier

Abstract

A deflector is a structure installed at the crest of a rigid barrier to prevent the over-spilling of debris flow from damaging the downstream infrastructures and human lives. Despite its clear practical value, the fundamental interaction mechanism of debris flow and deflector has not yet been elucidated scientifically. In this study, flume tests were conducted to calibrate a smoothed particle hydrodynamic (SPH) model to investigate the influence of deflector geometry (length and angle) on the flow-deflector interaction mechanism as well as reducing design barrier height. Water flows and viscous debris flows with a Froude number of around 5 were modelled to represent geophysical flows. Flume test and numerical simulation results reveal that the optimal deflector configuration has a normalised projected length (projected deflector length to frontal flow depth) of LP/h0 = 1.0 with angles (θ) of 0° and 45°. A modified analytical impact equation is proposed, which conservatively predicts the peak impact force exerted on a deflector with an upper bound to measured and computed values. The normalised barrier height (ratio between barrier height and frontal flow depth) also plays a key role in over-spilling dynamics. For a barrier without a deflector, over-spilling would occur when HB/h0≤ 9.0. However, for barriers with deflectors, over-spilling occurs only if HB/h0≤ 4.7. Installing a deflector allows reduction of barrier height by up to 50% while preventing over-spilling.