Debris flow impact forces on rigid barriers: existing practice versus DEM numerical results

As is well known, fast landslide risk mitigation is a very crucial issue in the territorial planning of mountain regions. In this framework the design of mitigation measures like sheltering structures plays an important role. In this perspective, in this paper the problem of the assessment of the maximum impact forces transmitted by dry granular (non-cohesive) masses (MIF) to rigid barriers is critically tackled by using a formula recently proposed by the authors, which has been derived from the interpretation of DEM numerical results. The formula defines a quite simple non-linear dependence of the maximum impact force on the Froude number and defines a change in the regime (from linear to quadratic) according to a suitable measure of the dynamic material stiffness, this evaluated by starting from the assessment of the compression wave propagation velocity within the impacting soil mass. The approach proposed by the authors is thus employed to (i) discuss the reliability of the existing practice procedures, (ii) highlight the reasons of the scatter among the values obtained by using the approaches proposed in the literature, based on hydrostatic, hydrodynamic and boulder impact theories, (iii) underline that the empirical formulas available in the literature do not take into consideration a series of factors, like, for instance, the front inclination and the void ratio, that in contrast severely affect the maximum impact force value.