Evaluation of rapid landslide impact forces against sheltering structures

A crucial role in the conception of landslide risk mitigation strategies is played by the design of mitigation measures aimed at reducing risk to acceptable values. In the case of extremely rapid landslides, such as debris flows, artificial obstacles are very common mitigation measures, designed either to stop or to deviate the flowing mass. In the design of these types of sheltering structures, crucial is the evaluation of the impact forces exerted by the flowing mass on the structure, commonly accepted, this latter, to be a function of many variables, such as structure location, geometry, local topographic profile, flowing mass height, velocity and so on. Protection structures dissipate the flowing mass energy either partially or totally and, for this purpose, they are set along the potential flowing path where the debris is transported and, more prevalently, deposited. This paper focuses on a procedure for simply evaluating the impact forces transmitted with time to quasi-rigid protection structures. The approach is based on the hypotheses of (i) employing a numerical code capable of describing the propagation of the rapid landslide in its downhill path and (ii) adding, in the evaluation of the impact force, the hydrodynamic and the quasi-static terms. Despite of its simplicity, the proposed procedure takes into account most of the engineering factors governing the problem, synthetized by the authors by using geometrical non-dimensional ratios. To clarify the proposed procedure, the results of numerical analyses are discussed and the influence of the above mentioned factors critically analysed.