Experimental analysis of the impact of dry granular debris flows against obstacles.

Debris flows exert enormous impact forces on obstacles in their path. Field measurements proves that the impact force consists of two distinct parts: the fluid dynamic pressure and the collisional force of single boulders. The estimation of the range of these force is necessary for a planning of structures against debris flows. As field monitoring and measurements are generally difficult and expensive, experiments are needed. Objectives of this work were to experimentally analyse the dynamic impact of stony debris flows on structures; to identify structure effects on extension and shape of the debris deposit; finally to propose an analytical expression for estimating the design force. Experiments were carried out on two sandy mixtures flowing down a steep chute and impacting on obstacles. Effects of mixture composition, of obstacle shape and orientation on force values and deposit extension have been examined, showing that only check-dams can significantly reduce the debris kinetic energy and retain the material.