The clogging mechanism of debris-flow material in the multiple outlets of sectional barriers

Debris flow is widely recognized as one of the most dangerous landslide phenomena, and thus the design of structural mitigation measures constitutes an important issue. Numerical and experimental investigations on the dynamics of interaction between a flowing mass and a retaining structure are necessary to properly design these structures. Both close and open rigid barriers act as debris flow breakers. However, in the perspective of preventing the loss of effectiveness of a retaining system, open rigid barriers are more widely used, but the their retention mechanisms in not fully understood. The present research focuses on rigid barriers with multiple outlets, separated by piles. The influence of the pile and outlet widths on the flowing mass has been analyzed both in terms of trapping efficiency and kinetic energy reduction. This has been accomplished by using numerical simulations, based on a discrete element solver. The correct mechanism investigation, carried out from a numerical point of view, has first required the implementation of a sliding static friction and a rolling resistance model in the discrete element-based selected code. Results show interesting outcomings: the larger the outlet widths are, the more debris flow breaking and trapping mechanisms are enhanced. Furthemore, in order to guarantee the self-maintainace of the barrier during a multiple surge flow event, the outlet width should be chosen about six times the mean grain radius.