Standardized Stress Model for Design of Torrential Barriers under Impact by Debris Flow (According to Austrian Standard Regulation 24801)

Abstract

Torrential checkdams with energy dissipating, filtering or deflecting function for debris flows are expected to be subject to extreme dynamic stress that requires the application of high safety standard for design, construction and maintenance. The standardized procedure for checkdam design has been developed from comparative calculations of common debris flow models from engineering practice and calibrated by impact measurements of debris flow laboratory experiments and data available from literature. The model is based on a combined static- dynamic stress approach, additional impacts by single objects like boulders are included. The dynamic area of the dynamic component is derived from a characteristic wetted cross section area of debris flow corresponding to the design event, which can be found at a characteristic cross section upstream of the checkdam. The static load is based on a hydrostatic fluid assumption and calculated analogously to water pressure (with debris flow density) and acts upon total construction height. The dynamic component is calculated according to the momentum equation and acts uniformly distributed on the dynamic impact area right below the overflow section up to a height of maximum 4 meters. The maximum local impact of a single boulder is defined to act on an area of 0.7 x 0.7 meter with 1MN. This new regulation shall guide practitioners for more objectives and save design of checkdams impacted by debris flows.