New simple method for measuring impact force on a flexible barrier from rockfall and debris flow based on large-scale flume tests

Accurate determination of impact loads is of great necessity for safe and economical design of flexible barriers. Nevertheless, measurement of the impact force on a flexible barrier is still an open problem due to the highly deformable flexible net under impact and stress concentration on force transducers. In this study, large-scale flume tests with new design of instrumentation were adopted to validate and optimise existing methods for measuring the impact forces on a flexible barrier. Specifically, single-boulder impact tests were conducted to verify the accuracy of those methods. A debris flow impact test was performed to quantitatively investigate the dynamic behaviour of a flexible barrier under the impact of a debris flow. Thanks to the well-designed instrumentation, the impact force distribution characteristics of a debris flow on a flexible barrier are discovered. During the interaction process, the debris flow first impacted on the bottom area of the flexible net, then the dynamic impact moved up with gradual deposition of debris material. It is found that the impact pressure on the central area of the net is much larger than that on two sides. Therefore, triangular-shaped load distribution is used to optimise the existing methods for measuring the impact force induced by a debris flow. Attributable to the good accuracy and simple instrumentation requirement, a new simple method can be generalized for real-time monitoring of impacts on flexible barriers installed in natural terrains