Load-attenuation mechanisms of flexible barrier subjected to bouldery debris flow impact

Abstract

The impulse load of boulders at the front of debris flows is critical to the design of structural defense measures, which are commonly constructed on hillsides to mitigate landslide risk. Field evidences have demonstrated the capability of some steel flexible barriers in intercepting debris flows with bouldery inclusions. However, there is still a lack of fundamental understanding of the load-attenuation mechanisms of flexible barriers, especially under bouldery debris flow impact. In this study, systematic tests of mono-disperse and bi-disperse bouldery flows impacting an instrumented flexible barrier were conducted using a geotechnical centrifuge. The impact kinematics and barrier responses, such as mobilized structural forces and elongation of cables, were recorded synchronously. The results reveal that the load-attenuation mechanism of flexible barriers for the frontal impact originates from the barrier deflections and extended interaction duration. Only 30% of the frontal momentum is transferred to the flexible barrier. The performance of the flexible barrier is compared with that of a rigid barrier model under identical testing conditions. It is found that the boulder impulse loads on flexible barrier are significantly attenuated, resulting in a “plateau” pattern of the impact time history. The practical implication is that the design of flexible barriers may not demand separate considerations of the bulk debris and individual boulder impact loads. Detailed examination of the state of debris deposited behind the flexible barrier indicates that the static dry debris is close to the active failure state due to the large barrier deflection.