Verification method for a protective structure supported by cables as a countermeasure against bouldery debris flow

In recent years, debris flows in small streams have increasingly caused the damage of communities in Japan. To mitigate these hazards, the Japanese government has introduced countermeasures to prevent debris flow damage. Steel pipe protective structure supported by cables (hereinafter called “cable dam”) has been proposed as a new protective measure for small stream channels. However, no case studies of cable dam currently exist, and its design method has not yet been developed. This study presents a rigorous verification foundation for cable dam designs, uniquely incorporating two factors: (1) dynamic load distribution and (2) frictional effects. The proposed verification method based on experimental and analytical approaches of cable dams offers a significant improvement. First, experiments were conducted to examine the debris flow load acting on a cable dam and the load acting on a cable directly. The experiment utilized an channel flume and a cable dam supported by a single cable. The results showed that the debris flow load on the proposed structure was constant regardless of the structure mass, while the load on the cable decreased as a cable dam mass increased. This decrease is attributed to the frictional effects between the cable dam behavior and the bottom base. Furthermore, it was found that the load on the cable can be estimated if both the acting load and frictional forces on the cable dam are known. Second, a numerical replicating the experimental setup was performed to develop a debris flow load model applicable to the cable dam design. The model represents a dynamic load, where the point of hydrodynamic force application shifts upward over time. The simulation closely matched the experimental results, highlighting the impact of dam friction on the cable load. These findings demonstrate that the dynamic load distribution model, accounting for cable dam friction, is applicable to the design of cable dams.