Structural countermeasures such as steel-net flexible barriers are nowadays widely installed in mountainous regions to intercept debris flow and rock avalanches (Fig. 1). The runup height and impact load are the key parameters for the design of debris-flow mitigation structures. However, for flexible debris-resisting structures, due to their elasto-plastic deformation under loading, the runup height and impact load are hard to be estimated by the current theoretical models.

A research team of Prof. SONG Dongri from Institute of Mountain Hazard and Environment, Chinese Academy of Sciences (IMHE-CAS) conducted theoretical analysis on the debris-flow impact issues. They propose general equations for debris impact under vertical jet and momentum jump modes (Fig. 2). Especially, the influence of flow regime and obstacle movement (in the form of a modified Froude number), state of granular material, compressibility (density change), and flow resistance within the jump volume are explicitly considered in the momentum jump model.

Through comparison between model prediction and experimental results, it is found that the vertical jet model prediction agrees well with the physical measurements. While the discrepancy between the momentum jump model and experimental results mainly comes from the inappropriate characterization of the unsteady flow properties (velocity and flow depth). Systematic parametric study demonstrates that the functionality of debris-flow flexible barrier primarily relies on the deflection of barrier, and the state of granular material also affects the impact load of dry granular flows (Fig. 3). These results greatly improve our understanding of debris flow impact and could enhance the design of flexible debris-resisting structures.

This research was supported by the National Natural Science Foundation of China (grant Nos. 42077256, 41925030, and 51809261), the Second Tibetan Plateau Scientific Expedition and Research Program (STEP, grant No. 2019QZKK0904), and the CAS “Light of West China” Program. The research titled “General equations for landslide-debris impact and their application to debris-flow flexible barrier” has been published online in Engineering Geology.

Fig. 1. Deformed flexible barrier in Sichuan Province, China (Image by SONG Dongri)


Fig. 2. Vertical jet mode (left) and Momentum jump mode (right). (Image by SONG Dongri)


Fig. 3. Effects of barrier deflection (left) and state of debris (right) on the model prediction (Image by SONG Dongri).


Contact:

Prof. SONG Dongri

Institute of Mountain Hazards and Environment, Chinese Academy of Sciences

Chengdu, Sichuan, 610041, China

E-mail: drsong@imde.ac.cn