Experimental study on the performance characteristics of viscous debris flows with a grid-type dam for debris flow hazards mitigation

A grid-type dam, which is an open-type dam, is an active structural countermeasure employed to mitigate the potential risk from and damage by debris flows. Although grid-type dams are widely used to control water-stone flows in Japan and other countries, they are not used in China due to the lack of knowledge regarding their suitability for controlling viscous debris flows. Viscous debris flows with a wide grain-size distribution are common in southwestern China. Using the known characteristics of such debris flows, we performed a series of flume tests designed to take three main factors into account: debris flow bulk density, channel gradient, and grid size. The goal of these tests was to investigate the dynamic processes and the performance of a grid-type dam in controlling viscous debris flows. The results of our analysis indicated that grid-type dams could effectively trap and regulate viscous debris flows. The sediment storage rate increased with the bulk density, concomitantly with a decrease in the reduction rate of bulk density and peak discharge; however, all parameters decreased with grid opening size. Additionally, based on theoretical analyses and experimental results, dimensionless relationship equations for grid-type dams were established that considered sediment storage rate, bulk density reduction rate, and peak discharge reduction rate. These equations make it possible to predict the effectiveness of controlling transported sediment using a grid-type dam. Moreover, they represent a reference for designing grid opening size, which could provide technical support for further practical engineering. Finally, we applied these equations to a case study of the Sandaoqiao Gully, where they were shown to be effective as a guideline in designing a grid-type dam to control a viscous debris flow.