The principal objectives of this research are to investigate the flow mechanisms of debris flows. This research consists of four major components: dimensional analysis of natural debris flows, development of a theoretical model for confined granular flows, flume model tests for investigating debris flow mobility, and a particulate study of dry granular flows by the Discrete Element Method (DEM)....[ Read more ]

The principal objectives of this research are to investigate the flow mechanisms of debris flows. This research consists of four major components: dimensional analysis of natural debris flows, development of a theoretical model for confined granular flows, flume model tests for investigating debris flow mobility, and a particulate study of dry granular flows by the Discrete Element Method (DEM).

Long-term observation of natural debris flows has been conducted in Dongchun, Yunnan province of China; the rheological properties and flow mechanisms were analyzed by dimensional analysis. Pore fluid viscosity, particle contact friction and collisions were found to influence the debris flows significantly.

A modified Savage-Hutter model for confined granular flows was developed, which can analyze channel confinement fundamentally and reproduce the evolution of the granular flows in the flume model tests well. The mathematical model further proved that the contact friction between solid particles is shear rate dependent for dense granular flows.

To verify the analytical model and to study different influence factors for debris flow mobility, flume model tests were conducted. Critical water contents were found to exist for different solid-water mixtures. The dry granular flows were significantly affected by the fine particle content and the mobility increased roughly in proportion to the logarithm of flow mass. By using a high speed camera, the reverse segregation in the deposition process was clearly observed.

Through the particulate study of granular flows in PFC^3D (Particulate Flow Code in Three Dimensions), the shear rate was found to develop along the travel direction. Specifically, it was enhanced in the front head and at the rear end. Based on the Savage number and granular temperature, granular flows can be classified into three different regimes (contact friction dominated flow, transitional flows and collision dominated flows). A dimensionless contact force can be derived to take particle size, dispersive stress and contact normal stress into consideration to explain the fundamental mechanisms of reverse segregation reasonably well.