Evening seminar on numerical and physical modelling of debris flow, Hong Kong

9 December, 2015 | 19:00 - 20:30

A debris flow can be one of natures most destructive hazards.
A debris flow can be one of natures most destructive hazards.

About this event

The influence of rheological parameters (i.e. yield stress and viscosity) and initial particle arrangements on the flow velocity (hence impact) and shape of final deposition is studied.

Debris flow is one of the most destructive natural hazards, due to its features of high mobility (high velocity and long run-out distance) and impact forces. A typical debris flow event is a multiphase flow, which includes a viscous fluid phase with dynamic surface and solid grains with various particle sizes from fines to boulders. Complex interactions take place between the multiple phases. In practice, the prediction of flow velocity and run-out distance is important for the design of debris-resisting barriers.

To better understand the dynamics of fluid-particle flow, an extended Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) model, with the Volume of Fluid (VOF) method incorporated, is developed and applied to simulate a series of laboratory tests of fluid-particle flows on an inclined small-scale flume. The flume consists of a reservoir on the top and a wider horizontal container at the toe.

The slope is 1m long and 0.2m wide, with adjustable slope angles ranging from 8 to 25 degrees. Semi-transparent liquids (CMC solutions) with varied viscosities are adopted for the calibration of rheological parameters and boundary conditions in the numerical simulations.

Slurries are prepared to represent clay-water mixtures as homogeneous fluids with varied densities and viscosities, and colored glass beads with uniform sizes (0.5cm, 0.8cm, or 1cm) and mixed sizes are added to constitute fluid-particle flows. Velocity profile, flow depth and the final deposition of slurry and particles are measured in the lab tests and systematically studied with the extended CFD-DEM model.

Many relevant mechanisms can be explored based on the experimental and numerical studies. The influence of rheological parameters (i.e. yield stress and viscosity) on the shape of final deposition is studied. It is found that at a given slope angle, either lower yield stress or lower viscosity will increase the frontal velocity at run-out, leading to an elongated fan-shape deposition. On the other hand, high yield stress results in a higher depth gradient as slurry is accumulated at the outlet.

Another interesting finding is that the initial particle arrangements can influence the flow velocity (hence impact) and its final deposition. For instance, particles migrating on the edge of the flow may slow down the flowing mixture, as they increase the basal resistance of the front. And this mitigation of mobility is less significant when the particles are spreading more uniformly in the initial configuration, because there will be more particles left in the bulk of the flow, rather than transported to the edge.

Registration Deadline: 20 Nov 2015

Priority will be given to ICE members, on a first-come-first served basis.


Dr Fiona Kwok

Dr Fiona Kwok is currently an Assistant Professor at the Department of Civil Engineering at the University of Hong Kong. She previously worked as a Geotechnical Engineer at Itasca Consulting Group in Minneapolis and CDM Smith in Los Angeles, USA. She graduated with a PhD in Engineering at the University of Cambridge, UK, in the area of geomechanics and she holds a BEng and MEng degree from Sheffield University, UK and Massachusetts Institute of Technology, USA (MIT) respectively.

Fiona's research focuses on developing a better understanding of soil and rock response by numerical simulation at the particle scale. She is selected as the Future Leader by American Rock Mechanics Association in 2015. She is registered as a Professional Engineer in California, USA.