Numerical modelling of system performance of debris barriers using the discrete element method

A debris flow is a torrential flow of a mixture of water, mud and debris that suddenly pushes ahead with a vanguard of huge boulders. As an important type of geo-hazard, they are a globally relevant problem posing significant risk to life and infrastructure, particularly in developing countries. In extreme cases, debris flows can lead to very high death tolls and economic cost: in the 1999 debris flows and flash floods in Vargas, Venezuela, an estimated 19,000 people died and the total damage was estimated at $1.9 billion.
Mitigation measures, such as debris barriers, are therefore needed, to reduce the threat posed by debris flows. Barriers can be dam-like (rigid and generally impermeable), or mesh-based (deformable and permeable). In both cases, evaluating the system performance of the barrier requires predicting the mass impacting the barrier, and then modelling the debris flow–barrier interaction. This is simpler, though still difficult, for rigid impermeable barriers, with rheological models often used to model the debris flow impact on the barrier. For deformable permeable barriers, the interaction is much more complex, both because the barrier deforms and because the barrier separates the different phases constituting the flow.
This project offers an opportunity to make advances that will save lives, by understanding the way in which debris flows interact with barriers. This is necessary to be able to develop minimum quality requirements and to guarantee system performance for barriers, which are key issues both for manufacturers and for end users of such protection systems.

This project will consider the performance of deformable permeable debris barriers, trying to address the following questions:
• What is the impact mass? (modelling the propagation of debris flows)
• How to characterise the impact dynamics and the energy dissipation mechanisms? (modelling the debris flow–barrier interaction)
• What is the system performance? (determining the ability of the barrier to stop the debris)

The project is based on the use of the Discrete Element Method (DEM) for modelling the propagation of debris flows and their impact on flexible barriers. The first part of the project involves testing different modelling approaches for the flexible barrier under impact from a single large boulder, using DEM and the Finite Element Method (FEM). The quality of the results, numerical performance, and usability of each approach will be determined. The modelling of the debris flow propagation is investigated separately, to identify the modelling choices and parameters needed for modelling realistic debris flows (initially dry ones, with water being considered in a second stage). The possibility to consider detailed topographic information to model more of the debris flow propagation, and even its initiation, will also be investigated. The interaction of debris and barrier will then be modelled, to determine the structural dynamic loading of the barrier. The target is to evaluate the system performance (also taking into account anchoring options for the barrier) to provide evidence-based design guidelines aiming to guarantee a level of system performance.
Numerical results obtained throughout the project will be compared with data from the literature. In addition, very detailed experimental data will be obtained through an existing collaboration with the group of Prof. Jian-Hua Yin at the Hong Kong Polytechnic University, who will provide experimental results from an instrumented large-scale physical model facility for testing debris flows and debris barriers (10.5m length, 8.5m height, 8m³ debris volume). This will provide a unique opportunity to validate the models used to describe both the debris flow and the debris barrier behaviour.

A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills. Project specific training will be provided on the Discrete Element Method and on the mechanics of granular materials, based on scientific training materials developed in the PARDEM and T-MAPPP EU Initial Training Networks. Further training will also be provided on technological aspects of debris barriers.

Candidates should have strong academic background (i.e. first or upper second class degree, Masters Degree or equivalent), with a background in Civil or Mechanical Engineering, Engineering Science, Mechanics, Applied Physics or a related discipline. A good understanding of granular materials and/or engineering numerical simulations would be advantageous.