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Figure 1: Coal covered by overburden at Wilpinjong mine site. |
The Wilpinjong mine site, situated near Mudgee in central NSW, is expected to produce up to 20 tonnes of coal a year. The coal bed sits around 5-7m below the ground, under what is known as overburden (the material that lies above the material to be mined). The top 80% of the overburden is thought to consist of loose sandy clay deposits, while the bottom 20% contains blocky shale deposits. Mining of this site will involve first blasting and then dozing of this overburden to expose the coal bed. In order for the mine to be economically sustainable, it is essential that the removal of this overburden is done efficiently.
Professor Jeff Loughran of James Cook University is working with Brisbane-based company Jaws Buckets and Attachments to model the process of clearing the overburden. Jaws specialises in the manufacture and marketing of ancillary equipment for ground engaging machinery. A particular specialization is dozer blade manufacture. The design of these blades has traditionally been based on empirical observations and trial and error methods. The granular nature of the material being moved makes the modelling of this process very difficult - existing semi-analytical techniques and continuum-based models fail to take into account the complex interactions occurring between both between individual particles and between particles and the machinery. Complex phenomena such as material compression and dilation, cohesion, adhesion and surcharge effects, lifting and remoulding of the cut, and discontinuous flow must also be taken into account.
The aim of this project is to approach this problem using discrete element modelling (DEM) techniques. DEM is a computational technique that treats granular material as a collection of 2D or 3D particles, with appropriate descriptions for particle-particle and particle-facet interactions. It has previously been used by Professor Loughran to model the flow of coal through transfer stations.
The specific objectives of this project are to:
- Simulate dozing of the lower 20 per cent of the Wilpinjong overburden which consists of a mixture of blasted shale and clay deposits with 2D models.
- Calibrate a 3D spherical discrete element model to match the 2D response.
- Apply the models to predict typical dozer performance (power, capacity) with a candidate Jaws blade.
- Diffuse the results to industry through a series of technical presentations.
Method of Modelling
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Figure 2: Modelling of coal dozing with spherical particles |
The blocky shale material will be initially simulated as a panel of rectangular rigid bricks whose physical size will be normally distributed between upper and lower bounds. These bounds will be set to approximately match that found on site following blasting. It will be assumed that the bricks are loosely connected and will be dominated by frictional sliding. The problem will be initially modelled in 2D - that is, the problem will be dealt with as essentially plane strain, but with a small finite depth. Figure 2 shows a 2D DEM model of the problem - essentially the centre plane of the dozer blade is modelled.
The numerical techniques employed to simulate the blocky material as an ensemble of bricks will be computationally intensive. Scale up to full 3D blade configurations will require a numerical mapping from a brick simulation to a sphere simulation. Hence, a series of numerical experiments will be run to estimate the physical properties of a set of spheres which replicate the global response of the brick models. Once calibrated, a detailed set of full industry scale 3D blade models can be run to simulate strip dozing of the blocky Wilpinjong site material.
The final component of this project will involve diffusion of simulation results to industry. At present, there are no published reports on the dozing of blocky materials; hence, there is a strong expectation that the results of the project will also be of high research value and will be able to be published in refereed journals and proceedings.
Contact
Prof Jeff Loughran
School of Engineering, James Cook University
Industry Contact
Barry Koster - Managing Director
Jaws Buckets and Attachments Pty Ltd
Reports
Final Report - August 2007
(2.74 MB PDF)
Project Proposal - November 2006
(275 KB PDF)