The South African gold mining industry has recently experienced a number of rock burst accidents. This has resulted in renewed focus on methods that can be used to mitigate this risk.
The South African gold mines are the deepest in the world and a large number of seismic events are recorded on a routine basis.
AUTHOR: Professor Francois Malan, Director: Mining Resilience Research Centre, Mining Engineering Department, University of Pretoria
This article first appeared in Mining Review Africa Issue 7 2018
The research programmes of the 1960’s and 1970’s, mostly led by the Chamber of Mines Research Organisation (COMRO) and in later years by CSIR Miningtek, have resulted in a number of innovative developments to assist with the creation of a safe mining environment.
These developments include numerical techniques based on elastic theory to simulate the stress concentrations in irregular tabular mining layouts, yieldable support systems with energy-absorbing capabilities and mining strategies such as preconditioning and centralised blasting to control the seismicity.
Not all of these techniques are perfect.
The commonly used assumption of an elastic rock mass at great depth and the design criteria associated with this, such as energy release rate, are only first order assumptions.
Extensive fracturing of the rock mass is encountered underground on some reef horizons and this affects the behaviour of the rock mass.
Improved mine design may hold the key
Part of the research currently conducted at the University of Pretoria’s Department of Mining Engineering is to investigate the development of improved design criteria for deep tabular layouts, which can be used to assess and to mitigate the risk of rock bursts.
Such criteria will be of particular interest for mining companies targeting remnant areas, as this may prolong the life of a number of older shafts.
A key area of the research is the use of limit equilibrium models in boundary element codes to simulate the fracturing of the rock mass on the reef plane.
This approach has allowed the effect of parameters, such as mining rate, to be investigated for the first time.
The model also computes energy dissipation in the fracture zone near the edges of the excavations.
This allows the released energy to be used as a measure of expected seismic activity and addresses a number of the weaknesses in the traditional usage of the energy release criterion for the design of deep gold mine layouts.
A key tool used for these studies is the TEXAN numerical modelling code developed by Professor John Napier, who is an Extraordinary Professor in the Department.
Gold mining company Harmony Gold is currently sponsoring the Harmony Gold Research Chair in Rock Engineering and Numerical Modelling in the Department and the current focus of the work is to examine the effect of mining rate on excavation stability.
The limit equilibrium model appears to have the ability to simulate the time-dependent behaviour of the rock mass and is used for these mining rate studies.
The rock engineering research team is currently led by Professor Francois Malan, who is also the Director of the Mining Resilience Research Centre (MRRC) in the Department.
The MRRC aims to assist the mining industry by contributing towards practically implementable solutions in safety, health, environment, social responsibility and community management.
The MRRC is well suited to enable multi-disciplinary collaboration between various Faculties and related departments at the University of Pretoria.
This allows the creation of large pools of experts to be involved with and to solve the many complex mining problems that currently exist.
Outstanding research achievements
The Department has received several accolades in the past year for the quality of the research conducted. Professor Napier has been elected as a foreign member of the National Academy of Engineering in the United States.
There are currently only 262 foreign members elected to this Academy.
In 2017, Professor Malan presented the International Society of Rock Mechanics (ISRM) Franklin Lecture.
The purpose of this lecture is to recognise ISRM members who have made a significant contribution to rock mechanics.
Also noteworthy is the recent award to PhD student, Dr Michael du Plessis, of the prestigious ISRM Rocha Medal for 2018.
This is an international award presented for the best PhD in Rock Mechanics for that particular year.
Du Plessis will receive this award at the ISRM Symposium in Singapore to be held in November 2018.
His supervisor, Prof Malan, was also awarded the Rocha Medal in 2001 and was awarded the ISRM Franklin Medal in 2017.
Since its inception in 1961 the Department of Mining Engineering at the University of Pretoria has contributed hugely to the mining industry by providing it with world-class mining engineering leaders.
The current Head of Department is Professor Ronny Webber-Youngman.
Under his leadership, the Department has established a sound foundation for future development of its teaching, research and community service.
A key initiative launched in recent years was the establishment of the Kumba Virtual Reality (VR) Centre.
The VR Centre strives to be an innovative resource for bringing real-world scenarios to learners to enhance their exposure to their chosen industry as well as allowing technical and other practitioners to simulate plans and designs in a risk-free environment with minimal time and resource allocation.
There are numerous operational benefits to be gained from interpreting and portraying actual data in the high-quality and realistic visual format offered by the VR Centre.
ABOUT THE AUTHOR
Professor Francois Malan started his career at the Chamber of Mines Research Organisation (COMRO) in 1993 and conducted research into the numerical modelling of rock mass behaviour.
He also gained experience on the laboratory testing of rock and the use of geotechnical instrumentation.
His particular interest during this period was the time-dependent behaviour of the rock in deep level mines.
He used this as a topic for his PhD thesis and this later won him the ISRM Rocha Medal (best PhD in the World in 2001).
COMRO was taken over by the CSIR as the Miningtek Division in 1993. Prof Malan started as principal researcher, and later became project manager, Research Area Manager and Programme Manager of the Rock Engineering Programme. During this period, he successfully completed a number of SIMRAC projects.
To gain more experience in industry, Prof Malan joined Groundwork Consulting in 2004. There he gained extensive experience in the testing of support units, support design, pillar monitoring and the layout design of bord and pillar mining.
In 2011, he was appointed as Senior Consultant Rock Engineering of Gold Fields in South Africa. His function was to oversee the entire rock engineering function of Gold Fields and this gave him significant experience in the layout and support design of deep level stopes.
When the Gold Fields operations were taken over by Sibanye (now Sibanye-Stillwater) in 2013, Prof Malan remained with Sibanye and continued with his duties as Senior Consultant Rock Engineering.
In 2018, Prof Malan joined the University of Pretoria as Associate Professor. He currently has more than 70 publications (conference and journals papers as well as books) to his name and has written a large number of research and consultancy reports.