Introduction

The first phase of the Ground Support Systems Optimisation (GSSO 1) research project was initiated in 2013. Among the main outcomes of the project was the production of the comprehensive book Ground Support for underground mines, a new empirical design approach to replace the poorly used civil engineering Grimstad and Barton (1993) ground support design chart, as well as initial work towards developing methods for probabilistic ground support design in mines.

The second phase (GSSO 2) began in September 2018 and was completed in September 2021. The project addressed two themes: ground support in extreme conditions, and the development of probabilistic design methods. Significant progress has been achieved towards advancing technologies within both themes. For example, we have constructed an extensive and high quality database of rockburst damage (over 2,000 linear metres of mapped rockburst damage), which will continue to expand with the ongoing use of the mXrap Damage Mapping app (also developed as part of GSSO 2). This will offer a unique opportunity to improve existing empirical methods for dynamic ground support design. Significant progress was made towards developing a robust ground support systems ‘survivability matrix’, as a function of seismic event magnitude and distance.

Shotcrete has been used in mining applications for more than three decades, but we still rely on guidelines from civil tunnelling engineering (Grimstad & Barton 1993) for designing shotcrete-based ground support systems.
In GSSO 2, a comprehensive parametric study was completed, investigating for the first time the interaction between fibre-reinforced shotcrete, rock reinforcement, and rock mass deformation mechanisms in a mining context. One significant finding was that in mining applications, better deformation control can generally be achieved when using fibre-reinforced shotcrete for filling the cavities in the drive’s profile, rather than applying a uniform layer thickness. As a result, a new understanding on how to optimise shotcrete applications to mining excavation is currently under development. This will open significant opportunities for optimising shotcrete-based ground support systems.

An increasing number of practitioners in the mining industry have recognised that probabilistic-based ground support design is the way of the future. Not only does it account for the many uncertainties associated with key input parameters and design assumptions, but it also enables engineering decisions to be taken based on rigorous statistical analyses. In GSSO 2, a series of user-friendly apps enabling the use of discrete fracture network (DFN) technology was developed. This is arguably the first practical tool easily accessible to mine site personnel for probabilistic ground support design in mining, and it opens a new world of possibilities towards strategic risk-based design of ground support systems in mines.

The need for GSSO 3

Ground support remains one of the largest costs of development mining. At the same time, it is the main means of reducing rockfall/rockburst risk in underground mines. The challenge to the mining industry lies in keeping these risks as low as practicable, despite the increasing hazard associated with deepening of mineral resources. Furthermore, controlling the costs and cycle time of installing efficient ground support systems remains at the forefront of most mining operations’ priorities.

The ACG, and previous sponsors of GSSO projects, identified four key gaps/opportunities where current ground support research warrants continuation from the previous GSSO phases, in order to achieve step changes in ground support practices. It is proposed that the following will form the four main research topics for GSSO 3:

  1. In situ dynamic testing of ground support using blasting.
  2. Development of empirical dynamic ground support design guidelines.
  3. Application of probabilistic ground support design tools.
  4. Optimisation of fibre-reinforced shotcrete based systems in underground mines.

The continuation of university-based research initiatives such as GSSO has important benefits to the mining industry. Given the current shortage of specialists in the field of mining geomechanics, it is critically important that industry will continue to support research projects that contribute to the development of postgraduate students. It is envisaged that GSSO 3 will support three PhD students.

Finally, the GSSO research project offers a unique collaboration between mining companies, ground support suppliers, and Canadian and Australian universities, and such an important collaboration is deemed worth continuing.

GSSO 3 research proposal

A research proposal was prepared based on a widely distributed discussion document, and incorporates feedback obtained from a comprehensive industry consultation process involving two workshops reaching geomechanics practitioners worldwide. The proposal includes four distinct sub-projects.

Sub-project #1: In situ dynamic testing of ground support using blasting

Sub-project #1 objectives

The main objective of the proposed in situ dynamic testing program using blasting as a dynamic source is to quantify the energy and displacement capacity of 12 ground support systems commonly used in rockburst-prone conditions in mines.

The following secondary objectives will also be pursued:

  • Quantify the level of ground motion (ppv) the 12 support systems tested can sustain.
  • Determine what proportion of the dynamic load is absorbed by the reinforcement compared to surface support.
  • Investigate the weakest links of the 12 support systems.
  • Quantify the effect of increasing bolt density on the capacity of the support systems tested.
  • Investigate whether it is possible to use the dynamic capacity of individual support elements from drop testing to infer the dynamic capacity of support systems.
  • Better understand assumptions behind the Canadian Rockburst Handbook design approach.

Sub-project #2: Development of an empirical dynamic ground support design method

Sub-project #2 objectives

The main objective of this sub-project will be to advance the development of the ground support system survivability matrix and, in particular, use a comprehensive high quality rockburst damage database to achieve an in depth understanding of the performance reliability of different support systems subjected to a wide range of dynamic loading.

A secondary objective will be to expand the database of rockburst damage built during GSSO 2. This expansion will aim at tripling the number of mines providing rockburst damage data and expand rockburst damage data involving shotcrete and different dynamic reinforcement.

The expanded database will also be used to investigate other empirical approaches for dynamic ground support design.

Sub-project #3: Application of probabilistic ground support design tools

Sub-project #3 objectives

The primary objective of Sub-project #3 is to implement probabilistic ground support design techniques at sponsors’ sites, based on a series of mXrap apps developed during GSSO 2. This will involve refinement and optimisation of the apps as required by sponsors.

For the block stability analysis approach, an important part of the implementation will be to work with sponsors’ sites to build and calibrate DFNs for the main structural domains of each sponsor’s mine to enable easy and rapid use of the app towards ground support optimisation at sponsors’ sites. This will be accompanied with training material covering the necessary theoretical background and software training with walkthrough examples.

Other objectives will include to improve automation in the data input and DFN calibration processes. More complicated block geometries, as well as pseudo dynamic loading functionalities, will be added to the apps.

For the rock mass modelling approach, a simple linear elastic stress solver will be implemented into mXrap to streamline the process of evaluating the probability of the depth of yielding.

Sub-project #4: Optimisation of shotcrete in underground mines

Sub-project #4 objectives

The primary objective of Sub-project #4 is to develop new specifications for fibre-reinforced shotcrete in mining, given the cavity filling strategy is implemented. The specifications will include shotcrete uniaxial compressive strength (UCS) and fibre dosage as a function of the rock mass quality (block size), intact rock strength (UCS), bolt spacing, and coverage of the lower walls.

Secondary objectives will include:

  • Proving the cavity filling strategy and modelling results from GSSO 2 based on a simple physical model to be tested in a laboratory.
  • Investigating whether there are benefits in the cavity filling strategy for foliated ground.
  • Tactical ground support design: adapting bolting standards to match ’shotcrete plugs’.

The ACG is seeking approximately AUD2.2M industry support over a period of four years to complete the project.

Reference

Grimstad, E & Barton, N 1993, ‘Updating the Q-system for NMT’, in C Kompen, SL Opsahl & SL Berg (eds), Proceedings of the International Symposium on Sprayed Concrete, Norwegian Concrete Association, Oslo, p. 21.

Sponsors

Financial and in-kind support will be provided by the following industry sponsors:

  • Agnico Eagle
  • BHP Nickel West
  • Canadian Malartic
  • DSI Underground
  • Evolution Mining
  • Geobrugg
  • Gold Fields Australia
  • Jennmar
  • MMG Limited
  • Normet
  • OZ Minerals
  • Rio Tinto
  • Sika
  • Vale Sudbury Operations

Researchers

Professor Yves Potvin, Project Manager
Associate Professor Johan Wesseloo
Dr Daniel Cumming-Potvin
Ms Denisha Sewnun
Mr Joseph Mbenza
Dr Matthew Heinsen Egan
PhD students

To obtain a copy of the project proposal, please contact the ACG:

Australian Centre for Geomechanics
The University of Western Australia (M600)
35 Stirling Highway
Crawley WA 6009
Australia
+61 8 6488 3300

Christine Neskudla
christine.neskudla@uwa.edu.au