Ground support an ever-evolving component of safe mining

Paul Couto, Associate Geotechnical Engineer, Cartledge Mining and Geotechnics

Numerous contributing factors to ground instability can be influenced by geotechnical engineers to ensure the longevity of mining excavations. Ground support is the final line of defence for geotechnical engineers to ensure safe, stable mines. This article focuses on ground support within the geotechnical fraternity, as it is normally the major focus point following falls of ground or rock burst incidents.

Geotechnical engineers work with natural materials that are not uniform and complex owing to their formation. Geotechnical engineers have numerous methods and tools to assess ground conditions within a mining environment. Major locational differences within the rockmass, during assessments are classified as ground control districts. This is the first complexity of the support design process, which is reliant on inputs from resource and structural geologists.

Secondly, a design is issued based on support units available on the market, within their engineered technical capabilities, and best practices for support design. Due to support units predominantly being engineered products (except natural timber products), the technical capabilities obtained from laboratory testing are used for a support design.

The design is then implemented, which requires numerous operators on different shifts using a variety of machines and equipment to install the support units as per the design and installation procedures. Operator performance is a major contributing factor to support performance as per design.. The implementation process requires a hands-on approach from the geotechnical engineers to ensure that the support is installed per the design layout and requirements. In most support design case studies, this step is critical, but the in most cases the least monitored and managed.

Finally, as mining progresses, stress changes within the rockmass occur, which changes the dynamics of the ground conditions. These might have been correctly estimated because of changing mining layouts during scheduling, however as the mine plan changes so does the stress distribution. These changes could ultimately affect the performance of the support design. An evolving mining operation requires evolving geotechnical processes and systems.

It is pertinent to highlight the small integrated steps of personal involvement from the geotechnical engineer to ensure the desired design outcome is practically achieved. These include, but are not limited to, the full understanding of the support unit’s capabilities in a laboratory and mine environment, the behaviour of the rockmass before and after support installation, the support installation processes, quality control and assurance on the support and most importantly, the efficiencies of the entire process in relation to the mining targets and production requirements.

The practicality and constant review of the implementation of the support design are critical to ensure the success of any support design system. This is the golden key in ensuring that the support design has its best chance of performing as per design based on the available information to the geotechnical engineer at the time.

As geotechnical engineers, we have the tough task of working with conditions that cannot be changed, like geological formations and discontinuities within the rockmass. Changes in the mine layouts to meet production targets are another of many hurdles we, as engineers, must overcome.  Advancements in support units and designs are constantly ongoing, however, the “one size fits all” approach can sometimes be detrimental.

Numerous support suppliers have teamed up or been bought out by major mining machine manufacturers so they can provide the machines and support units as a package to eliminate the challenge of poor support installation. It is always more economical to alter and change support units than it is to change the mining machinery let alone retrain operators on the new machinery. I believe this is a step in the right directions with purpose-built machines for purpose-built support units.

Often support designs and methods are based on what the neighbouring mines are using or have used because it worked there, or the mine personnel have previous knowledge of this support system. Yes, it works and probably works well, but numerous questions need to be answered. Critically, two stand out:

Does it work for OUR ground conditions?

Are there possible improvements to the design that could improve OUR performance?

Engineers must assess the entire process, from design to implementation, followed by constant back analysis. As the mine evolves, so should our systems and processes, as the design process is a guideline for an ever-evolving system. If rigidity to the system is applied, failures will occur.

As miners, our business is to remove economically valuable ore from the ground efficiently to ensure that we can make a safe, sustainable profit. Once we start designing support systems that don’t meet safety and mining efficiencies, then we, as geotechnical engineers, have failed.

When mine planners are challenged with meeting production targets, they alter the mine layouts. They control the controllables. The geological formation and position of the orebody regarding grade cannot be changed. Geology has been there for millions of years and is what we must work with. This is one of the uncontrollable that mining engineers cannot change, even though we would all love too.

The link between geology and mining engineering is a geotechnical engineer. We need to work hand in hand with both professions to ensure a desirable outcome. Geology cannot change, and understanding geology is critical for our designs. This can only be achieved in unison with the geologists. The constant production pressures and unforeseen changes to achieve production targets also need to be understood and managed in line with the mining engineers. So, a question to all geotechnical engineers is:

Why don’t we ensure that our systems and processes on operational levels change in unison with the ever evolving mine to ensure the ultimate designed performance of our last line of defence, ground support?

Having said this, we also need to pay attention to the fact that a hands-on approach during constant changes is required to ensure that the entire value chain produces the desired results. This, working in unison with two other professions, whilst constantly changing and adapting to the change in conditions is a recipe for success in support design.