Disclaimer: this text is issued from the article entitled «Support in underground hard rock mines» written by Evert Hoek, NSERC Industrial Research Professor, Department of Civil Engineering, University of Toronto, Toronto, Canada & David. F. Wood, Senior Engineer, Golder Associates, Vancouver, British Columbia, Canada
Rock support systems in underground mining are techniques and assemblies of tools and materials used to stabilize the rock around mine openings such as tunnels, stopes, and shafts to ensure structural stability and worker safety. Their primary objective is to maintain the strength of the rock mass while mining operations create cavities, preventing rock falls and controlling deformation in excavated areas.
The choice of the type of support installed in a particular underground excavation depends upon the extent of the zone of loosened or fractured rock surrounding that excavation. There are two main types of rock support systems: active and passive systems.
Active rock reinforcement
Underground mines use two principal types of rock reinforcement – tensioned mechanically anchored rockbolts and untensioned grouted or friction anchored dowels. It is important that the different ways in which this reinforcing systems work is fully understood and a brief discussion on this subject is given on the pages which follow.
Mechanically anchored rockbolts
Mechanically anchored rockbolts are the oldest and most widely used rock reinforcement method in Canadian underground mining. They work best in hard rock, where expansion shell anchors can grip well, allowing bolts to be tensioned to near their full strength. These bolts are particularly effective for stabilizing loose rock blocks near excavation surfaces caused by joints or poor blasting. Tensioning the bolts (typically to 70% of their breaking load) helps interlock the rock and prevent further loosening. Mesh is often added to catch smaller fragments. However, mechanically anchored bolts have drawbacks: they may lose tension over time due to blasting vibrations, in corrosive environments (e.g., massive sulphides), unprotected bolts may rust quickly and fail within a year. Good blasting and proper scaling can reduce the need for such support by minimizing the creation of loose rock.
Grouted or friction anchored dowels
A key disadvantage of mechanically anchored rockbolts is that if the anchor slips or the bolt fails, it loses all its support capacity, risking rockfall. In contrast, fully grouted or friction-anchored dowels maintain some support even if slippage or faceplate failure occurs, as the remaining dowel stays anchored.
However, dowels cannot be tensioned, so they must be installed before significant rock movement. This can actually be beneficial: when dowels are installed close to the advancing excavation face, before much movement occurs, they help retain the natural interlocking of the rock mass, which is crucial for its self-supporting strength. This approach, combined with careful blasting, allows dowels to effectively support a broader range of ground conditions than mechanically anchored bolts.
Grouted cables
Grouted cables are increasingly used as an alternative to rockbolts and dowels in mining due to their versatility, especially in areas with low headroom. They can be installed without tensioning or be tensioned prior to grouting, using modern simplified techniques. Grouted cables are highly effective for reinforcing ore or waste passes, as even when exposed sections wear down, the embedded portions continue to provide support.
Their flexibility allows the rock to move slightly without losing significant strength. In cut-and-fill mining, long cables can be pre-installed and progressively shortened as mining advances, with remaining sections naturally tensioned by the rock’s movement. Once the cables are reduced to around 2 meters, a new set overlaps to continue support.
Grouted cables are also valuable for stabilizing large or unstable rock zones, such as near faults, before stoping begins. Beyond mining, they are widely used in civil engineering for anchoring heavy structures and supporting large underground openings where traditional bolts are insufficient.
Passive rock support
In order to complement the reinforcement achieved using dowels, bolts or cables, rock support often includes the use of mesh, straps, shotcrete or steel sets. Each of these rock support elements is reviewed briefly in the notes which follow.
Mesh
A general guideline for rockbolt spacing is to place faceplates about three times the average spacing of natural weakness planes (e.g., joints, bedding planes) in the rock. For example, if rock blocks average 0.5 m in size, bolts should be spaced about 1.5 m apart with a length of around 3 m.
However, if joint spacing is very tight—say, 100 mm—it becomes impractical to install bolts every 300 mm. In such cases, mesh is used to retain small blocks between the bolts.
Two types of mesh are commonly used:
- Chainlink mesh: Very strong and flexible, but hard to install and incompatible with shotcrete due to air pocket issues.
- Weldmesh: Rigid, easy to install, and compatible with shotcrete, as its structure allows better adhesion and penetration.
Straps
When the rock mass surrounding an underground opening is very slabby, in other words, most of the weakness planes run in one direction, the strength of the rock mass is much higher in the direction of the weakness planes than it is across these planes. Under these circumstances, straps may be a more effective means of face support than mesh. These straps are placed between rockbolts and run across the planes of weakness. Straps placed parallel to the planes of weakness are generally a waste of money.
Shotcrete
While shotcrete is widely used in civil engineering, it is underutilized in mining, mainly due to logistical challenges and traditional attitudes. However, its benefits as a surface support system are now being increasingly recognized. Like mesh, shotcrete prevents small rock pieces from unraveling, maintaining rock mass interlock and stability. It is stronger, corrosion-resistant, and particularly useful in areas requiring long-term stability, such as ramps and haulages.
Modern steel fibre-reinforced microsilica shotcrete has replaced older, complex layered systems. This new form is applied in a single pass, reducing time and improving efficiency. With extensive research behind shotcrete mix design, the quality now depends largely on the operator’s ability to control water, air, and material flow to ensure consistent compaction, minimal rebound, and good coverage.
Shotcrete gains strength over time, allowing it to be used shortly after excavation. It is resilient to nearby blasting and performs well under progressive loading. Accelerators (up to 5%) are used to boost early strength, especially in high-stress zones, though careful design is required to avoid overstressing.
Additives like microsilica reduce rebound and improve application in wet or weak zones. Deformed steel fibres enhance post-crack strength, making the system more robust after initial cracking. Early issues with fibre handling and equipment wear have mostly been resolved, and fibre addition is now standard without causing major operational problems.
