What Does Ground Control Mean?
In the mining industry, ground control refers to the set of practices used to eliminate or reduce the risks associated with ground movements. Applying ground control methods requires an understanding of geology, rock stress, the properties of various rock types, and ground water.
Safeopedia Explains Ground Control
According to CDC, underground mining has one of the highest fatal injury rates of any US industry, with ground fall and rock bursts being the main causes of death. Thankfully, with better safety standards including control control methods, the number of deaths fell from 85 at the turn of the millennium to 27 in 2018.
Employers should ensure that proper ground control practices are followed and regular inspections are carried out before work begins to prevent any potential hazards. Some hazards that workers can be exposed to include:
- Being struck or crushed by falling materials disloged from the roof or walls of the mine
- Being swamped by steep or high stockpiled gravel or rock that suddenly flows down
Ground Failures in Hard Rock
Creating an opening in a rock mass causes the inherent stresses in the rock to be altered. Two important factors contribute to the failure of a rock mass around an underground opening: the characteristics of the rock and in-situ stress levels.
For openings excavated at shallow levels with jointed rock masses, failures commonly involve falling roof wedges or sidewall sliding.
For excavations that are deep, high-stressed, massive rocks with few joints, and jointed rock masses, failure progresses from brittle spalling and slabbing to a more ductile type of failure.
Rock bursts are particularly seen in hard rock mines and the damage mechanism includes rock bulking due to fracturing, rock ejection due to seismic energy transfer, and rockfall due to seismic shaking.
Some of the factors that affect seismicity include:
- Rock characteristics
- Pre-mining stresses
- The presence of geological structures
- The amount of material extracted
- Mine sequencing
Providing Rock Support
Providing support to rocks in an underground excavation improves stability and maintains its load-bearing capacity. The installation of rock support should be carried out as part of excavation to enhance the rock’s self-supporting aspect.
Different types of rock supports can be installed depending on the extent of the zone of loosened or fractured rock around the excavation. Two main types of rock support are:
- Active rock reinforcement
- Mechanically anchored rock bolts
- Grouted or friction anchored dowels
- Grouted cables
- Passive rock reinforcement
- Steel sets