Highwall stability is essential for open-cut mining. In these particular projects, otherwise known as open-pit mining, employs a technique in which rock and minerals are extracted from a borrow pit, or sandbox. For long-term highwall performance, the substance properties that makeup mining sites—or more specifically, the rocks and minerals found within the borrow—should be carefully examined, and the overall highwall safety considered.
What, exactly, are highwalls and highwall mining? Highwall is the unexcavated face of exposed overburden and coal in a surface mine. Additionally, highwall mining is another technique within mining practices sometimes conducted to recover additional coal. Presplit blasting facilitates highwall integrity and highwall safety. Learn more below.
Pit and Quarry notes there are several things that can prove hazardous in mining that involves highwalls. Geological structures can influence highwall stability. Other factors include how strong the rock mass is. Weathering, water inflow, surface drainage, and erosion can make highwalls unstable. Unsafe drilling and blasting procedures can undermine highwalls. Geotechnical data should be reviewed and modified. If this is not complete or the review is done by inexperienced civil engineers or geologists, highwall instability and rock-fall hazards can occur.
Ground instabilities can cause falling rock. Using heavy equipment can crumble highwalls and/or send falling rock onto work areas. Failure to control rockfall with rock-fall fences or barriers may result in injuries and highwall disintegration. If rock debris is not contained or removed, the workplace may become unsafe.
What Can Go Wrong?
Although it may look as stable as Mount Rushmore, by its very nature and purpose, a highwall can collapse without warning. People and machines may be buried in an instant. Highwall safety, therefore, is one of the most important aspects of overall mine safety. Continued testing, oversight, and maintenance will help ensure the integrity of highwalls at any one specific project or location. Working with an experienced team of mining specialists, like American Mine Services, can help mitigate risks and hazards.
If highwalls are being carefully monitored, wall failures can be prevented. Early detection allows mining personnel to plan and execute appropriate actions to prevent wall failures. Early detection saves time, money, and lives.
Who is at Risk?
The people most at risk in highwall problems include operators of mining machinery, surveyors, geologists, and mining engineers.
How to Spot a Potential Hazard
Constant vigilance is required to spot potential dangers and make corrections before a disaster occurs. Mining staff looks for structural weaknesses in the rock. Any movement along these discontinuities can cause the rock to slide or collapse. Signs of structural weakness include:
- A dip or shift in the bedding layers
- Formation of faults or fractures
- Evidence of seepage
- Erosion or seeping in the joints of the rock face
- Sliding of the rock face
- Indications that supporting material has been weakened
- Freezing/thawing cycles have compromised the integrity of the rock
- Falling rock is causing a hazard
- Rock mass failure such as:
- Sliding along a discontinuity.
- Wedge slides in two intersecting discontinuities.
- Buckling or toppling of a rock slab.
- Circular sliding along a failing rock surface.
Thanks to modern technology there are many new ways to monitor highwalls and note warning signs. However, innovations like remote sensing—while useful—should never be used to replace basic geotechnical investigative methods. Instead, they should be used to support the experienced observations of trained engineers and geologists. Attention to warning signs like tension cracks, evidence of loose materials, and unusual water flow is crucial to preventing geo-hazard events.
Highwall surface monitoring technology may include radar systems, robotic systems, and surveying target prisms. Instruments like inclinometers, borehole extensometers, and time domain reflectometers can be used to collect rock displacement data.
Many of the hazards of highwalls in mining can be eliminated by having wise geotechnical planning. Next, safe mine operations need to be in place and followed. To ensure the integrity of highwalls, early detection of failing highwalls is key. Taking preventative measures avoids loss of lives, destruction of expensive equipment, and ensures mines are productive, and repair costs are kept low.
Mining companies have strict rules regarding highwalls. The safety rules are strictly enforced. Best practices include:
- Training employees to recognize and report highwall hazards.
- Conducting thorough examinations before beginning work around highwalls
- Noting changing weather conditions and inspecting highwall for any signs of loose
- ground, cracking, spalling, large potentially hazardous rocks, or sloughing.
- Noting and reporting changes in mining methods or hazardous conditions.
- Making sure loose material is scaled before new work begins.
- Positioning equipment so it swings away from the highwall.
- Ensuring that highwalls are checked frequently by qualified professionals for any
- indication of hazards.
- Making sure slope spotting occurs regularly.
- Monitoring slopes with instruments.
In general, if a single bench or rock ledge is fifty feet high, mining employees are advised to stay fifty feet from the wall. There are no exceptions to this rule. In the case of a double ledge or bench of a hundred feet, it is advised that no one goes nearer than a hundred feet from those benches. Safety measures when working near a highwall are important to consider, learn more here.
If an employee notices movement or spots a discontinuity, he is to report his observation to a superior immediately. There is to be no picking up of any rocks along the highwall.
Overall Highwall Safety
In order to maintain the stability of the highwall, mining companies employ methods that maintain the bank, slope, and wall stability. They check frequently to ensure that places, where people are walking and working, are solid. When benching is indicated, the width and height of the bench are based on what equipment will be used there.
Loose materials in walkways are sloped or stripped ten feet from the highway. The danger of falling materials areas is clearly posted. Potentially falling materials are eliminated as quickly as possible. In hazardous ground conditions, barriers are erected. Before work begins in an area, ground conditions are examined by qualified professionals. Health and safety experts inspect ground conditions after any blasting occurs. Surface area highwalls are examined weekly or more frequently as deemed necessary.
Safety professionals check for:
- Signs of failing highwalls.
- Equipment that is not in safe operating condition.
- Improper use of blasting materials.
- Unsafe practices such as working too near a bad wall, bank undercutting,
- highwall dumping, or unsafe operation of equipment.
- Safety officials ensure that scaling is done reliably.
- Clutter on benches is noted and corrected.
In Mining Industries, Experience Matters
Enterprises like American Mine Services serve the mining industries. They facilitate the design, construction, and evaluation of mines, excavations, and tunnels. The company’s mining contractor professionals are in high demand around the globe. Their many projects include highwall work.
American Mine Services civil engineering professionals provide rock removal from high locations both as a safety measure and so that workers can access mining materials. In their rock removal projects, they use specialized equipment like climbing ropes and crane-supported platforms. The company can also provide blasting, drilling, mesh to avoid falling rock dangers, and ground support. The company is dedicated to ensuring highwall safety for its clients.