Since nearly half of the open pit surface mines in the U.S. produce sand and gravel (aggregate), lots of questions tend to come up about the equipment used in that type of mining. As you can imagine, it takes a range of both mobile and stationary equipment to run a sand and gravel operation. So in this article, we’ll categorize the most common surface mining equipment based on what functions they perform at a sand and gravel mine.
So, what are the most common types of surface mining equipment? The most common types of surface mining equipment fall into these categories:
- Earth Moving / Construction
- Extraction
- Material Hauling / Transportation
- Processing
- Storage / Stockpiling
- Shipping
- Facilities / Maintenance / Operations
Of course, we could simply list the specific pieces of equipment with some pretty pictures. But it’s very important to understand not only what equipment you’re likely to find at a surface mine, but also what functions that equipment performs and why it’s critical to mining operations. So, we’ll go into some detail on each piece of equipment and where it fits into the mining process, and then follow up with some common hazards and safety tips.
Common surface mining equipment at a sand and gravel mine can be categorized as follows:
- Earth Moving / Construction
- Bull Dozers (Dozers)
- Backhoes
- Graders / Scrapers
- Cranes
- Skid Steers
- Extraction
- Front End Loaders (Loaders)
- Power Shovels
- Bucket Wheels
- Draglines
- Dredges
- Material Hauling / Transportation
- Haul Trucks
- In-Pit Conveyors
- Overland Conveyors
- Bins / Hoppers / Feeders
- Processing
- Screens (Washing and Sorting)
- Crushers
- Classifiers
- Storage / Stockpiling
- Stack Conveyors
- (Dozers and Loaders to manage the pile)
- Shipping
- Mix Trucks (Concrete)
- Over-the-road Trucks
- Trains
- Barges
- Facilities / Maintenance / Operations
- Generators
- Fuel Tanks
- Water Trucks
- Personnel Transport Vehicles (Light Trucks)
- Forklifts
Keep in mind that many of these items have multiple purposes, performing a range of functions throughout the mine. While we may mention some equipment in more than one category, our focus is on their primary functions.
Earth Moving / Construction
Dozers – These are heavy, track-mounted vehicles with a wide forward-facing pusher blade at the front. While the blade is somewhat adjustable and can raise and lower, it’s used in a nearly vertical position to push mined material and dislodge layers of overburden.
Primary Functions:
- Clearing overburden
- Managing piles
- Building and maintaining roads
Backhoes – Backhoes can be wheel or track-mounted with an articulated boom and an inward-facing bucket for digging and scaling jobs. This type of equipment can range in size and is often used throughout the mine for a variety of digging functions.
Primary Functions:
- Digging holes, foundations, and trenches
- Clearing overburden debris
- Scaling rock walls (removing dangerous rock fall hazards)
- Loading material into trucks
- Lifting and carrying heavy items
- Breaking rocks with boom attachments
Graders / Scrapers – These are long, low, articulated, wheel-mounted vehicles primarily used during overburden removal and road building. Grading scrapers employ a low blade to level areas, such as roads, by scraping and collecting material from high spots and depositing material in low spots.
Primary functions:
- Leveling uneven areas
- Maintaining and leveling roads
Cranes – Designed specifically to lift, move, and place heavy objects and construction material, cranes can be truck-mounted or stationary.
Primary functions:
- Constructing buildings
- Erecting conveyor and processing structures
- Placing equipment
- Setting large piping and culverts in place
Skid Steers – These are small, often wheel-mounted (but can be track-mounted) vehicles with lifting arms and a variety of attachments that perform a range of activities throughout the mine. This type of vehicle distributes power to left and right wheels independently, making it capable of a zero-radius turn and allowing it to operate in small spaces. Skid steers are valuable for use in small-scale construction and earth-moving functions, operating similar to small dozers and front end loaders.
Primary functions:
- Quickly moving small volumes of overburden and mined material short distances
- Repairing roads and berms
- Assisting in construction
Extraction
Front End Loaders (Loaders) – Loaders are the workhorses of the surface mining industry, capable of excavating large volumes of material very quickly. These wheel-mounted vehicles can have rigid or articulated frames with a wide, deep forward-facing bucket at the front which can be hydraulically raised and lowered. Loaders commonly scoop large volumes of material into the bucket, move the material toward a haul truck, raise the bucket overhead, and dump the material into the bed of the truck.
They may also dump excavated material onto a pile or into a hopper that feeds an in-pit conveyor for transporting material to the processing plant.
Primary functions:
- Moving material, overburden, and large boulders as needed
- Excavating material in the pit
- Loading haul trucks and conveyors from a pile
- Managing the base of a pile
Power Shovels – These are very large, track-mounted digging machines with a forward facing bucket operated by cables (wire ropes rather than hydraulics) and supported by a stick and boom configuration. Power shovels are capable of excavating large volumes material in the bucket (or dipper), pivoting and lifting the dipper over an awaiting haul truck, and releasing the dipper door at he back of the dipper to dump material into the truck bed.
Primary functions:
- Excavating material
- Scaling rock walls
Bucket Wheel Excavators (BWEs) – Enormous track-mounted excavators, these machines are some of the largest excavators in the world. They operate by scooping material from a pit wall with forward-facing buckets mounted to a continuously upward rotating wheel.
Bucket wheels are typically measured in terms of their output in either cubic feet/meters or tons per hour. They can range in capacities from 161 tons per hour to over 70,000 tons per hour.
The largest of these vehicles may have up to 20 buckets and can be over 300 feet (96 meters) tall and over 700 feet (225 meters) long with a bucket diameter of almost 70 feet (21.3 meters).
As the wheel rotates upward, the buckets collect material from the pit wall. As the wheel rotates upward, gravity allows the material in each bucket to successively empty onto an overland conveyor that transports the mined material to the processing plant.
Primary functions:
- Removal of thick layers of unconsolidated overburden
- Continuous excavation of large massive volumes of material
NOTE – While bucket wheels are primarily used in surface coal operations rather than surface sand and gravel, they’re just too cool to exclude from this article.
Draglines – With a structure similar to a crane, draglines employ a boom and hoist mechanism with a cable system that extends (casts) and retracts (drags) a large inward-facing bucket to collect and scoop material. The bucket is cast outward and dragged toward the equipment, collecting material along the way. When full, the bucket is lifted and positioned over a waiting haul truck for transport to the processing plant.
One of the benefits of the dragline is that it’s designed to excavate material at locations below its elevation. So, it can excavate from above or alongside the pit.
Depending mostly on their size, draglines can be wheel-mounted, truck-mounted, or track-mounted.
Primary functions:
- Excavation without needing to be in the pit
- Excavation in wet or underwater locations
- Can be used for dredging
Dredges – Often mounted on floating platforms, dredges perform excavation in bodies of water, commonly rivers, canals, and harbors. Dredges can operate by suction or by mechanical digging devices, such as a dragline. They move sediments, shell, and other material from the bottom of the body of water to deposit it on land or for transport via barge.
Primary functions:
- Underwater or partially underwater excavation
- Clearing or deepening waterways for vessel passage
- Preparing for construction of bridges or moorage
Material Hauling / Transportation
Haul Trucks – These are large trucks with beds that can be raised to dump transported material, often from the pit to a stockpile or processing facility. They can range widely in haul capacities from 40 tons to nearly 500 tons.
Here are some examples of haul capacities and dimensions of haul trucks:
- 146 tons – 19.8 feet tall / 24.81 feet wide / 39.32 feet long
- 250 tons – 23.21 feet tall / 20.06 feet wide / 43.83 feet long
- 320 tons – 48.42 feet tall / 29.75 feet wide / 50.75 feet long
- 400 tons – 51.5 feet tall / 32 feet wide / 49.5 feet long
Primary functions:
- Transporting mined material
- Transporting overburden or waste material
In-Pit Conveyors – Often operating continuously over long distances, these conveyors transport excavated material from the pit to the processing facility.
Primary functions:
- Transporting mined material to a raw material stockpile or directly into the processing facility
Overland Conveyors – Designed to move high volumes, these powerful conveyors may run for miles to transport mined material to the processing facility or to move finished sand and gravel products to rail cars or barge shipping. They’re often uncovered, but may be covered in regions where rainfall can either adversely affect the material or add unwanted weight to a finished product.
Primary functions:
- Transporting high volumes of mined material over long distances
Feeders – Feeders are a specialized type of conveyor used to transport material short distances directly into a process or onto a small pile.
Primary functions:
- Transporting material short distances
Bins and Hoppers – Bins and hoppers are types of containers that accumulate and release material to help manage the flow of material. Material from a loader or conveyor typically enters the open-topped bin or hopper from above, where it can accumulate and be dispensed from the bottom at a controlled rate onto another conveyor.
Primary functions:
- Managing the flow of material onto a conveyor belt
Processing
Processing mined material at a sand and gravel mine is primarily a cleaning, filtering, and sorting process. Material is cleaned of debris, screened and separated size, and stockpiled by material type and dimension.
Grizzlies – A grizzly is the first stage in the screening process, prohibiting oversized rocks and boulders in mined material from entering the processing plant. The grizzly is a set of slanted parallel bars placed a few inches apart. Boulders and rocks too large to pass between the bars will slide down and away from the grizzly. Material rejected by the grizzly may be either crushed or used for other landscaping or erosion control purposes.
Primary functions:
- Prohibiting oversized rocks and boulders from entering the processing plant
Screens (Washing and Sorting) – A series of heavy-duty, gravity fed screening decks of successively decreasing opening sizes are used to separate and sort mined material. As material is fed into the series of screens from the top, each set of screens allows smaller material to pass through to the next screen. Screens may also vibrate forcefully to facilitate material separation and include an array of water sprayers to wash sand, mud, and clay off the stones.
At each level, the material that doesn’t pass through the screen is diverted and transported by conveyor to a stockpile dedicated to that size of material.
Sand and silt are collected at the bottom of the screening and washing process and pumped to the classifier for further processing and sorting of sand.
Primary functions:
- Cleaning and sort mined material
Crushers – Crushers do exactly what they sound like they do. They crush oversized stone to specific sizes for a variety of uses. The two main types are jaw and cone crushers that reduce rock size in different mechanical processes.
Jaw crushers tend to be used as a primary stage crusher to reduce the overall size of stone. They operate by crushing stone between a stationary jaw and an angled moving jaw.
Cone crushers can crush stone to more precise dimensions between a stationary housing and an oscillating cone-shaped mechanism.
Primary functions:
- Reducing the size of rock to specific dimensions
Classifiers – Classifiers are highly specialized filtering mechanisms designed to separate and dewater or dehydrate sand into coarse, medium, and fine grades.
Primary functions:
- Cleaning and separating sand into coarse, medium, and fine grades
Storage / Stockpiling
Stack Conveyors – At an aggregate (sand and gravel) mine, processed material is typically stored as inventory in stockpiles, large piles of individually sized and graded stone, gravel, and sand. Stockpiles can range greatly in size from 15 to more than 75 feet in height.
While stack conveyors rise high above a pile to deposit sorted material onto its stockpile by material type and dimensions, dozers and loaders may operate on or around the pile to ensure stability. Dozers may operate on large piles, pushing and distributing material to manage the pile’s slopes from above. And loaders may manage the base of the pile to remove overhangs or other potentially dangers conditions to avoid a unexpected slide or collapse.
Primary functions:
- Transporting processed material to designated stockpiles
Shipping
After material is fully processed, it can be shipped to customers in a variety of ways. It may satisfy orders for an individual commodity, a mix of commodities, or even as part of another finished product, such as concrete in situations where a concrete batch plant may be located onsite.
Over-the-road Trucks – Common tractor-trailer trucks that operate on civilian roads and highways may pick up and haul materials to regional customers. These open-topped aggregate trailers may be loaded by front end loader or conveyor to an average capacity of about 25 tons.
Railcars – Finished product may be transported by railcar at mines with a rail spur (a secondary rail track that leads to an onsite loading area). Each individual railcar can transport a capacity of about 110 tons of material.
Barges – Large volumes of commodities may be shipped to customers via barges for mines with shipping waterway access. Barges are commonly loaded with material transported by overland conveyor from stockpiles at other locations on the mine site. Each barge is capable of transporting about 1,500 tons of material.
Mix Trucks (Concrete) – When a concrete batch plant (or ready-mix plant) is located onsite, sand and gravel may be used in specific formulations to create concrete to meet a broad range of customer construction needs. Sand and gravel is mixed with cement to produce concrete for transport in mix trucks for local use. Mix trucks transport on average about 8 cubic yards or 16.2 tons of concrete each and must deliver the finished concrete customers within about 1.5hrs.
Primary functions:
- Transporting finished commodities and concrete to customers
Facilities / Maintenance / Operations
Generators – Often diesel-powered, onsite backup generators are stationary power plants designed to provide sufficient power to keep critical processing equipment and lighting operational during a power outage.
Primary functions:
- Providing continuous or temporary electricity to power material processing
Fuel Tanks – With a broad range of equipment and vehicles that run on liquid fuel, mines often have onsite gasoline and diesel fuel tanks for accessible refueling. Fuel tank sizes can range from 500 to 30,000 gallons, depending upon the need.
Primary functions:
- Providing onsite access to fuel
Water Trucks – Water trucks are typically rigid body trucks with a tank mounded on the back and a spray system that may distribute water in front of and behind the truck as it drives. Water trucks perform an important role in reducing airborne silica dust, which can cause long-term and potentially fatal respiratory diseases. Truck tank capacities can vary from 2,000 to 6,400 gallon.
Primary functions:
- Reducing airborne dust from mining and on haul roads
Personnel Transport Vehicles (Light Trucks) – Pickup trucks and other vehicles may be used onsite to transport miners and other personnel to areas where work or inspection is needed at the mine. Because mining terrain can vary greatly, it’s common that wheel chocks are used in every situation when the vehicle is left unattended.
Primary functions:
- Transporting personnel throughout the mine site
Forklifts – Also referred to as powered industrial trucks (PITs), forklifts can come in a very broad range of configurations. Regardless of their design, their primarily used for lifting, transporting, and placing heavy loads at relatively low heights over short distances. Forklifts can be designed for hard surfaces, such as concrete shop floors, or rough terrain and may be powered by gasoline, diesel fuel, propane, or electricity.
With adjustable forward-facing forks, forklifts are specifically designed to lift palletized loads.
Primary functions:
- Lifting, transporting, and placing heavy loads (often palletized)
Common Hazards
Mobile Equipment / Blind Spots – Injuries and fatalities from material handing and powered haulage is very common at surface mines. Mobile mining equipment is often very large and very loud. Drivers may operate the equipment within enclosed cabins with limited visibility and no ability to audibly communicate with pedestrians without use of a radio.
Vehicle blind spots can put workers on foot in dangerous situations. And the larger the vehicle, typically, the larger the blind spot.
Safety Tips:
- Wear high visibility clothing.
- Always give mobile equipment the right of way.
- Stay out of vehicle blind spots at all times.
- Always make eye contact with a driver before moving into an are where vehicles and mobile equipment are operating.
- Communicate with vehicle operators via radio or hand signals to coordinate with the driver prior to approaching any vehicle in operation.
- Ensure the vehicle is completely stopped prior to approaching.
Lifting Equipment – Whether working around a forklift or crane, there is always the potential for rigging to fail and loads to shift unexpectedly creating pinch and crush hazards.
Safety Tips:
- Ensure the equipment and rigging can support the load prior to lifting.
- Never walk under a suspended load.
- Stay a safe distance away from the load while it’s being moved.
- Communicate with the vehicle operator via radio and standard hand signals.
Hydraulics / Block and Crib – When hydraulic equipment such as forklifts, loaders, or dozers are being maintained or repaired, it’s extremely important to ensure that hydraulic components are blocked or cribbed to ensure that they cannot move unexpectedly if hydraulic pressures is suddenly lost.
Safety Tips:
- Immobilize and support hydraulic components prior to working on them.
- Ensure the equipment is de-energized and locked out / tagged out prior to working on.
- Never work under a machine component suspended with only hydraulic power.
Machine Motions and Actions – A range of hazards are present at a mine site in and around equipment that may expose miners to machine motions and actions. Here are some examples of machine hazards and safety tips so you can avoid having fingers, hands, or limbs pinched, crushed, severed, or drawn into mining equipment.
Safety Tips:
- Conveyor Rollers – Conveyors are very powerful machines operating at deceptively high speeds. Workers commonly suffer injuries (sometimes fatal) from trying to clear or repair a conveyor roller in motion. Always stop, de-energize, and lockout/tagout machinery that needs repair or maintenance with direct contact.
- Crushers – Crushers operate using extreme pressure to reduce stone to very small sizes. Never place hands, pry bars, or any tool inside an operating crusher. Always de-energize, lockout, and tagout before performing any work on a crusher.
- Classifiers – Some classifiers, such as screw classifiers, have open tops that expose rotating augers. Never place hands or tools in a classifier that’s in operation. Always de-energize, lockout, and tagout before performing any work on a classifier
- Ejected Material – While not a direct example of machine motions or actions, rocks may either fall from a conveyor or grizzly or be ejected from a crusher. Workers should stay a safe distance from grizzlies and conveyors and wear protective head gear and eyewear at all times.
Related Questions
What buildings and other structures are common to a surface mine?
Most surface mines will have an office and a maintenance shop in addition to a range of other structures onsite. Here are some examples of buildings and structures common at a surface mine:
- Gate and guard station
- Warehouse and storage facilities
- Maintenance shop
- Fuel tanks
- Electrical room
- Water reclamation plant and settling tanks/ponds
- Truck wheel wash
- Truck weigh station
- Concrete ready-mix batch plan
- Rail spur
- Barge loading dock