• What is Highwall Mining?

    Highwall mining is a hybrid of surface and underground mining technologies. Surface mines typically continue to remove overburden to gain access to the coal until they reach an economical limit where the cost of overburden removal exceeds the value of the coal. This point in the life of a surface mine is referred to as the final highwall. A highwall mining system is set up at the face of the final highwall. A continuous miner which is typically used in underground mines begins mining its way under the mountain. The coal is transported from the back of the miner to the surface on conveyance system that is incrementally increased in length as the miner advances into the mountain. The mining machinery is operated remotely from an operator’s cab that is located on the surface. The tunnel is mined the maximum distance allowed by equipment design and geological conditions. At that point, the equipment retracts from the hole and moves down the highwall and drives another entry parallel to the one it just mined.

  • Reserves

    What is the minimum mining height?

    30 inches – this is accomplished with a Bucyrus 25MO Miner with a 28 inch cutting head. However, 6 inches of clearance is recommended so that hole depths of 800- 1,000 feet can be attained on a regular basis.

    What is the maximum mining height?

    28 ft. and this would be mined in two passes. The upper half would be mined first and the system would be completely retreated and it would then ramp down and mine the bottom half.

    What is the required minimum interburden?

    2.5 times the seam heights

  • Mining Conditions

    What is your recommended sequence for multiple seam mining?

    There are trade-offs associated with both bottom up and top down and these tradeoffs need to be taken into context relative to the overall mine plan, geologic conditions and historic mining results. Our experience has been that we have seen slightly more bottom up than top down decisions.

    Is it possible to mine through auger holes?

    Yes, however, one can expect lower productivity and less reserve recovery. Generally, it is better to take the additional cuts necessary to eliminate the auger holes. The trade off for taking the additional cut is that additional mine permits are required.

    Is it possible to leave predetermined amounts of roof and floor coal?

    Absolutely. ADDCAR systems are equipped with gamma detection technologies that sense the differing emission rates of coal and rock. This differential is used to calculate the distance between the coal and rock interface in the roof and floor. This information is transmitted to the operator real time so that he can precisely control the miner head to leave the prescribed amount of roof and/or floor coal. As a cross check, video cameras mounted on the head and loading pan of the miner provide a visual aid for keeping the machine in seam

  • Mine Plan

    How much wall per month do I need to create to keep my highwall miner fully utilised?

    Several factors contribute to this calculation – however, a good rule of thumb is that 1,000 ft. of wall per month will be consumed by the highwall miner. To calculate the required amount of wall for your operation, go to Highwall Calculator and input your mine specific parameters and the wall required for your operation will be automatically calculated.

    What are the hole depths for various mining heights?

    Mining Height (in.)Typical Depth (ft.)Max Dept (ft.)
    32 – 488001,200
    48 – 841,0001,300
    Plus 841,2001,600

    What is a typical monthly output for varying mining heights?

    Mining Height (in.)Typical Tons Per MonthMax Tons Per Month
    32 – 4840,00080,000
    48 – 84110,000180,000
    Plus 84160,000300,000

    What is a typical rate of advance?

    100 – 150 feet per hour.

    What is the foot print of the machine and what is the minimum bench width?

    The footprint of the Broad Bench Machine is 90 ft. and the Narrow Bench Machine is 45 ft. You will need an additional 20 ft. if you want to drive small vehicles around the back (recommended). You will need 40 ft. if you want to drive haul trucks around the back.

    What is the cutting width?

    11.5 ft.

    What is a barrier pillar?

    A barrier pillar is left in place on regular intervals to prevent a collapse in the previously mined areas from migrating into the active work area.

    What is the typical width of a barrier pillar?

    6 – 12 ft.

    What is the typical width of a web pillar?

    5 – 8 ft.

    How are pillar widths determined?

    Pillar widths are determined via a geotechnical analysis. Inputs into the calculations include the strengths of the overlying strata, coal seam and floor, the depth of the overburden, the width and height of the planned entries, the type of materials in the roof and floor and the impact of any pre existing mining in the area.

    What is the spacing on barrier pillars?

    Typically, 10 holes are mined and the 11th one is skipped and this creates the barrier pillar. In really competent roof, as many as 20 holes may be mined before one skips a hole.

    How much of a barrier pillar has to be left between highwall entries and underground mine workings?

    At least 50 ft.

    What is it problematic to mine the point on a mountain?

    The point on a mountain narrows and reduces the lateral support required to hold the entry roof. Stress concentrations sometimes accumulate on points as well and the stratigraphy on a point may not be as consistent as it is in the body of the mountain.

    What is a typical crew size?

    An ADDCAR crew make up is presented below. Companies who opt to buy our system sometimes opt to operate with fewer employees.

    Miner Operator1
    Endloader Operator1
    General Labourer2

    What is typical tons per employee hour?


    What is the typical shift?

    12 hours – It is important to move the mining system in and out of the hole as quickly as possible and to not let the equipment set idle in the hole. The best way to accomplish this is to work two shifts per day – 12 hours. Production is typically 4 – 6 days per week and one day is reserved for preventive maintenance.

  • Equipment

    What incoming power is required?

    In the western coal seams (typically thicker), 7200 volts is used. In the eastern coal seams (typically thinner), 4160 volts is used.

    What is the size of the belt?

    48 inches

    What is the approximate tons per hour on the continuous miners?

    The tons per hour for the continuous miners is limited to the carrying capacity of the ADDCARs attached to it. Typically, larger ADDCAR systems are attached to the larger miners. The through put capacity for a system attached to each of the miners is presented below:

    Joy 14 CM 15900 – 1,300 tons per hour
    Bucyrus 25MO400 – 700 tons per hour

    How many gallons of water are used per day?

    Approximately 24,000

    How many gallons of diesel are used per day?

    Approximately 1,100 gallons. 1,000 gallons will be consumed by the diesel generator if it is powering the highwall system and the end loader loading the cars will use 100 gallons per day.

    How many kilowatts of electricity are used per month?

    320,00 kwh

  • Regulations

    Is a specific permit required for highwall mining?

    Yes, you can request a permit in the application process for your surface mining permits or you can modify an existing surface mining permit to include highwall mining.

    What is the number 1 reason for entrapment of highwall mining equipment?

    Cutting one entry into an adjacent entry. ADDCAR systems have a guidance system that ensures the machine is maintaining its predetermined azimuth.

    What are the permitting requirements for pre-law walls?

    The permitting requirements for prelaw walls vary from state to state, however, they are straight forward, less time consuming and less arduous than the permit requirements for a virgin property.

  • Markets

    Can you screen the ROM coal on the bench?

    If the coal is a met coal, it is likely you can screen on the bench. This is because met coal typical crumbles up into small pieces when it is mined thus making it easy to separate from the harder rocks. Steam coal does not separate as easily which results in excess coal losses if it is screened on the bench.

    How do you control out of seam dilution?

    First, one must determine the amount of floor coal and roof coal that must be left to ensure the roof and floor rock does not contaminate the coal to be mined. If the roof and floor are competent, it may not be necessary to leave roof or floor coal. Once the thickness of the roof and floor coal to be left is determined, the gamma sensors on the ADDCAR highwall mining system are calibrated to leave these recommended thickness. Information on the actual performance of the cutter head is sent real time to the operator and he adjusts the recommended thicknesses if he experiences any geologic anomalies. The entire cutting profile is mapped in a web based system that can reviewed at any time to verify the system has been mining in seam.

  • Commercial Issues

    What is the minimum time required for leasing a machine?

    ADDCAR has relationships with third party financial institutions who are knowledgeable with the industry and comfortable with providing leasing for the ADDCAR System. Contact details will be provided upon request.

    What is the minimum time required to enter into a contract mining agreement?

    6 months if ADDCAR has a window of opportunity in the proximity of the subject property. Approximately 12 months is required if a long distance mobilization is involved.

    How long does it take to set up the machine initially?

    A new machine can be erected and troubled shot within a week.

    How long does it take to move the machine in pit?

    Typically 24 hours.

    What support does the mining company provide to the highwall mining operation?

    Typically, a mining company tops of the stationary water tank three times a day, they push coal from the stacker and they haul coal from the pit. In addition, a mine typically provides a connection to the mine power system and surveys in the location for the tunnels. Most importantly, the mining company has to ensure that the highwall is available for mining.

    At what point is the coal delivered?

    As it comes off the tail of the stacker belt.

    What is the basis for payment and how are the tons calculated?

    Run of Mine Tons mined is the basis for payment. The tonnage is calculated using ADDCAR’s on board technologies which continuously ascertain the mining height and depth of mining. A density factor (supplied by the mining company) is applied to the volumes. Typically, these tonnages are trued up on a regular basis (monthly or quarterly) with certified belt scale weights.

    Is training available?

    Yes. ADDCAR strongly recommends hands on real life training. ADDCAR will provide a crew of experienced highwall mining professionals to work side by side with your miners to train them on the safe and efficient use of these technologies.