Material handling systems
Material handling can be complex for underground mining operations. The goal of mine haulage systems or material handling systems is to move rock masses from one location to another in the most efficient way while maintaining production rate and minimizing operating costs. With many varying mining methods, structure, distances, and changing faces or drawpoints, it is important to understand appropriate material handling systems. Within this section the topics of conveyor systems, locomotive tramming, scooptram to trucking, and scooptram to drawpoints will be discussed.
Conveyor belts can be an effective component of a material haulage system due to their high energy efficiency and relative simplicity. Depending on mine size and orebody geometry conveyors can be utilized as either a primary means of haulage or a secondary means. Developing a conveyor system generally has a high capital cost due to the construction of required infrastructure, however, In mines with a long life of mines the overall savings can be very lucrative .
A significant benefit of underground conveyors is their ability to greatly reduce underground trucking fleets and increased reliability. Conveyors are powered electrically, so they do not have the large ventilation requirements that truck fleets have. In large horizontally spread mines such as KGMH’s Lubin underground copper mine raw material is trammed directly to ore bins at conveyor feed locations . Lubin mine with over 165 km of conveyor belts underground and a significantly reduced trucking fleet, is an example of a mine utilizing conveyors as a primary means of haulage. Conveyor belt systems like Figure 1 are typically seen in large scale cave mines, coal mines, and underground soft rock.
Another application of underground conveyors is utilizing them together with a conventional trucking fleet as a means of secondary material handling. For mines with underground crushing capabilities such as Newmont-Goldcorp’s Musselwhite mine ore is hauled to a crusher underground and then conveyed the remaining 460 vertical meters to surface .
Key factors in determining the suitability of conveyor systems are production rate, the life of mine considerations, ventilation and ore body geometry. The primary consideration for the suitability of conveyor systems is the ore body geometry. New conveyor technology is allowing conveyance of material over steep grades. However, in general, conveyors are most suitable for horizontal or shallow dipping ore bodies. Typically uncrushed ore cannot be conveyed at a slope of more than 20 degrees . Conveyors achieve their maximum financial benefit from economies of scale, as such production rates must be high enough and consistent enough to justify replacing trucks. Conveyors are fixed installations which cannot be easily moved. Conveyor installations must be made with the life of mine in mind to ensure that the system will still be useful in the future. In underground mines that are ventilation constrained Conveyors can be used to reduce haul truck ventilation requirement thereby allowing for more production equipment to operate.
The principle types of the mine locomotive include: diesel, battery, trolley, battery/trolley, and to a very small degree, the flywheel form, together with compressed air powered.
The underground locomotives are primarily used in two different ways:
1) Gathering duty, secondary haulage, and shaft bottom work
2) Main road haulage
The former classification normally involves short hauls with relative few cars and demands a locomotive having the speed of 8km/hr. The latter classification generally involves a longer haul at higher speed, diesel and electrical locomotives are mostly used on this duty.
In selecting a locomotive, its weight and horse power must be proportioned to suit load, track grades and curvatures, conditions of tracks and types of bearings on the car.  In most cases when a locomotive tramming system is selected, it is in combination with one or more other transportation systems due to limitation of the rails. The proper weight of the rails to use will depend on a series of factors, weight of locomotive, cars and load, grade of the ground, speed of operation, length of the haulage distance as shown in Table 1 . As a result, a main locomotive haulage route is usually built.
Although conveyor system is the ideal choice for underground bulk transportation of minerals, it lacks the flexibility of underground locomotive system to transport men, minerals and supplies underground in both directions. If the circumstance at the mine dictates that there can be only one types of haulage system for both material handling and men/supply transportation, then the locomotive system should be selected for its multipurpose capability.  Moreover, even though locomotive transportation system demands a higher capital investment and longer construction time frame than truck haulage, the operating costs and maintenance costs are significantly lower. The choice of building locomotive tramming system is also affected by considerations such as ventilation, mine horizontal length.
Underground Haul Trucks
Haul trucks are a common mode of haulage in underground mines and often present within mines that are relatively shallow with ramp access. They are a dominate haulage method within mines ranging from <200m to 400m with an annual capacity of less than 1,000,000t per year . Hauls trucks are often favoured in mines because of the relatively low capital cost associated with them and the high flexibility in routing and capacity. However, haul trucks to incur high operating costs due to fuel consumption, maintenance, noise, heat, ramp traffic, and toxic emissions.
Haul trucks are often utilized with an LHD where they are loaded at a draw point and prepared for haulage out of the mine. They typically haul to surface or to an ore pass or crushing station where the load is to be dumped. For loading efficiency, haul trucks and LHDs should be mutually fitted for the fleet, further information on this topic can be found at the Equipment selection page.
The operating capacities for underground haul trucks range greatly depending on the operation, however, Caterpillar’s largest truck has a loaded capacity of 60 metric tonnes. During the design of the underground network system, dimensioning of the haul trucks must be taken into account. This involves width, turning radius, and inclination, these dimensions should be mutually selected with mine design. Incorrect or non-ideal dimensioning between equipment and mine design will result in decreased efficiency during operations, as well as safety . Along with design for dimensions, other design considerations should be accounted for such as a mechanics bay, parts inventory, and ventilation and cooling capacities. Due to the nature of diesel equipment and underground operating equipment, underground haul trucks require a lot of maintenance for production. Therefore, a well suited mechanics bay is a necessary requirement when a haul truck fleet is being utilized. Also, diesel engines produce toxic exhaust emissions and heat which can be deadly to surrounding workers. Ensuring proper ventilation is supplied is a necessity and may require more planning than an operation utilizing other modes of haulage transportation.
Haul trucks are often accepted as a preferred method for haulage when mine operations are considered small to medium sized with ramp access . This relates to a mine extending to a depth of 300m and <2500 tonnes per day, ideally, although, mining at greater depths and higher capacities is possible with haul trucks . At this depth, the ramp development cost paired with the low capital costs of haul trucks allow for greater returns. Beyond this depth, often shaft feasibility should be reviewed because of the operating cost to remove muck from a mine with haul trucks.
It should be noted that ventilation capacities and head fan sizing should be carried out prior to mine commissioning to ensure requirements are met. Worker protective equipment should also be reviewed in the budget with respect to haul trucks. This would include proper cool clothing, ear protection, and relevant gas monitors.
LHD or scooptram hauling is a versatile rock hauling method. In many mining methods, LHDs are the most common loading equipment. After mucking underground, LHDs can then load one of the previously discussed methods of material handling systems, or can haul the material to the next point within the material handling system to continue the production supply chain. Modern LHDs are semi-automatic for manual (on level) operation for mucking of ore in dangerous locations or under unsupported ground. Technology is also being tested and implemented to operate the through tele-remote operations. This technology will allow operators to operate the equipment from a remote location like an on-surface office. Additionally, operators can simultaneously operate three LHD units .
As LHDs are a mobile piece of equipment, they can be used in dynamic mine settings where they will change area or faces frequently. Conversely, LHDs can be used in a mine where they will be in the same area for large lengths of time. In the latter case, the previous types of material handling systems should be discussed. An example of LHD is the Kiirunavaara Sublevel caving mine . This particular sublevel cave (as seen in Figure 3) is 4.5km long. With this length of sublevel cave, it is likely that each drawpoint will be mined for a relatively short period before moving to the next production drift. As seen in the figure, LHDs are required to service a large number of drawpoints to load and haul material and dump in their respective ore pass.
Due to the flexibility of LHD equipment it is a suitable addition to most mining operations. LHDs are often used for mucking of stopes and will be present. The decision of suitability in respect to LHD implementation is the decision of what to dump material into at the end stage. LHDs can be used in shaft and ramp mines. That being said, if material needs to be moved a large distance LHDs are not as effective as other modes of material movement as it will affect the usage within production activities of mucking. With this, it is likely that LHDs must be paired with another form of material movement in ramp mines. The Shaft vs. Ramp Access has more information on this.
The previous suitability sections are a good resource to reference when determining the most effective point to transition from LHDs to other modes of transportation.
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