History of electric trucks in underground mining
Before the 1960s, when underground mine haulage was mainly on rails, electricity was the overwhelming choice for traction, along with lesser examples of internal combustion power.
The technology, with power from overhead wiring or batteries was mature, having originated in the late nineteenth century. Internal combustion rubber tyred trucks started to be used in tunnelling and mining in the 1930s and 1940s.
The benefits of electric rather than diesel powered rubber-tyred trucks in the underground environment, particularly in long decline haulage, includes less or no diesel particulates to be breathed by personnel, less vibration and noise for the operator, lower ventilation flows if heat is not an issue, and greater speed and therefore improved labour and equipment productivity.
Electric powered trucks were introduced to the International Salt Company’s room and pillar salt mine under the suburbs of Detroit, Michigan in 1939 where electric rail haulage had previously been used. Euclid internal-combustion engine trucks were fitted with electric motors and hauled bottom-dump semi-trailers. Two overhead wires, approximately 2 m apart and 5 m above the floor were strung up, and power supplied to the trucks through a hydraulically raised horizontal current collector. For areas without overhead wiring such as the face loading of the trucks by rope shovels, batteries supplied the power. This operation continued to 1961.
Figure 1. Semi-trailer electric truck at International Salt Company, Detroit, Michigan. The current collector is behind the operator and the truck is running on battery power. https://repository.mines.edu/handle/11124/5693. The United States Bureau of Mines gave the images to the Colorado School of Mines Russell L.and Lyn Wood Mining History Archive.
A room and pillar limestone mine at Crestmore, 80 km west of Los Angeles, installed an electric truck system and commenced production haulage up a 1-in-10, 9.8 m wide decline and surface haul road in 1956. This used Kenworth rear dump trucks equipped with an electric motor in place of a diesel engine. Direct current (DC) electric power was supplied by trolleybus-style twin wiring for both up and down traffic, fed through twin trolley poles on each truck. Electric trucks had a greater speed and productivity than diesel trucks, and half the haulage cost. Ventilation requirements were also reduced. Transport of development rock was still handled by Le Tourneau diesel trucks. In the production areas the electric trucks’ trolley poles were pulled down from the overhead wires and a trailing cable reel on the truck attached to a fixed power outlet, allowing the trucks to travel 110 m beyond the overhead wires. The electric haulage was discontinued in 1972. It is likely that in both of these early cases, age-expired electric trucks were replaced by one or more of the multiple choices of off-the-shelf diesel trucks available at the time.
Figure 2. Kenworth electric truck on the surface section haul road of Riverside Cement Company’s Crestmore, California limestone mine. Source: General Electric, 1956, General Electric Specifications No. RY-24343, Description of operation & electrical equipment.
Figure 3. Kenworth electric truck being loaded after reversing using a trailing cable (left) at Riverside Cement Company’s Crestmore, California limestone mine. General Electric, 1956, General Electric Specifications No. RY-24343, Description of operation & electrical equipment.
The 1980s saw a trend for increased electrification of underground mines. Electro-hydraulic drills were replacing compressed air machines and large high-powered secondary ventilation fans for decline development, prompting installation of extensive and high-capacity electric power reticulation. Many underground equipment manufacturers and some mining companies developed small numbers of electric trucks, taking three-phase alternating current (AC) power from bus bars (exposed conductors) using a current collector in a captive trolley running along overhead steel tracks. Manufacturers included Jarvis Clark, Wagner, MAN-GHH and Tamrock. An unusual example was a prototype automated electric truck developed by Inco at Inco’s Little Stobie mine in the Sudbury district, Ontario, Canada.
Figure 4. Cross and long-sections of a captive current collector similar to that for a truck, as used for an electric loader at the CSA mine, Australia. Source: Grant, B. P. M. and Roberts, M. L. (1988). Experiences with the electric overhead trolley system at the CSA mine, Cobar, in Underground Operators’ Conference, June 1988 (pp 121-127). The AusIMM North West Queensland Branch. With permission of AusIMM.
In some cases, relatively complicated turnouts allowed trucks to negotiate alternative tracks and enter workshops. Trucks were generally modifications of the manufacturers’ diesel models. Some electric loaders used similar current collectors. Because the collectors were captive in the tracks, batteries or small diesel engines were not applicable for off trolley track movements, and some trucks were fitted with a trailing cable reel. Users included mines in the United States, Canada, and Sweden. None of these installations are known to have continued in operation.
Also, during the early 1980s a more sophisticated prototype 50 t capacity electric truck was developed in Sweden by Kiruna Truck and ASEA, one of the predecessors of electrical equipment manufacturer ABB. This was based on the articulated Kiruna Truck underground diesel truck but with direct-current electric motors driving the front and rear axles. Three phase AC power at up 1000 V was supplied by three overhead bus-bars, located between two tracks attached to the backs underground or to posts and arms on surface. A detachable trolley with current collectors supported by an arm mounted on the truck ran along the underside of the bus bars.
Figure 5. Kiruna Electric truck current collector and overhead track. Source: Author.
Nickel cadmium batteries allowed limited operation away from the overhead power. The current collector was able to be quickly retracted from the overhead, and replaced as required with very little intervention by the operator. Production of the Kiruna Electric trucks resulted in a total of 35 50 t and later 35 t capacity vehicles supplied to 12 mines around the world, including six of the 50 t variety to Mount Isa Mines for development of the deep copper ore bodies. Trolley lines installed for Kiruna Electric trucks ranged from 1.3 km to 7.6 km in length.
Figure 6. Kiruna Electric 50 t truck loading from a chute at Ammeberg Mining’s Zinkgruvan mine in Sweden, 1995. Source: Author.
In 1995 the Kiruna Electric 35 t capacity model with AC traction motors in place of the DC motors was introduced. A third DC traction motor drove one axle when running from the battery. Later 50 t and 35 t trucks used AC traction motors and a small diesel engine to manoeuvre off the trolley line. Kiruna Electric was purchased by GIA, and in turn GIA was later purchased by Atlas Copco. Two Kiruna Electric installations in Canada, at Vale’s Creighton and Coleman mine, were still in operation as of 2024, Both mines have a strong commitment to electric trucks.
Manufacturers such as Sandvik and Epiroc have recently released lithium-ion battery powered articulated underground haul trucks based on their diesel-powered models. However, there has been recognition that there might be technical and economic restraints on the use of pure battery powered haul trucks operating on long decline haulage. Charging of batteries from an overhead power supply while the truck is in motion is a concept which has been advanced in the last few years by firms such as Boliden-Epiroc-ABB and BluVein, using an open-pit style trolley assist technology and a patented power rail respectively.
Electric trucks in underground mining have been operating from at least 1939, with irregular bursts of activity, and still in small numbers. The electrification of underground mines is progressing and it is likely that the operational advantages, and still to be established cost advantages, will result in expansion of this technology.
Sources and acknowledgements
This article is based on the paper, Weston, A J, 2024, ‘History of externally powered rubber-tyred electric vehicles in underground mining, Proceedings of the 9th International Conference and Exhibition on Mass Mining, Kiruna, Sweden, 17-19 September 2024 (MassMin 2024), pp 1194-1219.’ The work of David Hutnyak in the United States and his website on the history of trolley assist and associated subjects in open cut mining https://hutnyak.com/trolley.html is gratefully acknowledged. John Stanton from Epiroc supplied material on the Kiruna Electric trucks and recent developments with battery trucks. The paper and this article are unlikely to be a definitive history of the subject.