To transport materials off-road from one point to another, it is generally necessary to use specialised machines travelling on tracks.
There are several types of transport machines, each serving a specific purpose.
Small dump trucks
These are intermediate machines, situated between trucks used on roads and rigid dumpers. (see below) They have 3 or 4 axles. The two rear axles, which are drive axles, are mounted with single or twinned tyres. The front axle or axles, mounted as singles, are essentially steering axles but can sometimes also be drive axles.
Small Dump trucks are mainly used:
- On excavation or infrastructure works sites: highways, railway construction sites, dams, etc. They are used to transport materials on more or less established tracks. The distances covered can be considerable and average speeds high;
- in rock and sand quarries: They are used to transport materials from the quarry face to the crushing or processing stations. Very often they operate on established tracks and can be used for earthworks. They can reach peak speeds of around 70 km/h (43 mph). Depending on the model, the payload can range from 15 tons to 60 tons.
These trucks have 2 axles and a tilting skip. The rear axle is a drive axle, generally mounted with twinned tyres. The front axle is a steering axle, generally with single tyres; it is sometimes a drive axle, and occasionally mounted with twinned tyres.
There also exist rigid dumpers with 3 axles, where the 2 rear axles, which are drive axles, are mounted with singles.
Rigid dumpers are mainly used:
- in surface mines and rock and sand quarries;
- they are used to transport material from the face to the crushing or processing stations.
On excavation or infrastructure works sites: highways, railway construction sites, dams, etc. They are used to transport materials on more or less established tracks, sometimes covering considerable distances at high average speeds.
They can carry very heavy loads over distances ranging from 1 km to 40 km (1 ml to 25 ml).
The need for traction varies according to works site conditions.
These machines very often operate on more or less well-maintained, established tracks, and can be used for earthworks or stripping.
They can reach peak speeds of around 70 km/h (43 mph). Depending on the model, the payload can range from 15 tons to 360 tons.
The productivity of the operation depends on having the appropriate loading equipment (LOADERS or Shovels) for the means of transport used. In general, the aim is to minimise the number of passes required (3 or 4 at the most) to reach the DUMPER’s maximum payload.
The manufacturers provide very useful information on the subject.
These are articulated machines, made up of a tractor and a skip on a trailer. The tractor is equipped with one axle mounted with singles; the trailer has one or two axles mounted with singles. They can be of the 4×4, 6×4 or 6×6 type.
While these machines can be found on the same works sites as rigid dumpers (though articulated dumpers are rarely used at quarries), the main quality of an articulated dumper lies in its ability to travel across loose soil and uneven ground.
Unlike rigid dumpers, it does not necessitate the construction of compacted tracks.
Suitable for all-terrain use, able to carry loads ranging from 10 tons to 40 tons, and possessing considerable capacities for clearing the difficult ground, these machines are mainly used on infrastructure earthworks sites.
A combination of rigid dumper and articulated dumper, these machines are made up of a two-axle tractor and a one-axle skip. The tractor’s front axle is a steering axle, and always mounted with singles; its rear axle, which is a drive axle, and the skip axle can sometimes be mounted with twinned tyres.
Its bottom-dumping technique and high capacity mean that the use of this vehicle is restricted to large-scale works sites with a low gradient and softer materials (for example coal transport).
Bottom dumps are particularly suited to applications involving long cycles and a high average speed.
These machines are made up of a tractor and a skip, each equipped with one axle mounted with single tyres.
The skip is equipped with a blade, used to strip the soil and collect the material in the skip.
Scrapers are dual-purpose machines performing both loading and transport operations. They are found mainly on infrastructure works sites and at coal mines.
The work cycle (scraping) is voluntarily limited by the manufacturers for technical reasons. For further information, please refer to the manufacturer’s documentation.
There exist models with just one engine (in which case, it is necessary to use one or more bulldozers to move the scraper).
There are also machines with two engines that support one another, either loading or dozing, in what is known as tandem or push-pull operation.
On some scrapers, the skip is equipped with elevator buckets or loading screws.
These machines are made up of a two- or three-axle tractor with a coupling system.
The tractor’s front axle is always mounted with single tyres, while the two rear axles, which are drive axles, are usually mounted with twinned tyres.
Road trains generally tow two or three multi-axle trailers and travel at high speed on established tracks or on roads (the outward journey with a load and the return trip empty).
They are mainly used to transport timber (logging), coal or ore.
Note: All of the machines previously described are not continuously involved in transport operations. They are at a standstill at least during loading
and unloading. The percentage of travelling undertaken while loaded can range from 30% to 70%.
These machines have 2 axles and a forward-tilting skip. The two axles are generally driven axles, whilst the rear axle is also a steering axle. They travel at low speed (20 – 40 km/h, or 12.5 – 25 mph).
They carry small loads (0.5 – 9 tons). Site dumpers are highly manoeuvrable, and fitted with small tyres that give them traction and grip.
They are used for transport and clearing applications on a wide variety of sites (infrastructure, open parkland, etc).
By definition, these machines cover only limited distances. Operational speeds are relatively low.
There are several types of working machines, each serving a specific purpose.
Skid steers are compact machines whose rigid chassis houses a cabin combining both driver and operator stations.
They have two articulated arms equipped with either a bucket or another tool.
They are fitted with 4 identical-size drive wheels.
The driver changes direction by braking on the wheels situated on the side on which he wishes to turn (in the same way as for track-powered machines).
Generally equipped with a front bucket, loaders are used to take materials from the mine or quarry face, or from a dump, and deposit them at a nearby point (skip of a truck, crusher, etc.).
Mounted on 4 identical-size tyres, these machines are generally built on an articulated chassis.
We make a distinction between two families of loaders.
Loaders used for rehandling stock or for service operations.
These machines are used for numerous tasks on a large variety of sites (quarries – coating or concrete plants – incineration plants – public works contractors, etc.).
They can be fitted with 2 (very rare) or 4 drive wheels, of identical size. The bucket can be replaced by other tools.
Note: For rehandling work, operators are using increasingly large-scale loaders.
Loaders used in production
These machines are used at the location where the material is removed for loading onto transport machines (for example mine or quarry face).
The remarkable mobility of wheel powered loaders is sometimes used to advantage in what is known as “load and carry” applications, where materials are loaded at the mine or quarry face and transported directly to the crusher by the loader, without having recourse to trucks.
Under these conditions, the range of loaders sometimes reaches several hundred meters. Loaders are constantly growing in size (with buckets of up to 30 cu. m/39 cu. yd) and power (1 400 kW), and calling on increasingly complex transmissions (wheel-spin controller, torque converters).
They are equipped with 4 identical drive wheels.
Dozers or rubber-tyred dozers
Dozers are used to move materials by pushing them with the aid of a multidirectional front blade.
They can also assist with loading the self-propelled scrapers on earthworks or infrastructure works sites.
They are also used in the maintenance of the tracks, loading/unloading zones and storage areas at opencast mines.
Dozers are fitted with 4 identical drive wheels.
These machines, of the 4×2 and 4×4 type, are equipped with a bucket at the front and a backhoe at the rear.
The front tyres may be smaller than the rear ones.
These are multi-purpose tools, able to load with their bucket and dig trenches with their backhoe.
They can be found in all of the trades involved with construction, public works or earthworks.
These operating machines are made up of a chassis that houses a cabin combining both driver and operator stations. They have an articulated arm equipped with a backhoe.
They are either mounted on tracks or fitted with single or twinned tyres. In the case of twinned tyres, there is very often a ring between them, totally incompatible with radial technology.
Machines mounted on tyres, of the 4×4 type, are equipped with outriggers
to stabilise them during operations.
These operating machines are made up of a chassis that houses a cabin combining both driver and operator stations. They have a telescopic boom that can be fitted with numerous tools (fork, bucket, etc.). These machines, with 4 drive and steering wheels of identical size, can be equipped with outriggers for use
during operations at a great height. It is worth noting that each wheel can be turned in such a way as to allow specific types of movement (normal, crab-like, or in opposition).
The carrying capacity of these machines depends on the height of the telescopic boom and the speed in operation.
These machines, equipped with a central blade and sometimes a front blade, are generally mounted on 3 axles, with single tyres. The front axle is the steering axle (and sometimes a drive axle), while the rear axle or the two rear axles are drive axles.
Graders perform various tasks. In opencast mines and quarries, these machines are reserved for the maintenance or finishing of tracks. They are invaluable allies of earthmover tyres, and can also significantly reduce travelling times for transport machines. Proper maintenance of the tracks prevents accidental damage, in particular, tire punctures due to repeatedly driving over blocks of material that have fallen onto the tracks.
In earthworks, construction and public works, they carry out banking and the regulating of subgrades and fine finishes (laser work, gravel-slag mixture, gravel-sand mixture, cement, coating).
Underground mining machines
These very special machines operate in driftways and tunnels. They are designed to load and transport materials over short distances and at low speeds.
These machines, with the reduced overall size, are required to operate under difficult conditions. Tyres working in these conditions are subject to numerous damages (abrasion, tearing off of pieces of tread rubber, cuts, impacts, etc).
There are several types of vehicle, each serving a specific purpose.
These are very low trucks, generally with 2 axles and either a tilting skip or a fixed one equipped with an ejector. They are fitted with single tyres front
These are very low, articulated machines, with combustion or electric engine, two axles mounted with single tyres, and one or two articulated arms equipped with a bucket. For dangerous applications, these machines are remote-controlled or wire-guided. In this case, the “driver” remains at a safe distance.
Loaders known as LHDs (Load Haul Dumps) are used for both loading and transport.
These are very low, articulated machines, with two axles mounted with single tyres. They are used in underground mines for various operations.
Examples include drilling machines, truck-mounted platforms for ceiling maintenance, personnel transport machines, etc.
(civil and military intervention machines, truck cranes, etc.)
Truck cranes (tc)
These cranes are mounted on a truck with a reinforced chassis.
They are fitted with Truck tyres and intended only for on-road use. Compact and therefore more manoeuvrable, they excel on solid surfaces.
Their maximum lifting capacity is 100 tons.
Rough-terrain cranes (RT)
These cranes are not intended to travel on roads, nor cover long distances. They are equipped with a single cabin, combining both driver and operator stations.
They are fitted with Earthmover tyres, allowing them to comfortably overcome the obstacles encountered and giving them considerable rough terrain capabilities.
They have 2 or 3 axles which can be drive and/or steering axles, thereby giving them great manoeuvrability. Their maximum lifting capacity is 200 tons.
City Cranes (RT)
A new generation of RT cranes, with a single cabin but a new design (reduced overall size), is authorized to travel on the road.
They are called “City cranes”.
These cranes are fitted with Truck or Earthmover tyres. They can have up to 4 axles.
Their maximum capacity is 50 tons and their maximum speed is 90 km/h.
All-terrain cranes (AT)
These cranes, very often described as road cranes, travel mainly on the road (at up to 80 km/h or 50 mph) but also on sites.
They are fitted with Earthmover tyres, combining good travelling speeds and adhesion/traction.
They possess separate driver and crane-operator cabins.
The number of axles varies (from 2 to 10) according to the models. The tyres are fitted as singles and can carry up to 12 tons per axle.
These cranes have several drive axles and several steering axles, giving them great manoeuvrability and considerable adaptability in the work.
Their maximum lifting capacity is 1000 tons. All lifting operations are performed with the outriggers in position.
These are small machines without suspension, incorporating a single cabin, and fitted with 4 handling equipment type tyres. They operate on industrial sites (warehouses, workshops, etc.) and only rarely use roads.
These cranes are mounted on a reinforced chassis and used only on docks and intermodal depots.
They have several drive axles. All axles are steering. These cranes are fitted with earthmover tyres. All lifting operations are performed with the outriggers in position. They are very heavy and large; they are slow (5 to 6 km/h) and not easy to manoeuvre.
The most important dock crane have 7 dead axles and 5 moving axles. They are fitted with 96 tyres. Its are a lift capacity of 150 tons and a loading height capacity is 55 meters.
These machines are generally mounted on 3 steerings and/or drive axles.
Fitted with All-Terrain Earthmover tyres and capable of reaching high travelling speeds, these machines possess great rough-terrain capabilities and excellent manoeuvrability.
(road-rollers, finishers, etc.)
There are various types of Public Works/Civil Engineering machines designed exclusively for road construction.
Compactors are mainly used for public works.
Their role is to compact the ground, either to prepare and level it for road construction or to finish the road surfaces.
These machines can have different construction types:
- two axles equipped with drum rollers;
- a front axle equipped with a drum roller, and a rear axle mounted with two treaded tyres;
- a front axle equipped with a drum roller, and a rear axle mounted with smooth tyres;
- two axles mounted on tyres, with 2,3,4 or 5 smooth tyres.
These machines are mounted on tyres or tracks. Their role is to tear up coatings and concrete in order to prepare the ground for a fresh surface course.
They are equipped with a planing unit, adjusted by means of a manual or electric control system, a heating system for softening the coating material, and a conveyor belt for disposing of the coating in a rigid dumper.
Sometimes planers are fitted with a sprinkler system to avoid dust and protect the equipment against premature wear.
The tyres on these machines are exposed to very high temperatures.
These earthworks machines are used to prepare the land. They are mounted on 4 tyres, with a steering axle at the front and a drive axle at the rear.
They are fitted with a hopper and a tool that incorporates the stabilisers contained in the hopper (lime for example) into the soil.
Certain machines are equipped with 4 identical wheels, and others with smaller front tyres. These machines require considerable traction and flotation.
These machines are mounted on tyres or tracks and, as their name suggests, their role is to supply the finishers with coating materials.
Feeders receive the coating material by conveyor belt and feed it to the finishers.
In the road works sector, the finisher, as its name suggests, is used to “finish” the work by laying the surface course on top of the roadbed, prepared during prior earthworks.
It is a self-propelled vehicle, with a maximum travelling speed of up to 25 km/h (15.5 mph).
It is made up of:
- a hopper, which receives the coating (with a capacity of 3 cu. m to 25 cu.m, or 4 cu. yards to 33 cu. yards); The hopper is carried by tired wheels (2 or 4) that are steering and sometimes drive wheels.
- a frame supporting the translational heat engine, a product-transfer system and a control station; The frame is supported by a set of tracks or tyres (1 or 2 axles) operated by chains or hydrostatic transmission.
- a screed, vibrating or fixed, designed to spread the product in an even layer (known as the surface course) of up to 8.50 m (9.3 yd) in width. The depth of the layer (30cm/12 in. max.) is regulated by a manual, electric or optical device. The spreading speed can reach 30 m/mn (33 yd/mn). The screed’s smoothing plate is heated either electrically or using fuel oil or gas.
Appendix – Vehicle configuration
A mechanical part linking 2 wheels or turning units. An axle can be load-carrying or steering.
The drive axle
This is a set of mechanical parts, with (half-shaft) axles at each end which are driven by the engine and which receive wheels (turning units).
The drive axle can be fixed or steering.
The different types of chassis
These are represented symbolically in the form of multiplication.
The first figure is the number of turning units.
The second figure is the number of drive units.
The third figure is the number of steering units.