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The process of loading and hauling is a complementary service that contribute to the efficiency of mining process as a whole and it is an essential part of calculating a productive mining process. Loading and hauling are large contributors to cost per ton in mining. Underground miners are always on the lookout for ways to improve loading and haulage performance to lower cost per ton.

The invention of LHDs can be said to be a milestone in mining. Today, LHD machines are a backbone of modern production systems in most underground mines, and are used in a variety of mining methods. A load haul dump truck (LHD), also known as a scoop tram, is a specialized loading & hauling machine manufactured for the underground mining industry. LHDs are used to scoop extracted ore, such as coal, with a bucket, load it into the cart, and dump it in the bottom of the mine to undergo primary crushing before being hoisted to the surface out of the mine. 

LHDs are similar to conventional frontend loaders but developed for the toughest of hard rock mining applications, with overall production economy, safety and reliability in mind. They are extremely rugged, highly manoeuvrable and exceptionally productive. More than 75% of world's underground mines use LHD for handling the muck of their excavations.

There are various sizes and models of LHDs but most have a similar design. LHD consists of two parts, a front and rear carriage connected in the middle by an articulated joint. This joint is what allows the machine to steer. Each carriage stands on two rubber tires. The rear carriage contains the engine, driver's cabin and hydraulic pumps while the front carriage holds up the bucket. The hydraulics power the booms that hold the bucket, allowing it to load and lift several tons of material and also manoeuvre the machine through tight tunnels, even when fully loaded. Carrying capacities vary from one to twenty tons or more.

LHD have powerful prime movers, advanced drive train technology, heavy planetary axles, four-wheel drive, articulated steering and ergonomic controls. Their narrower, longer and lower profile make them most suitable for underground application where height and width is limited. As the length is not a limitation in underground tunnel and decline LHD are designed with sufficient length. The length improves axial weight distribution and bucket capacity can be enhanced. In mining there is limitation for shifting heavy equipment. Sometimes, an LHD has to be shifted through a shaft while dismantled.

LHDs are available in both diesel and electric versions. Diesel version is easily transportable from one location to another and have diesel engines as power drive of 75 to 150 HP or more. Engines are either water or air cooled. Diesel version LHD include a diesel exhaust treatment device that uses water, catalytic fume diluter, or similar substances to spray or bathe the exhaust device with water. This LHD is also commonly equipped with a device that automatically shuts off the fuel supply to the engine in emergency situations such as exceeding temperatures of exhaust gases. A ventilation system is also required for this LHD to counter the excessive exhaust fumes it creates inside a confined space.

Electric LHDs (eLHDs) may be powered using three different electric options: batteries, overhead power lines, and tethered trailing cables. Battery powered vehicles offer the highest flexibility; however, they are typically heavier than the other options and require regular recharging. A research study found that LHDs required 1.5-2 tonnes of batteries which only allowed for 2-2.5 hours of working time with an estimated recharge time of 2 hours. This resulted in a vehicle availability of approximately 50%. Overhead power lines that enable trolley mechanisms are impractical for LHDs that require a high degree of manoeuvrability. The use of tether trailing cables that are plugged into electrical infrastructure is typically the best option due to its ease of manoeuvrability. eLHDs are ideal where hauling distances are short and operations are repetitive.

The electric LHD offer particular advantages in underground applications through its emission-free drive and are therefore especially suitable for projects where ventilation is critical. Further advantages of the electric LHDs result from a low noise level. A constant torque and the resulting dynamics allow for more efficient loading of the muck pile. Furthermore, economic benefits result from a high reliability and a long-life span of the drive components. This means fewer spare parts and lower maintenance costs and hence lower overall operating costs. However, the limitations imposed by trailing cables present several drawbacks. These include reduced mobility, versatility, cable faults and relocation issues.

LHD productivity also relies on the size and density of the fragmented muck produced; therefore, the capacity selection is based on the expected muck size and distances to be travelled, horizontally and/or vertically. Most mines typically incorporate a fleet of LHD's with varying bucket capacities to meet their specific production targets. For example, a mine may employ two LHD's; one for stoping and one for development. Therefore, the determination of the size of an LHD in a mine plan is a function of the stope dimension and production requirements for the operation.

Typical bucket capacities range from 3 - 11.6 m3, with special machines designed to adhere to narrow-vein operations that have a capacity of 0.38 m3, which are commonly referred to as “micro-scoops”.

LHDs are designed for manual, semi-automatic or fully automatic operations.

Manual operation of the LHDs is the most common way of moving ore in an underground mine. The operator remains in the cabin on top of the vehicle throughout the load-haul-dump cycle. The side position of the cabin makes it possible for the operator to have a clear line of vision when the vehicle is moving forward or backward. Because remote control offers limited sensory perception, manual operation is faster than remote control and tele-remote control. The disadvantages of manual operation include lack of safety, driver fatigue and basic human errors.

An initial stage of automation is to operate the LHD by remote control while keeping it in sight. This technique is common practice in unsupported areas. An operator drives the vehicle manually to the brow (entrance) and then dismounts to drive it into the stope by radio remote control. At all times, the operator is close by and can see the LHD. Once the bucket is loaded, the operator climbs back onto the machine to drive manually to the dump point. This procedure is slow because of the constant switching between manual and remote operation. It is also unproductive, as the operator's limited view of the loading operation makes the bucket difficult to fill. Most importantly, it is not safe since the operator remains close to the remotely controlled vehicle and the unsupported ground.

Tele-remote operation is the next step in automation and is slowly gaining acceptance in the mining industry. Here, video cameras are installed on the LHDs to provide the remote operator with clear views forward and backward. The LHD is remotely operated during the complete LHD load/dump cycle. An operator can be located in a safe and comfortable environment a long distance from the vehicle but can still operate only one vehicle at a time. The view is not always clear so it can be difficult for the operator to manoeuvre the machine.

Because of the limited sensory perception of the operators running the machines remotely, the speed of the vehicles is lower, and this results in decreased productivity. Although the tele-remote operation has led to improved safety, costs are increased because of the additional expenses of the infrastructure required for tele-operation.

The next step in automation for LHDs is fully automated operation i.e. to allow them to drive autonomously. Operators are still required to monitor vehicles and must be involved at some points during the loading cycle, but they can operate one or several vehicles simultaneously from a safe environment. The operator's station can be located either outside the mine or inside the mine in a van or office. Since such vehicles will faithfully follow programmed instructions, management has the flexibility to control the performance of the vehicle and to influence its wear and tear.

Automatic Load Haul Dump (LHD) machines improves productivity and increase the security of the mine's personnel. There is also manpower savings with less travelling time and the possibility of using one operator for multiple machines. Maintenance costs may drop as well, a properly designed automatic machine will last longer since it requires less repair than a manual one. Other advantages of automation include process consistency and the ability to counter labour shortages. The main objective of automation is to imitate the maximum physical and intellectual human capacity to improve productivity through increased accuracy.