In mining there is limitation for shifting heavy equipment. Sometimes, an LHD has to be shifted through a shaft while dismantled. Their tramming capacities varies from 1 to metric tons. Their bucket size varies from 0. Bucket height range from 1. LHD are available in both diesel and electric versions. Engines are either water or air cooled. The speed of the vehicle is controlled mechanically. The transmission is controlled by a hydrostatic drive. In hydrostatic transmission, the motor drives a variable displacement pump hydraulically connected to a hydro-motor driving the axle via a gearbox.
The speed is controlled by changing the displacement volume of the axial pump. The power train consists of a closed loop hydraulic transmission, parking brakes, two-stage gear box and, drive lines. Service, emergency and parking brakes with fire resistant hydraulic fluid is used.
Head lights, audible warning signal, back up alarm and portable fire extinguisher are provided. For electric shock safety these LHD's power source gate end box are equipped with earth conductivity protection using pilot core  in electric trailing cable, which isolate complete power when earth continuity is broken.
LHDs are available with remote controls. These are essential to remove the material where the stope is unprotected from top. There can be fall of loose muck from top. There are LHD available with remote tramming facility and these can handle tons of ore per day.
An expert system for hydraulic excavator and truck selection in surface mining
From Wikipedia, the free encyclopedia. Under high stress levels, failure consists of brittle spalling and slabbing in the case of a massive rock mass with few joints, to a more ductile type of failure for heavily jointed rock masses. A rockburst may be defined as damage to an excavation that occurs in a sudden or violent manner and is associated with a seismic event.
Various rockburst damage mechanisms have been identified, namely expansion or buckling of the rock due to fracturing around the opening, rockfalls induced by seismic shaking and ejection of rock due to energy transfer from a remote seismic source.
Outbursts of rock and gas occur catastrophically in some coal, salt and other mines as a result of high rock stresses and large volumes of compressed methane or carbon dioxide. In quarries and surface mines, sudden buckling and heaving of rock floors has also been experienced.
Considerable research has taken place in several countries into the causes and possible alleviation of rockbursts. Techniques for minimizing rockbursts include altering the shape, orientation and sequence of extraction, the use of a technique known as destress blasting, stiff mine backfills and the use of specialized support systems. Sophisticated local or mine-wide seismic monitoring systems can assist in the identification and analysis of source mechanisms, although the prediction of rockbursts remains unreliable at the present time. In the Canadian province of Ontario, nearly one-third of all underground fatal injuries in the highly mechanized mining industry result rom rockfalls and rockbursts; the fatality frequency from rockfalls and rockbursts for the period was 0.
In less mechanized underground mining industries, or where ground support is not widely used, considerably higher injury and fatality frequencies due to falls of ground and rockbursts can be expected. The ground control related safety record for surface mines and quarries is generally better than for underground mines.
The design of underground excavations is the process of making engineering decisions on such matters as the locations, sizes and shapes of excavations and rock pillars, the mining sequence and the application of support systems. In surface mines, an optimum slope angle must be chosen for each section of the pit, along with other design aspects and slope support. Designing a mine is a dynamic process which is updated and refined as more information becomes available through observation and monitoring during the mining.
The empirical, observational and analytical design methods are commonly used. Empirical methods often use a rock mass classification system several such schemes have been developed, such as the Rock Mass System and the Rock Tunnelling Quality Index , complemented by design recommendations based on a knowledge of accepted practice.
Several empirical design techniques have been successfully applied, such as the Stability Graph Method for open stope design. Observational methods rely on the actual monitoring of ground movement during excavation to detect measurable instability and on the analysis of ground-support interaction. Analytical methods utilize the analysis of stresses and deformations around openings.
Some of the earliest stress analysis techniques utilized closed form mathematical solutions or photo elastic models, but their application was limited due to the complex three-dimensional shape of most underground excavations. A number of computer-based numerical methods have been developed recently. These methods provide the means for obtaining approximate solutions to the problems of stresses, displacements and failure in rock surrounding mine openings. Recent refinements have included the introduction of three-dimensional models, the ability to model structural discontinuities and rock-support interaction and the availability of user-friendly graphical interfaces.
In spite of their limitations, numerical models can provide real insights into complex rock behaviour. The three methodologies described above should be considered as essential parts of a unified approach to the design of underground excavations rather than independent techniques. The design engineer should be prepared to use a range of tools and to re-evaluate the design strategy when required by the quantity and quality of information available.
A particular concern with rock blasting is its effect on the rock in the immediate vicinity of an excavation. Intense local fracturing and disruption of the integrity of the interlocked, jointed assembly can be produced in the near-field rock by poor blast design or drilling procedures. More extensive damage can be induced by the transmission of blasting energy to the far field, which may trigger instability in mine structures. Blast results are affected by the rock type, stress regime, structural geology and presence of water.
Surface and Underground Excavations, 2nd Edition: Methods, Techniques and Equipment
Measures for minimizing blast damage include the proper choice of explosive, the use of perimeter blasting techniques such as pre-split blasting parallel, closely spaced holes, which will define the excavation perimeter , decoupling charges the diameter of the explosive is smaller than that of the blasthole , delay timing and buffer holes. The geometry of the drilled holes affects the success of a wall control blast; hole pattern and alignment must be carefully controlled.
Monitoring of blast vibrations is often performed to optimize blasting patterns and to avoid damage to the rock mass. Empirical damage blast damage criteria have been developed. Blast monitoring equipment consists of surface-mounted or down-the-hole transducers, cables leading to an amplifying system and a digital recorder. Blast design has been improved by the development of computer models for the prediction of blast performance, including the fragmentation, muck profile and crack penetration behind blastholes.
Input data for these models include the geometry of the excavation and of the drilled and loaded pattern, detonation characteristics of the explosives and dynamic properties of the rock. Scaling is the removal of loose slabs of rock from roofs and walls of excavations. It can be performed manually with a steel or aluminium scaling bar or by using a mechanical scaling machine. When scaling manually, the miner checks the soundness of the rock by striking the roof; a drum-like sound usually indicates that the ground is loose and should be barred down.
The miner must follow strict rules in order to avoid injury while scaling e. Manual scaling requires considerable physical effort, and it can be a high-risk activity.
For example, in Ontario, Canada, one third of all injuries caused by falls of rock occur while scaling. The use of baskets on extendable booms so that miners can manually scale high backs introduces additional safety hazards, such as possible overturning of the scaling platform by falling rocks. Mechanical scaling rigs are now commonplace in many large mining operations. The scaling unit consists of a heavy hydraulic breaker, scraper or impact hammer, mounted on a pivoting arm, which is in turn attached to a mobile chassis.
The main objective of ground support is to help the rock mass support itself.
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In rock reinforcement, rockbolts are installed within the rock mass. In rock support, such as that provided by steel or timber sets, external support is provided to the rock mass. Ground support techniques have not found wide application in surface mining and quarrying, partly because of the uncertainty of the ultimate pit geometry and partly because of concerns with corrosion. A wide variety of rockbolting systems is available worldwide. Factors to consider when selecting a particular system include ground conditions, planned service life of the excavation, ease of installation, availability and cost.
The mechanically anchored rockbolt consists of an expansion shell various designs are available to suit different rock types , steel bolt threaded or with a forged head and face plate. The expansion shell generally consists of toothed blades of malleable cast iron with a conical wedge threaded at one end of the bolt. When the bolt is rotated inside the hole, the cone is forced into the blades and presses them against the walls of the drillhole.
The expansion shell increases its grip on the rock as tension on the bolt increases.
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Bolts of various lengths are available, along with a range of accessories. Mechanically anchored rockbolts are relatively inexpensive and, therefore, most widely used for short-term support in underground mines. The grouted dowel consists of a ribbed reinforcing bar that is inserted in a drillhole and bonded to the rock over its full length, providing long-term reinforcement to the rock mass. Several types of cement and polyester resin-grouts are used. The grout can be placed in the drillhole by pumping or by using cartridges, which is quick and convenient.
Steel and fibreglass dowels of various diameters are available, and bolts can be untensioned or tensioned. The friction stabilizer commonly consists of a steel tube slotted along its entire length, which, when driven into a slightly undersized drillhole, compresses and develops friction between the steel tube and the rock. The drillhole diameter must be controlled within close tolerances for this bolt to be effective.
The Swellex rockbolt consists of an involute steel tube which is inserted in a drillhole and expanded by hydraulic pressure using a portable pump. Various types and lengths of Swellex tubes are available. The grouted cable bolt is frequently installed to control caving and stabilize underground stope roofs and walls. A Portland cement-based grout is generally used, while cable geometries and installation procedures vary.
LHD (load, haul, dump machine)
High-capacity reinforcing bars and rock anchors are also found in mines, along with other bolt types, such as tubular groutable mechanically anchored bolts. Steel straps or mesh, made from either woven or welded wire, is often installed in the roof or walls of the opening to support the rock between bolts. Mining operations should develop a quality control programme, which can include a variety of field tests, to ensure that ground support is effective. The behaviour of reinforced or supported rock masses remains incompletely understood. Rules of thumb, empirical design guidelines based on rock mass classification systems and computer programs have been developed.
However, the success of a particular design relies heavily on the knowledge and experience of the ground control engineer. A good quality rock mass, with few structural discontinuities and small openings of limited service life, may require little or no support.
However, in this case rockbolts may be required at selected locations to stabilize blocks that have been identified as potentially unstable. At many mines, pattern bolting, the systematic installation of rockbolts on a regular grid to stabilize the roof or walls, is often specified for all excavations.
In all cases, miners and supervisors must have sufficient experience to recognize areas where additional support may be required.