What is horizon or horizontal mining?

Answer 1

It's exactly what you think it is based on the (independent) meanings of the two words. Horizon or horizontal mining can be applied to extraction of material from seams of any stratified mineral such as limestone or ironstone, but it is more usually associated with coal - particularly where there are several seams that are inclined or folded and/or faulted.

Traditional methods of mining involved sinking a shaft to a seam and then following the undulations of the seam with underground roadways as the mineral is extracted. This in turn meant that the roadways following the working face followed the undulations of the seam making transport along them difficult. These roadways also required constant maintenance to counter the crushing effect of having been constructed through the area from which the mineral had been extracted.

Horizon mining involves long level roadways (horizons) being driven from the shafts to the extremity of the area to be mined. The levels of the horizons are chosen to intersect the maximum number of seams the maximum number of times. As the seams are intersected, headings will be driven into the seam so that the desired material may be extracted. This method of mining requires a thorough understanding of the geological structure of the area to be mined so that the level of the horizons can be chosen for optimum results.

This method of mining is popular in modern coal mines with seams worked from several horizons. The considerable capital outlay of driving horizons before production can begin is recouped by the advantage of having long straight level roadways of generous dimensions unaffected by the crushing effect of nearby extraction of the mineral.

The mineral being mined will generally be carried by conveyor belt from the working face to a loading point at the appropriate horizon. Here the mineral will be loaded into a train of mine cars, each of several tonnes capacity. These trains, with a payload of several hundred tonnes, will then be hauled at high speed by electric or diesel (ventilation permitting) locomotives to the shaft bottom for transfer to cages for ascent of the shaft.

In modern horizon mining, several horizons will be driven in the same direction from a vertical shaft. The horizons will, therefore, appear as a vertical stack of roadways which it is difficult to represent on a conventional mine plan. This being the case, it is usual to show the relative position of horizons on an isometric drawing for clarity.

Underground connections between horizons can be made by staple shafts (entirly underground shafts) or inclined drifts.

In modern coal mines, the workings are generally contained between two horizons with the vertical separation being dependent on the geological structure of the strata. The lower horizon would normally be used as the intake airway and the upper horizon used as the return airway. This takes advantage of the natural tendancy for the air, as it is heated by its passage around the mine, to rise to a higher level. It is standard practice for the intake airway, the lower horizon, to be used as the main haulage road as gravity will assist the coal on its journey from face to mine car.

Although horizon mining is widely held to have been developed in Germany in the early 20th century, its origins almost certainly date to the Duke of Bridgewater's coal mines at Worsley near Manchester. It was here in 1765 that a branch of the Bridgewater Canal was driven into the mine so that loaded boats could travel from the working face in the mine directly to Manchester, which was some 8 miles away - and without any double handling of the cargo. This caused the price of coal in Manchester to drop from (in modern units) 45p/tonne to 22p/tonne - a 50% reduction!

The fundamental requirement for a canal to be level produced what amounted to the first mining horizon.

The extent of the underground canals in the Worsley Mines amounted to 46 miles on three levels connected by underground locks and inclined planes. The boats used could carry about 10 tonnes each. The canal tunnel entrances to Worsley mines can still be seen. Underground access cannot be permitted because of the danger cave in and of explosive and toxic gases associated with coal mines.

In the 1770's, the Earl of Dudley extended a branch of the Birmingham Canal into his limestone mines within Dudley Castle Hill. Various branches were driven from this tunnel to serve all parts of the Castle Hill Mines. The length of these underground canals were maximised by following the strike (contour) of the seams once they had been reached.

In 1792 after a construction period of 8 years, the original tunnel was extended a distance of 3km to link with the Dudley & Stourbridge Canals. In 1841, it is recorded that this tunnel carried 41,000 boats.

In 1805, the Earl of Dudley promoted another branch from what was now the Dudley Canal Tunnel. This tunnel was driven west for a distance of a little more than 1km to the developing limestone mines in Wrens Nest Hill. It terminated in two loading basins. Each was large enough to hold 12 narrow boats, and each boat had a capacity of 25 to 30 tonnes.

In all, the network of underground canals within Dudley Castle Hill and Wrens Nest Hill can be considered to be on one horizon, being that they are all on the same level. This horizon intersects 2 beds of limestone 8 times. This can, therefore, be considered to be an excellent example of horizon mining long before the term came into common use. The underground canal system and limestone mines at Dudley, West Midlands, can be visited by contacting the Dudley Canal Trust on 01384 236275. A link to their web site is provided. Horizontal mining is also a data processing term that is applied in the structrual analysis of large software systems.