Advantages and Disadvantages of quarrying

Advantages of quarrying

There is no problem of roof control or ventilation. Full extraction of mineral is possible. No mineral is blocked in shaft pillars, support of main roadways, etc. as in underground mining. Quick return on capital and early extraction are possible without the need to wait for a long period of development work or unproductive work like shaft sinking, etc. Large output is available from a small area and supervision is easy owing to concentrated work. Artificial lights are necessary only after dark.

Dangers and hazards are less as compared to underground mining. There is no risk of gas explosion. Very few stringent mining regulations are applicable to quarries. For example, compared to underground mining less number of competent persons are to be appointed and less number of statutory inspections are necessary.

Better sanitary conditions can be maintained.

High efficiency of mine workers; ease in loading the tubs in unconfmed space and natural light gives high O.M.S. (output per manshift).

Female labour can be employed. All the members of a family are often employed and the accommodation problem is simplified.

Once the mineral is exposed, output can be easily varied to meet wagon supplies, or consumer demand.

Training of operatives is easier.

Large scale mechanisation is possible as there is no restriction on the dimensions of machines to be used. Unlike in underground mines, machinery working at high voltage can be employed.

Disadvantages.

Among the disadvantages of quarrying are:

Work is affected by weather. During winter nights, and summer mid-days efficiency of workers is very low. During rainy season unless effective steps are taken to dewater the mine mineral which is at the lower levels, cannot be worked and mining comes practically to a standstill.

Surface land is destroyed and is rendered unfit for agriculture and residential purposes.

Mining lease gives only underground rights; surface rights have to be acquired for quarrying.

The method is uneconomic for working mineral beds at depth.

Where quarrying aims at quick return on capital, outcrop mineral is also mined. As it is inferior in quality due to weathering .and percolation of water, the overall quality available to the consumers is affected in earlier phases of mining.

The quarried area and the OB heaps present an unpleasant sight. In some foreign countries the mining law requires that the quarried area should be filled up with overburden and restored to the pre-quarry state fit for agriculture. Marshy land, after extraction of underlying mineral and restoration of surface has, in a few cases, resulted in a good agricultural area. Such law requiring surface restoration to pre-quarry stage does not exist in India.

The overall O.M.S. is low due to a large labour force engaged in OB removal in manual quarrying.

A property with extensive area on the strike and containing a thick mineral bed moderately inclined, lying at shallow depth, is ideal for quarrying. In India coal seams with inclination as steep as I in 3 have been worked by mechanised opencast mining methods in Karanpura field. Seams at shallow depths which are actively gassy, liable to spontaneous heating or with bad roof should preferably be extracted by quarrying as the mining legislation for underground working of such seams is stringent.

Before the quarrying operations are undertaken it is necessary to vacate buildings and divert electric overhead lines, aerial ropeways, water mains, telephone lines, roads, railway lines, streams, etc. from the area which has to be quarried. The trees have to be cut. Sufficient space for dumping of overburden, not far from the quarry, has to be considered. Where mechanised opencast mining is to be adopted, plans should be prepared to show the contour lines and the thickness of coal and overburden at various points. An extensive area for dumping of overburden and good roads without steep inclinations and sharp curves should receive attention. Dumping yard for OB should be so selected that wind does not carry the dust to residential colony. By dumping of OB if the ponds, paddy fields, mango/coconut groves, not under the ownership of the mine owner, are likely to be affected, the compensation payable should not be ignored.

If heavy explosive charges have to be blasted as in mechanised quarries, the quarry site has to be far away from residential area (beyond 300 m.) Such heavy blasting may cause cracks in old buildings resulting in demand for compensation.

On the surface reference lines have to be marked on a square pattern, every 30 m apart, for monthly measurement of the excavation and they should extend 50 m beyond the limits of the proposed quarry. Junctions of the squares should be marked by permanent pegs in brick pillars.