Career (geology)

Various careers

One can distinguish the careers by the use of the rock which of it is drawn:

industrial Raw material : Limestone for the cement factories, clay for the terra cotta, etc;
decorative Rock : Plates of marble, granite for the tomb stones, etc;
Aggregate : Gravels and sands used by the building and public works

This last category is, in the France, by far most important in volume.

One can also distinguish the careers by their mode from extraction:

Careers of massive Rock : extraction of a geological layer of rather homogeneous rock and compacts by demolition with the explosive, more rarely by shifting, to see sawing;
Gravel pit and sand pit : Extraction of sedimentary, alluvial deposits or gravel or sand sailors.
There exist underwater careers (sand, gravel) and underground.

Careers of Aggregate: operation

By far most in France, the careers of massive Roche exploit their layer in order to little close always identical:

Drilling : Boring of vertical holes approximately 10 cm in diameter in the rock according to a spacing (the " maille") well defined.
Mining : The holes of boring are filled with explosives. The successive explosion of the holes coarsely splits up (<800 mm) the rock and the slaughtering.
Taken again : A back-digging shovel or a tire charger recovers the shot down rock and charges it in a machine with transport.
Rolling : A machine, more rarely a belt conveyer, conveys coarse materials to the installation of treatment.
Scalpage : Optional, the materials advance on isolated rails of the approximately 200 smallest Misters pass through. The fine materials are often unsuitable with the noble uses of the aggregates, the scalpage eliminates them.
primary Crushing : The coarse materials are broken by a direct mechanical stress, for example the closing of two jaws verticals or violent projection on a metal screen. One generally seeks to obtain materials going from 0 to 250 Misters
primary Criblage : at the conclusion of primary education crushing the materials are sent by belt conveyers on a series of vibrating grids. The size of the holes in the grids makes it possible to sort materials. Those sufficiently small to be marketed are put in stock, the others leave towards secondary crushing.
Put in pre-stock : Optional, the setting in stock and the resumption of materials intended for a secondary treatment make it possible to give a flexibility of operation to the factory. The primary part can thus function separately of the remainder of the installation.
secondary Crushing : the too large materials are broken by an often indirect mechanical action using the Attrition. The gyratory vertical conical crushers are current. One then seeks to reduce the size of largest to 50 Misters
secondary Criblage : Even principle that previously, but the too large materials pass by again in the secondary crusher, the others leave either towards tertiary crushing, or towards marketable stocks.
tertiary Crushing : one seeks to obtain materials lower than 14 mm in diameter.
tertiary Sifting : Several screens in series finish separating the aggregates in " coupures" increasingly fine.

Choice of the establishment of a career

The establishment of a career obeys several criteria:

geological obviously, materials suitable for a human use not being distributed geographically in a homogeneous way.
commercial: the proximity of the places of consumption is vital, transport cash for much in the selling price.
of safety
lawful and environmental: in France, the careers are subjected to a prefectoral authorization. The prefect draws up a departmental diagram which describes the zones where the exploitation of a career is possible. Many of other regulatory constraints are generally added; one can quote mainly:

constraints of town planning: the Local plan of Town planning of the commune where one wishes to establish the career, the SCOTT (consistency of RAINED several communes),…
the regulatory constraints aiming at the protection of nature and of the flora: classified national parks, landscapes, with in Europe; zones Natura 2000, Community Zone of interest for the birds (ZICO), special Protection zone (ZPS), and in France; Regional natural park (PNR), ZNIEFF, Order of the prefect of protection of biotope (APB), regional Natural reserve (RNR), etc

The superposition on a chart of the whole of these constraints makes it possible to realize of the possibility of openings of a career… but also which they are enormously reduced and poses today of serious problems of access to the resource in particular when it is known that the stone is the second natural matter most consumed after water (approximately 20 kg per day and in France).

Environmental impact

The impact of the careers on their long-term environment is different according to their mode from extraction:

the underground careers are often abandoned today. They represent a great danger of collapse because the water infiltrations weaken them. They can cause serious damage with the dwellings built above. Many in the east of France, but also in Paris region, they are attentively followed by the services of the prefecture and the B.R.G.M.;
the careers with open sky in massive rock modify in an important way the landscape, by creating cliffs, by cutting out hills, by creating deep holes in plain. The heights of winning face were not regulated before and of the faces of more than 30 meters were current. These important heights accentuated the vertiginous aspect of these changes;
It is difficult to measure the long-term impact of the extractions in the river beds or at sea, that depends on the ecological impact strength of the medium and the speed of the return of the alluvia. The extractions of the gravel pits on sedimentary layers often lead to the creation of new water levels by letting the ground water leave to the free air;

The impacts of the short-term careers are:

vibrations of the shootings of mine: Shootings not being never " parfaits" , they undergo a loss of energy. This energy leaves in the rock and transmits to the walls houses. The regulation fixes strict limits at the allowed maximum vibrations on the structures around the careers. The observance of the regulation does not prevent the complaints (of which some are not always insincerely and free from financial calculations);
vibrations of transport by truck: much less noticed, because nonspecific to the careers, their intensity is often quite higher than those of the shootings of mine;
noise: the apparatuses of crushing are particularly noisy, just like the noise of the rock falling into the bucket from an empty truck and the noise from the sound signalling hooters from retreat from the machines. The regulation there too frames the acceptable maximum noise levels in edge of exploitation in diurnal and night period;
dust: the circulation of the machines on the tracks, as well as crushing and the sifting raise much dust. In the careers whose rock is rich in silica (Brittany, Basse-Normandie, Massif Central…) this dust contains sufficient free silica to cause at the personnel of the site, the appearance of silicosis after a continuous and durable exposure (several years). In France the carriers must measure the repercussions of dust in edge of exploitation.

The carriers have thought for several years of the reduction of these impacts. The landscape integration of the sites at the end of the lifetime from now on is taken into account as of the opening of a site or renewal of its authorization of exploitation. A financial guarantee is required by the prefectures to guarantee that final excavation work will be well completed even if the owner goes bankrupt. These plans of repairing can be very thorough and open new prospects with the residents and the communes, as that of the careers of Fréhel (22) which proposes the creation of a deep water harbor on this pink sandstone coast. The sites " orphelins" , whose owners were lacking at the time of the repairing, by the trade union the UNICEM is gradually treated; The problems of noise and dust make them it object of treatments adapted to the situations: Boarding, containment, aspiration, filtration, water spraying, horns of retreat with fast damping of the signal, etc

Trades of the career

Heavy plant driver Carrier
, driver
Mason stone

See too

List of the stone quarries in France
Catacombs of Paris
Marl-pit
Compensatory measure
Conservative measure

External bonds

''' Exploitation of the limestone quarries '''
''' Exploitation of the chalk careers '''
''' Exploitation of the gypsum quarries '''
''' tools of the underground careers '''
Glossary

Simple: Quarry

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