Materials stemming from some chalk


Pebbles always made spawns of an exploitation by the men. Their collection formerly made live numerous craftsmen. Even if their exploitation was at first craft thanks to the help of horses, she became fast industrial in the 1950s by the setting-up of factories. But this exploitation was so intense counterpart more than 2 centuries than the number of collected pebbles represent approximately the stock staying on our coast. That is why to protect the Norman coast (which are coast the most threatened with France), the collection of pebbles since 1975 is forbidden. The takings are limited in the neighborhood of Cayeux where small about ten companies collects them and exports them all over the world.

Statue of the collector of pebbles to Saint-Jouin

Flints of the Country of Callus are ideally hard and resistant in chemicals, as bases or acids except for the acid fluorhydrique.
As they are, pebbles serve as ornamental materials or as construction for the fishermen's former houses or the manor houses of the region. Their neutrality and their hardness allow them to be excellent crushers. They are used in the glass-making thanks to their contribution in silica. The black pebble is most popular because it is of use to the manufacturing of the china made in the South of England. Certain flints enter the composition of ceramic, china and some cosmetics. Others crushed are made bits of gravel or sand sand (the abrasive paper). They are also used for the public works as the road paints.
The illegitimate pebble of Normandy would have been even of use to the construction of take-off strips for the American rockets in Cape Canaveral in Texas but also for the construction of a bridge in America!

The cement

Naturally, there are (or more) no careers in littoral cliff. The closest cement works are situated to Saint Vigor in about ten kilometers from Havre. The career is located on the right bank of the Seine, not far from the port of Havre and road accesses. We can discover it three coats of chalk of age and different compositions.

  • The chalk of Cénomanien is thirty meters in height, it is massive, glauconieuse and characterized by beds of flint
  • The chalk of Turonien is of a ten meter thickness and does not almost contain flint, which facilitates its extraction.
  • The chalk of Sénonien is soft. She is white, in flint and of a rough height of twenty meters. However, we can discover within this limestone of numerous fossils of marine animals, type foramminifères, coccolithes, which contributed to his training.

Over all this rock live a not exploitable material, called bare, consisted of silt and clay with flint.
Saint Vigor's career is exploited open-air. She is characterized by a face of an exploitable height of sixty meters. For safety reasons, the exploitation is made in staircase or flat working shape. The precrushing of the limestone is realized by mechanic shovels or "excavators with wheel shovel" during an easy extraction. Should the opposite occur, the developers use explosives to break the various coats of chalk. They are established for example by some dynamite exfoliate (bottom of the hole) surmounted by explosive nitraté. The latter are placed at the bottom of holes drilled obliquely or in a parallel to the face. During the shooting, the foot of these has to contain a strong load to bring down the base before the top, so blocks break some themselves on the others. The broken materials are got back by mechanic shovels or wheels shovels increasing the yields and facilitating the exploitation. The chalk is forwarded to a crusher which can be mobile or fixes. His purpose is to split up the stone in diverse pieces. She is then transported towards the cement works by long conveyor belts.

The materials of riprap of the antiiron oil harbor

The port of Havre Antifer is an oil terminal situated in the North of Havre and in the South of Étretat, in the municipality of Saint-Jouin-Bruneval. It is a port intended to welcome supertankers of 500 000 tons of a 30 meter draft. The setting-up of the site is bound to the geology and to the possibility of digging of a channel of access through sands aptiens. The presence of erratic blocks brought by icebergs during the last glaciation required the abandonment of trying to pick up with jars for the benefit of a sucking trying to pick up.

The dike 3,5 km in length required the extraction of big quantities of chalk taken by digging of the cliff. Here are the main stages of the construction of the port in images.

2 answers in Extraction

  1. Gaumer Says:

    In view of the volumes planned for the projects of exploitation of marine aggregates off saint valéry in callus, think you that it can have an impact on shingle beaches and cliffs?
    An inhabitant of élétot

    • Bhadmin Says:

      Not being implied in the searches on the impact of the exploitations of marine aggregates, my opinion on this question is hardly little supported. To my knowledge, there are no relations between the veneers of aggregates offshore and the littoral cords of pebbles and sand. A priori, thus he should have no incidence on the evolution of the coast.
      The impact of the panache turbide appears to me to be the essential and worrisome question. What are the precise zones (in 3D) which will be affected by a degradation of the environment? Are the mathematical models exact enough to predict this evolution?
      Look for answers with concerned laboratories (Rouen: UMRs CNRS 6143 and 6554 or national IFREMER).

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