Mining techniques Mines of Paris

1 mining techniques

1.1 open-air quarries
1.2 underground mining

1.2.1 piliers tournés
1.2.2 hagues et bourrages

mining techniques
open-air quarries

the primitive mining technique extract mineral seen on surface, in places millennia of erosion ancestors of paris basin s rivers seine, marne , bièvre exposed many levels of paris underlying stratification open air. minerals available surface, beginning paris highest elevations in valleys created erosion are: plaster deposits in upper reaches of right bank hills of montmartre , belleville; lower in valleys sand , limestone deposits nearest surface on paris left bank. underlying clay strata accessible surface in lowest points of seine, marne , bièvre river valleys.

underground mining

open-air quarrying became quite difficult , costly when desired minerals lay below surface, enormous amounts of earth , other unwanted deposits have removed before extracted. 1 means of avoiding problem dig horizontally hillside along mineral strata visible in flank, paris area had few mineral deposits, save gypsum, disposition of fulfilled these conditions. there few open-air stone quarries 15th century; instead, miners access targeted stone deposit through vertical wells, , dig horizontally there. although seems well-mining method began then, there evidence romans used technique mine clay under paris left bank montagne sainte-geneviève hill.

piliers tournés

no matter means used access underground mineral, miners had provide means of maintaining enormous weight of ceiling on horizontally-burrowed excavations. earliest means end, in technique called piliers tournés, became common late 10th century. tunnel dug horizontally along deposit, tunnels perpendicular first opened along way, , tunnels parallel initial tunnel opened through these. result grid of columns of untouched mineral deposit, or piliers tournés, prevented mine s collapse. in areas mineral removed in wider swath rest of mine, towards edge of exploitation, miners complement natural mineral columns piliers à bras, or stacks of stone creating supporting column between floor , ceiling.

gypsum mines, origin of famous plaster of paris, used technique added third dimension: of northern paris gypsum deposits measured 14 metres (46 ft) thick in places, miners create tunnel grids in top of deposit, begin extracting downwards. gypsum mine in particularly thick deposit had cathedral-like air upon depletion, because of towering columns , arches of mineral remaining. 1 example of sort of gypsum-mining remains in paris, in renovated grotto under buttes-chaumont gardens.

this method of burrowing effective short-term, on time relatively soft mineral, subject elements , earth s shifting, erode or fissure, endangering solidity of mine.

hagues et bourrages

another technique appearing towards 18th century, hagues et bourrages, both more economically , structurally sound. instead of tunnelling exploitable mineral, miners begin @ central point , extract stone progressively outwards; when had mined point left wide area of ceiling unsupported, erect line of piliers à bras, continue extraction beyond line, return build second parallel line of stone columns. space along both lines of columns transformed walls stone blocks, or hagues, , space between filled packed rubble , other mineral detritus (or bourrage). technique allowed more of targeted mineral extracted, , provided support both settle , shift mine ceiling supported.