Mendips header
 
 Home
 Overview maps
 Locality areas
  Cheddar Gorge
 Charterhouse
 Blackdown
 Burrington Combe
 Shipham & Rowberrow
 Crook Peak & Axbridge
 Banwell to Churchill
 Priddy
 Harptree & Smitham Hill
 Draycott & Westbury-sub
 -Mendip
 Wookey Hole & Ebbor
 Gorge
 Wells
 Great Elm & Vallis Vale
 Mells & the Wadbury Valley
 The Vobster area
 The Whatley area
 Torr Works & Asham Wood
 Beacon Hill
 Stoke St Michael & Oakhill
 Holwell & Nunney
 Shepton Mallet & Maesbury
 Gurney Slade & Emborough
 The Nettlebridge valley
 Geology
 Rocks of Mendips
 Fossils
 Geological timescale
 Ancient environments
 Geological structure
 Minerals and mines
  Minerals and mines
 Industrial archaeology
 Quarrying
  Stone as a resource
 Employment & the economy
 Quarrying & geodiversity
 Quarrying & the environment
 History of quarrying
 Caves and karst
 How caves form
 Dry valleys and gorges
 Dolines and sinkholes
 Mendip caves
 Going caving
 Hydrogeology
 Biodiversity
  Flora and fauna
 Typical Mendip habitats
 Special Mendip habitats
 Horseshoe bats
 Appendix of names
 Biodiversity of western
 Mendip
 Biodiversity of eastern
 Mendip
 External links
 Detailed site information
  Coal mining
  Mendip quarry companies
  East Mendip quarries
 Biodiversity of eastern
 Mendip
  West Mendip quarries
 Biodiversity of western
 Mendip
 Acknowledgements
 Site map
Quarrying and the environment
Introduction | Landscape |  Planning controls | Water and caves | Dust, noise and traffic | Blasting | Nature conservation

Blasting

Blast vibration has long been associated with quarries, but separating fact from fiction has often been a problem. Blasting is necessary to break rock from the ground, prior to it being taken for processing. In the early days of aggregate quarrying, explosives were not used particularly scientifically although some attempts were made to optimise use to minimise cost and maximise output. In most cases, high explosives would be detonated instantaneously — either packed into near vertical drill holes or occasionally into horizontal tunnels running into the face from quarry floor level. The latter could take six months to excavate and the blasting events were such big occasions that the local populace would turn out to watch. They were also the subject of reports in the national trade press. These methods would generate both considerable ground vibration and air blast ('overpressure') often perceived over a wide area. Indeed the residents on the higher ground on the outskirts of Bath, often reported hearing blasts from Emborough and Vobster, seven or eight miles away!

 

For safety, environmental and economic reasons blasting techniques have changed out of all recognition over the last 30 years. Instead of instantaneous detonation, explosives in each drill hole are initiated in a predetermined sequence so that there are delays of a few milliseconds between each activation. The shock waves generated not only direct much more energy into breaking up the stone effectively (and less into sound and air vibration), they create much lower levels of ground vibration in the surrounding area. The explosives used are now far safer to handle. Blocks which were initially too large to go through the crusher used to be broken up by secondary blasting which was particularly noisy and potentially very dangerous. This is now done by 'drop balling' or using jib-mounted breakers.

goto the British Geological Survey home page