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Drilling and blasting is the controlled use of
explosives An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
and other methods, such as gas pressure blasting pyrotechnics, to break rock for
excavation Excavation may refer to: * Excavation (archaeology) * Excavation (medicine) * ''Excavation'' (The Haxan Cloak album), 2013 * ''Excavation'' (Ben Monder album), 2000 * ''Excavation'' (novel), a 2000 novel by James Rollins * '' Excavation: A Mem ...
. It is practiced most often in
mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the econom ...
,
quarrying A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to reduce their envir ...
and
civil engineering Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewa ...
such as dam, tunnel or road construction. The result of rock blasting is often known as a rock cut. Drilling and blasting currently utilizes many different varieties of
explosives An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
with different compositions and performance properties. Higher
velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...
explosives are used for relatively hard rock in order to shatter and break the rock, while low velocity explosives are used in soft rocks to generate more gas pressure and a greater heaving effect. For instance, an early 20th-century blasting manual compared the effects of black powder to that of a wedge, and dynamite to that of a hammer. The most commonly used explosives in mining today are
ANFO ANFO ( ) (or AN/FO, for ammonium nitrate/fuel oil) is a widely used bulk industrial explosive. It consists of 94% porous prilled ammonium nitrate (NH4NO3) (AN), which acts as the oxidizing agent and absorbent for the fuel, and 6% number 2 fue ...
based blends due to lower cost than
dynamite Dynamite is an explosive made of nitroglycerin, sorbents (such as powdered shells or clay), and stabilizers. It was invented by the Swedish chemist and engineer Alfred Nobel in Geesthacht, Northern Germany, and patented in 1867. It rapidl ...
. Before the advent of
tunnel boring machine A tunnel boring machine (TBM), also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for microtunneling. They can be designed to bore thro ...
s (TBMs), drilling and blasting was the only economical way of excavating long
tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
s through hard rock, where digging is not possible. Even today, the method is still used in the construction of tunnels, such as in the construction of the
Lötschberg Base Tunnel , line = Lötschberg Line , location = Traversing the Bernese Alps in Switzerland , coordinates = – , system = BLS, SBB CFF FFS , status = , start = Frutigen, canton of Bern, , end = Raro ...
. The decision whether to construct a tunnel using a TBM or using a drill and blast method includes a number of factors. Tunnel length is a key issue that needs to be addressed because large TBMs for a rock tunnel have a high capital cost, but because they are usually quicker than a drill and blast tunnel the price per metre of tunnel is lower. This means that shorter tunnels tend to be less economical to construct with a TBM and are therefore usually constructed by drill and blast. Managing ground conditions can also have a significant effect on the choice with different methods suited to different hazards in the ground.


History

The use of explosives in mining goes back to the year 1627, when
gunpowder Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). T ...
was first used in place of mechanical tools in the Hungarian (now Slovak) town of
Banská Štiavnica Banská Štiavnica (; german: Schemnitz; hu, Selmecbánya (Selmec), ) is a town in central Slovakia, in the middle of an immense caldera created by the collapse of an ancient volcano. For its size, the caldera is known as the Štiavnica Mountai ...
. The innovation spread quickly throughout Europe and the Americas. The standard method for blasting rocks was to drill a hole to a considerable depth and deposit a charge of gunpowder at the further end of the hole and then fill the remainder of the hole with clay or some other soft mineral substance, well rammed, to make it as tight as possible. A wire laid in the hole during this process was then removed and replaced with a train of gunpowder. This train was ignited by a
slow match Slow match, also called match cord, is the slow-burning cord or twine fuse used by early gunpowder musketeers, artillerymen, and soldiers to ignite matchlock muskets, cannons, shells, and petards. Slow matches were most suitable for use aroun ...
, often consisting simply of brown paper smeared with grease, intended to burn long enough to allow the person who fires it enough time to reach a place of safety. The uncertainty of this method led to many accidents and various measures were introduced to improve safety for those involved. One was replacing the iron wire, by which the passage for the gunpowder is formed, with one of copper, to eliminate sparking that could ignite the powder prematurely. Another was the use of a
safety fuse The safety fuse is a type of fuse invented and patented by English inventor William Bickford in 1831. Originally it consisted of a "tube" of gunpowder surrounded by a waterproofed varnished jute "rope." It replaced earlier and less reliable metho ...
. This consisted of small train of gunpowder inserted in a water-proof cord, which burns at a steady and uniform rate. This in turn was later replaced by a long piece of wire that was used to deliver an electric charge to ignite the explosive. The first to use this method for underwater blasting was Charles Pasley who employed it in 1839 to break up the wreck of the British warship HMS ''Royal George'' which had become a shipping hazard at Spithead.''The National Cyclopaedia of Useful Knowledge'', Vol III, (1847) London, Charles Knight, p.414. An early major use of blasting to remove rock occurred in 1843 when the British civil engineer
William Cubitt Sir William Cubitt FRS (bapt. 9 October 1785 – 13 October 1861) was an eminent English civil engineer and millwright. Born in Norfolk, England, he was employed in many of the great engineering undertakings of his time. He invented a type o ...
used 18,000 lbs of gunpowder to remove a 400-foot-high chalk cliff near
Dover Dover () is a town and major ferry port in Kent, South East England. It faces France across the Strait of Dover, the narrowest part of the English Channel at from Cap Gris Nez in France. It lies south-east of Canterbury and east of Maids ...
as part of the construction of the South Eastern Railway. About 400,000 cubic yards of chalk was displaced in an exercise that it was estimated saved the company six months time and £7,000 in expense. While drilling and blasting saw limited use in pre-industrial times using
gunpowder Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). T ...
(such as with the
Blue Ridge Tunnel The Blue Ridge Tunnel (also known as the Crozet Tunnel) is a historic railroad tunnel built during the construction of the Blue Ridge Railroad in the 1850s. The tunnel was the westernmost and longest of four tunnels engineered by Claudius Crozet ...
in the United States, built in the 1850s), it was not until more powerful (and safer)
explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
s, such as
dynamite Dynamite is an explosive made of nitroglycerin, sorbents (such as powdered shells or clay), and stabilizers. It was invented by the Swedish chemist and engineer Alfred Nobel in Geesthacht, Northern Germany, and patented in 1867. It rapidl ...
(patented 1867), as well as powered
drill A drill is a tool used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driver chuck. Hand-operated types are dramatically decreasing in popularity and cordless battery-powered ones proliferating due to ...
s were developed, that its potential was fully realised. Drilling and blasting was successfully used to construct tunnels throughout the world, notably the Fréjus Rail Tunnel, the
Gotthard Rail Tunnel , it, Galleria del San Gottardo , other_name = , line = Gotthard Line , location = Traversing the Saint-Gotthard Massif in the middle of the Swiss Alps , coordinates = , os_grid_ref = , status = , system ...
, the
Simplon Tunnel , it, Galleria del Sempione , line = Simplon line, (Lötschberg railway line) , location = Traversing the Lepontine Alps between Switzerland and Italy , coordinates = – , system = Swiss Federal Railways (SBB CFF  ...
, the
Jungfraubahn The Jungfrau Railway (german: Jungfraubahn, JB) is a mountain railway in the Bernese Alps, connecting Kleine Scheidegg in the Bernese Oberland to the Jungfraujoch, across the Valais border. The railway, which uses a and racks, runs from th ...
and even the longest road tunnel in the world, Lærdalstunnelen, are constructed using this method. In 1990, 2.1 billion kg of commercial explosives were consumed in the United States (12 m3 per capita), representing an estimated expenditure of 3.5 to 4 billion 1993 dollars on blasting. In this year the Soviet Union was the leader in total volume with 2.7 billion kg of explosives consumed (13 m3 per capita), and Australia had the highest per capita explosives consumption that year with 45 m3 per capita.


Procedure

As the name suggests, drilling and blasting works as follows: *A blast pattern is created *A number of holes are drilled into the rock, which are then partially filled with explosives. *Stemming, inert material, is packed into the holes to direct the explosive force into the surrounding rock. *Detonating the explosive causes the rock to collapse. *Rubble is removed and the new tunnel surface is reinforced. *Repeating these steps until desired excavation is complete. The positions and depths of the holes (and the amount of explosive each hole receives) are determined by a carefully constructed pattern, which, together with the correct timing of the individual explosions, will guarantee that the tunnel will have an approximately circular cross-section. During operation, blasting mats may be used to contain the blast, suppress dust and noise, for fly rock prevention and sometimes to direct the blast.


Rock support

As a tunnel or excavation progresses the roof and side walls need to be supported to stop the rock falling into the excavation. The philosophy and methods for rock support vary widely but typical rock support systems can include: * Rock bolts or rock dowels *
Shotcrete Shotcrete, gunite (), or sprayed concrete is concrete or mortar conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique, first used in 1907 invented by Carl Akeley. It is typically ...
* Ribs or mining arches and lagging * Cable bolts * In-situ concrete Typically a rock support system would include a number of these support methods, each intended to undertake a specific role in the rock support such as the combination of rock bolting and shotcrete.


Gallery

Image:Blast_hole_drilling.jpg, Blast hole drilling with Tamrock Scout 700 File:Bingham Canyon Mine, west face detail, Utah.jpg, Blast-hole drilling at the
Bingham Canyon Mine The Bingham Canyon Mine, more commonly known as Kennecott Copper Mine among locals, is an open-pit mining operation extracting a large porphyry copper deposit southwest of Salt Lake City, Utah, in the Oquirrh Mountains. The mine is the largest m ...
, Utah. Note the pattern of drill holes being prepared for blasting. Image:Charging_with_anfo.jpg, Loading blast holes with
ANFO ANFO ( ) (or AN/FO, for ammonium nitrate/fuel oil) is a widely used bulk industrial explosive. It consists of 94% porous prilled ammonium nitrate (NH4NO3) (AN), which acts as the oxidizing agent and absorbent for the fuel, and 6% number 2 fue ...
Image:P1010759.JPG, Rock surface newly blasted. This is called pre-split, it's a technique to leave a smooth face. Image:Sideling_hill_road_cut.jpg,
Sideling Hill Sideling Hill, also Side Long Hill, is a long, steep, narrow mountain ridge in the Ridge-and-Valley (or Allegheny Mountains) physiographic province of the Appalachian Mountains, located in Washington County in western Maryland and adjacent Wes ...
road cut formed by rock blasting File:Rixö granitbrott 7.jpg, Tire blasting mats for fly rock prevention and dust suppression. File:Blast notice.png, Map describing the clearance zones during blasting in a limestone quarry. These notices are produced by surveyors (see
topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sc ...
). File:Prospect Quarry.jpg, Blast hole drilling in a
dolerite Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grain ...
quarry at Prospect Hill,
Sydney Sydney ( ) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about towards the Blue Mounta ...
, Australia


See also

*
Building implosion In the controlled demolition industry, building implosion is the strategic placing of explosive material and timing of its detonation so that a structure collapses on itself in a matter of seconds, minimizing the physical damage to its immedia ...
*
Demolition Demolition (also known as razing, cartage, and wrecking) is the science and engineering in safely and efficiently tearing down of buildings and other artificial structures. Demolition contrasts with deconstruction, which involves taking a bu ...
*
International Society for Explosive Engineers The International Society of Explosives Engineers (ISEE) is a tax-exempt professional body founded in 1974 to advance the science and art of explosives engineering.. Headquartered in Cleveland, Ohio, it is the primary international organization fo ...


References


External links


"Air Curtain Fences Blast"
''Popular Mechanics'', August 1954, pp. 96–97, the delicate controlled blast in 1954 to connect the two reservoirs at a Canadian Niagara Falls power station. * * This is an extensive survey of techniques used in the early 20th century. {{DEFAULTSORT:Drilling And Blasting Tunnel construction Mining techniques Explosives Civil engineering