Coal combustion products ( CCP s), also called coal combustion wastes (CCWs) or coal combustion residuals (CCRs), are categorized in four groups, each based on physical and chemical forms derived from coal combustion methods and emission controls:
114-590: The Orange–Fish Tunnel , constructed between 1966 and 1975, is an 82.8-kilometre (51.4-mile) long irrigation tunnel in central South Africa , built to divert water from the Orange River to the Fish River valley. It is the longest continuous enclosed aqueduct in the southern hemisphere. For many years, large areas in the Eastern Cape experienced severe water shortages because of little rainfall in
228-850: A catalyst for converting polyethylene into substance similar to crude oil in a high-temperature process called pyrolysis and utilized in waste water treatment. In addition, fly ash, mainly class C, may be used in the stabilization/solidification process of hazardous wastes and contaminated soils. For example, the Rhenipal process uses fly ash as an admixture to stabilize sewage sludge and other toxic sludges. This process has been used since 1996 to stabilize large amounts of chromium(VI) contaminated leather sludges in Alcanena , Portugal. The majority of CCPs are landfilled, placed in mine shafts or stored in ash ponds at coal-fired power plants. Groundwater pollution from unlined ash ponds has been
342-404: A coal combustion product that is composed of the particulates that are driven out of coal-fired boilers together with the flue gases . Ash that falls to the bottom of the boiler's combustion chamber (commonly called a firebox) is called bottom ash . In modern coal-fired power plants , fly ash is generally captured by electrostatic precipitators or other particle filtration equipment before
456-443: A 9 in (23-centimetre) thick mass concrete lining. The ground was excavated entirely by the drill-and-blast technique. The lining was done using a travelling shutter - concrete arrived first thing Monday morning, and continued unstopped until Saturday afternoon. The concrete mix was specially developed for the project, and the "cement" content was 50% Slagment a.k.a. PFA ( Pulverised Fuel Ash ). The mix contained retarders to enable
570-481: A component in geopolymers , where the reactivity of the fly ash glasses can be used to create a binder similar to a hydrated Portland cement in appearance, but with potentially superior properties, including reduced CO 2 emissions, depending on the formulation. Another application of using fly ash is in roller compacted concrete dams. Many dams in the US have been constructed with high fly ash contents. Fly ash lowers
684-464: A continuing environmental problem in the United States. Additionally some of these ponds have had structural failures, causing massive ash spills into rivers, such as the 2014 Dan River coal ash spill . Federal design standards for ash ponds were strengthened in 2015. Following litigation challenges to various provisions of the 2015 regulations, EPA issued two final rules in 2020, labeled as
798-463: A decrease in hydraulic conductivity and cohesiveness. The effect of fly ash on soils and microorganisms in the soils are influenced by the pH of the ash and trace metal concentrations in the ash. Microbial communities in contaminated soil have shown reductions in respiration and nitrification. These contaminated soils can be detrimental or beneficial to plant development. Fly ash typically has beneficial outcomes when it corrects nutrient deficiencies in
912-453: A filler material. High fly ash content mixes contain nearly all fly ash, with a small percentage of Portland cement and enough water to make the mix flowable. Low fly ash content mixes contain a high percentage of filler material, and a low percentage of fly ash, Portland cement, and water. Class F fly ash is best suited for high fly ash content mixes, whereas Class C fly ash is almost always used in low fly ash content mixes. Asphalt concrete
1026-531: A further river system. The Orange–Fish Tunnel, together with its network of canals, weirs and balancing dams, has enabled these areas to be restored and has made the irrigation of thousands of hectares of additional land possible. The main purpose of the tunnel is to divert water from the Gariep Dam to the Eastern Cape Karoo for irrigation, household, and industrial use. The tunnel forms part of
1140-486: A kiln at about 1000 °C. This approach has the principal benefit of reducing the amount of clay required. Another type of fly ash brick is made by mixing soil, plaster of Paris, fly ash and water, and allowing the mixture to dry. Because no heat is required, this technique reduces air pollution. More modern manufacturing processes use a greater proportion of fly ash, and a high pressure manufacturing technique, which produces high strength bricks with environmental benefits. In
1254-449: A large factor in the decision making process. Civil engineers usually use project management techniques for developing a major structure. Understanding the amount of time the project requires, and the amount of labor and materials needed is a crucial part of project planning. The project duration must be identified using a work breakdown structure and critical path method . Also, the land needed for excavation and construction staging, and
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#17327800116261368-497: A large uniformity coefficient and it consists of clay-sized particles. Engineering properties that affect the use of fly ash in embankments include grain size distribution, compaction characteristics , shear strength , compressibility , permeability , and frost susceptibility . Nearly all the types of fly ash used in embankments are Class F. Soil stabilization is the permanent physical and chemical alteration of soils to enhance their physical properties. Stabilization can increase
1482-467: A pipe jack, with the span of some box jacks in excess of 20 metres (66 ft). A cutting head is normally used at the front of the box being jacked, and spoil removal is normally by excavator from within the box. Recent developments of the Jacked Arch and Jacked deck have enabled longer and larger structures to be installed to close accuracy. There are also several approaches to underwater tunnels,
1596-936: A report by the Environmental Integrity Project , Earthjustice , the Prairie Rivers Network, and the Sierra Club . Tennessee In 2008, the Kingston Fossil Plant in Roane County spilled 1.1 billion gallons of coal ash into the Emory and Clinch Rivers and damaged nearby residential areas. It is the largest industrial spill in the U.S. Groundwater surrounding every single one of the 16 coal-burning power plants in Texas has been polluted by coal ash, according to
1710-421: A specialized method called clay-kicking for digging tunnels in clay-based soils. The clay-kicker lies on a plank at a 45-degree angle away from the working face and rather than a mattock with his hands, inserts with his feet a tool with a cup-like rounded end, then turns the tool with his hands to extract a section of soil, which is then placed on the waste extract. Clay-kicking is a specialized method developed in
1824-575: A study by the Environmental Integrity Project (EIP). Unsafe levels of arsenic, cobalt, lithium, and other contaminants were found in the groundwater near all the ash dump sites. At 12 of the 16 sites, the EIP analysis found levels of arsenic in the groundwater 10 times higher than the EPA Maximum Contaminant Level ; arsenic has been found to cause several types of cancer. At 10 of the sites, lithium, which causes neurological disease,
1938-434: A tube can be sunk into a body of water, which is called an immersed tunnel. Cut-and-cover is a simple method of construction for shallow tunnels where a trench is excavated and roofed over with an overhead support system strong enough to carry the load of what is to be built above the tunnel. There are two basic forms of cut-and-cover tunnelling: Shallow tunnels are often of the cut-and-cover type (if under water, of
2052-747: A tunnel than a sufficiently strong bridge). Some water crossings are a mixture of bridges and tunnels, such as the Denmark to Sweden link and the Chesapeake Bay Bridge-Tunnel in Virginia . There are particular hazards with tunnels, especially from vehicle fires when combustion gases can asphyxiate users, as happened at the Gotthard Road Tunnel in Switzerland in 2001. One of the worst railway disasters ever,
2166-432: A tunnel. Bridges usually require a larger footprint on each shore than tunnels. In areas with expensive real estate, such as Manhattan and urban Hong Kong , this is a strong factor in favor of a tunnel. Boston's Big Dig project replaced elevated roadways with a tunnel system to increase traffic capacity, hide traffic, reclaim land, redecorate, and reunite the city with the waterfront. The 1934 Queensway Tunnel under
2280-537: A water-bearing fissure that within 24 hours filled a mile of tunnel with water; and one of the Plateau drives intersected methane, that burned for three months. The project was divided into three sections - Inlet, Plateau and Outlet, each of about 27 kilometres (17 mi). In the Contract Documents it was anticipated that that there could be one construction fatality for every mile of tunnel. The tunnel
2394-444: Is a composite material consisting of an asphalt binder and mineral aggregate commonly used to surface roads. Both Class F and Class C fly ash can typically be used as a mineral filler to fill the voids and provide contact points between larger aggregate particles in asphalt concrete mixes. This application is used in conjunction, or as a replacement for, other binders (such as Portland cement or hydrated lime). For use in asphalt pavement,
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#17327800116262508-488: Is allowed in this tunnel tube, and motorcyclists are directed to the other tube. Each level was built with a three-lane roadway, but only two lanes per level are used – the third serves as a hard shoulder within the tunnel. The A86 Duplex is Europe's longest double-deck tunnel. Pulverised Fuel Ash Fly ash , flue ash , coal ash , or pulverised fuel ash (in the UK)— plurale tantum : coal combustion residuals ( CCRs )—is
2622-606: Is an important component of any stabilization project. This allows for the establishment of design criteria, and determination of the proper chemical additive and admixture rate that achieves the desired engineering properties. Stabilization process benefits can include: Higher resistance (R) values, Reduction in plasticity, Lower permeability, Reduction of pavement thickness, Elimination of excavation – material hauling/handling – and base importation, Aids compaction, Provides "all-weather" access onto and within projects sites. Another form of soil treatment closely related to soil stabilization
2736-424: Is disposed of in landfills and ash ponds . Ash that is stored or deposited outdoors can eventually leach toxic compounds into underground water aquifers. For this reason, much of the current debate around fly ash disposal revolves around creating specially lined landfills that prevent the chemical compounds from being leached into the ground water and local ecosystems. Since coal was the dominant energy source in
2850-415: Is generally included in the range 0.01–1 ppm for bituminous coal. The concentrations of other trace elements vary as well according to the kind of coal combusted to form it. Two classes of fly ash are defined by American Society for Testing and Materials (ASTM) C618: Class F fly ash and Class C fly ash. The chief difference between these classes is the amount of calcium, silica, alumina, and iron content in
2964-505: Is intended to carry both the Istanbul metro and a two-level highway, over a length of 6.5 km (4.0 miles). The French A86 Duplex Tunnel [ fr ] in west Paris consists of two bored tunnel tubes, the eastern one of which has two levels for light motorized vehicles, over a length of 10 km (6.2 miles). Although each level offers a physical height of 2.54 m (8.3 ft), only traffic up to 2 m (6.6 ft) tall
3078-433: Is produced, as well as the proportion of fly ash to bottom ash in the waste product. This is due to the different chemical make-up of the coal based on the geology of the area the coal is found and the burning process of the coal in the power plant. When the coal is combusted, it creates an alkaline dust. This alkaline dust can have a pH ranging from 8 to as high as 12. Fly ash dust can be deposited on topsoil increasing
3192-494: Is relatively long and narrow; the length is often much greater than twice the diameter , although similar shorter excavations can be constructed, such as cross passages between tunnels. The definition of what constitutes a tunnel can vary widely from source to source. For example, in the United Kingdom, a road tunnel is defined as "a subsurface highway structure enclosed for a length of 150 metres (490 ft) or more." In
3306-516: Is soil modification, sometimes referred to as "mud drying" or soil conditioning. Although some stabilization inherently occurs in soil modification, the distinction is that soil modification is merely a means to reduce the moisture content of a soil to expedite construction, whereas stabilization can substantially increase the shear strength of a material such that it can be incorporated into the project's structural design. The determining factors associated with soil modification vs soil stabilization may be
3420-401: Is sometimes necessary during the excavation of a tunnel. They are usually circular and go straight down until they reach the level at which the tunnel is going to be built. A shaft normally has concrete walls and is usually built to be permanent. Once the access shafts are complete, TBMs are lowered to the bottom and excavation can start. Shafts are the main entrance in and out of the tunnel until
3534-515: Is that the open building pit is muted after tunnel construction; no roof is placed. Some tunnels are double-deck, for example, the two major segments of the San Francisco–Oakland Bay Bridge (completed in 1936) are linked by a 160-metre (540 ft) double-deck tunnel section through Yerba Buena Island , the largest-diameter bored tunnel in the world. At construction this was a combination bidirectional rail and truck pathway on
Orange–Fish River Tunnel - Misplaced Pages Continue
3648-698: Is the Siloam Tunnel , built in Jerusalem by the kings of Judah around the 8th century BC. Another tunnel excavated from both ends, maybe the second known, is the Tunnel of Eupalinos , which is a tunnel aqueduct 1,036 m (3,400 ft) long running through Mount Kastro in Samos , Greece. It was built in the 6th century BC to serve as an aqueduct . In Ethiopia , the Siqurto foot tunnel , hand-hewn in
3762-518: Is used as a replacement for Portland cement in concrete . The use of fly ash as a pozzolanic ingredient was recognized as early as 1914, although the earliest noteworthy study of its use was in 1937. Roman structures such as aqueducts or the Pantheon in Rome used volcanic ash or pozzolana (which possesses similar properties to fly ash) as pozzolan in their concrete. As pozzolan greatly improves
3876-519: Is used as self-leveling, self-compact backfill material in lieu of compacted earth or granular fill. The strength of flowable fill mixes can range from 50 to 1,200 lbf/in (0.3 to 8.3 MPa ), depending on the design requirements of the project in question. Flowable fill includes mixtures of Portland cement and filler material, and can contain mineral admixtures. Fly ash can replace either the Portland cement or fine aggregate (in most cases, river sand) as
3990-399: Is used in an optimal way to replace cement in concrete production, it must be processed using beneficiation methods like mechanical air classification. But if fly ash is used as a filler to replace sand in concrete production, unbeneficiated fly ash with higher LOI can be also used. Especially important is the ongoing quality verification. This is mainly expressed by quality control seals like
4104-770: The Orange–Fish Water Scheme where it diverts water from the Orange River to the Great Fish River and the semi-arid areas of Eastern Cape province. The Orange River is the largest river in South Africa by volume, and the longest. It rises in the Drakensberg Mountains of Lesotho and flows Westwards through increasingly drier country to discharge into the South Atlantic at Oranjemund, where, through evaporation and abstraction,
4218-569: The Balvano train disaster , was caused by a train stalling in the Armi tunnel in Italy in 1944, killing 426 passengers. Designers try to reduce these risks by installing emergency ventilation systems or isolated emergency escape tunnels parallel to the main passage. Government funds are often required for the creation of tunnels. When a tunnel is being planned or constructed, economics and politics play
4332-641: The Bureau of Indian Standards mark or the DCL mark of the Dubai Municipality. In the past, fly ash produced from coal combustion was simply entrained in flue gases and dispersed into the atmosphere. This created environmental and health concerns that prompted laws in heavily industrialized countries like the United States that have reduced fly ash emissions to less than 1% of ash produced. Worldwide, more than 65% of fly ash produced from coal power stations
4446-471: The Port Authority of New York and New Jersey was not aware of this bill and had not asked for a grant for such a project. Increased taxes to finance a large project may cause opposition. Tunnels are dug in types of materials varying from soft clay to hard rock. The method of tunnel construction depends on such factors as the ground conditions, the groundwater conditions, the length and diameter of
4560-848: The Queens-Midtown Tunnel between Manhattan and the borough of Queens on Long Island ; the Detroit-Windsor Tunnel between Michigan and Ontario ; and the Elizabeth River tunnels between Norfolk and Portsmouth, Virginia ; the 1934 River Mersey road Queensway Tunnel ; the Western Scheldt Tunnel , Zeeland, Netherlands; and the North Shore Connector tunnel in Pittsburgh, Pennsylvania . The Sydney Harbour Tunnel
4674-472: The River Mersey at Liverpool was chosen over a massively high bridge partly for defense reasons; it was feared that aircraft could destroy a bridge in times of war, not merely impairing road traffic but blocking the river to navigation. Maintenance costs of a massive bridge to allow the world's largest ships to navigate under were considered higher than for a tunnel. Similar conclusions were reached for
Orange–Fish River Tunnel - Misplaced Pages Continue
4788-679: The United Kingdom of digging tunnels in strong clay-based soil structures. This method of cut and cover construction required relatively little disturbance of property during the renewal of the United Kingdom's then ancient sewerage systems. It was also used during the First World War by Royal Engineer tunnelling companies placing mines beneath German lines, because it was almost silent and so not susceptible to listening methods of detection. Tunnel boring machines (TBMs) and associated back-up systems are used to highly automate
4902-610: The canton of Glarus . The borehole has a diameter of 8.03 metres (26.3 ft). The four TBMs used for excavating the 57-kilometre (35 mi) Gotthard Base Tunnel , in Switzerland , had a diameter of about 9 metres (30 ft). A larger TBM was built to bore the Green Heart Tunnel (Dutch: Tunnel Groene Hart) as part of the HSL-Zuid in the Netherlands, with a diameter of 14.87 metres (48.8 ft). This in turn
5016-475: The metric system , but special dispensation was made for this project to use Imperial measure throughout, which was half-built at the time. Construction started in 1966; preliminary works included a tarred road running parallel to the route of the tunnel, and three towns, Oviston at the North end, one in the middle called "Mid-shaft", on the watershed plateau some 600 feet higher than on either side, and "Teebus" at
5130-489: The water table . This pressurizes the ground ahead of the TBM cutter head to balance the water pressure. The operators work in normal air pressure behind the pressurized compartment, but may occasionally have to enter that compartment to renew or repair the cutters. This requires special precautions, such as local ground treatment or halting the TBM at a position free from water. Despite these difficulties, TBMs are now preferred over
5244-686: The "CCR Part A" and "CCR Part B" rules. The rules require some facilities to retrofit their impoundments with liners, while other facilities may propose alternative designs and request additional time to achieve compliance. In March 2023 published a proposed rule that would strengthen wastewater limits for discharges to surface waters. Coal contains trace levels of trace elements (such as arsenic , barium , beryllium , boron , cadmium , chromium , thallium , selenium , molybdenum and mercury ), many of which are highly toxic to humans and other life. Therefore, fly ash obtained after combustion of this coal contains enhanced concentrations of these elements and
5358-689: The 16th century as a metaphor for a narrow, confined space like the inside of a cask. Some of the earliest tunnels used by humans were paleoburrows excavated by prehistoric mammals. Much of the early technology of tunneling evolved from mining and military engineering . The etymology of the terms "mining" (for mineral extraction or for siege attacks ), " military engineering ", and " civil engineering " reveals these deep historic connections. Predecessors of modern tunnels were adits that transported water for irrigation , drinking, or sewerage . The first qanats are known from before 2000 BC. The earliest tunnel known to have been excavated from both ends
5472-638: The 1960s. The main idea of this method is to use the geological stress of the surrounding rock mass to stabilize the tunnel, by allowing a measured relaxation and stress reassignment into the surrounding rock to prevent full loads becoming imposed on the supports. Based on geotechnical measurements, an optimal cross section is computed. The excavation is protected by a layer of sprayed concrete, commonly referred to as shotcrete . Other support measures can include steel arches, rock bolts, and mesh. Technological developments in sprayed concrete technology have resulted in steel and polypropylene fibers being added to
5586-716: The 1971 Kingsway Tunnel under the Mersey. In Hampton Roads, Virginia , tunnels were chosen over bridges for strategic considerations; in the event of damage, bridges might prevent US Navy vessels from leaving Naval Station Norfolk . Water-crossing tunnels built instead of bridges include the Seikan Tunnel in Japan; the Holland Tunnel and Lincoln Tunnel between New Jersey and Manhattan in New York City ;
5700-1128: The American Coal Ash Association. Coal ash uses include (approximately in order of decreasing importance): Other applications include cosmetics , toothpaste , kitchen counter tops, floor and ceiling tiles, bowling balls , flotation devices, stucco , utensils, tool handles, picture frames, auto bodies and boat hulls , cellular concrete, geopolymers , roof tiles , roofing granules, decking, fireplace mantles , cinder block , PVC pipe , structural insulated panels , house siding and trim, running tracks, blasting grit, recycled plastic lumber , utility poles and crossarms, railway sleepers , highway noise barriers , marine pilings , doors, window frames, scaffolding, sign posts, crypts, columns, railroad ties, vinyl flooring, paving stones, shower stalls, garage doors, park benches, landscape timbers, planters, pallet blocks, molding, mail boxes, artificial reef , binding agent, paints and undercoatings, metal castings , and filler in wood and plastic products. Owing to its pozzolanic properties, fly ash
5814-531: The CCPs such as arsenic, beryllium, boron, cadmium, chromium, chromium VI, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, and vanadium, along with dioxins and polycyclic aromatic hydrocarbons . There is no US governmental registration or labelling of fly ash utilization in the different sectors of the economy – industry, infrastructures and agriculture. Fly ash utilization survey data, acknowledged as incomplete, are published annually by
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#17327800116265928-663: The Environment issued a fine of $ 1 million to Constellation. Nearby residents filed a lawsuit against Constellation and in 2008 the company settled the case for $ 54 million. In 2014, residents living near the Buck Steam Station in Dukeville, North Carolina , were told that "coal ash pits near their homes could be leaching dangerous materials into groundwater". Illinois has many coal ash dumpsites with coal ash generated by coal-burning electric power plants. Of
6042-577: The Ghatghar dam project in Maharashtra, India. Due to the spherical shape of fly ash particles, it can increase workability of cement while reducing water demand. Proponents of fly ash claim that replacing Portland cement with fly ash reduces the greenhouse gas "footprint" of concrete, as the production of one ton of Portland cement generates approximately one ton of CO 2 , compared to no CO 2 generated with fly ash. New fly ash production, i.e.,
6156-709: The Middle Ages, crosses a mountain ridge. In the Gaza Strip , the network of tunnels was used by Jewish strategists as rock-cut shelters, in first links to Judean resistance against Roman rule in the Bar Kokhba revolt during the 2nd century AD. A major tunnel project must start with a comprehensive investigation of ground conditions by collecting samples from boreholes and by other geophysical techniques. An informed choice can then be made of machinery and methods for excavation and ground support, which will reduce
6270-471: The Plateau Section were Orange River Contractors (Orco), which was composed of firms from South Africa, France, and the United States. By the time construction was complete, there had been 34 fatalities. The Outlet section had two shafts and an outlet drive, to discharge the water into the existing Great Fish River watercourse. The Outlet Section was contracted to J. C. I. di Penta, a consortium that
6384-501: The South end. These towns included such facilities as a clubhouse, tennis courts, a community hall, primary school, clinic, etc. At Oviston there was also a power station to provide electricity to the tunnels and to the towns, and also an 80-kilometre (50 mi) transmission line. Other facilities included contractor's yards, a testing laboratory, and offices for the staff. The tunnel is 5.35 metres (17.6 ft) in finished diameter, with
6498-509: The United Kingdom, fly ash has been used for over fifty years to make concrete building blocks . They are widely used for the inner skin of cavity walls . They are naturally more thermally insulating than blocks made with other aggregates. Ash bricks have been used in house construction in Windhoek, Namibia , since the 1970s. There is, however, a problem with the bricks in that they tend to fail or produce unsightly pop-outs. This happens when
6612-729: The United States for many decades, power companies often located their coal plants near metropolitan areas. Compounding the environmental issues, the coal plants need significant amounts of water to operate their boilers, leading coal plants (and later their fly ash storage basins) to be located near metropolitan areas and near rivers and lakes which are often used as drinking supplies by nearby cities. Many of those fly ash basins were unlined and also at great risk of spilling and flooding from nearby rivers and lakes. For example, Duke Energy in North Carolina has been involved in several major lawsuits related to its coal ash storage and spills into
6726-536: The United States, the NFPA definition of a tunnel is "An underground structure with a design length greater than 23 m (75 ft) and a diameter greater than 1,800 millimetres (5.9 ft)." The word "tunnel" comes from the Middle English tonnelle , meaning "a net", derived from Old French tonnel , a diminutive of tonne ("cask"). The modern meaning, referring to an underground passageway, evolved in
6840-411: The United States. Seventy-five percent of the fly ash must have a fineness of 45 μm or less, and have a carbon content, measured by the loss on ignition (LOI), of less than 4%. In the US, LOI must be under 6%. The particle size distribution of raw fly ash tends to fluctuate constantly, due to changing performance of the coal mills and the boiler performance. This makes it necessary that, if fly ash
6954-468: The arid Karoo . The situation was aggravated by the reduction in capacity of many of the existing dams due to heavy silt deposits. The project to alleviate this situation comprised two interdependent engineering schemes — neither of which was of any use without the other. First, a dam had to be built across the Orange River, then a tunnel had to be driven to take the water across the watershed into
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#17327800116267068-425: The ash. The chemical properties of the fly ash are largely influenced by the chemical content of the coal burned (i.e., anthracite , bituminous , and lignite ). Not all fly ashes meet ASTM C618 requirements, although depending on the application, this may not be necessary. Fly ash used as a cement replacement must meet strict construction standards, but no standard environmental regulations have been established in
7182-400: The blocky nature of rocks, the exact location of fault zones, or the stand-up times of softer ground. This may be a particular concern in large-diameter tunnels. To give more information, a pilot tunnel (or "drift tunnel") may be driven ahead of the main excavation. This smaller tunnel is less likely to collapse catastrophically should unexpected conditions be met, and it can be incorporated into
7296-532: The bricks come into contact with moisture and a chemical reaction occurs causing the bricks to expand. In India, fly ash bricks are used for construction. Leading manufacturers use an industrial standard known as "Pulverized fuel ash for lime-Pozzolana mixture" using over 75% post-industrial recycled waste, and a compression process. This produces a strong product with good insulation properties and environmental benefits. Fly ash particles have proved their potential as good reinforcement with aluminum alloys and show
7410-525: The burning of coal, produces approximately 20 to 30 tons of CO 2 per ton of fly ash. Since the worldwide production of Portland cement is expected to reach nearly 2 billion tons by 2010, replacement of any large portion of this cement by fly ash could significantly reduce carbon emissions associated with construction, as long as the comparison takes the production of fly ash as a given. Fly ash properties are unusual among engineering materials. Unlike soils typically used for embankment construction, fly ash has
7524-502: The concrete mix to improve lining strength. This creates a natural load-bearing ring, which minimizes the rock's deformation . By special monitoring the NATM method is flexible, even at surprising changes of the geomechanical rock consistency during the tunneling work. The measured rock properties lead to appropriate tools for tunnel strengthening . In pipe jacking , hydraulic jacks are used to push specially made pipes through
7638-597: The concrete to be placed up to six hours after mixing, and it also contained accelerators, to enable the shutter to be moved after only eighteen hours. The speed of the shutter was about 1,000 feet (300 m) a week. The tunnel ranges in depth below the surface between 80 metres (262 ft) and 380 metres (1,247 ft). It is on a gradient of 1:2000. It was engineered by the British firm of Consulting Engineers, Sir William Halcrow & Partners, in association with Messrs Keeve Steyn and Partners of Johannesburg. The Client
7752-399: The concrete's final strength and increase its chemical resistance and durability. Fly ash can significantly improve the workability of concrete. Recently, techniques have been developed to replace partial cement with high-volume fly ash (50% cement replacement). For roller-compacted concrete (RCC)[used in dam construction], replacement values of 70% have been achieved with processed fly ash at
7866-403: The demand for virgin materials that would need quarrying and cheap substitution for materials such as Portland cement . About 52 percent of CCPs in the U.S. were recycled for "beneficial uses" in 2019, according to the American Coal Ash Association. In Australia about 47% of coal ash was recycled in 2020. The chief benefit of recycling is to stabilize the environmentally harmful components of
7980-409: The entire tunnelling process, reducing tunnelling costs. In certain predominantly urban applications, tunnel boring is viewed as a quick and cost-effective alternative to laying surface rails and roads. Expensive compulsory purchase of buildings and land, with potentially lengthy planning inquiries, is eliminated. Disadvantages of TBMs arise from their usually large size – the difficulty of transporting
8094-442: The exhaust gases and is collected by electrostatic precipitators or filter bags. Since the particles solidify rapidly while suspended in the exhaust gases, fly ash particles are generally spherical in shape and range in size from 0.5 μm to 300 μm. The major consequence of the rapid cooling is that few minerals have time to crystallize, and that mainly amorphous, quenched glass remains. Nevertheless, some refractory phases in
8208-457: The existing moisture content, the end use of the soil structure and ultimately the cost benefit provided. Equipment for the stabilization and modification processes include: chemical additive spreaders, soil mixers (reclaimers), portable pneumatic storage containers, water trucks, deep lift compactors, motor graders. Fly ash is also used as a component in the production of flowable fill (also called controlled low strength material, or CLSM), which
8322-445: The federal standard for drinking water . Fly ash can contaminate surface water through erosion , surface runoff , airborne particles landing on the water surface, contaminated ground water moving into surface waters, flooding drainage , or discharge from a coal ash pond. Fish can be contaminated a couple of different ways. When the water is contaminated by fly ash, the fish can absorb the toxins through their gills. The sediment in
8436-441: The final tunnel or used as a backup or emergency escape passage. Alternatively, horizontal boreholes may sometimes be drilled ahead of the advancing tunnel face. Other key geotechnical factors: For water crossings, a tunnel is generally more costly to construct than a bridge. However, both navigational and traffic considerations may limit the use of high bridges or drawbridges intersecting with shipping channels, necessitating
8550-416: The flue gases reach the chimneys. Together with bottom ash removed from the bottom of the boiler, it is known as coal ash . Depending upon the source and composition of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO 2 ) (both amorphous and crystalline ), aluminium oxide (Al 2 O 3 ) and calcium oxide (CaO),
8664-532: The fly ash must meet mineral filler specifications outlined in ASTM D242 . The hydrophobic nature of fly ash gives pavements better resistance to stripping. Fly ash has also been shown to increase the stiffness of the asphalt matrix, improving rutting resistance and increasing mix durability. Coal and shale oil fly ashes have been used as a filler for thermoplastics that could be used for injection molding applications. More recently, fly ash has been used as
8778-400: The following elements or compounds found in trace concentrations (up to hundreds of ppm): gallium , arsenic , beryllium , boron , cadmium , chromium , hexavalent chromium , cobalt , lead , manganese , mercury , molybdenum , selenium , strontium , thallium , and vanadium , along with very small concentrations of dioxins , PAH compounds , and other trace carbon compounds. In
8892-405: The ground behind a TBM or shield. This method is commonly used to create tunnels under existing structures, such as roads or railways. Tunnels constructed by pipe jacking are normally small diameter bores with a maximum size of around 3.2 metres (10 ft). Box jacking is similar to pipe jacking, but instead of jacking tubes, a box-shaped tunnel is used. Jacked boxes can be a much larger span than
9006-599: The heat of hydration allowing thicker placements to occur. Data for these can be found at the US Bureau of Reclamation. This has also been demonstrated in the Ghatghar Dam Project in India . There are several techniques for manufacturing construction bricks from fly ash, producing a wide variety of products. One type of fly ash brick is manufactured by mixing fly ash with an equal amount of clay, then firing in
9120-640: The immersed-tube type), while deep tunnels are excavated, often using a tunnelling shield . For intermediate levels, both methods are possible. Large cut-and-cover boxes are often used for underground metro stations, such as Canary Wharf tube station in London. This construction form generally has two levels, which allows economical arrangements for ticket hall, station platforms, passenger access and emergency egress, ventilation and smoke control, staff rooms, and equipment rooms. The interior of Canary Wharf station has been likened to an underground cathedral, owing to
9234-735: The improvement of physical and mechanical properties. In particular, the compression strength, tensile strength, and hardness increase when the percentage of fly ash content is increased, whereas the density decreases. The presence of fly ash cenospheres in a pure Al matrix decreases its coefficient of thermal expansion (CTE). It may be possible to use vacuum distillation in order to extract germanium and tungsten from fly ash and recycle them. Fly ash, in view of its alkalinity and water absorption capacity, may be used in combination with other alkaline materials to transform sewage sludge into organic fertilizer or biofuel . Fly ash, when treated with sodium hydroxide , appears to function well as
9348-435: The inevitable smoke and steam. A major disadvantage of cut-and-cover is the widespread disruption generated at the surface level during construction. This, and the availability of electric traction, brought about London Underground's switch to bored tunnels at a deeper level towards the end of the 19th century. Prior to the replacement of manual excavation by the use of boring machines, Victorian tunnel excavators developed
9462-468: The large TBM to the site of tunnel construction, or (alternatively) the high cost of assembling the TBM on-site, often within the confines of the tunnel being constructed. There are a variety of TBM designs that can operate in a variety of conditions, from hard rock to soft water-bearing ground. Some TBMs, the bentonite slurry and earth-pressure balance types, have pressurized compartments at the front end, allowing them to be used in difficult conditions below
9576-502: The leakage of ash into the water basin. The recycling of fly ash has become an increasing concern in recent years due to increasing landfill costs and current interest in sustainable development . As of 2017 , coal-fired power plants in the US reported producing 38.2 million short tons (34.7 × 10 ^ t) of fly ash, of which 24.1 million short tons (21.9 × 10 ^ t) were reused in various applications. Environmental benefits to recycling fly ash includes reducing
9690-969: The length. A pipeline differs significantly from a tunnel, though some recent tunnels have used immersed tube construction techniques rather than traditional tunnel boring methods. A tunnel may be for foot or vehicular road traffic , for rail traffic, or for a canal . The central portions of a rapid transit network are usually in the tunnel. Some tunnels are used as sewers or aqueducts to supply water for consumption or for hydroelectric stations. Utility tunnels are used for routing steam, chilled water, electrical power or telecommunication cables, as well as connecting buildings for convenient passage of people and equipment. Secret tunnels are built for military purposes, or by civilians for smuggling of weapons , contraband , or people . Special tunnels, such as wildlife crossings , are built to allow wildlife to cross human-made barriers safely. Tunnels can be connected together in tunnel networks . A tunnel
9804-629: The lower deck with automobiles above, now converted to one-way road vehicle traffic on each deck. In Turkey, the Eurasia Tunnel under the Bosphorus , opened in 2016, has at its core a 5.4 km (3.4 miles) two-deck road tunnel with two lanes on each deck. Additionally, in 2015 the Turkish government announced that it will build three -level tunnel, also under the Bosporus. The tunnel
9918-420: The main mineral compounds in coal-bearing rock strata . The use of fly ash as a lightweight aggregate (LWA) offers a valuable opportunity to recycle one of the largest waste streams in the US. In addition, fly ash can offer many benefits, both economically and environmentally when utilized as a LWA. The minor constituents of fly ash depend upon the specific coal bed composition but may include one or more of
10032-483: The older method of tunnelling in compressed air, with an airlock/decompression chamber some way back from the TBM, which required operators to work in high pressure and go through decompression procedures at the end of their shifts, much like deep-sea divers . In February 2010, Aker Wirth delivered a TBM to Switzerland, for the expansion of the Linth–Limmern Power Stations located south of Linthal in
10146-540: The operation of empty and loaded trains at the same time. The temporary way is replaced by the permanent way at completion, thus explaining the term " Perway ". The vehicles or traffic using a tunnel can outgrow it, requiring replacement or enlargement: An open building pit consists of a horizontal and a vertical boundary that keeps groundwater and soil out of the pit. There are several potential alternatives and combinations for (horizontal and vertical) building pit boundaries. The most important difference with cut-and-cover
10260-409: The pH and affecting the plants and animals in the surrounding ecosystem. Trace elements, such as, iron , manganese , zinc , copper , lead , nickel , chromium , cobalt , arsenic , cadmium , and mercury , can be found at higher concentrations compared to bottom ash and the parent coal. Fly ash can leach toxic constituents that can be anywhere from one hundred to one thousand times greater than
10374-493: The past, fly ash was generally released into the atmosphere , but air pollution control standards now require that it be captured prior to release by fitting pollution control equipment . In the United States, fly ash is generally stored at coal power plants or placed in landfills. About 43% is recycled, often used as a pozzolan to produce hydraulic cement or hydraulic plaster and a replacement or partial replacement for Portland cement in concrete production. Pozzolans ensure
10488-549: The potential of the ash to cause groundwater pollution is significant. In the US there are documented cases of groundwater pollution that followed ash disposal or utilization without the necessary protection having been put in place. Constellation Energy disposed fly ash generated by its Brandon Shores Generating Station at a former sand and gravel mine in Gambrills, Maryland , during 1996 to 2007. The ash contaminated groundwater with heavy metals. The Maryland Department of
10602-522: The project is completed. If a tunnel is going to be long, multiple shafts at various locations may be bored so that entrance to the tunnel is closer to the unexcavated area. Once construction is complete, construction access shafts are often used as ventilation shafts , and may also be used as emergency exits. The New Austrian Tunnelling method (NATM)—also referred to as the Sequential Excavation Method (SEM) —was developed in
10716-490: The proper machinery must be selected. Large infrastructure projects require millions or even billions of dollars, involving long-term financing, usually through issuance of bonds . The costs and benefits for an infrastructure such as a tunnel must be identified. Political disputes can occur, as in 2005 when the US House of Representatives approved a $ 100 million federal grant to build a tunnel under New York Harbor. However,
10830-951: The pulverized coal do not melt (entirely), and remain crystalline. In consequence, fly ash is a heterogeneous material. SiO 2 , Al 2 O 3 , Fe 2 O 3 and occasionally CaO are the main chemical components present in fly ashes. The mineralogy of fly ashes is very diverse. The main phases encountered are a glass phase, together with quartz , mullite and the iron oxides hematite , magnetite and/or maghemite . Other phases often identified are cristobalite , anhydrite , free lime , periclase , calcite , sylvite , halite , portlandite , rutile and anatase . The Ca -bearing minerals anorthite , gehlenite , akermanite and various calcium silicates and calcium aluminates identical to those found in Portland cement can be identified in Ca-rich fly ashes. The mercury content can reach 1 ppm , but
10944-482: The risk of encountering unforeseen ground conditions. In planning the route, the horizontal and vertical alignments can be selected to make use of the best ground and water conditions. It is common practice to locate a tunnel deeper than otherwise would be required, in order to excavate through solid rock or other material that is easier to support during construction. Conventional desk and preliminary site studies may yield insufficient information to assess such factors as
11058-470: The setting of concrete and plaster and provide concrete with more protection from wet conditions and chemical attack. In the case that fly (or bottom) ash is not produced from coal, for example when solid waste is incinerated in a waste-to-energy facility to produce electricity, the ash may contain higher levels of contaminants than coal ash. In that case the ash produced is often classified as hazardous waste . Fly ash material solidifies while suspended in
11172-430: The shear strength of a soil and/or control the shrink-swell properties of a soil, thus improving the load-bearing capacity of a sub-grade to support pavements and foundations. Stabilization can be used to treat a wide range of sub-grade materials from expansive clays to granular materials. Stabilization can be achieved with a variety of chemical additives including lime, fly ash, and Portland cement. Proper design and testing
11286-542: The sheer size of the excavation. This contrasts with many traditional stations on London Underground , where bored tunnels were used for stations and passenger access. Nevertheless, the original parts of the London Underground network, the Metropolitan and District Railways, were constructed using cut-and-cover. These lines pre-dated electric traction and the proximity to the surface was useful to ventilate
11400-604: The state's 24 coal ash dumpsites with available data, 22 have released toxic pollutants including arsenic , cobalt , and lithium , into groundwater, rivers and lakes. The hazardous toxic chemicals dumped into the water in Illinois by these coal ash dumpsites include more than 300,000 pounds of aluminum, 600 pounds of arsenic, nearly 300,000 pounds of boron, over 200 pounds of cadmium, over 15,000 pounds of manganese, roughly 1,500 pounds of selenium, roughly 500,000 pounds of nitrogen, and nearly 40 million pounds of sulfate, according to
11514-511: The strength and durability of concrete, the use of ash is a key factor in their preservation. Use of fly ash as a partial replacement for Portland cement is particularly suitable but not limited to Class C fly ashes. Class "F" fly ashes can have volatile effects on the entrained air content of concrete, causing reduced resistance to freeze/thaw damage. Fly ash often replaces up to 30% by mass of Portland cement, but can be used in higher dosages in certain applications. In some cases, fly ash can add to
11628-400: The tunnel drive, the depth of the tunnel, the logistics of supporting the tunnel excavation, the final use and the shape of the tunnel and appropriate risk management. There are three basic types of tunnel construction in common use. Cut-and-cover tunnels are constructed in a shallow trench and then covered over. Bored tunnels are constructed in situ, without removing the ground above. Finally,
11742-494: The tunnel's length of 83 km (52 mi) was the longest continuous enclosed aqueduct in the southern hemisphere and the second-longest water supply tunnel in the world. Over 200 000 m of concrete was used to line the tunnel which has a maximum throughput of 54 m/s (1,900 cu ft/s). Construction was not without incident, and was tested both by flood and by fire. - the Inlet tunnel drive South from Shaft 2 intersected
11856-428: The two most common being bored tunnels or immersed tubes , examples are Bjørvika Tunnel and Marmaray . Submerged floating tunnels are a novel approach under consideration; however, no such tunnels have been constructed to date. During construction of a tunnel it is often convenient to install a temporary railway, particularly to remove excavated spoil , often narrow gauge so that it can be double track to allow
11970-618: The volume was far less than it was at the location of the Gariep Dam . The inlet tower at 30°41′26″S 25°45′46″E / 30.69056°S 25.76278°E / -30.69056; 25.76278 takes water from the Gariep Dam at Oviston ; the name Oviston is an acronym based on the Afrikaans Oranje-VISrivier TONnel . After traversing due south under the Suurberg mountain plateau, it releases
12084-572: The water can also become contaminated. The contaminated sediment can contaminate the food sources for the fish, the fish can then become contaminated from consuming those food sources. This can then lead to contamination of organisms that consume these fish, such as, birds, bear, and even humans. Once exposed to fly ash contaminating the water, aquatic organisms have had increased levels of calcium , zinc, bromine , gold, cerium, chromium, selenium, cadmium, and mercury. Soils contaminated by fly ash showed an increase in bulk density and water capacity, but
12198-433: The water quality. Each of the four inlets can be sealed off to allow complete de-watering of the tunnel for routine maintenance. Tunnel A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each end, though there may be access and ventilation openings at various points along
12312-629: The water to the Teebus Spruit (tunnel outlet at 31°25′22.5″S 25°38′14″E / 31.422917°S 25.63722°E / -31.422917; 25.63722 ), to the Groot Brak River and onwards to the valleys of the Great Fish River and the Sundays River . The tunnel is on what is called a "self-cleansing" gradient of 2% from north to south. During construction, South Africa changed over from Imperial measurement to
12426-575: Was constructed to provide a second harbour crossing and to alleviate traffic congestion on the Sydney Harbour Bridge , without spoiling the iconic view. Other reasons for choosing a tunnel instead of a bridge include avoiding difficulties with tides, weather, and shipping during construction (as in the 51.5-kilometre or 32.0-mile Channel Tunnel ), aesthetic reasons (preserving the above-ground view, landscape, and scenery), and also for weight capacity reasons (it may be more feasible to build
12540-563: Was formed by two firms - Johannesburg Consolidated Investment Company (JCI) from South Africa, and Impresa Ing. di Penta from Italy. The intake tower is situated on the south bank of the Gariep Reservoir at Oviston , approximately 19 km (12 mi) upstream of the dam wall. Seen from above, the intake tower is shaped like a four-leaf clover with each leaf containing an inlet gate - all at different levels. In this manner, water can be drawn from different levels to help control
12654-420: Was found in the groundwater at concentrations more than 1,000 micrograms per liter, which is 25 times the maximum acceptable level. The report concludes that the fossil fuel industry in Texas has failed to comply with federal regulations on coal ash processing, and state regulators have failed to protect the groundwater. The effect of fly ash on the environment can vary based on the thermal power plant where it
12768-708: Was opened in 1976. The Contractor on the Inlet Section was Batignolles-Cogefar-African Batignolles, a consortium of French, Italian, and South African firms. There was an inlet drive and two inclined shafts. At each entry was a small alcove with a small statue of Saint Barbara , the Patron Saint of those who use explosives - tunnellers, miners and artillerymen. By the time construction was complete, there had been 17 fatalities, all but one were related to railway operations rather than tunnelling per se. The mid-section had three deep vertical shafts. The contractors on
12882-732: Was superseded by the Madrid M30 ringroad , Spain, and the Chong Ming tunnels in Shanghai , China. All of these machines were built at least partly by Herrenknecht . As of August 2013 , the world's largest TBM was " Big Bertha ", a 17.5-metre (57.5 ft) diameter machine built by Hitachi Zosen Corporation , which dug the Alaskan Way Viaduct replacement tunnel in Seattle, Washington (US). A temporary access shaft
12996-566: Was the South African Department of Water Affairs . Halcrow's senior partner, Sir Alan Muir-Wood , sometimes known as "the father of modern tunnelling", worked on many of the world's leading tunnel projects, including the Orange-Fish Tunnel; the senior Engineer in charge of the design & supervision was Barry Kidd, who died young, before construction was completed. The tunnel was opened in 1975. When completed
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