Misplaced Pages

#361638

39-584: The Blackwall Rock was a reef in the River Thames in East London . The rock provided a useful shelter for moored vessels, but also proved a hazardous obstruction to river navigation. It was removed in the early 19th century following the opening of the adjacent West India Docks . Blackwall Rock was located a short distance upriver of Blackwall Stairs, the southern end of a causeway from Poplar High Street which crossed extensive marshland , between

78-402: A concern. Vibratory pile hammers contain a system of counter-rotating eccentric weights, powered by hydraulic motors, and designed so that horizontal vibrations cancel out, while vertical vibrations are transmitted into the pile. The pile driving machine positioned over the pile with an excavator or crane, and is fastened to the pile by a clamp and/or bolts. Vibratory hammers can drive or extract

117-427: A finished structure. The term "pile driver" is also used to describe members of the construction crew associated with the task, also colloquially known as "pile bucks". The most common form of pile driver uses a heavy weight situated between vertical guides placed above a pile. The weight is raised by some motive power (which may include hydraulics , steam , diesel , electrical motor, or manual labor). At its apex

156-466: A greater force on the already moving pile, driving it further into the ground. The reaction of the explosion rebounding from the resistance of the pile drives the piston upward. As the piston rises, the exhaust ports open, releasing the exhaust gases to the atmosphere. After the piston stops its upward movement, it again falls by gravity to start another cycle. Vertical travel leads come in two main forms: spud and box lead types. Box leads are very common in

195-428: A habitat for mobile benthic organisms. These biotic reef types take on additional names depending upon how the reef lies in relation to the land, if any. Reef types include fringing reefs , barrier reefs , and atolls . A fringing reef is a reef that is attached to an island. Whereas, a barrier reef forms a calcareous barrier around an island, resulting in a lagoon between the shore and the reef. Conversely, an atoll

234-425: A pile. Extraction is commonly used to recover steel I-beams used in temporary foundation shoring. Hydraulic fluid is supplied to the driver by a diesel engine-powered pump mounted in a trailer or van, and connected to the driver head via hoses. When the pile driver is connected to a dragline excavator , it is powered by the excavator's diesel engine. Vibratory pile drivers are often chosen to mitigate noise, as when

273-668: A skeletal framework. A microbial mound might be built exclusively or primarily by cyanobacteria . Examples of biostromes formed by cyanobacteria occur in the Great Salt Lake in Utah , United States, and in Shark Bay on the coast of Western Australia . Cyanobacteria do not have skeletons, and individual organisms are microscopic. However, they can encourage the precipitation or accumulation of calcium carbonate to produce distinct sediment bodies in composition that have relief on

312-470: Is a ring reef with no land present. The reef front, facing the ocean, is a high energy locale. Whereas, the internal lagoon will be at a lower energy with fine grained sediments. Both mounds and reefs are considered to be varieties of organosedimentary buildups, which are sedimentary features, built by the interaction of organisms and their environment. These interactions have a synoptic relief and whose biotic composition differs from that found on and beneath

351-505: Is developed. The reaction-based machines operate at only 69 dB at 23 ft allowing for installation and extraction of piles in close proximity to sensitive areas where traditional methods may threaten the stability of existing structures. Such equipment and methods are specified in portions of the internal drainage system in the New Orleans area after Hurricane Katrina , as well as projects where noise, vibration and access are

390-622: The Old Norse word rif, meaning "rib" or "reef". Rif comes from the Proto-Germanic term ribją meaning "rib". Reefs may be classified in terms of their origin, geographical location, depth, and topography . For example a tropical coral fringing reef, or a temperate rocky intertidal reef. A variety of biotic reef types exists, including oyster reefs and sponge reefs , but the most massive and widely distributed are tropical coral reefs . Although corals are major contributors to

429-476: The Rigs-to-Reefs program), scuttling ships , or by deploying rubble or construction debris . Other artificial reefs are purpose built (e.g. the reef balls ) from PVC or concrete. Shipwrecks become artificial reefs on the seafloor. Regardless of construction method, artificial reefs generally provide stable hard surfaces where algae and invertebrates such as barnacles , corals, and oysters attach;

SECTION 10

#1732786674362

468-753: The River Thames , Robert Edington wrote that he surveyed the rock under the direction of the Corporation of the City of London 's harbourmaster , Captain John Raymond Snow. Prior to his survey, Edington was under the impression that the rock was 40 by 30 feet (12.2 m × 9.1 m); Abraham Rees 's Cyclopædia , published shortly before Edington's survey, had given these measurements. Rees asserted that newspaper reports of one of Thomas Boddington 's West Indiaman vessels being wrecked on

507-555: The Southern United States and spud leads are common in the Northern United States, Canada and Europe. A hydraulic hammer is a modern type of piling hammer used instead of diesel and air hammers for driving steel pipe, precast concrete , and timber piles. Hydraulic hammers are more environmentally acceptable than older, less efficient hammers as they generate less noise and pollutants. In many cases

546-578: The accumulation of attached marine life in turn provides intricate structure and food for assemblages of fish. Pile driving A pile driver is a heavy-duty tool used to drive piles into soil to build piers, bridges, cofferdams , and other "pole" supported structures, and patterns of pilings as part of permanent deep foundations for buildings or other structures. Pilings may be made of wood, solid steel, or tubular steel (often later filled with concrete), and may be driven entirely underwater/underground, or remain partially aboveground as elements of

585-481: The adjacent unconsolidated surface with varying relief. They can be found in depth ranges from intertidal to deep water and provide a substrate for a large range of sessile benthic organisms, and shelter for a large range of mobile organisms. They are often located in sub-tropical, temperate, and sub-polar latitudes. Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about

624-495: The construction is near residences or office buildings, or when there is insufficient vertical clearance to permit use of a conventional pile hammer (for example when retrofitting additional piles to a bridge column or abutment footing). Hammers are available with several different vibration rates, ranging from 1200 vibrations per minute to 2400 VPM. The vibration rate chosen is influenced by soil conditions and other factors, such as power requirements and equipment cost. A piling rig

663-425: The crane holding the pile driver — This draws air into the cylinder. Diesel fuel is injected into the cylinder. The weight is dropped, using a quick-release. The weight of the piston compresses the air/fuel mixture, heating it to the ignition point of diesel fuel. The mixture ignites, transferring the energy of the falling weight to the pile head, and driving the weight up. The rising weight draws in fresh air, and

702-434: The cycle continues until the fuel is depleted or is halted by the crew. From an army manual on pile driving hammers: The initial start-up of the hammer requires that the piston (ram) be raised to a point where the trip automatically releases the piston, allowing it to fall. As the piston falls, it activates the fuel pump, which discharges a metered amount of fuel into the ball pan of the impact block. The falling piston blocks

741-624: The device. However, there is evidence that a comparable device was used in the construction of Crannogs at Oakbank and Loch Tay in Scotland as early as 5000 years ago. In 1801 John Rennie came up with a steam pile driver in Britain. Otis Tufts is credited with inventing the steam pile driver in the United States . Ancient pile driving equipment used human or animal labor to lift weights, usually by means of pulleys , then dropping

780-659: The dominant noise is caused by the impact of the hammer on the pile, or the impacts between components of the hammer, so that the resulting noise level can be similar to diesel hammers. Hydraulic press-in equipment installs piles using hydraulic rams to press piles into the ground. This system is preferred where vibration is a concern. There are press attachments that can adapt to conventional pile driving rigs to press 2 pairs of sheet piles simultaneously. Other types of press equipment sit atop existing sheet piles and grip previously driven piles. This system allows for greater press-in and extraction force to be used since more reaction force

819-424: The drilled hole. He conceded that the resulting explosion might blow the caisson "to atoms, and probably be the death of some of the poor men". Early attempts to break the rock with explosives were largely unsuccessful. William Jessop was engaged by Trinity House to undertake the rock's removal; he subcontracted Ralph Walker as a consultant and James Spedding as engineer. Labourers from Trinity House undertook

SECTION 20

#1732786674362

858-655: The entrances of the West and East India Docks . The rock was always a hazard to river traffic, as it sometimes lay less than 3 feet (1 m) below the surface at low tide . The entrance to the West India Docks , just to the south-west of the rock, was substantially obstructed by the reef upon the docks' opening in 1802. In 1803, in his Strictures on the Alarming Progress of the Blackwall Rock in

897-429: The exhaust ports, and compression of fuel trapped in the cylinder begins. The compressed air exerts a pre-load force to hold the impact block firmly against the drive cap and pile. At the bottom of the compression stroke, the piston strikes the impact block, atomizing the fuel and starting the pile on its downward movement. In the instant after the piston strikes, the atomized fuel ignites, and the resulting explosion exerts

936-482: The framework and bulk material comprising a coral reef, the organisms most responsible for reef growth against the constant assault from ocean waves are calcareous algae, especially, although not entirely, coralline algae . Oyster larvae prefer to settle on adult oysters and thereby develop layers building upwards. These eventually form a fairly massive hard stony calcium carbonate structure on which other reef organisms like sponges and seaweeds can grow, and provide

975-608: The framework builders. The corals which build reefs today, the Scleractinia , arose after the Permian–Triassic extinction event that wiped out the earlier rugose corals (as well as many other groups). They became increasingly important reef builders throughout the Mesozoic Era. They may have arisen from a rugose coral ancestor. Rugose corals built their skeletons of calcite and have a different symmetry from that of

1014-674: The location in Earth's history . In addition, reef structures within a sequence of sedimentary rocks provide a discontinuity which may serve as a trap or conduit for fossil fuels or mineralizing fluids to form petroleum or ore deposits . Corals, including some major extinct groups Rugosa and Tabulata , have been important reef builders through much of the Phanerozoic since the Ordovician Period. However, other organism groups, such as calcifying algae, especially members of

1053-492: The physical work. It is also possible that Richard Trevithick worked on the project at some time. Jessop's proposal used a chisel, operated from a barge much as with pile driving . This method successfully reduced the height of the rock by 15 feet (4.6 m), after which a cylindrical coffer dam (also described as being like a diving bell ) was employed to allow workers' access to remove rubble. The works lasted from 1804 to 1808, and cost £42,000. Of this, Spedding's contract

1092-598: The red algae ( Rhodophyta ), and molluscs (especially the rudist bivalves during the Cretaceous Period) have created massive structures at various times. During the Cambrian Period, the conical or tubular skeletons of Archaeocyatha , an extinct group of uncertain affinities (possibly sponges), built reefs. Other groups, such as the Bryozoa, have been important interstitial organisms, living between

1131-574: The river". Most sources give the rock's dimensions as 300-by-150-foot (91 m × 46 m), and an 1846 report by the Tidal Harbours Commission described it as an outcrop of plum-pudding stone . The opening of the West and East India Docks in 1802 and 1803 respectively necessitated the removal of the rock, which obstructed safe navigation to their entrances. Edington proposed the use of prison labour; he recommended that "a hulk with 200 convicts be moored near adjoining

1170-465: The rock were incorrect, and that the relatively recent installation of piling and booms prevented ships from coming near the reef. Edington's subsequent measurements gave the rough dimensions as 600 by 150 feet (183 m × 46 m). He surmised that the cost of the rock's removal—even with the use of prison labour —would be £50,000, and was surprised by some contract tenders who proposed fees of little more than £1,000. He gathered specimens of

1209-438: The rock, and said that it was not a "natural stone". He stated that he had been told the rock was first discovered in the early 18th century when an Indiaman was wrecked upon it—possibly retelling the story refuted by Rees in 1802. Edington described the rock's composition as "a strong cemented iron stone, formed by an elective attraction of the lapidious or earthly basis, to the very numerous metallic particles always suspended in

Blackwall Rock - Misplaced Pages Continue

1248-431: The rock, where these convicts should be employed, with proper instruments in drilling and blasting it up". He then recommended the use of ordnance; his proposal employed an iron caisson to create a dry working area, with explosives being driven into a 24-inch (61 cm) hole. The system would ensure that the explosion would drive the force through the rock, breaking it, rather than forcing the explosive charge back through

1287-421: The rugosan corals (which disappeared in the late Permian). An artificial reef is a human-created underwater structure, typically built to promote marine life in areas with a generally featureless bottom, to control erosion, block ship passage, block the use of trawling nets, or improve surfing . Many reefs are built using objects that were built for other purposes, for example by sinking oil rigs (through

1326-471: The scleractinian corals, whose skeletons are aragonite . However, there are some unusual examples of well-preserved aragonitic rugose corals in the Late Permian . In addition, calcite has been reported in the initial post-larval calcification in a few scleractinian corals. Nevertheless, scleractinian corals (which arose in the middle Triassic) may have arisen from a non-calcifying ancestor independent of

1365-857: The seafloor. Cyanobacterial mounds were most abundant before the evolution of shelly macroscopic organisms, but they still exist today. Stromatolites , for instance, are microbial mounds with a laminated internal structure. Whereas, bryozoans and crinoids , common contributors to marine sediments during the Mississippian period , produce a different kind of mound. Although bryozoans are small and crinoid skeletons disintegrate, bryozoan and crinoid meadows can persist over time and produce compositionally distinct bodies of sediment with depositional relief. The Proterozoic Belt Supergroup contains evidence of possible microbial mat and dome structures similar to stromatolite and chicken reef complexes. Rocky reefs are underwater outcrops of rock projecting above

1404-431: The surrounding sea floor . However, reefs are held up by a macroscopic skeletal framework, as what is seen on coral reefs. Corals and calcareous algae grow on top of one another, forming a three-dimensional framework that is modified in various ways by other organisms and inorganic processes. Conversely, mounds lack a macroscopic skeletal framework. Instead, they are built by microorganisms or by organisms that also lack

1443-620: The weight is released, impacting the pile and driving it into the ground. There are a number of claims to the invention of the pile driver. A mechanically sound drawing of a pile driver appeared as early as 1475 in Francesco di Giorgio Martini 's treatise Trattato di Architectura . Also, several other prominent inventors— James Nasmyth (son of Alexander Nasmyth ), who invented a steam-powered pile driver in 1845, watchmaker James Valoué , Count Giovan Battista Gazzola , and Leonardo da Vinci —have all been credited with inventing

1482-408: The weight onto the upper end of the pile. Modern piledriving equipment variously uses hydraulics, steam, diesel, or electric power to raise the weight and guide the pile. A modern diesel pile hammer is a large two-stroke diesel engine. The weight is the piston , and the apparatus which connects to the top of the pile is the cylinder. Piledriving is started by raising the weight; usually a cable from

1521-553: Was £26,000. The removal of the rock caused nearby sandy shoals to disappear. John William Norie 's Sailing Directions for the River Thames , published in 1847, makes no mention of a navigational hazard in the area of the former rock. Reef Earth's largest coral reef system is the Great Barrier Reef in Australia, at a length of over 2,300 kilometres (1,400 miles). The word "reef" traces its origins back to

#361638