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Cofferdam 02

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  • 1. 1) CofferdamFrom Wikipedia, the free encyclopediaJump to: navigation, searchA cofferdam on the Ohio River nearOlmsted, Illinois, built for the purposeof constructing the Olmsted Lock andDamA cofferdam during the construction oflocks at the Montgomery Point Lock andDam.ConstructionA cofferdam (also called coffer[1]) is an enclosure beneath the water constructed toallow water to be displaced by air for the purpose of creating a dry work environment.Commonly used for oil rig construction and repair, bridge and dam work, theofferdam is usually a welded steel structure that is temporary, typically dismantledafter work is completed. Its components consist of sheeting, wales, and cross braces.The cofferdam is also used on occasion in the shipbuilding and ship repair industry,when it is not practical to put a ship in drydock for repair or alteration. An example ofsuch an application is certain ship lengthening operations. In some cases a ship isactually cut in two while still in the water, and a new section of ship is floated in tolengthen the ship. Torch cutting of the hull is done inside a cofferdam attacheddirectly to the hull of the ship, and is then detached before the hull sections are floatedapart. The cofferdam is later replaced while the hull sections are welded togetheragain. As expensive as this may be to accomplish, use of a drydock may be even moreexpensive. See also caisson. 1
  • 2. Naval architectureA cofferdam may also refer to an insulating space between two watertight bulkheadsor decks within a ship. A cofferdam may be a void (empty) space or a ballast space.Cofferdams are usually employed to ensure oil or other chemicals do not leak intomachinery spaces. If two different cargoes that react dangerously with each other arecarried on the same vessel, one or more cofferdams are usually required between thecargo spaces.The division between the tanks and the hull of a double-hulled vessel is not normallycalled a cofferdam, although it carries this functionDesign and Construction of a Cofferdam at FormerMGP Site, St. Augustine, FLMoretrench worked with ThermoRetec of Durham, NC to design and build acofferdam adjacent to a former MGP site in St. Augustine, Florida. Followingapproval of a Remedial Action Work Plan (RAWP), and entry of the AdministrativeOrder on Consent (AOC) initiating site work, cofferdam construction began.Cofferdam construction.The purpose of the cofferdam was to provide a protective barrier for the AnastasiaRiver, and its marine life, from potential impacts of remedial activities at the formerMGP site. The cofferdam was built by driving sheet piles along the outer edge of amarsh area, and placing successive lifts of reinforced geogrid, geofabric, andcompacted soil to build an earthen berm inside the sheet piles. The earth bermprovided the access forthe construction of the next day’s sheeting installation. Sheetpile joints were sealed with a marine sealant to further minimize movement of waterthrough the piles.Drainage pipes and valves were installed through the cofferdam tofacilitate drainingof clean water from the marsh during low tides. Turbiditymonitoring results during and following construction were below actionlevels.Despite challenges posed by the changing tidal conditions of the river, and theunstable soil characteristics of the marsh,cofferdam construction was completed ontime and on budget.MORE TRENCHContact Information:11001 Fern Hill DriveRiverview, FL 33569Tel: 813/741-0256Fax: 813/672-4754E-mail:aschuman@mtacfl.comMORETRENCHServicesCofferdam and berm under construction.Completed cofferdam. 2
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  • 4. WELCOME TO GROUNDFREEZINGGround freezing is a technique that has been used extensively forgroundwater control and excavation support in the undergroundconstruction industry for over 100 years. The process involves the circulation of a refrigerated coolant through a series of subsurface pipes to convert soil water to ice, creating a strong watertight material. The material is so strong, in fact, that it is routinely used as the only method of groundwater control and soil support for the construction of shaftshundreds of feet into water-bearing soils.Most ground freezing systems are quite similar in principal. Thesingle most important co mponent of a ground freezing system is the subsurface refrigeration system, consisting of a series of refrigeration pipes installed with various drilling techniques. Depending upon the application, the coolant can be brought to temperatures well below -150 degrees celcius. Ground freezing can be achieved by using either a large portable refrigeration plant or liquid nitrogen. After the initial freezing has been completed and thefrozen barrier is in place, the required refrigeration capacity issignificantly reduced to maintain the frozen barrier. 4
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