The Baltimore Harbor Light , officially Baltimore Light and historically Baltimore Harbor Lighthouse is a privately owned caisson lighthouse in the Chesapeake Bay in Maryland . First lit in 1908, it sits at the mouth of the Magothy River , marking the channel which leads northwest to the opening of the Patapsco River , which then leads into the Baltimore harbor . The light is located adjacent to the mouth of the Magothy River . At the time of its construction, it was the world's tallest caisson lighthouse due to the deep sediment of its location. It was the world's first nuclear powered lighthouse for a brief time in the 1960s.
22-468: Although a lighthouse had been requested at the site since 1890, it was not until 1904 that construction actually began. In October of that year a violent storm struck the construction site, upturning the caisson and sending it to the bottom of the Bay. The contractor defaulted on the work, and it was not until late in 1905 that construction could resume. The lens was finally installed and the light lit in 1908. It
44-528: A box caisson with pinpoint accuracy. An open caisson is similar to a box caisson, except that it does not have a bottom face. It is suitable for use in soft clays (e.g. in some river-beds), but not for where there may be large obstructions in the ground. An open caisson that is used in soft grounds or high water tables, where open trench excavations are impractical, can also be used to install deep manholes, pump stations and reception/launch pits for microtunnelling , pipe jacking and other operations. A caisson
66-476: A shaft at the required depth. The operator monitors the MTBM's location, orientation and hydraulic devices via a computer console, a CCTV camera or Gyro unit. Some systems use video cameras in the jacking shaft and at the separation plant. Gyro Control have generally replaced cameras for location and digital feedback. In most microtunneling operations the machine is launched through an entry eye and pipes are pushed behind
88-424: A suitable foundation material is encountered. While bedrock is preferred, a stable, hard mud is sometimes used when bedrock is too deep. The four main types of caisson are box caisson , open caisson , pneumatic caisson and monolithic caisson . A box caisson is a prefabricated concrete box (with sides and a bottom); it is set down on prepared bases. Once in place, it is filled with concrete to become part of
110-596: A suitable sub-foundation. These piles are connected by a foundation pad upon which the column pier is erected. Caisson engineering has been used since at least the 19th century, with three prominent examples being the Royal Albert Bridge (completed in 1859), the Eads Bridge (completed in 1874), and the Brooklyn Bridge (completed in 1883). To install a caisson in place, it is brought down through soft mud until
132-428: Is a watertight retaining structure used, for example, to work on the foundations of a bridge pier , for the construction of a concrete dam , or for the repair of ships . Caissons are constructed in such a way that the water can be pumped out, keeping the work environment dry. When piers are being built using an open caisson, and it is not practical to reach suitable soil, friction pilings may be driven to form
154-559: Is excavated by clamshell excavator bucket on crane. The formation level subsoil may still not be suitable for excavation or bearing capacity . The water in the caisson (due to a high water table) balances the upthrust forces of the soft soils underneath. If dewatered, the base may "pipe" or "boil", causing the caisson to sink. To combat this problem, piles may be driven from the surface to act as: H-beam sections (typical column sections, due to resistance to bending in all axis) may be driven at angles "raked" to rock or other firmer soils;
176-458: Is required. Shallow caissons may be open to the air, whereas pneumatic caissons (sometimes called pressurized caissons ), which penetrate soft mud , are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. An airlock allows access to the chamber. Workers, called sandhogs in American English, move mud and rock debris (called muck ) from
198-520: Is sunk by self-weight, concrete or water ballast placed on top, or by hydraulic jacks. The leading edge (or cutting shoe ) of the caisson is sloped out at a sharp angle to aid sinking in a vertical manner; it is usually made of steel. The shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. An open caisson may fill with water during sinking. The material
220-510: Is used to provide a gap between the inner edge of the tunnel and the outer edge of the liner. The gap is 1 ⁄ 2 to 1.5 inches (13 to 38 mm). A lubricant , often bentonite slurry , is injected into this gap. The pressure of the lubricant prevents the gap from collapsing. Depending on the geology a 35mm overcut may create ground subsidence. For road and rail crossings, this 35mm is reduced so prevent more than 10mm subsidence. As much as hundreds of tons of force may be required to push
242-555: The pressurized environment of the caisson must decompress at a rate that allows symptom-free release of inert gases dissolved in the body tissues if they are to avoid decompression sickness , a condition first identified in caisson workers, and originally named "caisson disease" in recognition of the occupational hazard. Construction of the Brooklyn Bridge , which was built with the help of pressurised caissons, resulted in numerous workers being either killed or permanently injured by caisson disease during its construction. Barotrauma of
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#1733093380598264-587: The Coast Guard be granted access to the lighthouse for occasional checkups on the still-active light. BHL created a website with history and other information about the lighthouse. [REDACTED] Media related to Baltimore Harbor Light at Wikimedia Commons Caisson (engineering) In geotechnical engineering , a caisson ( / ˈ k eɪ s ən , - s ɒ n / ; borrowed from French caisson 'box', from Italian cassone 'large box', an augmentative of cassa )
286-513: The H-beams are left extended above the base. A reinforced concrete plug may be placed under the water, a process known as tremie concrete placement . When the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. A monolithic caisson (or simply a monolith ) is larger than the other types of caisson, but similar to open caissons. Such caissons are often found in quay walls, where resistance to impact from ships
308-435: The base of the caisson. When the caisson hits bedrock, the sandhogs exit through the airlock and fill the box with concrete, forming a solid foundation pier. A pneumatic (compressed-air) caisson has the advantage of providing dry working conditions, which is better for placing concrete. It is also well suited for foundations for which other methods might cause settlement of adjacent structures. Construction workers who leave
330-586: The ears, sinus cavities and lungs and dysbaric osteonecrosis are other risks. Microtunneling Microtunneling or microtunnelling is a tunnel construction technique used to construct utility tunnels from approximately 0.5–4 m (1 ft 8 in – 13 ft 1 in) in diameter. Because of their small diameter, it is not possible to have an operator driving the tunneling machine, so they have to be remotely operated. Microtunnel boring machines (MTBM) are similar to larger tunnel boring machines (TBMs). The MTBM and jacking frame are set up in
352-415: The edge of the workspace to a water-filled pit, connected by a tube (called the muck tube ) to the surface. A crane at the surface removes the soil with a clamshell bucket . The water pressure in the tube balances the air pressure, with excess air escaping up the muck tube. The pressurized air flow must be constant to ensure regular air changes for the workers and prevent excessive inflow of mud or water at
374-416: The liner from sliding out backwards. So while the liner behind the interjack does not move, those sections in front of it receive additional pushing force. San Francisco startup Petra demonstrated a thermal drilling robot that can tunnel through Sioux Quartzite , "the hardest rock on earth" that would normally require dynamite. It can create 18–60 in (460–1,520 mm) diameter tunnels. It disintegrates
396-429: The machine and liner forward. The jacking frame containing hydraulic rams produces these forces. The entrance shaft must be strong enough to support the forces it generates. In addition to the jacking frame, smaller jacks, called “interjacks”, may be inserted between sections of tunnel liner. These push two liner sections apart. Friction on the liner sections between the interjack and the tunnel entrance helps to prevent
418-417: The machine. This pipe jacking process is repeated until the MTBM reaches the reception shaft at the far end. The speed of the advancing machine is limited to the speed at which the pipe is inserted into the entry eye via the hydraulic rams in the jacking frame. The friction of the ground around the pipe increases in proportion to the tunnel length. Two practices can minimize this friction. First, over-cutting
440-401: The permanent works, such as the foundation for a bridge pier. Hollow concrete structures are usually less dense than water so a box caisson must be ballasted or anchored to keep it from floating until it can be filled with concrete. Sometimes elaborate anchoring systems may be required, such as in tidal zones . Adjustable anchoring systems combined with a GPS survey enable engineers to position
462-558: Was added to the National Register of Historic Places as Baltimore Light Station on December 2, 2002. In June 2006, Baltimore Light was sold at auction to private owners by the General Services Administration for $ 260,000; the U.S. Coast Guard maintains rights to operate a light on the structure. The new owner, BHL, LLC of Annapolis, was a partnership of private citizens, 4 couples. The terms of sale dictate that
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#1733093380598484-608: Was the last lighthouse to be constructed on the Chesapeake. In May 1964, the Baltimore Light became the world's first, and only American lighthouse, powered by nuclear power, as a test of the SNAP-7B 60 Watt radioisotope thermoelectric generator . One year later the RTG was removed and a conventional electric generator was installed. Currently the lighthouse is solar-powered . The structure
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