Industrial construction in an underwater environment
Underwater construction is industrial construction in an underwater environment. It is a part of the marine construction industry. It can involve the use of a variety of building materials, mainly concrete and steel. There is often, but not necessarily, a significant component of commercial diving involved. Some underwater work can be done by divers, but they are limited by depth and site conditions, and it is hazardous work, with expensive risk reduction and mitigation, and a limited range of suitable equipment. Remotely operated underwater vehicles are an alternative for some classes of work, but are also limited and expensive. When reasonably practicable, the bulk of the work is done out of the water, with underwater work restricted to installation, modification and repair, and inspection.
Construction below the water table is mostly managed by using cofferdams or pressurised caissons to exclude water sufficiently to work above the local water level within the enclosure, though it may also be possible to keep the water level down by pumping it out as fast as it seeps in, thereby artificially lowering the water table at the worksite.
Underwater rock blasting, or dredging of softer sediments, to clear an area of a navigational hazard, to excavate a canal or basin, or to prepare for foundations.
Piling, including piles driven to serve directly as the support member, and sheet piles, which may be used as formwork for cast concrete, or for constructing cofferdams, to allow the enclosed area to be dewatered.
Caissons and cofferdams may be used to allow unimmersed work below the surface level of the water. In closed caissons the internal pressure may be raised to keep water out. Occupants need to use an airlock for access, and may require decompression stops when exiting.
Underwater demolition, for removal of damaged structure in repair work, or to prepare an area for new construction.
Underwater inspection of underwater structures, installations, and sites is a common diving activity, applicable to planning, installation, and maintenance phases, but the required skills are often specific to the application. Much use is made of video and still photographic evidence, and live video to allow direction of the inspection work by the supervisor and topside specialists. Inspections may also involve surface preparation, often by cleaning, and non-destructive testing. Tactile inspection may be appropriate where visibility is poor. Inspection can also be done using remotely controlled underwater vehicles.
The most commonly used materials in marine construction are concrete and steet.
Occupational safety and health issues
Underwater work by divers on construction sites is generally within the scope of Diving regulations. The work may also come within the scope of other occupational heath and safety related regulations.
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^"Diving Regulations 2009". Occupational Health and Safety Act 85 of 1993 – Regulations and Notices – Government Notice R41. Pretoria: Government Printer. Archived from the original on 2016-11-04. Retrieved 3 November 2016 – via Southern African Legal Information Institute.
^Staff (1977). "The Diving at Work Regulations 1997". Statutory Instruments 1997 No. 2776 Health and Safety. Kew, Richmond, Surrey: Her Majesty's Stationery Office (HMSO). Retrieved 6 November 2016.