inward at an angle of 30 degrees . Because each bulkhead is customized , this unusual geometry was not a problem ; Ayres created a design that allowed one caisson in the bulkhead to flip up at an angle instead of staying vertical .
Another six months is typically necessary for the construction of the bulkhead , and then it ’ s ready for installation .
HOW DOES IT WORK ?
Those who have seen the floating bulkhead installed often compare it to a garage door closing . Each bulkhead is made up of separate caissons with ballast tanks . To submerge it , the ballast tanks are sequentially filled with water until the whole bulkhead is floating in a vertical position . Once it is in this position , the bulkhead is either pushed or pulled into place at the gate opening for sealing . The bulkhead is then positioned and stabilized by powered hoists or other manual rigging devices . Typically , every bulkhead ultimately seals on each vertical side and along the bottom at the gate opening . The manner of sealing and bearing for the floating bulkhead can vary with each facility ; some bear and seal against existing dam structures , while others require that side- or bottom-sealing surfaces be added as an integral part of the dewatering system . The seal material varies as well and is selected based on the condition of existing or installed sealing surfaces on the facility . The Conowingo facility , for example , requires that Crofton fabricate a custom sealing surface on the floating bulkhead for each installation .
Variations in the formwork used to construct the dam , coupled with the age of the concrete , require that the floating bulkheads be installed without seals at the beginning of every installation . Divers , using the bare steel sealing surfaces of the bulkhead as a template , measure the required thickness of the seals every foot . Following these measurements , the bulkhead is refloated , the seals are custom-fabricated from wood and soft foam rubber , and the bulkhead is reinstalled . The crest gate is then lifted , and the developing differential pressure compresses the soft rubber seals into the “ nooks and crannies ” of the concrete surfaces of the gate opening , creating an effective seal .
It doesn ’ t take long .
“ Typically , the process at the Conowingo facility takes one week to complete . That includes removing the floating bulkhead from a rehabilitated gate opening , rehabilitating the floating bulkhead seals , and reinstalling it at a new
Floating Bulkheads Across the Country Designed by Ayres Associates
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