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
4│TRENDS