Lake Chautauqua Bridge
In a joint venture with Raymond International, Kiewit's Eastern Marine District was awarded a $19 million contract to construct 1.35 miles of bridge approaches and substructures across Lake Chautauqua, in southwestern New York as part of the 284-mile long Southern Tier Expressway. Raymond International had been awarded a contract in 1973, but a federal court injunction halted construction due to environmental issues. NYSDOT assured authorities that proper ecological precautions would be taken during construction on the lake and surrounding watershed.
In late 1978 and early 1979, personnel and equipment were mobilized to start marine operations, which included the construction of 20 piers on precast concrete cylinder piles. Environmental concerns and the unique design of the bridge substructure made it necessary to pour the footings using a dewatered form. This led to the design and application of an innovative construction method to build the pier footings in four sequential phases.
The first phase consisted of pouring a precast element on a submersible barge used as a working table. The precast element was an 11-inch thick reinforced concrete slab, 10-inches wider and longer than the plan's footing dimension. The slab had 45-inch diameter corrugated metal pipes embedded vertically to allow for the passage of 36-inch tubular concrete pilings. After the slab was poured, Robishaw flexifloat units were placed around the perimeter on the outer 5 inches of the slab and interlocked using neoprene to provide a watertight seal. The working table was then towed to deep water and submerged to float the form system free.
Phase two was complete once the floating form system was placed in its proper location and the 36-inch diameter tubular concrete piling was driven using a Manitowoc 4000W Ringer and Conmaco 300 hammer mounted on a flexifloat barge.
Phase three consisted of several operations starting with the placing of inner tubes, which were inflated with water, and a 6-inch layer of sealing grout tremied in the opening, using the tubes as a soffit. Supporting friction collars were then placed on the piles to resist uplift, and after a short cure period, the footing form was dewatered. Minor leaks were plugged, and structural grout was placed to ensure a bond between the piles and the soffit slab, allowing most of the supporting hardware to be removed. A 6-foot pile plug was poured in the top of each pile, and reinforcing steel was set in the footing.
The formwork for a starter wall, which allowed later column or wall pours to be accomplished above water, was set in place with precast channel markers which outlined the location of the submerged footing. After footing concrete was barged in buckets to the pier location and poured, the starter wall formwork and form floats were stripped and returned to shore for use on another footing.
A crane barge was used to complete the fourth and final phase, erecting the formwork and making subsequent pours above the water for either columns and caps or walls.
Variations of the "floating concrete box" system were reportedly used in Canada and were found to be considerably faster than conventional sheet-pile cofferdam methods. Compared to traditional methods, the approach caused less underwater soil disturbance, minimizing environmental impact.
