The project required 32 drilled shafts, 4 foot in diameter, from 130 to 168 feet deep to repair the 40 year old failing bridge over the Christina River which carries about 90,000 vehicles a day. All drilled shafts were fully cased and excavated to bedrock underneath the existing bridge, which at the time was closed to traffic, with only 50 foot of head room clearance.
Due to the fear that excessive vibration may cause additional damage to the bridge, oscillators were used to start the permanent casing, the shafts were excavated using bentonite slurry down to the rock and then the remainder of the casing was welded together and driven with vibratory hammers. With this process the 100+ feet of casing was able to be installed without affecting the existing structure. The 50,000 pound full length reinforcing cages were lifted over the deck of the bridge, lowered down through cut outs in the concrete decking and installed in the excavated drilled shaft below. A. H. Beck and DelDOT worked together to develop a Self-Consolidating Concrete mix design for the application. The emergency project had a national spot light and crews worked 24 hours a day, 7 days a week to complete the daunting task of reopening the bridge. DelDOT reported upon the full reopening of the bridge that there was a significant time savings achieved during the construction of the drilled shafts.
CONTRACTOR: J.D. Eckman, Inc.
OWNER: Delaware Department of Transportation