DelDOT/James T. O'Brien Old bridge replacement plan is delayed.

Completed in February, the 45-ft-high embankments on each side of Indian River Inlet were built as part of a now-cancelled $34-million contract in advance of a planned 1,400-ft-long bridge just west of the five-span, 860-ft-long steel-girder structure it would replace. DelDOT says soils in the embankments achieved only 60% of expected compaction six months later. At that rate, DelDOT estimates it would take up to seven years to achieve the 95% consolidation needed for construction to proceed. Dennis O’Shea, DelDOT assistant director of design, says that while stability issues are not uncommon given the area’s inherently wet organic soils, “we didn’t expect this.” Similar material has been used before, but now “it may be more of an extreme situation, as this is a very large structure.”

Both embankments are composed of an organic clay mix— up to 30 ft thick on the north side and 60 ft thick on the south side—beneath a 25-ft layer of sand. The north approach, expected to settle 58 in., has settled more than 6 ft, O’Shea says. The south approach has settled 46 in., or 1 ft more than expected. Both embankments also shifted laterally to the west by 9 in. and 18 in., respectively.

DelDOT has ramped up inspections of the scour-prone, 45-year-old bridge—the only direct link between coastal towns and northeastern Maryland—and has now opted for a 2,600-ft bridge with a 1,000-ft clear span over water and 1,600 ft over land, eliminating the large embankments. It issued an RFQ last month and hopes to award a design-build contract in 2008. The length will add $20 million to the $150-million cost estimate.

DelDOT/James T. O'Brien New embankments each settled far more than expected on either side of inlet.

DelDOT considered embankment repairs, but “there’s no estimate on how much more fill would be required to stabilize the approaches or even if it would work,” says spokesman Darrel Cole. Under the new proposal, the bridge would be completed in 2011, about a year later than initially planned. The original design called for a concrete-arch cable-stayed bridge, but O’Shea says DelDOT will leave the choice of structure up to the design-build teams.

DelDOT is reviewing the original design for a possible claim but will not speculate beyond stating that the wick drains are not dissipating pore-water pressure at the predicted rate. Larry Kuhn, vice president of Kuhn Construction Co., Hockessin, Del., contractor for the approaches, says that local embankment projects typically use surcharge fill to help speed compaction. “The amount of additional material is the engineer’s decision,” he says, noting that some 10 ft of surcharge was used.

Tallahassee-based Figg Engineering Group, the lead engineer, defended its subcontractor, geotechnical engineer MACTEC Inc., Atlanta, in a statement. “[MACTEC’s] work has been continually monitored and reviewed by experts from the Federal Highway Administration, a DelDOT-retained independent consultant and others,” stated Figg project manager W. Denney Pate. He added that, to date, all findings have shown the existing embankments to be safe.