New Indian River Inlet Bridge, United States of America

The new Indian River inlet bridge project is a replacement development being carried out in Sussex County, in the US state of Delaware, by DelDOT (Delaware Department of Transport).

The existing bridge that crosses the Indian River connecting Bethany Beach and Dewey Beach has suffered from tidal erosion, because exposure of the steel 'H' piles to salt water has caused problems and it has come to the end of its useful life.

The current three-span concrete deck bridge only has support piers in the water and no supporting towers; it is still in use while the new structure is being built, and receives annual bathymetric inspections, as well as constant monitoring by the University of Delaware (pier sensors and sonar monitoring). The bridge was initially planned to open in 2011, but due to some constructional defects the opening will now take place during 2012. The old bridge will eventually be dismantled.

The construction of the new bridge is expected to cost an estimated $150m, a figure which has gone $20m over the original estimate and has caused some controversy.

A problem with the construction of the ramps (to lead into the new bridge) in 2006 has led to a change in the ramp design. In the original design, the ramps were sinking more than required.

The new ramp design includes piers instead (piles sunk into soil). The fault was blamed on a geotechnical survey carried out prior to the ramp construction. To involve the public in the design of the new bridge DelDOT called for a public vote between 27 April and 11 May 2009 on the choice of lighting fixtures on the pedestrian walkways, the colour of the cable stays, and the design on top of the pylons.

Design of the new Indian River inlet bridge

The new bridge design includes two 240ft towers on each side of the bridge with single plane cable stays. The foundations for the two towers will be supported by 36 inch square piles (produced by Bayshore Concrete Products).

The bridge will be 2,600ft long with a 900ft (305m) span over the inlet of the Indian River, with 1,700ft of bridge deck over the land.

This radical change in design from the original bridge means that all supports are out of the water, so erosion caused by salt water to the structural elements will not be a problem.

The clearance from the deck to the water is 45ft (old bridge 35ft clearance) to allow for navigation of shipping along the river. There are two 12ft travel lanes, a 10ft outside shoulder, and a 4ft inside shoulder in both directions.

In addition there is a single 12ft wide sidewalk accessible from the east side of the bridge. There are also reduced embankment heights leading into the bridge for a more open view of the estuary.

Ramp mitigation

The flawed ramps built in 2006 using around 250,000cu yd of sand, stone and the taller half of the approaches (150,000–180,000 cu yd) had to be removed in the new design. DelDOT spent about $8.1m to build the ramps with the section scheduled for removal costing about $6m (the removed material is expected to be recycled).

Removing the sections took 100 days starting in April 2008, costing $2.7m. A longer bridge length is now required because of the continuing problems encountered with the approaches for the new bridge. The embankments underwent settlement beyond the original predictions and shifted leaning toward the west impacting on adjacent roads.

Contrary to predications, the movement did not stop. The foundations of the new bridge towers were completed in 2009 and the towers themselves were completed in 2010.

Repair works on the cracks that appeared on the bridge deck were initiated in September 2010 and were completed by December 2010. The bridge has 152 stay cables. It will open to traffic with two of the four lanes in early 2012. The other two lanes will open in summer 2012. The approach roads and local roads will be improvised in the first half of 2012. Demolition of the old bridge will commence in spring 2012. The bridge demolition and the entire project will be completed by 2013.

Contractors involved in construction of the new Indian River inlet bridge

In February 2008, DelDOT awarded the contract for construction of the bridge to Skanska Southeast (Bayshore Concrete Products who are producing the concrete piles are a subsidiary of Skanska Southeast). The design of the bridge was carried out by Figg Engineering Group and the structural engineering contract was awarded to Buckland & Taylor Ltd.

Additional contractors, including PCL Civil Constructors and VSL International. O'Connell & Lawrence, were asked by DelDOT in February 2008 to investigate the problems with the original ramps for the new bridge.

In February 2011, Dover-based George and Lynch won the contract for the demolition of the old bridge and the construction of roadway approaches.