By Sam Walker on December 9, 2013
Two days of dredging from the Oregon Inlet navigation channel to an area under the Bonner Bridge has wrapped up, but it will be several days before the N.C. Department of Transportation knows if the span is any closer to reopening to traffic.
The dredge Alaska, which has been digging out the chronically clogged channel since early November, spent Saturday and Sunday moving sand from near Bodie Island spit to an area where sand surrounding a set of pilings had washed away, forcing the state to shut down the 50-year-old bridge a week ago.
Sonar scans and visual inspections by divers of the area around bent 166 Monday morning were promising, according to an NCDOT news release.
Bents, also commonly known as piers, are clusters of pilings that support a bridge.
About 30,000 cubic yards of sand were pumped during the weekend to the area of bent 166, which is near the southern curve of the bridge.
“I want to sincerely thank all of the hard-working NCDOT crews and the dredge crews for pushing through the harsh elements to try to complete this repair work as soon as possible,” said Transportation Secretary Tony Tata.
Another dive and sonar scan is planned for Wednesday, weather and current permitting, to give more time for the sand to settle and compact.
“We bring the sand up to an elevation where we know we have the appropriate embedment of the piles,” Pablo Hernandez, NCDOT resident engineer said on Friday. “Then we want to overfill so we get the deadweight of the sand helping to accelerate the compaction process, and then we will make our evaluations if we can open the bridge.”
Sand scouring around bent 166 had dropped the level of sand to as little as 13 feet around some of the 10 pilings. Engineers say they want at least 20 feet of sand supporting the piles that make up the bent.
In addition to work taking place on the support structure underneath the bridge, NCDOT is also performing a survey of the deck in the area of Bent 166 to make sure that there has not been any movement.
The NCDOT has awarded a $1.6 million contract to Carolina Bridge Company Inc. of Orangeburg, S.C. to bring in sandbags and four-foot tall A-Jacks to provide support to the bridge pilings and to prevent further scour from occurring.
A-Jacks interlocked together will be placed around the perimeter of the support structure at Bent 166. Crews will then place sandbags inside the line of A-Jacks.
An additional two layers of A-Jacks and sandbags will then be placed on top of the base layer for a total of 10-12 feet of additional protection. This will allow sand to collect over the sandbags and A-Jacks, providing additional support to the structure, the NCDOT said.
Crews have begun mobilizing equipment and materials to the bridge site. NCDOT and the contractor are working together to develop a timeframe for the repairs.
In addition to the emergency repair work, Carolina Bridge Company Inc. will also begin driving two test piles later this week near the general vicinity of bent 166.
The test piles will allow NCDOT’s geotechnical staff to gather data about the load piles can carry, and will help in the analysis of this situation, as well as for future repairs, according to the statement.