NCDOT Use of Lightweight Aggregate Fill for Bridge Approach Repair and Improvements

By Jody Wall, Carolina Stalite Company

The North Carolina Department of Transportation has used lightweight aggregate fill on two projects in the past few years to decrease settlement on bridge approaches.

The first of the two bridges discussed is Tranters Creek Bridge Approach in Washington, NC. The project was designed by the NCDOT Geotechnical Unit and constructed by Atwell Construction. The project consisted of widening and raising an existing bridge approach embankment as part of a bridge replacement project. The existing soils consisted of roadway embankment fill underlain by alluvial muck. The embankment fill was a very loose to loose, silty fine to coarse sand. The alluvial muck was 9 feet to 16 feet thick and generally has SPT values of 2 to 4 blows per foot. The area from station 16+25 to 19+98 on the west side of the bridge was undercut 2 feet and covered with an embankment stabilization fabric and backfilled to subgrade level with lightweight aggregate fill. Details were obtained from NCDOT plans.

The other project was NC 133 over Allen Creek in Wilmington, NC. It was also designed by The NCDOT Geotechnical Unit and it was constructed by APAC. The project consisted of removal of approximately 300 linear feet of failed roadway on Hwy 133 on each side of the Allen Creek Bridge. The roadway which was about 2 years old was experiencing settlement and asphalt separation in multiple areas. The subgrade soils in the remediation area were very soft with SPT numbers of weight of hammer to 2 blows per foot in many areas. The asphalt removed from the area was over 18 inches thick in isolated areas of the roadway prior to the repair. The extent of the cracks and settlement made the repair necessary. Approximately 3500 yd3 of lightweight aggregate fill was used on each of the projects.

These two projects are great examples of how lightweight aggregate fill used in load compensation applications can quickly and easily solve existing construction issues.

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