Stone Arch Lightweight Backfill
The Job
This stone arch lightweight backfill project is located in Somerset, New Jersey. The stone arch bridge, constructed in the 1800s, was experiencing significant scour at the bases of the arch. This caused differential settlement of the structure, and deterioration of the wing walls.
The bridge is adjacent to a historic mill structure. Due to historic preservation requirements, the structure had to be maintained in kind, as opposed to replaced.
The bridge was originally bearing on shallow stone foundations.
The Challenge
As part of rehabilitating the structure, structural engineers designed two new mass footings in the stream bed to underpin the edges of the stone arch. Then, to strengthen the arch designed a 12″ thick reinforced concrete arch overlay on top of the stone arch for the full length/width of the bridge.
In order to compensate for this additional weight, designers determined that a lightweight fill material was needed to reduce the chances of inducing settlement.
Designers also evaluated remedial deep foundations but determined that lightweight fill was the fastest and most economical solution.
The Solution
After the structure had been rehabilitated, CJGeo installed 325CY of 30lb/cuft CJFill-Ultra Lightweight to complete the stone arch lightweight backfill installation. Placed in lifts up to 4 feet thick, the work was took just three days.
By using 30lb/cuft non-permeable cellular concrete, the dead load on the underlying soil decreased by up to 935lbs/sqft relative to compacted soil backfill.
Cellular concrete is self-consolidating and pumpable hundreds of feet. Therefore, single side access was not a problem, and no compaction equipment was necessary.
A crew of two workers completed the pour using continuous wet batch generation. CJGeo chose wet batch generation due to the relatively small daily volume of material placement.
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