Route 47, originally built to connect Camden, NJ with Wildwood and Cape May in the southern part of the State, is primarily two-lane. With significant retail growth in the Vineland/Millville area along the northern half of the highway exacerbating traffic congestion on this already high-volume stretch, New Jersey Department of Transportation (NJDOT) initiated a $16M capital improvement program that included three miles of road widening. Where NJ Route 55 passes over Route 47, earth retention was required to support cuts up to 15 to 20 feet deep, excavated to create additional northbound and southbound lanes. NJDOT plans called for the two retention systems to be constructed as permanent soil nail walls with cast- in-place (CIP) finished facing.
Soil Nail Wall Design and Construction
Soil nail wall construction was accomplished in two phases. Moretrench completed work along the northbound side of Route 47 before mobilizing to the southbound lane.
At each abutment location, three 75 kip, double corrosion protection tiebacks were installed to restrain abutment movement during subsequent earth retention work. The specially fabricated nails consisted of epoxy coated, 1-inch grade 50 dywidag bars with double corrosion corrugated protection. Up to four levels of soil nails were installed at 15° from horizontal through the predominantly sandy soils for an average nail length of 33 feet for the two middle tiers and 18 feet for the upper and lower tiers. The nail bearing-plates were fabricated with headed studs to provide shear connection to the CIP wall. Twelve soil nails were each fitted with six strain gauges to monitor and assess the performance of the soil nails during and after construction. Drainage board, feeding into an underground system installed by General Contractor Agate Construction Co., Inc, was installed between all soil nails before placement of a 4-inch thick shotcrete fascia reinforced with welded wire fabric. A total of 6,200 square feet of wall was installed for the project.
The work was performed in the shoulder of busy Route 47 and directly beneath the active Route 55 overpass, with a severely limited working bench of approximately 20 feet from face of wall to the existing Route 47 curb line. Extremely low headroom beneath the overpasses added to the challenge of tieback and upper level soil nail installation. Since the project specifications only permitted one third of the area in front of the bridge abutments to be shotcreted at a time, construction sequencing was crucial.
Despite the adverse conditions and restrictions, Moretrench successfully completed the work within the timeframe, allowing construction of the CIP wall to proceed on schedule.