The project consisted of the design and construction of foundation support and retaining walls for the Potomac Yard Park North Pond area. An MSE retaining wall system was used to support a bike path on the western portion of the park, while a cast-in-place concrete wall on piles was used on the southern and eastern portion of the site to support a steel pedestrian pier for a scenic overlook and a boat ramp to access the pond. This portion of the park was the northern end of a 23-acre park that separates new residential structures on the west from the CSX/WMATA rail line on the east. GeoConstructors, Inc. provided the design-build services for the foundation support of all the walls, design-supply and installation of the MSE walls and installation of the cast in place walls.
Potomac Park is a 23-acre urban park located in the Brownfield development of Potomac Yard along Route 1 in Alexandria.
Main project challenges at the site consisted of very soft clayey industrial fill soils, underlain by Potomac clay soils which are prone to stability problems. The original geotechnical report required undercutting of the fill soils for foundation support and stability analyses showed additional soil improvement or wall embedment up to 8 ft would be needed to provide for an adequate factor of safety for global stability of the walls. Therefore, a solution was needed to minimize/eliminate undercutting the very soft industrial fill soils and to provide adequate settlement control; while obtaining adequate global stability in the Potomac marine clay soils which were prone to deep-seated stability failures.
Factor of Safety of 0.71 without embedment, undercut or piles
Factor of Safety of 1.54 with piles and no undercut or extra embedment
To minimize undercutting of the industrial fills, control settlement and obtain adequate global stability a driven H-pile solution was chosen as the most economical solution to support the cast in place walls. Approximately 44 piles were driven 32 ft below the bottom of footing in 2 days to support the cast in place walls which were up to 21 ft tall. This provided a factor of safety in excess of 1.5 for global stability and limited settlement to less than an inch. For the MSE walls which ranged in height from 9 to 21 ft tall, it was determined that embedding the walls an additional 1.5 ft, was sufficient to provide adequate global stability and control settlement.
MSE Wall Installation
Pouring the concrete Leveling Pad for the MSE Walls
Placing concrete panels on the Leveling Pad and backfilling with stone
Connecting steel soil reinforcing strips to panels
Driving piles for the CIP wall foundation to eliminate over-excavation and increase stability
CIP wall footing poured prior to piles being cut down
Placement of pipe thru MSE wall panel
CIP wall foundation construction adjacent to MSE wall construction
Placement of steel cages for CIP wall
Placement of formwork prior to concrete pour
Concrete being pumped into forms for CIP wall
Finished CIP wall butting up to MSE wall