Anchored Double Tier Retaining Walls on Sloping Embankment-Paper

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The paper describes the design and performance of anchored, double-tier retaining walls at Hunters Point South, a waterfront park in Queens, New York. The reclaimed site contained variable fill over soft organic clay, sands, glacial till, decomposed rock, and schist bedrock. Groundwater levels were influenced by tides, and the project required extensive regrading.<br /><br />Cantilever walls, up to 22 feet high, were built in two rows along a steep embankment. Where the walls conflicted, they were joined as U-shaped sections with shared base slabs. Individual walls were designed to meet bearing, sliding, and overturning requirements under static and seismic loading. Global-stability analyses showed that the walls needed ground anchors to achieve the required safety factor under permanent conditions. Analyses also considered rapid drawdown, flood levels, storm surges, and seismic loading.<br /><br />Twenty-one production anchors were installed and tested. A trial test on the first production anchor sustained three times its design load; the estimated ultimate grout–soil bond strength was about 917 psf, above the 750 psf assumed in the initial design. Proof tests applied 1.5 times the design load, with anchors locked off at 1.1 times design load. Nine anchors met both apparent-free-length acceptance criteria. Several fell below the minimum, but the estimated additional elongation was small. Three exceeded the maximum criterion; however, their load–displacement behavior or measured loads indicated acceptable performance, illustrating that total elongation can overstate elastic movement.<br /><br />Lift-off tests showed that anchor loads were maintained, and calculated bond stresses indicated satisfactory safety factors. The authors conclude that the anchors adequately improved global stability and that acceptance assessments should distinguish elastic from plastic deformation rather than rely solely on total elongation.

Keywords

anchored retaining walls

double-tier walls

ground anchors

global stability

proof testing

seismic loading

waterfront park

soft clay foundation

load-displacement behavior

bond strength