SUMMARY

This is Earth Engineering Inc.'s preliminary due-diligence geotechnical report on the Logan Triangle in North Philadelphia, dated June 4, 2015. It was prepared for Logan West Associates, L.P., connected to the Goldenberg Group. The report itself is the first 28 pages; the rest is maps, boring profiles, and field logs.

 

 The planned development is a Lowe's, a BJ's Wholesale Club, two retail buildings (P1 and P2), a community center and a fieldhouse. It's meant to go on the part of the site with the shallowest fill.

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What they did. They drilled 15 test borings and dug 28 test pits in spring 2015. They also used Lippincott Engineering's 1986 investigation (38 borings and 5 test pits), 

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WHAT IS IN THE GROUND

• Demolition fill: about 2–18 ft of brick, concrete, wood, tires and other debris from the demolished homes. Old basement slabs and paving between homes are still intact underneath.

• Ash and cinder fill: found as deep as about 45 ft, and very loose. This is the main problem. Earlier tests showed it partly dissolves in water, loses strength when saturated, and can shrink a lot.

• Soil fill, residual soils and weathered schist lie below that. The earlier studies also found soft creek-bed (alluvial) soils at about 30–35 ft.

• No bedrock was reached. Shallowest groundwater was about 8 ft down.

 

MAIN RECOMMENDATIONS

• Foundations: Lippincott's 1986 load tests showed ordinary shallow footings would settle too much. So the large buildings need driven piles, and their floor slabs should also sit on piles.

  • Lowe's: about 1,300 timber piles at 40 ft, or about 1,215 steel pipe piles at 45 ft.

  • BJ's: about 1,100 timber piles at 35 ft, or about 1,030 steel piles at 40 ft.

  • P2: steel piles at about 50 ft (H-piles about 55 ft). The fill is deepest here, so this spot is the least certain.

  • Fieldhouse, community center and P1: these may be able to use normal footings if the ash fill is dug out and replaced. The fill there is about 10 ft, 13 ft and 0–19 ft deep. Short timber piles are the fallback.

  • Pre-drilling: every pile option costs more if the demolition fill and old slabs aren't removed first, because the top 8–10 ft of each pile location would then need pre-drilling.

• Sitework: the report prefers removing and processing the demolition fill across the whole site; the cheaper option is removing it only where needed. Either way, pavements need geogrid reinforcement and thicker sections. Even then, settlement from the ash fill stays a long-term risk for pavements.

• Utilities: lines in streets being dedicated to the City will probably need pile support to meet City/PWD requirements. Building over the existing old sewers should be avoided.

• Stormwater: no infiltration anywhere on site, because water breaks down the ash fill.

• Athletic fields: natural grass rather than synthetic turf, so settlement is cheaper to repair, with at least 3 ft of the subgrade dug out and replaced.

• Earthwork: ash fill can't be reused as structural fill. Demolition fill can be reused only after processing (debris crushed to 3 in or less, wood and metal removed). The report also gives criteria for imported fill and compaction.

 

The pile counts are rough estimates, since no finished floor elevations or structural loads were available yet. EEI says a final geotechnical investigation is needed for each building before design.