Geotechnical Assessment of the Manhattan Cruise Terminal Piers: Analysis of Timber Piles in Soft Organic Silts-Paper

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The study evaluated the geotechnical conditions of Pier 88 at Manhattan’s Cruise Terminal after settlement and structural distress were reported at the facility. The pier’s main deck is supported by approximately 2,500 timber piles driven into very soft organic silts and clays.<br /><br />Investigations included new offshore borings, laboratory soil testing, and sonic/ultrasonic nondestructive testing of 32 timber piles. The soil profile generally consists of soft organic silt over bedrock, with a sand layer near the offshore end. Nondestructive testing indicated an average pile length of about 70 feet, but capacity calculations showed that roughly 100 feet of equivalent pile length would be needed to achieve the historical design allowable capacity of 18 tons. Possible pile splices or timber fins could explain this difference, but the testing could not verify them. The authors note that parallel seismic testing or full-scale axial load tests may have provided more reliable capacity estimates.<br /><br />The piles were analyzed primarily as friction piles. Estimated allowable capacity was 8 tons per individual 70-foot pile and 18 tons per 100-foot pile; group effects reduced these capacities to approximately 5.25 and 11.75 tons per pile, respectively. Axial and lateral analyses generated soil-spring curves for structural modeling.<br /><br />Settlement analyses estimated that consolidation of the organic soils had reached about 95% since the pier was built in 1935. Under typical cluster loading, estimated consolidation settlement was approximately 14–17 inches. Additional downdrag from soil deposited above the original mudline could increase total settlement to about 21 inches for the assumed 100-foot piles, or 30 inches for 70-foot piles. Future settlement under unchanged loading was expected to be limited, but added loads could cause excessive settlement. The analyses broadly matched observed settlement, while some areas appeared to have exceeded pile design capacity due to later additions and renovations.

Keywords

Pier 88

Manhattan Cruise Terminal

geotechnical investigation

timber piles

settlement analysis

organic silts and clays

nondestructive testing

pile capacity

consolidation settlement

structural distress