Foundations for the Sohio Corporate Headquarters-PDF

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The Sohio Corporate Headquarters project in downtown Cleveland comprises a 46-story tower and a nine-story atrium. Tower column loads reach 11,400 kips under dead and live loading and nearly 15,000 kips with wind. A two-phase investigation included 27 borings, piezometers, laboratory testing, and pressuremeter tests.<br /><br />The subsurface profile consists of fill and alluvial sands over lacustrine silts and clays, followed by stiff to very dense glacial till, dense sand and gravel, weathered shale, and competent shale. Groundwater occurred at separate levels in the upper sands and near the shale.<br /><br />Footings were recommended for the atrium, with an allowable bearing pressure of 5 ksf and estimated settlement of no more than one inch. For the tower, a mat was rejected because predicted long-term settlement was 2.5–4.5 inches. Piles were considered but had drawbacks including noise, predrilling, and less certain uplift resistance. Caissons socketed into shale were selected, partly to avoid requiring workers to inspect caisson bases in an area where gas had been encountered.<br /><br />Laboratory tests assessed concrete-to-shale bond under different moisture and curing-pressure conditions. The design adopted a conservative socket-friction value of 160 psi, supplemented by assumed end bearing and reduced friction in weathered shale. Required sockets in competent shale ranged from 3 to 16 feet. Construction specifications addressed concrete placement and bottom cleanliness.<br /><br />A full-scale caisson load test and instrumentation program were used to verify design assumptions. Although sand leakage caused some load to be carried by the overburden, the load remaining on the socket was sufficient to support the selected design values. Instrumented production caissons were also planned for monitoring load transfer during tower construction.

Keywords

Sohio Corporate Headquarters

Cleveland

high-rise foundation

caisson foundation

shale socket

geotechnical investigation

tower column loads

groundwater conditions

settlement analysis

load testing