High Rise

Projects: Geotechnical Exploration, Foundation Design, Construction Inspections

Geotechnical Engineering

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Situation

No sooner had a real estate developer begun erecting a new 35-story high-rise residential tower than he got the bad news: deep foundation costs would exceed estimates by over $1 million dollars and postpone completion by two months. The problem surfaced at the start of construction, when full-scale load tests revealed that available friction would prove insufficient to drill the deep foundations. ATC was contacted and asked to review this geotechnical conclusion and provide alternatives.

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Results

ATC reevaluated the entire foundation system and concluded that the design shaft lengths could be reduced, without compromising safety, to save $300,000. Construction time was not lost; in fact, the schedule was reduced by approximately four weeks. Noting that subsurface data was limited, ATC initiated a rapidly executed program of additional soil borings and rock coring to further describe subsurface stratigraphy and obtain additional data for detailed foundation analyses. A three-week program of soil boring and reevaluation prevented delays, as initial foundation elements were installed concurrently.