Lafayette College - Keefe Residence Hall, Easton, PASITE-BLAUVELT Engineers was retained as the geotechnical engineer-of-record for three (3) campus building projects on the Lafayette College campus, the most challenging of which was the six-story Keefe Residence Hall that is located on the side of a steep hill. A preliminary geotechnical investigation indicated that the underlying rock surface was extremely irregular and tended to dip down the hillside. The results of our investigations confirmed the irregularity of the underlying rock surface and quality, and more importantly, indicated the presence of many widespread void zones and weak, fractured rock that would have a severe impact on foundation design and construction. Such conditions mandated the use of a deep foundation system to provide sufficient lateral stability for the new structure.Our design for the drilled pier foundation called for the use of small diameter (30 in.) piers advanced through the weathered, fractured near surface rock, and a variable length (24 in.) diameter rock socket. The rock socket lengths were varied to ensure that the pier was founded in continuous rock and was not underlain by the voids which were indicated by air-track percussion probes completed during the final investigation. For economy, ease and speed of construction, our recommendation was that the drilled pier contractor make use of a down-hole percussion hammer to advance the rock sockets through heavily-fractured zones and voids into sound limestone. Such equipment was ultimately selected and resulted in the contractor's completion of the drilled-pier installation two (2) weeks ahead of schedule and within budget. |
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