Rock-Socketed Caissons in Yonkers Gneiss

This paper describes the design and construction of rock-socketed caissons in hard gneiss for a mid-rise building in Yonkers, New York. The design considered lateral and uplift loading conditions, in additional to vertical loads. Because the presumptive design parameters for rock sockets in the building code were so low, the work included two Osterberg load-cell tests and two lateral load tests on production caissons to justify the use of higher values. The lateral load resistance was verified by a load test. Construction considerations included problems of ordering casings due to wide variability in the depth of rock. To address this situation, the authors made probe holes at every caisson location. The paper also discusses: use of temporary and permanent casings, video-camera inspection techniques and equitable payment methods for drilling through obstructions.