Capacity of Drilled Shafts for the Proposed Susquehanna River Bridge

In an effort to reduce the required rock socket lengths for a new bridge over the Susquehanna River near Harrisburg, Pennsylvania, full scale Osterberg Cell load tests were performed on two rock sockets in strata of the Gettysburg Formation. Within each socket, two different zones of interest were identified. One of the objectives of the testing was to compare the side resistance obtained from the load tests with that obtained using empirical methods found in AASHTO and Pennsylvania Department of Transportation publications. Based on the results of this testing, ultimate side resistance exceeded empirical calculations in three of the four zones (977, 757, and 1,006 kPa (20, 16, and 21 ksf) observed versus 407, 304, and 359 kPa (8, 6, and 7 ksf) predicted). For one zone, side resistance was approximately 40% of predicted values (192 kPa (4 ksf) observed versus 497 kPa (10 ksf) predicted), apparently due to construction difficulties.