Drilled Shaft Response in Piedmont Residuum Using Elastic Continuum Analysis and Seismic Piezocone Tests

The axial load-displacement-capacity response of drilled shaft and bored pile foundations can be evaluated during the analysis and design stage using an elastic continuum framework and results from in-situ testing methods, in particular, the seismic piezocone test (SCPTù). The SCPTù is an optimal and economical means for collection of geotechnical data because the same sounding provides up to five separate measurements with depth: cone tip resistance (q_t), sleeve friction (f_s), porewater pressure (u₂), time rate of consolidation (t₅₀), and shear wave velocity (V_s). Moreover, the SCPTù provides information on soil behavior at both ends of the stress-strain-strength curves, namely the peak strength and geostatic stress state for evaluating axial pile capacity and the small-strain stiffness (G_max = ρ_t⋅V_s2) for the initial soil-pile deformations. Using a Randolph-type analytical elastic pile model, the approach can handle either traditional top down compression loading by dead-weight or reaction beam systems, or the more recent Osterberg cell that juxtaposes base and side resistances in opposite directions. A case study involving O-cell tests on a drilled shaft in Piedmont residuum and partially-weathered rock in Atlanta are presented.