Interaction between soil and full scale drilled shaft under cyclic lateral load

Analysis procedures for cast-in-drilled-hole (CIDH) bridge foundations commonly involve the use of a b&barbelow;eam on n&barbelow;onlinear W&barbelow;inkler f&barbelow;oundation (BNWF) analysis in which the soil reaction (p) is related to shaft lateral deflection (y) through prescribed curves. The p-y curves used in practice were derived from lateral load testing of small diameter driven steel piles (diameter, d < ∼600 mm). These curves are based on calibrating the results of BNWF analysis against pile head load-deflection data, pile head load-maximum moment data, and in some cases moment profiles. The pile moments used in these calibration exercises were derived from field curvature measurements using linear moment-curvature relationships. Similar procedures for analysis of p-y curves have been used for drilled shafts, despite their larger diameter and the nonlinear behavior of reinforced concrete sections.; This research involved field testing of a d = 1.8 m CIDH shaft/column at a stiff clay site and the development of p-y curves from section curvature measurements. Innovative features of the testing and data reduction included the high precision and redundancy of within-shaft instrumentation, the incorporation of moment curvature nonlinearity into the data reduction for p-y, quantifying uncertainty in p-y curves through rational treatment of curvature data variability, and measurement of soil pressure at the shaft-soil interface. Non-linearity in p-y curves obtained by the data reduction procedure reflects only non-linearity associated with shaft-soil interaction. This is an important feature of the results, as previous data reduction routines, by using linear moment-curvature relations, have lumped both shaft and soil nonlinearity into p-y curves.; The results show considerably stiffer field-derived p-y curves near the ground surface, an effect not incorporated into existing models. This effect results in model bias towards underprediction of p-y modulus and failure load near the ground surface. Insights into the mechanics of p-y response are obtained from the soil pressure cell data, which enables the relative contributions of soil normal and shear stresses on p-values to be inferred. The relative contribution of normal stresses increases with shaft deflection, as passive pressures are mobilized on the face of the shaft.