Abstract:

CIDH shafts are among the most common support structures in highway construction. Typically, drilled shafts have simple, prismatic geometries; yet, they display a complex, inelastic response under applied loading. The two major factors that affect their behavior are the interaction between the shaft and surrounding soil media, and the material inelasticity of the shaft itself. In this dissertation the results of the two single shaft tests are reported. Both specimens are two two-foot diameter reinforced concrete drilled shafts that extend 24 feet below ground line. The specimens include one in a flagpole configuration extending 13.3 feet above ground line and the other capped at the surface in a fixed-head configuration. The test site consists primarily of low plasticity alluvial clay that is expected to exhibit an undrained response to the cyclic lateral loading. The quasi static loading was applied with a hydraulic control system in displacement-control mode, with the full suite of loading taking several days to complete for each test.

Both specimens had extensive instrumentation suites to document shaft behavior during the tests, including fiber-optic and electrical sensors for measuring strains, displacements and rotations. The test data have been reduced to provide complete load-deflection backbone curves for loading in both directions, curvature profiles at pre-yield deflection levels, hysteresis curves documenting the cyclic behavior of the shaft soil system at pre-yield displacements. Finally p-y curves for both tests are generated using a piece-wise polynomial fitting procedure. Additionally, p-y curves for the fixed-head specimen include the effects of shear deformations in their formulation.

The p-y curves obtained from the experiments are shown to differ from what would be predicted using the standard API model, with the data indicating stronger curves at shallow depths where the shaft-soil interaction is most pronounced. We also compare results of various tests to evaluate head fixity effects on p-y curves and the adequacy of the diameter effect built into API p-y guidelines.