Interface Stresses between Soil and Large Diameter Drilled Shaft under Lateral Loading

Abstract

Results are presented of a field testing program for a full-scale, large diameter cast-in-drilled-hole (CIDH) shaft/column under large displacement cyclic lateral loading. The test shaft was extensively instrumented to enable high-precision section curvature measurements in addition to measurements of contact pressure at the soil-shaft interface around the shaft perimeter. Among the principal objectives of the testing was to characterize the soil-shaft interaction across a wide displacement range in order to gain insight into the adequacy of existing design guidelines (which are based principally on the testing of small diameter piles) for the large diameter shafts commonly used to support highway bridges. The component stresses of resistance and the effects of nonlinear soil resistance to relative displacements between the soil and shaft are presented. The authors conclude that the relative contributions of normal stresses were seen to increase with shaft deflection, as passive pressures were mobilized on the face of the shaft. The authors note that this suggests the side friction mobilized early in the test and provided the majority of the resistance at low displacement levels. Large diameter shafts could have added capacity from side friction, which the current design models do not incorporate.