Effect of Casing and High-Strength Reinforcement on the Lateral Load Transfer Characteristics of Drilled Shaft Foundations

Abstract

Increased seismic flexural demands on drilled shaft foundations have led to significant increases in the amount of steel reinforcement, leading to a greater number and/or larger sized steel bars and increased possibility of anomalies within drilled shafts due to reduced apertures between the reinforcement for concrete passage. High-strength steel reinforcement and/or permanent steel casing may be used to provide increased structural resistance in addition to mitigating the concern for voids or other potential anomalies. However, the comparison of lateral load transfer characteristics of drilled shafts with and without permanent steel casing and/or high-strength reinforcement bars has not been previously investigated, which raises questions regarding the suitability of existing analytical approaches for application in these circumstances. This paper presents the full-scale lateral response of drilled shaft foundations constructed with and without steel casing and with high- or mild-strength reinforcement. The lateral loading performance of a cased shaft without internal reinforcement exhibited similar characteristics to a cased shaft with internal reinforcement. Similar lateral loading performance between uncased shafts with mild- and high-strength reinforcement was also observed. The observations and test results indicate that high-strength reinforcement can be used without detriment to the lateral performance of drilled shafts, despite reduced physical confinement provided by transverse reinforcement. Back-calculated soil reaction-displacement (p-y) curves indicated significant differences between shafts of similar nominal diameter, indicating nonnegligible effects of soil–foundation interface and diameter.