DFI Journal - The Journal of the Deep Foundations Institute

Volume 6, Issue 2, January 2012

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Behavior of Axially Loaded Drilled Shaft Foundations with Symmetric Voids Outside and Inside the Caging

Masood Hajali, Ph.D. and Caesar Abishdid


"Drilled shaft foundations usually carry very high design loads, and often serve as a single load-carrying unit. These conditions have created a need for a high-level of quality assurance during and after construction process. During the construction process, different types of anomalies such as necking, soft-bottom gap at the base, voids and soil intrusions can occur. Anomalies throughout the length can significantly reduce the axial load capacity of the drilled shaft. This paper studies the effect of voids inside and outside the reinforcement cage on the strength and structural capacity of drilled shafts. The objective of this research is to quantify the extent of loss in axial strength and stiffness of drilled shafts due to presence of three different types of symmetric voids throughout their lengths; also, to evaluate the potential for buckling of longitudinal bars within the various types of voids. To complete these objectives, fifteen large-scale drilled shaft samples were built and tested using a hydraulic actuator at the Florida International University’s (FIU) Titan America Structures and Construction Testing (TASCT) laboratory. During the static load test, load-displacement curves were recorded by the data acquisition system (MegaDAC). Results show that the presence of symmetric voids outside the rebar cage (void Type C) that occupy 40% of the cross sectional area of the drilled shafts cause 27% reduction in the axial capacity, while the symmetric voids that penetrate inside the core (void Type B) cause 47% reduction in the axial capacity. The findings indicate that the voids Type B decrease the capacity and stiffness of drilled shafts more than other types due to the resulting inadequate confinement of the concrete and reinforcement."