Response of Full Scale Drilled Shafts in Loose Soils Exposed to Induced Vibrations

A number of studies have been conducted in an effort to understand wave attenuation and ground response during installation of deep foundations. This research stems from the need to better understand the effect of vibration on green concrete. “Green concrete," is defined as freshly placed and maturing concrete within 24 hours after initial placement. Construction activities create vibratory inducing forces, which unaccounted for or unmitigated, have detrimental effects to existing and newly in-place structures. The differences between common construction vibrations and those produced during deep foundation construction are the amplitudes and duration of vibrations. The study focuses on effects during the installation of deep foundations through vibratory methods and age effect of the vibrations on green concrete. The installations follow the Florida Department of Transportation (FDOT) guidelines. The field investigation monitors peak particle velocities during installation, and their effect on green concrete. The principal findings from the field study were: (1) vibrations with peak particle velocities of up to 2.5 in/sec do not cause damage to green concrete at distances of two times the shaft diameter and beyond, and (2) in general, a spacing of three times the shaft diameter is a safe specification for ensuring that shaft vibration does not damage the concrete.