FieldP–ycurves in weathered rock

Abstract

In weathered and decomposed rock profiles, the lack of an acceptable analysis procedure for estimating lateral load–displacement response of drilled shafts is compounded by the unavailability of weathered material properties, including the material's lateral subgrade reaction modulus. Such deficiency often leads to the overdesign of the drilled shaft foundation. Six field tests were conducted on drilled shafts to investigate the shape and magnitude of P–y curves in weathered rock material at three locations in North Carolina. The tested shafts were instrumented using dial gages, strain gages, and continuous vertical inclinometers. The measured load versus deflection data are used to study the stiffness response of weathered rock. Measured lateral responses are compared with the results estimated based on a "weak rock" model and a stiff clay model. The comparison shows that Reese's weak rock model overestimated the resistances of the tested shafts while the stiff clay model consistently underestimated the measured shaft resistances. The measured and computed results are analyzed and discussed.Key words: drilled shaft, weathered rock P–y curve, subgrade modulus, ultimate resistances in weathered rock, verification tests.