A review of research on the shaft resistance of rock-socketed piles

Abstract

Shaft resistance generally dominates at the service loads of rock-socketed piles and therefore is always a topic of large research interest. This paper reviews the research progress that has been made in the last four decades in understanding the shear mechanism of the pile–rock interface and in calculating the shaft resistance. First, particular attention is given to notable previous studies of the shear mechanism and the method for calculating the shear strength at the pile–rock interface. Next, some commonly used design methods and many empirical correlations between the ultimate shaft resistance fsu and the unconfined compressive strength σc of the intact rock are summarized, and the factors considered in these design methods (e.g., roughness, joints, discontinuities, smear, construction, and disturbance) are compared. Also, the factors that influence the shaft resistance of rock-socketed piles are summarized. Then, by evaluating briefly the existing theoretical methods, the limitations of elastic normal stiffness and the two-dimensional shear model are discussed. Finally, combined with a comparison between the elastic and elastoplastic solutions of the normal stress increment with the radial displacement increases and an analysis of paths of radial and tangential stress and possible crack formation of the bore wall during expansion, three modification methods using the elastoplastic solution to calculating the increment of normal stress are proposed to calculate shear strength at the pile–rock interface and some suggestions are also made for future research to optimize the calculation of shaft resistance.