Side Load–Transfer for Drilled Shaft in Soft Argillaceous Rock with Volumetric Changes in Postfailure of Asperity

An important issue in the quantification of side resistance in drilled shaft design is how to conduct a credible analysis of the shear behaviors between the shaft and ambient geomaterials. In the previous literature, the primary emphasis was on establishing a logical physical model where the interactions between the shaft and the rough socket wall can be exclusively characterized in the form of the so-called triangular asperities model. The modeling can well elaborate on the dilatancy behavior before the occurrence of asperity failure. After the energy release at the asperity failure, volumetric changes in the interface could occur in the postfailure stage; however, these changes cannot be fully taken into account in most existing methods. This study analyzes a newborn scrap after asperity failure under upper and lower constraints based on the kinematics rule and gives a better understanding of the mobilization of residual shearing. Particularly, a dilatancy index is introduced to describe the postfailure volumetric changes in the interface, either dilatancy or contraction. It could also highlight an alternative vertical load-transfer function updated with a bilinear shear mobilization curve, and four different general solutions to the load-transfer equation are given in a chart for engineers. The proposed method is verified by using direct shear tests and case histories, and the predictions agree well with the observations. Parametric studies demonstrate that the dilatancy index is significantly affected by the asperity inclination and the frictional angle, rather than the half chord length.