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For drilled piles in rock stratum, predictions of axial load-deformation response offer guidance for the preliminary design. In this development, the profiles of socket wall would be idealized as similar triangular asperities, and the expansion of the shaft is laterally confined across the socket wall under constant normal stiffness conditions (CNS). The side shear resistance contributes from the overriding (dilation) and degradation (shearing) of asperities, and the degradation of asperities develops asynchronously. In particular, a correlation is derived between asperity geometry properties and the global strength by including a simplified degradation criterion of the asperity. The proposed model can be considered as a generalization of Patton's model, extending the case of regular triangular asperities to the similar ones. On this basis, the predicted shear mobilization relative to displacement can then be employed to update the load transfer function. Semi-analytical solutions to this problem have been conducted by a finite-difference scheme. Based on the validation of a case study, the proposed prediction exhibits general accuracy with reference to the field observations. To investigate the effect of asperity inclination on the ultimate and residual strengths, a parametric study has also been conducted afterwards. Comparing with an existing method, the prediction from the proposed model captures a ductile response and depicts a notable nonlinear behavior. [ABSTRACT FROM AUTHOR]

Direct shear tests on samples containing similar triangular asperities have been carried out under constant normal stiffness (CNS) conditions, and observations demonstrated that there exists local lift-off of shallower asperities across the interface, resulting in a redistribution of local stresses and further impacting the global shear behavior. This study further modifies the existing theoretical model based on multiple-asperity configurations, previously presented by the authors. The proposed method relates the normal and shear stresses on the individual asperity to interface strength and corresponding displacement in terms of the asperity inclination and contact areas. The emphasis is on quantifying the number of shallower asperities that would be lifted off when the closely contacted asperities are dislocated by an amount of interface dilation. In addition to the mechanism of local lift-off itself, the resultant redistribution of global shear stress on remaining asperities can be also taken into account. The proposed model is verified by predicting experimental observations published elsewhere, and the comparison appears to be satisfactory. [ABSTRACT FROM AUTHOR]

The properties of socket wall significantly affect the loading capacity of a rock socketed pile, and the shear mobilization relies heavily on the roughness of the socket surface and the boundary condition in reality. In this study, laboratory tests have been conducted to investigate the performance of concrete-rock interface shear under constant normal stiffness (CNS) condition and, in particular, an alternative profile to characterize the interface roughness is assembled as series of similar triangular asperities. The profiles of rock samples differing in the dimension of asperities have been divided into five categories (including one kind of regular triangular asperities for comparison). Direct shear tests on the samples are carried out under CNS conditions, with different initial normal loads and normal stiffnesses. The observations indicate that the shear behavior of concrete-rock interface is highly dependent on the uniformity of asperity geometry; compared with the roughness of similar triangular asperities, the one of regular asperities behaves more brittleness and shows a higher peak strength as well as a lower residual strength. In addition to the general tendency, it is found that the local lift-off of some asperities is pronounced relied heavily on their heights, and the redistribution of local stresses can further affect the global shear behavior. The size-dependent sequence of asperity failure can be also observed, confirming the earlier theoretical anticipation reported by the authors. Careful observations during this testing made it possible to develop a micromechanics-based model published elsewhere, and the comparison between them are presented. [ABSTRACT FROM AUTHOR]