Abstract
Working loads applied to bored piles in the chalk are almost entirely resisted by shaft adhesion. But the shear strength of in-situ chalk-concrete interfaces is only poorly known, and there is little understanding of the mechanisms involved in the development of this strength. This thesis describes a programme of direct shear tests performed under constant normal stiffness conditions. The shearing characteristics and bond strength of chalk-concrete interfaces were studied while varying the geometry of the interface, the normal stress and the stiffness. Three types of chalk with widely different intact dry densities (1.4, 1.7 and 2.1 Mg/m3) were used. Conclusions are drawn regarding the importance of adhesion in contributing to the strength of the interface, and it is noted that the intact strength of the chalk has a significant influence on the magnitude of this strength. The effect of the morphology of the interface and the normal stiffness applied to it are shown to be of lesser significance. The importance of these factors in pile design is discussed.