BASIC FEATURES OF SOIL STRUCTURE INTERFACE BEHAVIOUR

Abstract Firstly experimental data of friction along piles in sand are presented; the corresponding element test (direct shear test between a granular soil and a rough construction material) is described, showing the effect of the initial conditions and of the prescribed path. The phenomenon is described by a mathematical model of interface behaviour which employs the concepts of directional dependence and rheological interpolation. The element tests used in that approach are direct shear tests at constant normal stress, at constant volume, and (pseudo) oedometers. The resulting incremental relationship between contact stresses and relative displacements is numerically integrated for several loading conditions and compared with direct shear experiments at prescribed normal stiffness. It is shown that the maximum mobilized shear stress during such a test can be considered as a monotonic function of this stiffness parameter. A finite element application comparing the predictions of various interface constitutive equations (among them the previous one) shows the influence of the main parameter being the dilatancy rate. A simplified evaluation of the mobilized friction shear along piles, anchors, nails, is then proposed for use in the so-called t-z curves method. Attention is focussed on the determination of these curves, either from special direct shear tests or from the theoretical interface model.