Elasto-plastic behavior of the Fontainebleau sandstone based on a refined continuous strain deviation approach

The elasto-plastic behavior of the Fontainebleau sandstone is studied from experimental and numerical points of view on the basis of a series of conventional triaxial compression tests. Five distinct stages of the axial strain curve are quantified in terms of four stress thresholds (crack closure stress σcc, crack initiation stress σci, crack damage stress σcd and short-term peak strength σp). The onset of dilation and total volumetric strain reversal occur at axial stress level 30–50% and 50–80% of σp, respectively. A refined continuous strain deviation (RCSD) method is proposed to more accurately define the elastic parameters. Other internal state variables are determined accordingly. Some important information are gained as follows: (1) the Poisson's ratio decreases with the increase of the confining pressure; (2) at the same stress level, the higher of the confining pressure, the smaller of the negative plastic volumetric strain (dilatancy); (3) the evolution of the friction-like coefficient and the plastic volumetric strain can be described with an exponential function and a hyperbolic function, respectively. A strictly experimental based constitutive model is proposed to study the elasto-plastic behavior of the Fontainebleau sandstone. All numerical aspects including formulations, algorithms and experimental validations, are presented in detail.