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 σ_cc, crack initiation stress σ_ci, crack damage stress σ_cd and short-term peak strength σ_p). The onset of dilation and total volumetric strain reversal occur at axial stress level 30–50% and 50–80% of σ_p, 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.