BEHAVIOR OF BEREA SANDSTONE UNDER CONFINING PRESSURE .1. YIELD AND FAILURE SURFACES, AND NONLINEAR ELASTIC RESPONSE

Results of a comprehensive experimental study of Berea sandstone involving uniaxial and triaxial compression experiments (sigma-1 > sigma-2 = sigma-3) are presented in terms of axial and circumferential strains versus axial stress, as well as the failure stress states for different confining pressure. Based on these results a failure surface and an initial yield surface have been proposed, and since the clastic response of Berea sandstone is nonlinear, a constitutive model is given in terms of the hypoelasticity theory. The shear and bulk moduli are found to depend on confining pressure and volume strain, respectively, and the equations for this variation with confining pressure and deformation are obtained.