Small strain deformation characteristics of two chalks subjected to varying stress conditions

The paper presents an attempt to consider the small strain characteristics of two high-porosity chalks from the northern Negev desert in Israel. Special attention was given to anisotropy, nonlinearity and stress regime; compression or tension. A theoretical and experimental framework for considering these aspects is presented and employed. The experimental programme included testing of air-dried hollow cylinder specimens under conditions of uniaxial compression, radial compression and radial tension. Results of the laboratory testing indicate that the chalks tested display a high degree of anisotropy in the modulus of deformation measured parallel and perpendicular to the direction of sedimentation. The stiffness of the chalks was found to be significantly higher perpendicular to the direction of sedimentation, despite the apparent massive uniform appearance of the intact rock. The chalks displayed significant non-linear stress-strain behaviour, with a strong tendency for the stiffness to decrease as deviator stress is increased, The ratio between material stiffness when subjected to compressive deviatoric stresses in comparison to tensile deviatoric stress was found to be very close to unity.