The effect of water content on the mechanical response of a high-porosity chalk

Abstract

The paper deals with the effect of water content on the stress–strain response and compressive strength of a high-porosity chalk. Specimens were tested in three different testing configurations: uniaxial compression of solid cylinders, radial compression of hollow cylinders, and hydrostatic compression of hollow cylinders. Special tools for the local measurement of axial and lateral deformations were developed and proven effective in the testing of the chalk even at water contents as high as 45%. The data illustrate the transition from linear to nonlinear stress–strain response when water content is below about 8%. The small strain modulus of deformation within the plane of material symmetry was found to be 30% larger than its counterpart perpendicular to the plane of material isotropy, regardless of water content. These aspects of chalk response are not yet properly integrated into constitutive models aimed at describing the deformation of chalk units in the field. A Lade-type failure criterion was developed for the compressive strength of the chalk within the plane of material isotropy. It was found that results of radial compression of hollow cylinders correlate well with uniaxial compression data in the construction of the failure criterion.