Rate dependence of dry, oil- or water-saturated chalk

The rate dependence of dry, oil- or water-saturated high-porosity outcrop chalk is investigated based on whether the fluid effect could be excluded from a governing material parameter, the b-factor. The b-factor is used in geotechnical engineering to establish the difference in evolution of load between stress-strain curves when applying different loading rates. The material investigated is outcrop chalk from Stevns, Southern part of Denmark, with a porosity of 43 to 44% and subjected to varying loading rates. The Biot critical frequency is a function of the fluid properties viscosity and density, and the material properties porosity and permeability. The critical frequency is interpreted as a measure of the solid-fluid friction and hence relevant to use for subtracting the fluid effect to arrive at a pure material parameter. The results show a correlation between the b-factor and the Biot critical frequency.