Determination of the matrix indentation modulus of Meuse/Haute-Marne argillite

Nanoindentation tests were carried out on Meuse/Haute-Marne argillite. The aim of this first experimental investigation was to quantify the indentation modulus of the argillaceous matrix in order to specify micromechanical models already developed for this material. We opted for an order of magnitude of indentation depth h which was much larger than the “small” matrix inclusions size (1 μm in size) and much smaller than “big” quartz and calcite inclusions size (between 10 μm and 50 μm) to enable the measurement of a homogeneous matrix behavior. The experimental frequencies of indentation modulus were further compared to a superposition of Gaussian probability densities in order to estimate the indentation modulus of each constituent. A two-constituent model—with the two mean values 5.2 and 23.0 GPa—was found to fit well with the experimental data.