Measuring the pore size distribution of a soil sample during the saturated triaxial compression using non-Newtonian fluids

While there are many methods available for the characterization of pore space of soils, most of them are not suitable for observing the gradual changes of the pore sizes of a given sample during the process of its compaction. Non-Newtonian fluids have been utilized recently for approximating the pore size distribution, providing not only a cheaper and more accessible alternative to the classical porosimetry techniques but also a method that allows to keep the sample undisturbed and to be used repeatedly. In particular, the so-called ANA method [1] computes the effective pore size distribution based on a set of saturated flow experiments with different shear-thinning fluids, such as the aqueous xanthan gum solutions of different concentrations.

We will discuss a methodology to measure the progressive changes in the pore size distribution of the sand sample placed in the standard triaxial test chamber where it is subject to a drained compression. After every compression step (i.e. after increasing the pressure level maintained in the chamber, thus further compacting the sample), a sequence of permeability measurements with fluids of different rheology is performed and the effective pore size distribution is approximated. The ANA approach is used in our case since the similar yield-stress method [2] requires using larger hydraulic gradients, which would disturb the effective stress imposed on the compressed sample.

[1] Hauswirth, S.C., Abou Najm, M.R., Miller, C.T., 2019. Characterization of the Pore Structure of Porous Media Using non-Newtonian Fluids. Water Resources Research 55, 7182–7195. https://doi.org/10.1029/2019WR025044

[2] Rodríguez de Castro, A., Agnaou, M., Ahmadi-Sénichault, A., Omari, A., 2020. Numerical porosimetry: Evaluation and comparison of yield stress fluids method, mercury intrusion porosimetry and pore network modelling approaches. Computers and Chemical Engineering 133. https://doi.org/10.1016/j.compchemeng.2019.106662