When considering materials with different pore populations, it is not easy to distinguish macro- and micro-pores. Indeed, different results can be obtained using different criteria. In this study, a new approach was proposed for the discrimination between micro- and macro-pores. This approach is based on the higher sensitivity of micro-pores to water content change, in particular to water content increase, as compared to the macro-pores. Moreover, application of this approach systematically ensures the saturation of micro-pores. For the materials with single pore population, the diameter corresponding to the main air entry value (AEV) is defined as the boundary between macro- and micro-pores. For the materials with two pore populations, there are two AEVs. If the pore size of unsaturated soil deduced from the soil suction is larger than the one corresponding to the second AEV or in case of saturated soil samples, the diameter corresponding to the transitional suction between the two AEVs is defined as the border – in this case, the defined micro-pores correspond to those that are not significantly affected by drying but can be significantly affected by wetting. Otherwise, the diameter corresponding to the second AEV is considered as the border. A similar procedure can be applied to the materials with three (or more) pore populations. This approach was verified based on the observations of the microstructure of saturated MX80 and MX80 bentonite/sand mixture.

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