The matrix potential of fine-grained soils at the liquid limit

The liquid and plastic limits (Atterberg limits) are of key importance in soil mechanics because they determine, in a simple way, the interaction between the solid and liquid phases in soils, and thus provide the possibility of classifying soils into groups with similar mechanical properties. It has been observed that all fine-grained soils have an almost equal undrained shear strength and hydraulic conductivity at the liquid limit as well as for the matrix suction. The results of the experimental tests of several researches have shown the values of the matrix suction at the liquid limit to be between 0.5 kPa and 7 kPa. The aim of the present study was to determine the matrix potential of fine-grained soils at the liquid limit by using the experimentally obtained thickness of the adsorbed water film on the external surfaces of clay minerals. The double-porosity model for the pore space geometry was considered as well as the assumption that, at equilibrium, the water in the clay mineral aggregates and macropores of fine-grained soils is in the same energy state. The obtained values of the matrix potential ranged from − 2.2 kPa to − 8.6 kPa, depending on the adopted value of the Hamaker constant for the soil–water system.