UNSATURATED HYDRAULIC CHARACTERIZATION OF CARBONATIC ROCK IN THE LABORATORY

The hydraulic conductivity and water retention properties are needed to predict fluid flow and solute transport in unsaturated porous media. We developed two methods, one based on Wind’s evaporation method for soils and the other on a quasi-steady centrifuge method, to measure in the laboratory the water retention and hydraulic conductivity of coherent porous rock. We applied these methods to calcarenite, a sedimentary carbonatic rock of marine origin. The calcarenite are little compacted, with a granular skeleton of lithoclasts and bioclasts in a fine, granular, carbonatic matrix, cemented to some degree. This rock is widely found in the Mediterranean basin. It often constitutes a thick layer of the vadose zone. Three lithotypes with varying proportions of lithoclasts, bioclasts, matrix, and cement were used for the tests; two of them (A and B) came from the same quarry but different depths and the third (M) from a quarry in another area. The water retention curves are similar near saturation for all three lithotypes. For matric potential below -20 cm, the curves differ; at the same matric potential the water content of lithotype M exceeds that of lithotypes A and B; moreover, at higher matric potential the retention curve of M shows smaller slope than those of A and B. Therefore M has a greater water-retention capacity and spread of pore-size distribution. Hydraulic conductivities are greater for A and B than for M over the entire range of matric potential investigated, though at high water content the differences are small. Therefore the hydraulic behavior of the analyzed rocks is very similar near saturation while it differs for unsaturated conditions. These accurate measurements of unsaturated hydraulic properties indicate the expected range and degree of spatial variability of these carbonatic rocks, in support of quantitative interpretation of the behavior of water within them.