Unsaturated Hydraulic Properties of Rocks: How to Measure Them In the Laboratory and In the Field?

Knowledge of the water retention curve and of the unsaturated hydraulic conductivity are needed to quantify the movement of water in the unsaturated zone. Many methods to determine unsaturated hydraulic properties are available but they are not always adaptable to both rocks and soils.

This work presents a broad overview of experiments carried out in the laboratory and in the field to measure the hydraulic properties of porous and fractured rocks by newly developed methodologies and adapted methods originally used for soil. The difficulties in using commercial devices designed to be used with soil are pointed out, such as tensiometers and probes to measure the water content in the field (TDR, TDT), and the different solutions to overcome some of them are explained.

Particular emphasis is on the advantages of using centrifugal force to hydraulically characterize porous rock in the laboratory, and on the proper functioning of both ceramic plate and ceramic cup tensiometers given the problems of contact surface between the ceramic and the medium. Modifications in preparation procedures of samples to be used with suction table and Wind's methods are presented. Field tests with the aim of hydraulic characterization of fractured rock outcrops using different approaches, such as infiltrometer ring and electrical measurements, are described.

The overview of experimental tests carried out highlights both similarities and differences between soils and rocks related to measurement of hydraulic properties. Resolving the difficulties is essential in order to treat unsaturated transport phenomena as an integral process that involves soil and rock without artificial boundaries.