Mesure des potentiels d'humidité dans les sols non saturés au moyen de tensiomètres classiques et osmotiques

¹ Assistant à la Faculté des Siences de Toulouse. Institut de Mécaniques des fluides, Toulouse.
² Chargé de Recherches au C.N.R.S. Docteur ès sciences physiques. Laboratoire de Mécaniques des Fluides, Grenoble.

Résumé

As used in the physics of unsatured porous media a tensiometer is an instrument which measures the free energy level in terms of pressure of environmental water by balancing it locally. The interpretation and improvement of this type of measurement requires accurate knowledge of the mechanism involved in achieving equilibrium between the tensiometer and its porous environment. It is this mechanism which is analysed. The transfer function of a conventional water tensiometer with a response time t' = 1/K'S is shown and the effect of each part of the tensiometric system is considered, i.e. a manometer of sensitivity S, the circuit, and a porous plug of conductance K'. For a tensiometer in a porous medium this notion has to be completed in terms of the properties of the latter. A systematic check on the dynamic behaviour of the tensiometer is then essential. The underlying feature of the osmotic tensiometer is that it measures in terms of pressure the difference in chemical potential between a solution and the dissolvent, in this case water. Measured suction values are apt to be very high. The emphasis is laid on practical design problems.