THERMODYNAMICS OF WATER-PERMEATED UNWELDED PYROCLASTS .1. EQUILIBRIUMPROPERTIES

We report here the results of an investigation of thermodynamic equili brium properties of systems constituted by Phlegraean unwelded pyrocla sts, dry or saturated with water. We have experimentally measured the porosity of samples of Phlegraean rocks and determined the values of t he heat capacity and of thermal expansion of dry and water-perfused tu ffs having different texture structures. Also the energetics of the pr ocess of adsorption of water on the large internal surface of these po rous materials has been investigated. The amount of heat exchanged dur ing the reversible formation of an adsorbed layer has been determined, in dependence of its thickness and as a function of temperature. The coherent picture emerging from the ensemble of all these measurements is that of a direct connection between the processes of adsorption/des orption and the stress of the porous rock. In very unsaturated soils t hese processes may constitute a much more efficient mechanism of trans formation of thermal energy into soil deformation, compared with that of thermal expansion of the solid matrix.