Relationships between porosity and physical mechanical properties in weathered volcanic rocks

Volcanic rocks are frequently found under weathered/altered conditions. Degradation and transformation can occur both at the surface and at large depth causing a progressive change in the physical mechanical properties. Degradation can cause an increase in porosity and this can control the rock behavior. In this paper we discuss the relationships between porosity characteristics, micro-structure and texture, and the mechanical behavior of lava at different degrees of weathering (lavas from the Campi Flegrei, Italy). The performed laboratory tests include: uniaxial compression, indirect tension, and uniaxial compression with ultrasonic wave measurements. A description of the mechanical behavior is obtained and a detailed description is performed through a series of pre and post failure non destructive analyses. Porosity values have been related to stress and strain relationship, in addition pore size characterization is presented in a companion abstract/manuscript. Results are interpreted in the key of degree of weathering and its related characteristics. An empirical linking between the change in strength with the degree of alteration is presented and discussed.