Abstract Lava rocks are widespread geotechnical materials but remain less studied than other lithologies regarding their mechanical behaviour and links with physical properties. This study presents a comprehensive characterisation of Azorean lavas with diverse textures and mineral compositions, developing new empirical models to predict their engineering parameters. A total of 113 blocks, from basalts to trachytes, were collected from S. Miguel Island (Azores, Portugal) and analysed for index properties (porosity, density, P -wave velocity), strength (uniaxial compressive and tensile), and elastic moduli. Triaxial tests under confinement further yielded cohesion and friction angle parameters based on the Mohr–Coulomb and Hoek–Brown criteria. Open porosity ( n eff ) was the principal control on mechanical behaviour. Low- to medium-porosity lavas ( n ef f 15%) were less competent (17–57 MPa). Samples with n eff > 12.5 ± 2.5% displayed a plastic deformation at 10 MPa confinement. Low- to medium-porosity basalts and trachyandesites exhibited medium-to-high strength, whereas trachytes accommodated more deformation. Water saturation caused an average 3% reduction in tensile strength and a decrease in density, independent of lava type or texture. Cohesion (5–17 MPa) and friction angles (28–55°) of the studied lavas provide a more complete mechanical database on Azorean volcanic rocks. Statistically significant empirical equations were derived to estimate strength parameters from key properties, such as n eff . These models, applicable from basalts to trachytes, are a predictive tool for future geotechnical applications in the Azores Archipelago.
Pereira et al. (Thu,) studied this question.