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<p>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, <i>P</i>-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 (<i>n</i><sub><i>eff</i></sub>) was the principal control on mechanical behaviour. Low-&#xa0;to&#xa0;medium-porosity lavas (<i>n</i><sub><i>ef</i>f</sub> &lt; 15%) showed variable unconfined compressive strength (30–156&#xa0;MPa), while high-porosity lavas (<i>n</i><sub><i>eff</i></sub> &gt; 15%) were less competent (17–57&#xa0;MPa). Samples with <i>n</i><sub><i>eff</i></sub> &gt; 12.5 ± 2.5% displayed a plastic deformation at 10&#xa0;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&#xa0;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 <i>n</i><sub><i>eff</i></sub>. These models, applicable from basalts to trachytes, are a predictive tool for future geotechnical applications in the Azores Archipelago.</p>

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Engineering Properties of Lava Rocks from S. Miguel Island: Insights from Laboratory Testing and New Empirical Correlations

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年2月12日

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  • Maria Luísa Pereira,
  • Isabel Fernandes,
  • Matilde Costa e Silva,
  • Lucia Pappalardo,
  • Vittorio Zanon,
  • Paulo Amaral

摘要

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 (neff) was the principal control on mechanical behaviour. Low- to medium-porosity lavas (neff < 15%) showed variable unconfined compressive strength (30–156 MPa), while high-porosity lavas (neff > 15%) were less competent (17–57 MPa). Samples with neff > 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 neff. These models, applicable from basalts to trachytes, are a predictive tool for future geotechnical applications in the Azores Archipelago.