Volcanic rock masses exhibit temporal and spatial
variability, even at the scale and duration of engineering
projects. Volcanic processes are dynamic, resulting
in rock masses ranging from high-porosity, clay-rich, fractured,
and soil-like to low-porosity, high-strength, brittle,
and massive. Based on a number of studies in a variety
of geological settings, such as active and fossil geothermal
systems, on the surface of active volcanoes and up to
3000mbelow the surface, the work presented in this article
shows the relationship between geological characteristics
and mechanical parameters of volcanic rocks. These are
then linked to the resultant challenges to tunnelling associated
with themechanical behaviour of volcanic rocks and
rock masses, ranging from ductile failure such as squeezing
and swelling to dynamic failure such as spalling and
rockburst.
This article highlights some of the key parameters that
should be incorporated in site and laboratory investigations
to build representative ground models in volcanic
rocks and rock masses. Rock mass characterisation needs
to address the highly variable and anisotropic nature of volcanic
rocks, ranging from millimetre to decametre scale.
Ground models must include not only the mechanical
properties, such as strength and stiffness, of typical lab
investigations, but also petrophysical properties, such as
porosity, and geological conditions, such as alteration.
Geomechanical characterisation of these rock masses requires
an understanding of geological processes to select
appropriate field, lab and design tools. In volcanic rocks,
perhaps more than any other rock types, the geology is
critical to characterising and understanding the behaviour
in response to tunnelling.