Calculating the cohesion and internal friction angle of volcanic rocks and rock masses

Rock failure criteria are key input parameters for models designed to better understand the stability of volcanic rock masses. Cohesion and friction angle two defining material variables Mohr-Coulomb criterion. Although these can be determined from laboratory deformation experiments, they rarely reported. Tabulated data rocks, calculated using published triaxial results, show that cohesion decrease with increasing porosity. If porosity is known, empirical fits provide laboratory-scale estimations. We present a method upscale generalised Hoek-Brown criterion, discuss considerations assumptions associated upscaling, recommendations potential end-users. A spreadsheet provided so modellers (1) estimate (2) values use in large-scale volcano modelling. Better constrained will increase accuracy models.