Thermal and mechanical responses of pre-existing cracked rock samples under uniaxial loading: effects of heat treatment and grouting

Abstract

Jointed rock masses generally experience high-temperature conditions across various geological infrastructures such as nuclear waste repositories, petroleum drilling sites, hydrothermal exploration areas, etc. This study examines the heat-treated rock samples with pre-existing cracks subjected to uniaxial static loading under both ungrouted and grouted conditions. Rock samples, prepared from model rock with pre-existing cracks oriented at 30° joint orientation with horizontal, have been subjected to heat treatment ranging from 30 to 400 °C for 24 h. The rose plots show that un-grouted samples have a more uniform fracture distribution at lower temperatures, but distinct orientations emerge at higher temperatures, especially at 0°, 90°, and 180°. Cement-grouted samples consistently display higher fracture densities and more defined orientations at equivalent temperatures. The grout influences the alignment and increases fracture density due to additional stress and micro-cracks. The mechanical behaviour of the samples has been evaluated through uniaxial compression loading and fracture propagations tracked using digital image correlation (DIC) analysis using MATLAB. Results showed that samples show increased nonlinearity and micro-crack formation as temperature rises. Post-peak behaviour shifts from brittle to strain-softening with higher temperatures, indicating increased ductility. Grouting enhances peak strength below 100 °C, but strength decreases for both grouted and un-grouted samples at higher temperatures due to matrix and grout degradation. However, fracture initiation primarily occurred at the pre-existing crack tips in all samples except for those grouted at lower temperatures. Fracturing mechanisms shifted from tensile cracks to shear crack dominance with increasing temperature.

Keywords

Thermal effects / Mechanical response / Pre-existing crack / Grouting / Uniaxial loading

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