A new method to replicate high-porosity weak rocks subjected to cyclic freezing-thawing: Sand 3D printing and digital image correlation explorations

Three-dimensional (3D) printing is an emerging technology capable of producing exact replica specimens in rock mechanics. In this work, the sand 3D printing was explored to model the influence of cyclic freezing and thawing (F-T) for high-porosity weak rocks, which is one of the serious threats to rock stability in a cold region. The evolution of pore structure in the printed specimen during the F-T cycles was interpreted by the nuclear magnetic resonance (NMR) relaxation analysis. A series of Brazilian splitting tests combined with the digital image cor-relation (DIC) were conducted on these specimens experiencing different F-T cycles. The structural and me-chanical degradation of the prepared specimens is reproduced, with a 44.30% increase in porosity and a 39.39% reduction in tensile strength at the end of 10 F-T cycles. Printed specimens deform in a less brittle manner in response to the F-T treatment. The accelerating rate of strain dispersion change was proposed to identify the precursor characteristics during the loading process. The F-T treatment induces the occurrence of precursor earlier than the peak stress, with the precursor stress ratios for the F-T untreated and treated specimens in the ranges of 99.62%-99.75%, and 97.15%-97.93%, respectively. Finally, the mechanical property degradation of fractured rock specimens after the F-T cycles is revealed, and a strong correlation between the mechanical property and the number of F-T cycles that display an exponential decay function is found. The sand 3D-printed specimens are shown to exhibit the changes in the pore structure, mechanical properties, failure pattern, strain distribution, and deformation evolution which resemble high-porosity weak rocks subjected to cyclic F-T.