Study on the subzero temperature dynamic fracture behavior of saturated rocks and development of a fracture toughness modified model

Rocks in high-altitude cold regions are subjected to prolonged subzero temperatures and intense diurnal temperature variations, leading to complex fracture behaviors that threaten slope stability and engineering safety. To investigate the dynamic fracture characteristics and underlying microscopic mechanisms of saturated rocks under different freezing conditions, dynamic tests were conducted on marble, granite, and sandstone using a Split Hopkinson Pressure Bar (SHPB) system combined with high-speed photography and digital image correlation (DIC). Scanning electron microscopy (SEM) was used to observe fracture surface morphology at various subzero temperatures. Based on the experimental results, an empirical fracture toughness correction model was proposed, integrating the dual effects of freezing-induced densification and frost heave damage. The results reveal significant lithological differences in fracture responses: the fracture toughness and energy of marble and granite peak near –10 °C and then decrease, while sandstone shows a continuous increase as temperature drops. Crack propagation velocity also exhibits strong temperature dependence, peaking at –10 °C for marble and granite, and rising steadily for sandstone. Subzero temperatures promote roughening and increased frost-induced cracking in marble and granite, especially below –10 °C, while sandstone shows a densification trend with noticeable frost cracking only at –40 °C. The fracture behavior of porous sandstone is mainly governed by pore ice formation, while dense granite and marble are primarily affected by thermal contraction. The proposed model achieves high fitting accuracy across all rock types, effectively capturing the complex evolution of fracture toughness under freezing conditions. This study provides theoretical support for understanding rock fracture in cold-region slopes and contributes to stability evaluation and engineering design.