Mechanical behaviors and progressive fracture processes of dry basalt after Martian cryogenic freeze-thaw cycles

The steep Martian terrain features numerous notches and alcoves that could potentially be adapted as temporary shelters. By sealing their entrances and modifying the interior space, these alcoves can be transformed into habitable structures. Given their prolonged exposure to Martian temperature fluctuations, it is crucial to understand the mechanical properties of alcove rocks to design appropriate shelter parameters. This study investigates the mechanical behavior of basalt specimens subjected to Martian cryogenic freeze-thaw (F-T) cycles (−143∼35 °C) and subsequent uniaxial cyclic loading tests. The test results indicate that the longitudinal wave velocity, peak stress, and elastic modulus of basalt specimens degrade to varying degrees with an increasing number of F-T cycles. At higher stress levels, the ratio of dissipated energy density to elastic energy density in basalt specimens subjected to different F-T treatments converges to approximately 0.25. During the uniaxial cyclic loading tests, both cumulative acoustic emission (AE) counts and average maximum principal strains of the specimens increase stepwise. For specimens after F-T treatment, the spectral-domain characteristics can be classified into three frequency bands, with the middle and high frequencies predominating. The application of the Gaussian Mixture Model (GMM) clustering algorithm enhances the analysis of AE results, facilitating the identification of tensile and shear cracks. As the number of F-T cycles increases, the percentage of shear cracks in basalt specimens decreases from 76.5% (0 cycle) to 53.5% (7 cycles).