Experimental study on ultrasonic characteristics of frozen sandstone under uniaxial compression

As one of the main means of non-destructive testing, ultrasonic waves can effectively detect damage inside rock, which provides an important basis for the evaluation of rock mechanical properties. This study investigates the ultrasonic characteristics of frozen sandstone during loading and the effect of different temperatures. Combined with the deformation and failure process of the frozen sandstone sample, variation in ultrasonic velocity, amplitude, frequency spectrum, quality factor, and energy during loading were analyzed. The results show that (1) the amplitude of ultrasonic first increased, then decreased, then increased again with the increase in axial stress (σ1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sigma_{1}$$\end{document}), and decreased with the decrease in temperature. (2) The amplitude and arrival time of the first wave decreased as the temperature decreased. The amplitude of the first wave increased with the increase in σ1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sigma_{1}$$\end{document}, while the arrival time is reversed. (3) The ultrasonic velocity (vp\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$v_{p}$$\end{document}) increased as the temperature decreased. vp\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$v_{p}$$\end{document} increased rapidly in the compaction stage and increased slowly in the elastic stage. Before the peak stress, when the stress level of sandstone samples was 0.88–0.93, vp\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$v_{p}$$\end{document} reached its peak and then decreased rapidly due to the initiation and expansion of cracks. (4) The spectral peaks increased with the increase in σ1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sigma_{1}$$\end{document} and decreased with the decrease in temperature. In addition, the quality factor and accumulated energy of the ultrasonic increase first and then decrease during loading. The relationship between the ultrasonic velocity and stress of frozen sandstone at different temperatures was established using logarithmic function fitting.