Study of soil strength variation patterns under temperature changes using piezoelectric testing technology

China's extensive permafrost regions necessitate studying strength changes in frozen soil to ensure structural stability and safety. To quantitatively assess soil mechanics under varying conditions, this paper investigates the silty soil in Northeast China using piezoelectric ceramic testing and triaxial testing of freeze-thaw cycles and freezing conditions. The study explores strength variation patterns and structural change mechanisms of silty soil during these processes and establishes soil strength evaluation indices based on piezoelectric signal energy. The principal findings are: (1) Strength of silty soil decreases parabolically with increasing freeze-thaw cycles, with the initial cycle having the most significant impact, particularly for soil with optimal water content. (2) Lower freezing temperature can effectively improve silty soil's elasticity modulus, failure strength, and cohesion, with more pronounced improvements observed between - 2 degrees C and - 5 degrees C compared to -5 degrees C to -10 degrees C, while the internal friction angle shows no clear change pattern. (3) Monitoring signals of smart aggregate are related to the properties of smart aggregate and the tested soil. The strength deterioration index (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\:SDI)$$\end{document} defined by signal energy correlates greater than 98% with the failure strength of soil at room temperature. Low water content samples exhibit higher energy vectors under the same conditions. (4) The strength enhancement index \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\:\left(SEI\right)$$\end{document} defined by signal energy correlates greater than 90% with failure strength of frozen soil. High-frequency signals are more responsive to temperature fluctuations. The aforementioned indices provide invaluable insights with regard to the implementation of piezoelectric ceramic testing technology within the field of geotechnical engineering.