Investigations on the freezing characteristic and flexural mechanical properties of frozen loess

Abstract

The exploitation of deep resources increases with the implementation of the western development strategy. The artificial freezing technique is used for shaft construction when facing complex geological conditions. Due to the large deformation of frozen soil wall, disasters often occur during shaft excavation, such as freezing pipe deflection, and rupture. The flexural mechanical property of frozen loess is important for the design of shaft construction in the western region. In this study, the nuclear magnetic resonance (NMR) tests of frozen loess were carried out under different freezing temperatures, and the evolution law of unfrozen water content in frozen loess was investigated. The results show that the pore ice content increases rapidly when the temperature decreases from −1 °C to −7 °C; then the phase transition of residual unfrozen water becomes difficult as the further decrease in temperature. The flexural tests of frozen loess with different water content (10%, 15%, 20%, 25%) were carried out at different freezing temperatures (−5 °C, −10 °C, −15 °C, −20 °C). The flexural strength of frozen loess increases with the decrease of unfrozen water content, and it increases first and then decreases as the initial water content increase. The flexural toughness gradually increases at −5 °C and − 10 °C with the increase of water content, while increasing first and then decreasing at −15 °C and − 20 °C. The roughness of the fracture surface increases with the decrease in temperature.