Field observations on hydro-thermal regimes of loess cut slopes in cold and arid regions: A comparative study of sunny and shady slopes

Abstract

In cold and arid regions, the maintenance of roadways and railways faces significant challenges due to serious spalling and sheet erosion, rill erosion, and shallow sliding of loess slopes. Moreover, the frequency and severity of these shallow failures, as well as the vegetation cover, differ greatly between sunny and shady slopes, further complicating slope maintenance. This study focuses on field observations conducted over two consecutive years along a highway at the western end of Chinese Loess Plateau, specifically examining soil temperatures and moisture content within two cut slopes. By analyzing the differences in hydro-thermal regimes within a depth of 100 cm between the sunny and shady slopes, and considering the meteorological data collected at the study site, the research aims to provide insights into these failures of loess slopes. The results indicate that the shady slope undergoes significant seasonal freeze-thaw cycles from the surface down to a depth of 100 cm. The freezing duration ranges from 96 to 120 days, with a freezing index ranging from −250 °C·d to −850 °C·d. Additionally, the shallow layer on the shady slope experiences significant daily freeze-thaw cycles in late autumn and early winter. In contrast, the sunny slope experiences minimal seasonal freeze-thaw processes. Although the shallow surface layer of the sunny slope undergoes some daily freeze-thaw cycles in late winter and early spring, the amplitudes of soil temperature fluctuations are significantly smaller compared to those on the shady slope. Given that the precipitation is concentrated in summer and autumn, the moisture content of the soil on the shady and sunny slopes exhibits noticeable seasonal changes. The soil layers on the shady slope tend to be relatively dry, while those on the sunny slope remain relatively moist. The moisture content within the observed depth on the sunny slope remains relatively consistent, while on the shady slope, a clear gradient is evident. The moisture content of the shallow slope layers within a depth25 cm primarily responses to heavy rainfall events, with a greater response observed on the shady slope compared to the sunny slope. The field-observed hydro-thermal data collected in this study serve a valuable basis for implementing revegetation strategies and enhancing the stability of loess slopes in cold and arid regions.