Effect of freezing on mechanical behaviour of peaty soils: a case study on ecological fragile zone of Qinghai Tibet Plateau, China

Considerable engineering infrastructure has been constructed in cold regions with widespread peaty soil deposits, particularly in Western Sichuan Plateau, China. However, the mechanical properties of frozen peaty soils remain poorly documented in the literature. In this paper, a series of unconfined compression tests were carried out on frozen peaty soil at varying freezing temperatures and time. The experimental results indicated that the mechanical behaviours of frozen peaty soil are characteristic of elastic-plastic deformation, greatly affected by freezing temperature. The measured UCS varies from 40 kPa to 1062 kPa when the freezing temperature is between 0 °C and -25 °C, and the freezing time is between 6 h and 30 h. The UCS increases sharply when the freezing temperature decreases to -15 °C from 0 °C, and the rate of increase of UCS slows down, when the freezing temperature is lower than -15 °C. The results of environmental scanning electron microscope demonstrated that the connection strength between ice and soil structure was improved owing to complete freezing, resulting in a significant increase in the cohesion of the ice-soil skeleton and playing a key role in improving the macroscopic mechanical strength. Keywords: organic matter; frozen soil; unconfined compression strength; microstructure