1. Introduction Generally speaking, frozen soil comprises a variety of rocks and soil types at temperatures below 0 °C containing ice. Depending on its freezing state and duration, frozen soil can be divided into short-term frozen soil, seasonally frozen soil, and permafrost, which can be further divided into unstable permafrost (above −0.5 °C), sub-stable permafrost (−0.5 °C to −3 °C), and stable permafrost (below −3 °C) according to the average annual ground temperature.
