Moraines, characterized by the accumulation of rock and soil debris transported by glacial activity, present unique challenges for tunnel construction, particularly in portal sections, due to prevailing geographical and climatic conditions that facilitate freeze-thaw action. Despite these challenges, there is a dearth of studies investigating the influence of freeze-thaw action and water content on the mechanical properties of moraines, and no research on calculating surrounding rock pressure in moraine tunnels subjected to freeze-thaw conditions. In this study, direct shear tests under freeze-thaw cycles were conducted to examine the effects of freeze-thaw cycles and water content on the mechanical properties of frozen moraine. A comprehensive parameter K, integrating the number of freeze-thaws and water content, was introduced to model cohesion c. Drawing on Terzaghi Theory, we propose an improved algorithm for calculating surrounding rock pressure at the portal of moraine tunnels. Using a tunnel as a case study, surrounding rock pressure was calculated under various conditions to validate the Improved Algorithm's efficacy. The results show that: (1) Strength loss exhibits a linear trend with the number of freeze-thaw cycles at water content levels of 4% and 8%, while at 12% water content, previous freeze-thaw cycles induce more significant damage to the soil. (2) Moraine saturation peaks between 8% and 12% water content. Following repeated freeze-thaw cycles, moraine shear strength initially increases before decreasing with varying water content. (3) The internal friction angle of moraine experiences slight reductions with prolonged freeze-thaw cycles, but both freeze-thaw cycles and water content significantly influence cohesion. (4) Vertical surrounding rock pressure increases after the initial freeze-thaw cycle, particularly with higher water content, although freeze-thaw cycles have minimal effect on it. (5) Freeze-thaw cycles lead to a substantial increase in lateral surrounding rock pressure, necessitating reinforced support structures at the arch wall, arch waist, and arch foot in engineering projects to mitigate freeze-thaw effects. This study provides a foundation for designing and selecting tunnel support structures in similar geological conditions.

Soils in ice-free areas of Elephant Island (South Shetland Islands) have been forming since the last deglaciation following the glacial retreat that started in the area probably later than 9.7-5.5 ka. In paraglacial landscapes, landforms and processes in transition from glacial to nonglacial conditions are experiencing rapid environmental adjustments under conditions of climate change. Soils are highly sensitive and can be good descriptors of these transitional changes. A soil sampling campaign was undertaken for characterizing soils developed on moraines and marine platforms, underlain by metamorphic rocks and with distinctive periglacial features. Eight soil profiles were sampled to investigate the processes involved in their development and the relations with main landforms and processes of ice retreat. The stony Cryosols with mosses and lichens coverage are developed in permafrost environment with an active layer depth of 15-150 cm. Soil organic C content (0.16-1.6%) and large variations of P, K and N contents are related to ornithogenic activity. Soils on moraines and platforms show differences that reflect the more recent exposure of moraines that preserve most the characteristics of the parent material. More vegetated soils on platforms show Cs-137 and Pb-210(ex) activities (11 and 25 Bq kg(-1), respectively) at the topsoil whereas absence of Cs-137 and depleted levels of Pb-210(ex) occurred in more recently exposed and less developed soils on moraines. Fallout radionuclides are good tracers for identifying characteristics of soil development and providing information on environmental changes of interest to understand the soil response to actual changes in unstable paraglacial environments.