Research on the Shear Characteristics of Moraine under Freeze-Thaw Action and the Surrounding Rock Pressure

Moraines are special rock and soil mass formed by the accumulation of large amounts of debris material transported by glacial action. Due to the geographical and climatic conditions prevailing, freeze-thaw action can pose a challenge to the construction of tunnels through this type of rock, especially in portal sections. The geological conditions of moraine surrounding rocks in Tibet, China, was investigated, and set up a direct shear test of freeze-thaw cycles to study the influence of the number of freeze-thaw cycles and water content on the mechanical properties and indicators of frozen moraine, introduced a comprehensive parameter K for the number of freeze-thaw cycles and water content, fit the formula for the cohesion c. The results show that the freeze-thaw cycles and water content have significant influence on the cohesion c. And proposed a formula for calculating the surrounding rock pressure applicable to the tunnel portal section of moraine surrounding rocks based on the Terzaghi theory. Taking a tunnel of Changlin Railway as an example, the surrounding rock pressure under different conditions was calculated to verify the reasonableness of the formula. The study shows that freeze-thaw cycles and water content are important factors affecting changes in the mechanical properties of moraines, and freeze-thaw action has different degrees of influence on the surrounding rock pressure in the portal section, which should be fully considered in the construction of the project.