Impact of Soil Composition on the Shear Strength of Frozen Soils

The shear strength of frozen fine-grained soils plays a crucial role in infrastructure design in permafrost regions. This study employed a temperature-controlled direct shear device to investigate the effects of mineralogy and temperature on the shear strength of soils prepared in the laboratory from commercially available kaolinite, montmorillonite, and rock flour (quartz). Tests were performed under normal stresses of between 100 kPa and 300 kPa and temperatures from −10°C to +4°C. At −10°C, the cohesion intercept in kaolinite-dominant specimens decreased by nearly 57% and the friction reduced by 24% when kaolinite content rose from 10% to 50%. Montmorillonite-dominant specimens showed a smaller reduction in the cohesion intercept (18%) but a greater decrease in friction angle (38%) over the same increase in montmorillonite content. Under thawed conditions (temperatures at or above 0°C), the cohesion intercept approached zero while the friction angles significantly reduced. These results demonstrate the nonlinear influence of clay mineralogy on frozen soil strength and provide practical insights to predict foundation performance in cold regions affected by the thawing permafrost as the climate changes.