Statistical Examination of the Shear Strength of Frozen and Unfrozen Fine-Grained Soils

Climate change causes an increase in the temperature of permafrost. This increases the amount of unfrozen water in the permafrost soils, which will reduce their shear strengths. Such reductions may result in the failure of foundations, buildings, pipelines, and other earth structures. Many factors, including temperature, normal stress, plasticity characteristics of soil, and type of soil, impact the shear strength of frozen and unfrozen soils. This study leverages a statistical design of experiments (DoE) to investigate the impact of temperature, normal stress, and soil type on the peak shear strength of frozen soils. The DoE includes input parameters consisting of temperatures ranging from −10°C to +4°C in increments of 2°C, normal stresses of 50, 100, 200, and 300 kPa, and a selection of 10 fine-grained laboratory-prepared soils. The design optimized the 960 experiments required to explore each factor individually to 37 randomized experiments. These experiments were then conducted using a custom temperature-controlled direct shear device. The findings from the DoE were compared with the traditional one-variable-at-a-time (OVAT) approach. It was determined that DoE offers a valuable understanding regarding the importance of individual parameters affecting peak shear strength. Among these parameters, temperature was found the most influential factor, followed by soil type and normal stress. An increase in the temperature decreased the peak shear strength for temperatures between −10°C and −2°C. Further increases in temperature from −2°C to +4°C densify the soil, leading to a slight increase in the peak shear strength. An increase in liquid limit was seen to decrease the peak shear strength. While the DoE approach provides an acceptable analysis of the significance of the various parameters on the peak shear strength, the predicted values were not reliable due to limitations, such as an oversight of critical boundaries and inability to capture the fundamental differences between the behavior of frozen and unfrozen soil.