Silt fraction effects of frozen soils on frozen water content, strength, and stiffness

Abstract

The strength and stiffness of soil mixtures vary with regard to the particle composition and the properties of soil mixtures that critically change when water, which is a component in soils, is frozen. The objective of this study is to evaluate silt fraction effects of frozen sand-silt mixtures on the frozen water content, shear strength, and stiffness. The sand-silt mixtures are prepared in a shear box at a fixed relative density of 60% and a fixed degree of saturation of 15% with various silt fractions ranging from 0 to 100% in weight (Wsilt/Wsand × 100%). A time domain reflectometry (TDR) probe, bender elements, and thermocouple are installed in the shear box, and the direct shear apparatus is placed in the freezing chamber. After the sand-silt mixtures are frozen at −5 °C, the direct shear tests are conducted. The TDR signals and shear waves are monitored before and after the freezing phases for the estimation of the volumetric water content and stiffness, respectively. Test results show that the void ratio, volumetric frozen water content, shear strength, and shear wave velocity are at a minimum near a silt fraction of 30%. As the relationships between the volumetric frozen water content and peak shear strength, as well as between the volumetric frozen water content and shear wave velocity after freezing, are linear, the peak shear strength correlates well with the shear wave velocity after freezing. Furthermore, as the residual shear strength and shear wave velocity before freezing are related to the silt fraction, the residual shear strength is bi-linearly proportional to the shear wave velocity before freezing. This study suggests that the void ratio and frozen water content of sand-silt mixtures are affected by the silt fraction. Thus, the silt fraction effects should be considered for the characterization of the strength and stiffness of frozen soils.