Effects of frozen water content and silt fraction on unconfined compressive behavior of fill materials

Characteristics of ice constituent and soil particles primarily determine the mechanical properties of fill materials in extreme regions. The objective of this study is to investigate the unconfined compressive behavior of sand-silt mixed fill materials with various frozen water contents and silt fractions (SFs). Sand-silt mixtures at a relative density of 60% and degrees of saturation of 15% to 25% are prepared at SFs of 0% to 70% in weight. The volumetric water contents are measured at ±5 °C in a freezing mold, and uniaxial compression tests are conducted after freezing. Test results show that the volumetric frozen water content is proportional to the void ratio because these values decrease equivalently when SF < 30% and increase when SF > 30%. The unconfined compressive strength (UCS) and stress at maximum curvature point (MCP), except those of clean sand (SF = 0%), increase with the volumetric frozen water content and void ratio owing to ice-bonding and SF effects. The strength ratio (UCS/MCP) and visualized fracture mode present brittle-to-ductile transitional characteristics according to the SF. This study demonstrates that frozen water content, SF, and fracture mode should be considered when sand-silt mixed materials are used for filling in extreme regions.