Abstract: This paper investigates the strength characteristics of water-rich sandy gravel subjected to freezing, as this soil is often encountered in Beijing. A series of triaxial compression tests has been performed on sandy gravel samples obtained at mining station of Beijing Metro at different temperatures (?5℃, ?10℃, ?15℃, ?20℃) and confining pressures (0.0、0.3、0.8、1.3、2.0、3.0、 4.0 MPa and 8.0 MPa).The results show that: the behavior of frozen sandy gravel is dominated by strain softening, and the ideal plastic failure mode occurs only when the soil experiences high negative temperature and confining pressure; the strength, cohesion and friction angle of the soil all increase with the decrease of temperature. The variation of strength with temperature satisfies an exponential distribution, while the changes in cohesion and friction angle follow a linear relationship; the strength and elastic modulus of frozen sandy gravel increase as the confining pressure increases, but the increasing rate descends gradually. The Mohr - Coulomb criterion can still be used effectively to characterize the soil’s compressive response at low confining pressure. The failure mode of frozen sandy gravel is represented by shear failure with diagonal fractures on the lateral sides of the specimen. Tensile failure occurs when the specimen is subjected to a low confining pressure, and it is influenced by the formation of ice significantly. The mechanism of volumetric inflation has been found when a high level of temperature and confining pressure is applied to the specimen.

Key words: strength of frozen soil, frozen sandy gravel, mechanical properties, triaxial compression test