Mechanical properties of seasonally frozen and permafrost soils at high strain rate

Abstract

Frozen soils, especially seasonally frozen soils, have a great impact on the seismic performance of bridge pile foundations. To account for this impact on pile foundations during seismic events, it is necessary to evaluate the mechanical properties of naturally frozen soil samples. This paper focuses on the mechanical properties of naturally frozen silty soils at a relatively high strain rate. High quality specimens of both permafrost and seasonally frozen soils were prepared by block sampling and machining. Both horizontal and vertical specimens were prepared to investigate the effect of specimen orientation. Unconfined compression tests were performed at temperatures ranging from −0.7°C to −11.6°C, at a constant deformation rate corresponding to a strain rate of 0.001/s. Testing results including soil characteristics and mechanical properties such as stress–strain curves, compressive strength, yield strength, modulus of elasticity, strain values at unconfined compressive and yield strength, and strain value at which 50% of the compressive strength is achieved are presented. The impact of temperature, dry density, water content, and specimen orientation on the mechanical properties is discussed. For permafrost, the ultimate compressive strength of horizontal specimens is substantially higher than that of vertical specimens at the same testing temperature and this strength anisotropy is likely due to ice wedge formation, commonly observed in lowland permafrost. In general, the ultimate compressive strength of naturally frozen specimens is lower than that found in previous studies for remolded frozen silty soils.