Experimental study of naturally frozen soil mechanical properties for seismic design of pile foundations.

摘要

Frozen soils, especially seasonally frozen soils, have a significant effect on the seismic performance of bridge pile foundations. To account for this effect, it is necessary to evaluate frozen soils' mechanical properties. This thesis focused on obtaining the mechanical properties of naturally frozen ice-rich organic soils in Alaska. High-quality specimens of both seasonally frozen soil and permafrost were prepared by block sampling and machining following a procedure designed to minimize mechanical and thermal disturbances. 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 that corresponds to a strain rate of about 0.1%/s. Test results included soil characteristics and mechanical properties (stress-strain curves, compressive strength, yield strength, and modulus of elasticity). In descending order of importance, the factors that affect the mechanical properties of frozen soils are temperature, water content or dry density, and specimen orientation. Pile response, particularly the curvature at the upper or lower plastic hinge, is sensitive to frozen soil resistance or the p-multiplier.