Experimental Study of Frozen Soil Mechanical Properties for Seismic Design of Pile Foundations

Abstract

A recent study has shown that seasonally frozen ground have great impact on the seismic performance of bridges in cold regions; it not only alters the overall bridge dynamic properties, but also affects the failure mechanisms of the bridge substructure system. The soil lateral resistance approach is widely used in the seismic design of bridge pile foundations. Knowledge on the lateral resistance of frozen soils, including both seasonally frozen soils and permafrost at shallow depths, is needed for designing pile foundations in the broad cold regions including Alaska. In fact, a few key mechanical parameters for the frozen soils are required in order to construct the p-y curve for modeling frozen soils. Although there have been studies on the mechanical properties of frozen soils, most existing studies were based on remolded, artificially frozen soil samples, which do not necessarily represent the soil in the field. How much impact the remolding process and disturbances have on the frozen soil strength and stress-strain behavior is not clear. This paper describes an experimental program aiming to fill the knowledge gap by providing these key frozen soil parameters for typical Alaskan soils. Unconfined uniaxial compression tests are conducted for typical soils found in Alaska in order to obtain the stress-strain behavior. Soil types to be tested include organic, silty and sandy frozen soils. Variables considered include density, water/ice content, temperature and sample orientation. A majority of the test specimens will be naturally frozen soils with minimal thermal disturbance. The test results will provide needed strength parameters for constructing frozen soil lateral resistance curves. The differences found in mechanical properties between natural and artificial samples will provide insight into the mechanics of frozen soils and shed light on how the frozen soil test data in the literal could be used in today's seismic design of bridge foundations in cold regions