Characterization of Seasonally Frozen Soils for Seismic Design of Foundations: Fid-Bau Portal

Characterization of Seasonally Frozen Soils for Seismic Design of Foundations

Shelman, Aaron / Tantalla, James / Sritharan, Sri / Nikolaou, Sissy / Lacy, Hugh

Abstract

An experimental investigation was performed on five widespread soil types common in the United States to characterize the effects of freezing temperatures on the unconfined compressive strength ( $q_{u}$ ), the modulus of elasticity ( $E$ ), and strain at the unconfined compressive strength ( $ε_{q_{u}}$ ). Soil specimens were subjected to monotonic and cyclic loading with varying strain rates at temperatures ranging from 20 to $- 23 ° C$ (68 to $- 9.4 ° F$ ). When compared with test results at 20°C (68°F), testing at $- 20 ° C$ ( $- 4 ° F$ ) showed an increase in $q_{u}$ by a factor of 100, an average increase in $E$ by a factor of 300, and an average decrease in $ε_{q_{u}}$ by 5% strain. Increase in the soil compaction, moisture content, and applied strain rate amplified the cold temperature effects on $q_{u}$ . Additional testing at $- 20 ° C$ ( $- 4 ° F$ ) resulted in an increase in $ε_{q_{u}}$ with no change in $E$ when the applied strain rate was increased. Cyclic experimentation produced data trends comparable to the monotonic experimentation for the mechanical properties but allowed residual deformation as a function of cold temperature to be identified. To assist with current seismic design practice, experimental trends were incorporated into a $p - y$ curve development and the impact of observed soil response as a function of temperature is demonstrated using a series of pushover analyses on a column continued into the subsurface as a drilled shaft foundation.