Creep Deformation and Long-Term Strength of Ice-Rich Permafrost in Northern Alaska

The degradation of permafrost alters deformation and long-term strength, posing challenges to existing and future civil infrastructure in northern Alaska. Long-term strength is a critical parameter in the design of civil projects; yet data on the creep deformation and long-term strength of undisturbed permafrost in northern Alaska remain limited. Soil particle fraction, unfrozen water content, temperature, and salinity may interactively affect creep deformation and long-term strength of permafrost; however, their interactive effects are not well understood. In this study, field samples of relatively undisturbed permafrost from the upper 1.5 meters of the Arctic Coastal Plain near Utqiaġvik, Alaska were first retrieved and analyzed. The permafrost was characterized as saline ice-rich silty sand and non-uniformly distributed ice. We conducted constant stress creep tests, unconfined compression strength tests, and unfrozen water content tests to assess the mechanical and physical properties of the permafrost cores. The results indicated that the long-term strength of the permafrost decreased by nearly 90% from -10℃ to -2℃. At -10℃, the long-term strength increased by approximately 120% as the soil particle fraction rose from 0.14 to 0.26. The strengthening effect of soil particles diminished at higher temperatures and higher salinity due to the influence of unfrozen water. A quantitative tool has been developed to predict the long-term strength of ice-rich permafrost, incorporating the effects of soil particle fraction and temperature. The findings of this study can potentially support infrastructure design and planning in northern Alaska in the context of global climate change.