Geotechnical Design of Permafrost and Wetland Mitigation for Colorado State Highway 5

Colorado State Highway 5 within the Summit Lake Park region has experienced severe roadway damage due to permafrost degradation and freeze–thaw cycling. Passing through a sensitive alpine wetland complex, current roadway configuration has yielded inadequate pavement performance, accelerated permafrost degradation, disrupted surface and subsurface water flow paths, and altered ecological processes. Roadway reconstruction utilizing an air convection embankment (ACE) was selected as the preferred design alternative to meet project priorities of permafrost and wetland restoration and improved roadway performance. A subsurface investigation was conducted, and a two-dimensional finite element model was developed to evaluate the passive cooling capabilities of the ACE and its effects on the soil temperature profile and active zone depth. Model results revealed positive mitigative effects on permafrost degradation, with diminishing cooling capabilities over time due to ongoing global climate warming. Due to the coarse, angular embankment material, and porous nature of the ACE, thaw-settlement of the roadway is anticipated to be minimized, and surface water is expected to diffuse through the embankment, contributing to restoration of the downgradient hydrologic regime. All images and illustrations within this paper are attributed to FHWA, unless marked otherwise.