ARRC Rail Alignment Improvements Birchwood, Alaska Railroad Design — Construction in Marginally Frozen Relic Ice and Soil

Alaska Railroad Corporation (ARRC) is actively realigning several portions of track in-between Anchorage and the Matanuska Valley. This project focused on a curve straightening at MP 133 near Birchwood, Alaska. The design was complicated by anomalous subsurface conditions consisting of relic massive ice, frozen soils and normally consolidated clays that were encountered throughout the proposed alignment. Encountering massive ice in this area is unusual and rare since the Anchorage climate can not sustain massive ice growth. Massive ice consisted of up to 95% ice interbedded with silty clay with thickness up to 35 ft. Various design options were considered to support the proposed 30 ft high track embankment including: excavating the ice, thawing, maintaining the ice, bridging and realigning the proposed rail.