Freeway Extension Project Island Permafrost Section Foundation Deformation Characteristics

Bei'an to Heihe freeway locates in the China high latitude permafrost region, the permafrost is in the depredating stage, has low altitude and unstable characteristics, and affects the stability and operation safety of freeway. Employed the geological exploration and interior experiment method to obtain the permafrost type and mechanics performances; employed field monitoring method to study the permafrost degrading process and foundation deformation characteristics. Study results show that: the mechanical indexes of soil decrease significantly with frozen soil melted, and water content greater, void ratio higher, the descendant ranges are larger; the permafrost under the widen subgrade degrades from two sides to middle in the frozen period due to the thermal resistance effect of widen subgrade, the upper limit has declined 2.7 m and lower limit has raised 0.7 m; the vertical displacement of subgrade and foundation has obvious accelerating process with the new subgrade filling, the time of vertical displacement reaches a steady state is closely related with the stability of foundation permafrost, under the function of widen subgrade loading and permafrost thawing settlement, the maximum vertical displacement of widen subgrade foundation and original subgrade respectively reach 40.2 and 18.6 cm.