Linearity Engineering in Permafrost Areas
CHENG Guo\|dong, HE Ping (State Key Laboratory of Frozen Soil Engineering, CAREERI, CAS, Lanzhou Gansu 730000, China)
Much of linearity engineering, such as railways, highways and pipelines, has been built in permafrost areas in North America and Russia. The linearity engineering in permafrost areas, especially in warm permafrost areas, often cause severe problems from long\|term thaw settlements, decline of permafrost table on the embankment, roadway cracking, foundation elevation, differential deformation, slope slip etc., due to soil thawing and refreezing. Many techniques, such as varying thickness of gravel fill, foam board type insulation, heat pipes, air convection cooling ducts, have been used in permafrost regions attempting to limit or prevent thawing of frozen foundation soils below highway and railway embankment and pipelines. There is a brief summary on the techniques in the paper. It is useful to engineering construction in permafrost areas of China, especially to Qinghai-Tibet Railway. Necessary embankment height to prevent thaw and differential settlement is often economically impractical, especially true in discontinuous and warm permafrost areas. Rock fill embankments and rock fill cover materials, which create convective air circulation to enhance ground freezing during freezing periods and provide shading during warmer periods, have been utilized in Russian railway embankments and Alaska highway which cross thaw\|unstable ice\|rich frozen ground terrain. Air convection cooling ducts were also used in permafrost roadway embankment. It function in convection only in winter. When the adjacent soil warms the air inside the duct, causing it to expand and rise up the exhaust stack, at the same time drawing in cool air at the inlet. Dampers were included, and are manually closed in summer. Air convection cooling ducts were of significant benefit in retarding thaw of the of the foundation soils, particularly when used in conjunction with insulation layers placed to reduce summertime heat gains in the soils cooled by the duct system. Insulation layer is one of methods to prevent or control thawing of frozen subgrade soils and reduce the quantity of fill required. The research data shows that heat pipes, operating through transport of a gas, a liquid, or liquid and vapor through a phase change, as a viable technique, maintain soil stability in ice\|rich permafrost by drawing heat from the ground. Peat as an underlay material, with a frozen conductivity nearly twice its thawed value, should be better suited to preserving a frozen sate than a thawed one in an attempt to reduce or prevent differential settlements. Pile foundation is the optimal type of foundation for bridges and buildings in permafrost regions.
【Fund】： 中国科学院寒区旱区环境与工程研究所知识创新工程项目 (CACX2 10 0 13) ;; 中国科学院资源环境领域知识创新工程重大项目(KZCX2 30 6)资助
【CateGory Index】： P642.14
【CateGory Index】： P642.14