高温多年冻土区冻土地基预先融化技术研究现状及展望

在气候变暖背景下,多年冻土退化加剧,高温冻土将会在更大范围出现,保护冻土原则的适用性将受到经济、技术、环保合理性的挑战.在条件适宜高温冻土区,根据建筑结构和基础类型,采用预先融化技术(简称预融技术)处理冻土地基可在经济合理的前提下,保证工程的安全可靠性和长期稳定性.回顾了国内外冻土区预先融化技术的经验,总结和展望了预融技术在工程设计、施工及运行中的三个基本步骤,包括施工前多年冻土的融化、已融土的密实和固结,工程运行期间保持融化和防止冻胀措施的实施.预融技术主要利用蒸汽,热、冷水的对流换热和电流热效应,以及改变地表热状况来融化下伏多年冻土.保持融化的方法主要包括改变地表反射率和地基土的结构,融土保温以及利用主动和被动升温传热装置等(如热管技术).结合中国东北的一些预融技术运用实例,如漠河机场工程等,简要评述了预融技术的应用效果.

Techniques for Prethawing Permafrost: Review and Prospect

Under a warming climate and resultant accelerated degrading permafrost,warm permafrost might occur in a large extent.The technical and economic feasibility and environmental protection for the design principle of permafrost protection will be significantly challenged.The prethawing technique of permafrost,if applied properly to engineering infrastructures and foundation and geotechnical settings in warm permafrost regions,might ensure the technical feasibility and long-term stability of engineering foundations.The prethawing techniques of permafrost foundations are reviewed and prospected,which include the basic steps and concerned solutions during the design,construct and operation/maintenance phases,based on the studies and experiences on cold regions engineering and the successful application cases of prethawing techniques in China and overseas.The three basic steps are: 1) thawing permafrost before construction,2) consolidation and compaction of thawed soil,and 3) keeping the thawed,frost-susceptible soils from being refrozen and frost heaving. Commonly prethawing techniques used for permafrost include,but not limited to,1) convective warming with hot steam,hot or cold water,2) electric heating,and enhanced warming by modifying ground surface.The techniques for keeping the thawed soils from being refrozen mainly includes modification of ground surface,such as reduction of surface albedo,and/or alteration of soil structures to have a function of thermal insulation or diode,and application of active and passive warming devices or systems,like thermosyphons.Some cases of prethawing techniques in Northeast China,such as the Mohe Airport,were reviewed.