Adaptive Countermeasure Research On Expressway Construction In Permafrost Region Of Eastern Part Of Qinghai-tibet

Gonghe—Yushu expressway was started to be built in 2010.In the permafrost region,Gonghe—Yushu expressway is parallel to 214 national road and they have the similar permafrost geological condition and permafrost engineering disaceses.Strict requirements of construction were put by Gonghe—Yushu expressway,and one of the most severe difficulties in the construction of Gonghe—Yushu expressway is doubtlessly permafrost.Even some experience has gainned from the highway or railway construction in permafrost region of Qinghai-Tibet,it still can not satisfy the strict requirements of the construction of Gonghe—Yushu expressway.This research is to find an adaptive strategy of Gonghe—Yushu expressway construction in permafrost region of eastern part of Qinghai-Tibet,including stability techniques of permafrost subgrade,ways of investigating on-site diseases.Site investigation and field tests are carried out and combined with practical application and theoretical analysis.a comprehensive test system for expressway construction in permafrost region was built and used to study the performance ofsubgrade structure.Finally,6 recommended subgrade structure is proposed with detailed description of their mechanisms,design principle and applicable condition.The results of this research are significantly meaningful for evaluating engineering geological condition of permafrost region and guiding the design construction,maintenance,repairing of expressway in permafrost region.(1)The distribution and types of permafrost between along 214 national road and Gonghe—Yushu expressway was proved to be similar.Because climate continuously becomes warm,permafrost ground temperature increases,permafrost table drops,some permafrost disappears,much unfavorable geology of permafrost exists along the Gonghe-Yushu expressway.All above things make a huge threat on the existing expressway and the expressway under construction in permafrost region.The main engineering problems include congelifraction,seasonal frost heaving,perennial frost heaving,freezing-thawing grassy hump,ice cone,freezing-thawing solifluction,hot melt pond,hot melt slump,hot melt erosion,different levels of permafrost degradation in different areas.(2)Since 1982,annual average temperature of permafrost region in eastern part of Qinghai-Tibet keeps rising with an average speed of 0.069?/a.Mnitored data of the year 2003 to 2014 shows that permafrost ground temperature changing speeds of 6 positions(JiangLuLing,ZuiMaTan,HongTuPo,HuaShiXia,ChangShiTou mountain,DuoGeRong)are respectively 0.0.13?/a,0.012?/a,0.010?/a,0.016?/a,0.007?/a,0.082 ?/a.Speed of permafrost table moving down of HuaShiXia K414+580 section in 214 national road is about 0.06m/a.Permafrost of 6 positions(JiangLuLing,ZuiMaTan,HongTuPo,HuaShiXia town,DuoGeRong,QingShuiHe)is absorbing heat,Permafrost of ChangShiTou mountain is releasing heat,Permafrost of ChaLaPing is stable.Speed of Permafrost thickness decreasing in HuaShiXia is 0.53m/a.Earth's surface freezing index of K369+100 and K391+100 are calculated by corrected Stefan formula,prediction equation of thawing depth is also solved.(3)Based on catastrophe series appraisal method,evaluation model of permafrost geology was established based on the permafrost conditions and natural conditions.Based on the four typical pennafrost condition s and three kinds of ground temperature the engineering geology along the expressway were evaluated and analyzed and is consistent with the obsearvtion in practical engineering.(4)Long-term test system was estabilished,including heat exchange of geogas under different pavements,cooling mechanism of rockfill subgrade,cooling mechanism of thermosyphon,cooling mechanism of ventilating pipe,creep deformation of high temperature permafrost,temperature field of subgrade slope affected by slope exposure,bearing capacity of pile foundation and interaction between piles and soil.Long-term monitoring equipment was equipped and used to measure the long sequence basic data of stability of permafrost and engineering.Reliable test data was obtained for engineering evaluation and optimization of the highway construction technology and the disease treatment technology in permafrost region.(5)Monitored data of field test was analyzed to study the engineering effect of 7 Long-term test systems,including heat exchange of geogas under different pavements,cooling mechanism of rockfill subgrade,cooling mechanism of thermosyphon,cooling mechanism of ventilating pipe,creep deformation of high temperature permafrost,temperature field of subgrade slope affected by slope exposure,bearing capacity of pile foundation and interaction between piles and soil was proved,scientific basis was provided for optimizing different design parameters.(6)According to specific situation of permafrost region in eastern part of Qinghai-Tibet,6 measures of adjusting and controlling convection of expressway built in the region were put forward.6 measures were ventilating pipe subgrade,rock block subgrade,thermal insulating layer subgrade,rock block-ventilating pipe composite subgrade,thermosyphon subgrade,thermosyphon-thermal insulating layer subgrade.Operating principle and range of application and design principle and subgrade design and construction technique and methods were detailedly described.They can be used to guide the design and construction work of expressway in permafrost region.