SECONDARY FREEZING-THAWING HAZARDS AND ANALYSIS ON THEIR CAUSES ALONG PERMAFROST REGIONS QINGHAI-TIBET RAILWAY ROADBED

Secondary freezing-thawing hazards in permafrost regions Qinghai-Tibet railway roadbed are key of the railway safe use. This paper summarized seven types main secondary freezing-thawing hazards along the permafrost regions Qinghai-Tibet railway roadbed which would impact on railway transportation in future, such as cracking of road shoulder and berm, frost crack of abutment, protection slope and culvert, drumlin and ice sheet, frost heaving and frost mound, thaw lakes, thawing groove and frost weathering etc., after careful survey for the Qinghai-Tibet railway that has been used for about 1.5 years. Via observation of the secondary freezing-thawing hazards, to analyze their character and cause of formation. This will offer to the important reference basis for prevention and cure of the disease of Qinghai-Tibet railway roadbed.