Highway was often get strong destroy by the various natural disasters in mountain area. Collapse and debris flow concentrate in middle mountain.which elevation is more than 1500 metres. High peak period of their burst is simultaneous with the maximum period of precipitation in every year. Frequency of its burst has close relation with weathering degree

content of debris

condition of bed rock and tributary situation in flank hillside of highway. Thaw sinking developed in frozen regions. Every year frozen ground begin thawing and like slush in April. The road surface is muddy and sink

which rate is 3. 0 cm/yr in north slope of Tianshan. It is frozen in November. The temperature of south slope (the sun-slope) rise quickly in spring and the frozen ground was sinking first. In summer seasonally thawing layer was thicker with higher temperature. The temperature of sun-slope fall slowly in autumn

so ihe thawing layer freeze later. Harm degree of thaw sinking depened on the thick of seasonally thawing layer. Because old highway was built on the new moraine.which has more ice. its original steadiness condition was brokon and the ice thaw. It cause the highway sinking and collapse on a large scale. The intact ratio of highway is only 10—20 percent.