Abstract：To understand the formation mechanism of longitudinal crack of Qinghai—Tibet highway in permafrost region，the mechanical model of longitudinal cracks in subgrade is constructed during freezing and thawing processes by numerical simulation，based on the in-situ observation of thick ice layer in the cross-section K3020+200 and the testing data of temperature field in the cross-section K3016+000. The formation process of thick pure ice layer under road shoulder and its effect on subgrade stability are analyzed. The observation in the cross-section K3020+200 shows that the thick pure ice layer exists under road shoulder and natural ground surface. The time-history curves of ground temperature at different depths in the cross-section K3016+000 show that the change in ground temperature is larger near the ground surface；the change in temperature in subgrade lags behind that at ground surface；the upper limits of permafrost at road shoulder and slope toe decrease by ground surface water infiltration from road shoulder，slope and slope toe，i.e. the distribution of upper limits presents arch shape. The results show that the infiltration of ground surface water leads directly to the formation of thick pure ice layer；the formation and thawing of thick pure ice layer are immediate causes of nonuniform deformation of subgrade and formation of longitudinal cracks.
2010, Vol. 29 
