Hydrothermal Effect Of Supra-permafrost Groundwater On The Stability Of Subgrade In Permafrost Region

For the groundwater overflow and cracking deformation of the slope roadbed in the permafrost area of Qinghai-Tibet Highway,this paper firstly carried out ground temperature and water level monitoring on the slope roadbed in the Beilu River area of Qinghai-Tibet Highway,and analyzed the hydrothermal change law and deformation characteristics of the slope roadbed through the monitoring results.On this basis,the numerical model of coupled heat-moisture-stress for various working conditions of the roadbed is constructed and calculated,and the data obtained from actual measurements and calculations are compared and analyzed.The following conclusions are obtained.(1)Field hydrothermal monitoring results show that in the high-temperature perennial permafrost zone of the Beilu River area of the Qinghai-Tibet Highway,the polythermal effect of asphalt pavement significantly reduces the upper limit of the lower perennial permafrost;There is a significant difference in the ground temperature between the two sides of the roadbed in the experimental section,and there is also a significant difference in the degree of deformation of the upper limit of the frozen soil in the lower part of the left and right slope footings.Free water,which exists in the warm season,clearly flows and collects on the sunny slopes of the lower terrain.(2)For the monitored roadbed in the Beilu River area,the shape of the upper limit of permafrost in the lower part of the roadbed surface is similar to a "concave" shape,i.e.the upper limit of permafrost under the foot of the slope on both sides is higher than the center of the roadbed.The upper permafrost depth of the lower part of the foot of the slope on the left side of the roadbed is lower than the foot of the slope on the right side;Under the action of the upper soil self-weight and vehicle load,the lower deformation unevenness will be further intensified,resulting in uneven deformation of the pavement and sinking damage.(3)Theoretical calculations show that a slope sloping towards the sun will si gnificantly increase the range of temperature influence on the lower part of the s haded slope;The involvement of rainfall extends the thermal influence in the per mafrost,increases the overall water content,and leads to an increase in the settl ement deformation of the roadbed.The water on the frozen layer will transfer an d concentrate on the sunny slope of the lower terrain,and cause the settlement deformation value of the roadbed to increase,significantly affecting the stability of the roadbed.