Study On Differential Settlement Mechanism And Characteristics Of Widened Subgrade In Permafrost Regions

In recent years,the Qinghai Tibet region has developed rapidly.With the gradual implementation of the national highway network planning,it is imperative to build high-grade highways in permafrost regions.In view of its special geographical location and geological environment,it is also an important construction scheme to upgrade the existing secondary highways.In order to study the influence of widening project on the temperature and deformation of Subgrade in permafrost regions,this paper takes the widening subgrade in permafrost regions as the research object,analyzes the distribution law of temperature and deformation of widening subgrade by centrifugal test and finite element simulation,evaluates the long-term stability of widening subgrade in permafrost regions,and determines the widening scheme in permafrost regions.The conclusions are as follows:(1)Based on the site survey data of Qinghai-Tibet highway,the geotechnical centrifuge of Chang’an University was improved,and the centrifugal model test monitoring system and temperature field realization device were developed to reproduce the internal stress environment and external climate environment of the permafrost to the new and old subgrade.Through the centrifugal model test,it was found that the permafrost widening subgrade was obviously affected by the "Shady-Slopes and Sunny-Slopes" effect,and the temperature on the sunny slope side was 2～After 10 years of widening,the deformation difference between the two sides of the shoulder reaches 3.2cm.(2)Based on ABAQUS extended development,the actual boundary conditions under the influence of ground radiation,solar radiation,wind speed,convective heat transfer and other factors are compiled,and the analysis model of permafrost widening subgrade temperature field is established to study the long-term thermal stability of permafrost layer after widening.The results show that:the temperature of shady slope is lower than that of sunny slope all year round,and the temperature difference between the two sides of slope toe can reach 4.7℃;increasing the subgrade height properly can maintain the temperature of frozen soil,with the filling height of subgrade increases from 2.5m to 5.5m,the maximum thawing depth increases by 0.25m;increasing the widening width will accelerate the degradation of frozen soil,with the widening width increases from 3.5m to 5.5m,the maximum thawing depth decreases 0.83m.(3)Based on the temperature of widened subgrade and ABAQUS extended development,the UMAT subroutine of modified Duncan model is compiled.Using sequential coupling method,the permafrost widened subgrade deformation model is established to analyze the deformation law under the influence of temperature.The calculation results show that the deformation of the shady slope side is obviously smaller than that of the sunny slope side,and the maximum discrepant deformation between different slope reaches 4cm;with the widening width increases from 3.5m to 5.5m,the maximum discrepant deformation of the widening subgrade increases by 9.4cm;with the filling height of the subgrade increases from 2.5m to 5.5m,the maximum discrepant deformation of the widening subgrade increases by 8.4cm.(4)The maximum deformation,settlement rate,upper limit of frozen soil and two seasons permafrost temperatures are selected as the stability evaluation criteria.Based on the theory of spatial scale effect,the thermal stability and deformation stability of widened subgrade under different working conditions are analyzed,and the optimal widening scheme is found.