Stability Analysis Of The Permafrost Subgrade Under Vehicle Load

The permafrost in my country is mainly distributed in the high mountains of Northeast China,the Xiaoxing’an Mountains,the northern Songnen Plain and the Qinghai-Tibet Plateau.The total area is about 2.15×10~6km~2,of which the Qinghai-Tibet Plateau permafrost is about1.4×10~6km~2.The Qinghai-Tibet Plateau has unique geography and special climatic conditions,dominated by permafrost with high temperature and high ice content.This type of permafrost has high thermal sensitivity and poor thermal stability,and is more susceptible to the influence of seasonal changes.Since the Qinghai-Tibet Highway was opened to traffic,the upper limit of permafrost has been gradually lowered due to the increase in temperature and man-made disturbances on the Qinghai-Tibet Plateau.The ice-bearing layer has accelerated melting and degradation,which has aggravated the destruction of roadbeds along the road and has a certain impact on traffic safety.This paper takes the Qinghai-Tibet highway subgrade as the research object,considers the influence of vehicle load on the long-term stability of the subgrade,and studies the evolution characteristics of the stability of the permafrost subgrade under different temperature boundary conditions.The main research contents include:First,the main types of diseases of permafrost roadbeds and the factors affecting the stability of permafrost roadbeds are summarized;the heat transfer methods of permafrost roadbeds under steady and unsteady conditions are analyzed,and water migration is considered to establish water,Thermal and mechanical three-field coupled finite element analysis model.Secondly,according to the characteristics of the effect of vehicle load on the roadbed,a vehicle-road coupled vibration model based on two degrees of freedom was established,and the calculation formula of vehicle load was deduced.Finally,considering the impact of climate warming and vehicle load on the long-term stability of frozen soil roadbeds,a numerical analysis model of three-field coupling of water,heat and force was established using ABAQUS to study the temperature increase of 2.6°C in the Qinghai-Tibet Plateau in the next 50 years and limit the temperature increase of 1.5°C at the end of this century.Under the condition of 1.5°C,the time-effect change law and characteristics of the temperature field and deformation field of permafrost roadbed.The research results show that:(1)When the temperature rises by 2.6°C in the next 50 years,the area of the subgrade melting core in January will increase year by year,the average temperature in the melting core will gradually increase,and the freezing line will gradually move down.After 50 years,the distance of the freezing line at the center line of the subgrade will be the natural ground surface is about 5.7m;in July,the depth of melting of the roadbed increases year by year,the temperature inside the roadbed increases as a whole,and the melting range gradually increases.(2)When the temperature is limited to 1.5°C at the end of this century,the size and distribution of the temperature in the subgrade and the position of the freezing line remain basically unchanged over time.(3)Under the effect of vehicle load and gravity,the top surface of the roadbed will be"concave"after 50 years.If the temperature rises to 2.6°C in the next 50 years,the maximum settlement of the roadbed in January and July will be 18.13mm and 18.52mm,respectively.If the temperature rise at the end of this century is controlled at 1.5°C,the roadbed settlement in January and July will be the maximum settlement is 8.76mm,which is 51.68%and 52.69%lower than the former.