Study On Performance Of Roadbed Improved Soil Under Freeze-thaw And Cyclic Loading And Unloading

In recent years,the scale and quality of China’s comprehensive transportation network have jumped,and the breadth and depth of coverage have been continuously improved,of which more than 50 projects are located in the cold regions of China.In order to meet the needs of the project for the amount and stability of the subgrade filler,it is not only necessary to improve the original road subgrade soil,but also face a thorny problem of frost heave and melting and sinking.The extreme temperature in the mountainous areas of northern Hebei can reach 40℃ in summer,and the minimum temperature in winter is as low as-30 ℃,and the road subgrade in the area is repeatedly frozen and melted all year round,especially in early spring,the temperature difference between day and night is large,and some road sections of the roadbed will experience a freeze-thaw cycle a day,which will affect the life of the road and traffic safety.In addition,the cyclic vehicle load is also the main reason for affecting the service life of the road,and the performance of the road surface will gradually decrease under the continuous influence of traffic load.The freezing and melting effect of the subgrade is simulated by the freeze-thaw test of the cement lime double-doped modified subgrade filler,and the vehicle load effect of the subgrade is simulated by the three-axis conventional loading and cyclic loading and unloading test.The similarities and differences of the evolution of mechanical parameters of cement lime double-doped modified subgrade filler in conventional loading and cyclic loading and unloading tests are discussed,and the different effects of different working conditions on subgrade improved soil are analyzed from the energy point of view.The specific content is as follows: First of all,the physical parameters of the original soil and the improved soil of the subgrade are obtained through the basic geotechnical test.Then,the freeze-thaw test and the conventional triaxial compression test and the stress-type cyclic loading and unloading test were carried out on the cement lime double-mixed modified soil.The evolution of improved subgrade filler volume strain,peak strength,elastic modulus,Poisson’s ratio,and damage mechanism under cyclic loading and unloading and freeze-thaw conditions was investigated.The results show that under the same freeze-thaw condition,the confining pressure increases,the mechanical properties of the improved soil increase,and the peak---confining pressure evolution equation under the two stress paths can be expressed as the same power function;however,the evolution trend of elastic modulus and Poisson’s ratio is not the same.Cyclic loading and unloading accumulates more damage under the same volume strain than conventional triaxials,resulting in less load carrying capacity.Based on the first law of thermodynamics,the deformation process of improved subgrade filler under various working conditions is analyzed from the perspective of work and energy,and the energy conversion and deformation failure inside the improved soil of the subgrade under cyclic plus unloading stress path are explained.Finally,the effect of more freeze-thaw cycles on the mechanical properties of improved subgrade fillers was predicted by GM(1,1)model,and the life of subgrade soil was predicted.