Research On Mechanism And Treatment Method Of Semi Rigid Base Heave In Large Temperature Difference Area

The transverse band-shaped uplift disease induced by the time-temperature effect characteristics of semi-rigid base roads in desert areas poses a great threat to the service life of roads and the safety of driving operations.To this end,on the basis of the existing research of the research group,based on the disease investigation and the composition design of the cement-stabilized grading crushed stone mixture,on the premise of satisfying the strength and performance of the base material,the optimal gradation and fine aggregate type for the uplift disease are proposed,and the prediction model of the thermal expansion coefficient is established.Numerical simulation of expansion and shrinkage of cement stabilized graded crushed stone base using discrete element particle flow PFC 3D at the mesoscopic level.At the mesoscopic level,the discrete element particle flow PFC 3D is used to carry out the numerical simulation of the expansion and shrinkage of the cement-stabilized graded crushed stone base,in order to prove and explain the generation mechanism of the macro uplift disease of the semi-rigid base road.The following research conclusions were obtained:（1）The survey results show that the uplift disease develops and changes under the periodic influence of the "time-temperature effect" characteristic,and it is necessary to propose solutions from the perspective of optimizing the composition and design of the base material.The special environmental and climatic conditions,coupled with the long continuous section of the highway base,affect the release of internal temperature stress and induce uplift diseases.By adjusting the amount of aggregate in each grade and the type of fine aggregate in the grading,a grading with better skeleton compactness can be obtained.（2）Under the characteristics of time-temperature effect,the gradation type has obvious influence on the expansion and shrinkage of the base.The gradation type with more coarse aggregate content and coarse gradation should be designed within the grading range of dense skeleton,such as C-B-3 inverted S gradation.Under the premise of satisfying the strength performance of the base,the amount of cement should be appropriately reduced,and the same stone chips as the coarse aggregate should be selected for fine aggregate.The base material is most obviously affected by the temperature load at 40℃～50℃.In the long run,when the temperature stress accumulated inside the cement stabilized graded crushed stone base cannot be released,the thermal expansion effect accumulated inside the base will be better than the cold shrinkage effect,resulting in the occurrence of uplift disease.The prediction model of thermal expansion coefficient of cement stabilized graded crushed stone base course modified based on Kerner model is more suitable for the prediction of thermal expansion coefficient of base material.（3）The numerical simulation results of the expansion and shrinkage of the water-stabilized base layer based on discrete element particle flow PFC 3D show that when the temperature stress of the cement-stabilized macadam base cannot be released,from the perspective of expansion force,there will be a large expansion force inside the base layer,and the force chain near the maximum expansion force is in an upwardly convex state.From the perspective of expansion displacement,as the temperature increases,the longitudinal expansion displacement is similar to the actual situation,and the upward expansion displacement near the maximum expansion force will manifest as the occurrence of uplift disease.This corroborates and explains the mechanism of macro uplift disease of semi-rigid base road.