Study On The Transition Layer Between Semi-rigid Base And Subgrade Based On The Durability Of Subgrade Soil

Subgrade plays a supporting role to the pavement structure, while the property of subgrade soil changes as the effect of water and bad along the running. And the strength attenuation appears easily, which would result in the damage of pavement. The transition layer between subgrade and semi-rigid base could decrease the influence of subgrade defect on pavement structure. But now there is no systematic design method to guide the design of transition layer. So the durability of subgrade soil and its impact is studied, and then the design method of transition layer is proposed basing on the function of transition layer.Water has an important influence on the property of subgrade soil, and the fine-grained soil retains water strongly, so its property is easier to be impacted by water. First, the permeation and capillarity of silt and clay are simulated through laboratory test, and then the influence of soil group on the water migration and the durability are analysed. Second, the disease of pavement caused by subgrade with high water content is summarized by means of field survey. At last, the quantitative analysis of the fatigue life of pavement structure is proceeded combined with the application environment.Resilient modulus of subgrade soil is an important parameter in pavement structure design, which reflects the durability of subgrade soil. First, the stress-dependent and water sensitivity of soil are analysed separately, and then the coupling model is built by using matric suction. Second, the variation tendency of resilient modulus is researched based on the change of water conten and vehicle load. At last, the division method fot the grade of traffic volume is converted from vehicle number to axle load, and then the allowable minimum strength of subgrade for the typical asphalt pavement structure with semi-rigid base is suggested under different level of traffic volume.The elastic layer system theory is the basic for the design of pavement structure. First, the influence of thickness and modulus on the mechanics characteristic of the layered structure is researched, then the immediate influence factor is found out, thereafter the idea that the transit ion layer could minis h the influence of subgrade strength attenuation on pavement structure effectively is come up. Second, the function of transition layer is researched in terms of mechanical mechanism, which contains reinforcing the understructure and weakening the load, and then the influence of structure parameters such as thickness, modulus on the function is studied. Finally, basing on the reinforcement, the prediction model on equivalent modulus is established, after that the optimum reinforcement theory and the best modulus are put forward, which can meet the structure stress and make use of the strength of transition layer fully.Graded aggregate has enough strength and can moderate deformation. It’s a good material to construct transition layer, and the perfect graduation is important to the performance of the structure. First, different grading design methods are discussed, and it’s found that all these methods are different forms of fractal theory, also the fractal feature of aggregate is presented. Second, fractal features of aggregate in specification of different country are analysed, and then the scope of gradation is optimized by the solid volume rate, CBR and secondary coefficient of volumetric expansion. At last, the rationality of the suggested gradation range is examined by laboratory tests.The transition layer is applied in the maintenance works of a highway. First, the disease is examined, and it’s showed that the strength attenuation of subgrade is the key factor to destroy the pavement structure, so the transition layer is suitable to use in the engineering. Second, the optimum reinforcement theory is used to design the transition layer basing on the traffic volume, and the result achieves the structure checking. At last, the construction technology and quality inspection standards of graded aggregate are summarized.