Analysis On Asphalt Pavement Structure Based On Layered Elastic System Theory

The designed life of the high grade asphalt pavement structure in china usually is 15 years, but the phenomenon that the actual service life is lower than the designed life is more widespread, and damage appears earlier. People pay more attention on the surface deflection of the pavement and the tensile stress at the bottom of structure layers. In order to save the manufacturing cost, the concept of high modulus base and thinner surface course is adopted in the pavement designing. But in the process of investigating to many highways which are broken in early phase, the highways still have high whole strength and the value of surface deflection is quite small. The pavement is a complex structure; its different combination forms will make different layers to form different mechanical response. To achieve the logical combination, each influence factor should be considered generally instead of one influence factor which can improve the whole performance obviously. So the paper included six chapter analyses the method of the pavement structure design.Chapter one is the introduction of the paper. It mainly introduces the method of designing asphalt pavement; expatiate on the development of the layered elastic theory in designing and calculating the pavement. At last, it introduces the purpose and the work of this paper.Chapter two introduces the layer elastic theory mechanical, which is the method of researching on the stress and the displacement of the layer elastic structure under load, at first. It can get the relationship of the deformation and the displacement though the mechanic condition of balance, the geometrical condition and the physical condition. The ax- symmetric topic is one condition of the layered elastic system theory. The stress and the displacement expression which are applied on any ax-symmetric space topic of layered elastic system theory can be solved by using the Love Method on the ax-symmetric topic. While calculating the idiographic program, it is need that finding the boundary of the force and displacement, confirming the integration constant. After this the stress and displacement component can be solved.The mostly task of Chapter Three is compile the program. After study and research the ax-symmetric topic of the layered elastic system theory, the author use Fortran compile the program of stress and the displacement which are on the action of the vertical ax-symmetric uniform distribute load. The sub-works include : the force of cartwheel is simplified representation to the circular vertical uniform distribute load, and the mathematical function is also confirmed; On the basis of pavement's actual working condition , the method of calculating the boundary of the stress and displacement which belongs to the stress and displacement common function are confirmed. And then the integral constant coefficient matrices are confirmed by the boundary condition, and solved by the subprogram of calculating equation sets; The calculating subprogram of Bessel function is compiled by the Fortran; In the process of computing the stress and displacement's equation, a complicated function's infinite integral which is composed by the Bessel function and exponential function. The paper adopts relative error method to taking the numerical calculation and compiles the infinite integral as the main program.Chapter Four mainly research the pavement structure's influence of vehicular load changing. The paper takes a typical semi-rigid base asphalt pavement structure as the research object, and using six kinds of the axle loads which are 100KN, 120KN, 140KN, 160KN, 180KN and 200KN to simulating the standard axle loads and overloads. Under the condition of overload, because of the increasing of the axle load of the vehicle, the load radius and the uniform distribute load which are caused by the vehicle have great changes. Assuming the spacing interval of the load's action center of circle is fixed, the ground area of the tire which belongs to different axle load can be calculated by some common calculating formula. The force response of the pavement structure including the surface deflection of the pavement, the compression stress, the sheer stress, and the tensile stress which are changing with the axle load were analyzed by the Program of the Chapter Three. Because the max sheer stress of the surface has great influence on producing the rut behavior or not, and the regularities of distribution of the sheer stress is relatively complex on the processed of the former work of this paper, the max sheer stress of the surface layer is confirmed as the research object. Choosing four calculations points with different position, the values of the four stress that isσ_z,σ_r,σ_θandτ_rz,which are under the standard of the axle force and changing with the thickness of surface layer, are calculated by the Program. And then three principal stresses are obtained. The max sheer stresses are calculated by the formula of the max sheer stress and the distributed regularities are explain by the chart.Chapter Five analyses force response of the pavement structure dues to the changes of the material parameters and the layers parameters of the structure. While constructing process of pavement structure will be influenced by the environment factor, the actual pavement will not achieve the demand of the designation, and will appear unnecessary damage earlier. At first, the paper discusses the changing tendency of the force response included the surface deflection, the tensile stress at the bottom of base, the tensile stress at the bottom of the sub-base , which is due to the changing of the surface modulus under the condition of different axle load. The force response caused by the surface thickness, the base modulus, the base thickness, the sub-base modulus, the ground base modulus and the ground base Poisson ratio are determined by the same analyzing method. During the forgoing work, only one parameter changes, keeping other parameters invariable. But the influence rule caused by only one parameter can be confirmed. While several parameters changing together, it is unbelievable to analyses the influence caused by the parameter changes. The part two of the Chapter Two solves this problem by designing the orthogonal experimental. Five influence factors that is the surface modulus, the surface thickness, the base modulus, the base thickness and the sub-base modulus are chosen though analyzing. And each factor has four levels. So the L1 6(4 5)orthogonal meter is adopted to research the influence. After taking the results to direct analyses, the range of each factor can be calculated. The degree of the influence rule belongs to pavement structure caused by the five parameters changes though the values of each range. Chapter Six is the last part. And this chapter is summarization of this paper in which the content and direction are also pointed out for further study.