| Settlement calculation of pavement or airport runway under traffic load is one of most concerned problems in engineering area, as well as a key subject in academic area. Limited by geographic conditions, many express highways and airport runways have to be built on thick soft soil foundation. For its high compressibility and low strength, soft soil should be improved by composite foundation technology to satisfy the strict requirement of deformation. Subjected to traffic load, the pavement and foundation should be taken as a whole system of interaction, and of which deformation characteristics are worth studying.Firstly, the paper introduced the present study state on dynamic characteristics of soft subgrade and composite foundation, generalized the present study state on interaction of pavement and foundation from theory study, experimental modeling and numerical analysis aspects. Subsequently, the theory of elasto-plastic constitute and dynamic finite element method(FEM) are summarized, the difference and applicability of total stress method and effective stress method are described. Then, dynamic features of pavement materials, soft soil and composite foundation are depicted simply.The features and present study state of traffic load are generalized, and the typical structure of pavement is introduced. Then the paper summarized the present study state on dynamic pore pressure model of soft subgrade and composite foundation, established empirical dynamic pore pressure model respectively, and the model parameters are obtained based on formers' indoor dynamic triaxial tests.A dynamic elasto-plastic FEM program is compiled, and is verified by comparing the calculated results with analytical solutions. Many types of dynamic load can be used to analyze the problems of interaction of soils and structures with this program. And it is necessary to use effective stress method to study dynamic deformation problems of soil subgrade.For convenience, traffic load is simplified as half-sinusoidal load, and the soil of subgrade is assumed to be strain-hardening. The deformation characteristics of pavement section and soft soil subgrade under traffic load are analyzed, considering the effects of load (including type, amplitude and frequency) and parameters of soft soil (including resilient modulus, cohesion, internal friction angle, Poisson ratio, damping ratio et al). With the established dynamic pore pressure model, the calculated results of total stress method and effective stress method are compared. Consolidation settlement induced by dispersion of residual pore pressure is calculated, and the effect of pore pressure on pavement settlement is discussed.The deformation characteristics of pavement section and composite foundationunder cyclic traffic load are analyzed with the FEM program. With the dynamic pore pressure model of composite foundation established, the effects of pore pressure, horizontal load, parameters of pavement structure, soft subsoil and composite foundation on pavement deformation are discussed in detail. Taking the traffic load as moving point load, the deformation characteristics of longitudinal section of pavement and composite foundation under moving point load are analyzed, considering the effect of pore pressure, traffic velocity, parameters of pavement structure and subgrade.Finally, two examples of pavement section and soft subgrade, longitudinal section of airport runway and composite foundation are calculated. And the results show that the calculated settlement agree well with that of measured.The paper established the dynamic pore pressure models of soft soil subgrade and composite foundation, compiled the dynamic FEM program of undrained effective stress method, considering the elasto-plasticity of foundation soil as well as the interaction of pavement and foundation, thoroughly analyzed the deformation characteristics of pavement and foundation, and these results are instructive for the construction of pavement or airport runway.
|
PDF Full Text Request