Coupled Discrete-Continuum Numerical Analysis Of Pile Penetration

Pile foundation has widely used in the civil engineering practices at home and abroad because of its advantages of high bearing capacity, large stiffness, small settlement, well stability, powerful applicability and so on. Among the existing pile-sinking methods, more and more people use static pile driver and high frequency vibrating hammer for pile installation to reduce the noise, vibration and air pollution that producing in the construction process. No matter using hydraulic jacks or high frequency vibrating hammer to press piles into the ground, the influence on the soil around the pile during the installation of pile is the emphasis that researchers focus on. At present, most of the numerical analyses of the pile penetration mechanisms are by the finite element method which is based on small strain continuity assumption. However, the application of discrete element method which is based on non-continuum mechanics is more conducive to reveal the mechanism of pile installation as the soil is a discontinuous granular material. When using the discrete element method to analysis the large scale model, it needs to generate a large number of particles. As a result, the requirement for the calculation performance of the computer is higher and the calculation time is long. It has become a bottleneck problem of discrete element method. Therefore, many researchers develop the discrete-continuous coupling analysis technology which can take advantage of each modeling scheme while at the same time minimizing the requirement for computational resources.Under the above background, full coupling between FLAC and PFC codes is made possible through built-in socket connections and then the thesis developing a coupled discrete-continuous numerical model to analyze the mechanisms of pile penetration from the macro and micro aspects. The first part of this paper is the literature review, which is focus on elaborating the pile penetration mechanism by high frequency hydraulic vibratory then the development and the existing achievements about high frequency hydraulic vibratory is reviewed,also the development and application of the discrete element in the geotechnical engineering are summarized at the same time. After reviewing the research background and the existing available literature, the thesis provides a brief introduction to the related theory of the FLAC/PFC2D coupled numerical simulation calculation method and illustrates the treatments to the interface between discrete and continuous of coupled numerical simulation in detail, the realization of the coupled calculation program and the coupled calculation framework are also introduced at the same time. By using discrete-continuous coupled numerical methods, the numerical analysis of pile driving mainly includes two sections that is the mechanism of jacked pile and the high frequency vibration pile driving in this paper. In the analysis of piles penetration mechanism, it is focus on studying the law of the development of the pile tip resistance and the pile shaft resistance in the process of pile installation and observing the behavior of the soils around the pile including the stress, the movement of the soil particles, the porosity and the coordination number. A series of research results indicate that the installation of displacement pile causes complex changes to the behavior of soils surrounding the pile.