Dispersion Properties Of Periodic Pile Barriers In Saturated Soil And Its Application In Ambient Vibration Attenuation

Multi-row pile barrier has been proved to be an economic and effective wave barrier and widely used to reduce/isolate ambient vibraions in civil engineering.While it has become a new research topic in recent years to study the vibraton reduction property of multi-row pile barriers based on the periodic theory in the solid-state physics.So far,most researches were focused on the filtering property of periodic pile barriers in single-phase soil,and those for saturated soil were relatively limited;generally,the real disperision analyses were conducted and any forms of material viscosity were neglected;besides,it was assumed in these studies for simplicity that the ambient vibratons were mostly induced by stationary excitation source,thus ignoring the case of moving excitation source.However,it has been found that the material viscosity,the excitation frequency and velocity of the moving loads have significant effects on the vibration mitigation performance of the wave barriers,and the relevant influencing mechanisms remain to be revealed.Therefore in this thesis,a new algorithm for calculating the complex dispersion relations of the periodic systems is proposed based on the Bloch-Floquet theory,and further implemented through the Partial Differential Equation(PDE)Module of the commercial finite element software COMSOL 5.1.Then,with the proposed algorithm,the complex dispersion properties of the scattering and locally-resonant periodic pile barriers are comprehensively investigated;the producing mechanisms and influence factors of the attenuation zones are discussed,especially for the influence of pore-fluid viscosity and pile-material viscosity,as well as the soil permeability.Further,a hybrid-type periodic pile barrier is designed by combining the mechanical characteristics of the scattering and locally-resonant periodic pile barriers;the corresponding vibration mitigation properties in saturated soil are studied through the complex dispersion analysis,and compared with those of the scattering and locally-resonant periodic pile barriers.Finally,the periodic-pile theory,especially the attenuation-zone property,is extended to the vibration mitigation analysis for the case of moving loads;the corresponding vibration mitigation mechanism is revealed,and numerical simulations are conducted to estimate the vibration-reduction effect of the scattering,locally-resonant and hybrid periodic pile barriers under the moving loads,thus validating the feasibility of applying the attenuation zones of periodic pile barriers for ambient vibration reductions/isolations.The main innovative achievements of this thesis are drawn as follows.(1)A more generalized methodology for computing the complex dispersion of the periodic system is proposed,and implemented through the PDE Module of the commercial finite element software COMSOL 5.1,thus making the complex dispersion analysis of the periodic pile barrier in the saturated soil become feasible.(2)The complex dispersion properties of the scattering-type periodic solid pile barrier in saturated soil are comprehensively studied by using the implemented algorithm.The propagation and attenuation properties of three typical elastic wave modes,i.e.,the high-speed longitudinal-wave modes,low-speed longitudinal-wave modes and shear-wave modes,are analyzed,and the shear-wave attenuation zones are obtained,which are more accurate than those obtained by traditional real dispersion analysis.Further,the influence of various physical and geometric parameters,especially the pore fluid viscosity and soil permeability,on the vibration mitigation properties is revealed.(3)The complex dispersion properties of the locally-resonant-type periodic in-filled pile barrier in saturated soil are comprehensively studied.The producing mechanism of the shear-wave attenuation zones is revealed,i.e.,the local anti-resonance effect of the soft filling material;the influence of the Young's modulus,density,filling radius,and especially the viscosity of the filling material on the shear-wave attenuation is investigated by parametric studies.(4)A hybrid periodic pile barrier in saturated soil is designed to produce wider shear-wave attenuation zones in a lower frequency range,which combines the mechanical characteristics of the scattering and locally-resonant types of periodic pile barriers.The producing mechanisms of the attenuation zones and the influence of the pile material viscosity are further revealed through the complex dispersion analysis.(5)The theoretical results of the periodic pile barrier are successfully applied to study its filtering property under the moving load.The attenuation zones of the periodic pile barrier for the moving load are determined in theory,thus revealing the relevant vibration-mitigation mechanism thoroughly.Finally,several numerical simulations are conducted to evaluate the vibration mitigation performance of the aforementioned scattering,locally-resonant and hybrid types of periodic pile barriers under different moving loads,thus validating the theoretical results.Based on the study of this thesis,a new method for analyzing the complex dispersion relations of periodic systems is proposed,a deep insight into the vibration-mitigation mechanisms of different types of periodic pile barriers can be gained,and a full understanding for the influence trends and influencing mechanisms of different design parameters on the vibration mitigation performance of periodic pile barriers can also be achieved.Basically,this thesis provides meaningful guidance for the theory of periodic structures,especially for designing periodic pile barriers to reduce/isolate ambient vibrations in practical engineerings.