Dynamic Analyses Of Ground And Tunnel Responses Due To High-speed Train Moving Loads

In the last decades, with the convenience and efficiency improvements provided by the remarkably growing construction of high speed train(HST) all along the world there come the negative effects of the vibrations emitted from the train running to the residence, sensitive equipments and high-tech production facilities in the vicinity of the train track, which propel the researches in the prediction and evaluation of field vibration from engineering and environmental aspects. With the increasing of the train operation speed, the vibrations of track and ground will also go larger. When the train speed approaches to the critical velocities of track structure and ground, extremely large vibrations will occur in the track structure and ground, which becomes a serious thread to the safe operation of high-speed train.In the thesis, an semi-analytical substructure solution and a finite element simulation method are proposed to study the dynamic interaction of train track and ground under the impact loads from the high-speed train running, and the according vibrations of ground alongside the raillines.In the first part, the dynamics behaviors of layered ground are studied under the impact loads, and the generation and propagation of waves in ground are discussed herein, thereafter the ground responses are studied for several typical ground types. Based on these fundamental works, a Moving Green Function method has been introduced to solve he dynamics of ground with the moving loads inside or on the surface of the ground..The ground vibration problem under the train loads running on track structure resting on ground surface is more practical from the engineering point of view. To consider the wave propagation in the layered soil media with infinite half space, a more elaborate soil-structure model is proposed in this study. The vibration propagation in structures and ground induced by train passage is investigated by thesubstructure method with due consideration of dynamic interaction between a track system comprising rails and sleepers, and underlain layered ground.The total system is first divided into two substructures; the track and the ground, which are first formulated separately. The track system under train axles loads is supported by the discretely spaced sleepers via the sleeper-pads whereas the ground system of the viscous-elastic layered soils undergoes an array of sleepers' loads. The modeling is made such that rails are represented by an Euler beam, sleepers and rail-pads by a number of discrete springs and dampers under the beam, and the ballast is replaced by an extending top layer together with the ground by a layered viscoelastic medium. These substructures are then integrated to meet the displacement compatibility and force equilibrium conditions at their interface. The dynamics are solved in frequency-wavenumber domain by applying the Fourier transform procedure. Based on the assumption of a constant train speed, the time domain responses are evaluated from the inverse Fourier computation. The dispersive characteristic of layered ground and the phase shifted axle loads lead drastically different response features, depending on the moving speed. The consequence is classified as pseudostatic for a low-speed while as dynamic for a high-speed situation. The effect of discrete arrangement of sleepers proved better in interpreting the heavily damped vibration transmission along track that matches the measurement data.Also in this thesis, a 2.5D finite element and boundary element hybrid method is developed to solve the full three dimensional dynamics problem of complex ground and track properties under train moving loads. By applying the Fourier transform of wave number in the train moving direction to the governing equations of ground dynamics and track motions, the full three-dimensional problem can be deduced to a two-dimensional plane strain problem with wave number variable. Hence the computation efforts can be greatly deduced while keeping satisfying numerical accuracies.From the comparison of the field test d...