Numerical Analysis For Reduction Of Traffic-induced Ground Vibration

High-speed railways and high-grade roads are important infrastructures for national economy growth. However, the passage massive and high-speed trains may generate ground vibrations, which will propagate through the soil and impinge on surrounding industrial and residential areas, and may cause malfunctioning of some sensitive equipments, discomfort people and damage buildings. It is possible to avoid or mitigate these adverse effects by providing a suitable wave barrier around the vibration sources, and therefore it is of a practicable significance to lead investigations into the material, layout and dimensions of such barrier structures.Railway traffic induced ground vibration and the isolation project have been a subject with increasing research interests in recent years. In general, a few references on this subject preferred to employ elastic model to simulate soil responses under the traffic dynamic excitation. In this thesis, a more sophisticated elastoplastic model was employed. The ground vibration caused by high-speed train was analyzed with a three-dimensional numerical model by software LS-DYNA. Particularly, barriers which are composed of different materials (open trench, inundated water trench, different density of geofoam in-filled trench, and concrete in-filled trench) and a reinforced concrete pile with different dimensions were numerically analyzed subjected to railway traffic loads. The main research works are as follows:Firstly, a geometry model was built by LS-DYNA with elastic and elastoplastic material models. The numerical results were compared with in-situ tests to verify this model. Secondly, train-induced ground vibration was respectively investigated without protection barrier and with protection barriers of open trench, in-filled trench. Thirdly, the ground vibration level is studied at different train speeds. Finally, the isolation efficiency of a reinforced concrete pile barrier is comparatively investigated for different dimensions. From these studies, following understandings and conclusions can be made:â‘ Train speed is the key factor for the ground vibration level. Ground vibration is strong around the railway, and gradually decreases along with the increasing distance from vibration source. The vibration acceleration level is high within the 25m away from the vibration source, which entails effective isolation measures.â‘¡The vibration load increases with promoting train speed, resulting in enhanced ground vibration level. However, the decreasing rate of vibration acceleration level is more rapid in a low train speed.â‘¢Open trench can effectively attenuate ground vibration. For instances, peak acceleration is largely reduced. It may turn to be inundated water trench in rainy area, slightly reducing its attenuation effect. Soft material like geofoam in-filled trench can reduce ground vibration effectively. Hard material like reinforce concrete pile in-filled trench has less isolation effectiveness compared with the soft material.â‘£Parameter study reveals that barrier length and depth determine the protection zone and the reduction of vibration magnitude, depending on the relative dimensions to vibration wave length. At high train speed condition, the isolation effect is prominent associated with depth rather than width. Within one wave length zone behind the barrier, isolation effect is almost not changed by increasing barrier's length and depth. At the location far away from one wave length to vibration resources, vibration level decreases 4dB when the barrier length increases 0.4 times wave length. Furthermore, when barrier depth increases by 0.4 times wave length, the vibration level decreases 6dB.