Rahman M., Orr T.

Wave barriers in the form of back filled trenches are often installed in the ground to reduce the ground vibrations induced by man-made sources, such as traffic and machine foundations. This type of ground vibration and ground vibrations due to tunnel boring machines (TBMs) could be a major problem in densely populated urban areas and for structures housing sensitive equipment. No previously published research has been found in the literature on the use of backfilled trenches to provide a screen to the vibrations due to TBMs. In this paper the results of a numerical study, using a 3-D finite element model with infinite elements, to investigate the effectiveness of backfilled trenches in reducing the ground surface vibration due to tunnelling activities are presented. The ABAQUS V 6.4 finite element software has been used to construct the model and three-dimensional eight noded linear brick and reduced integration elements are employed for the ground and the tunnel lining. Reduced-integration elements use fewer integration points in each direction than the fully integrated elements, hence reducing the running time, especially in three-dimensional finite element analyses. In the model, the top layer is brown clay, the middle layer is Dublin boulder clay and the bottom layer is limestone. The effects of variations in the geometrical and material properties of the backfill trench on reducing the ground vibrations have been studied. The findings of this study are that the percentage reduction in the vibration velocity increases with increasing depth of the wave barriers and that softer backfill material yields a better screening effect than stiffer material.