EFFECTS OF SURFACE TOPOGRAPHY ON GROUND MOTION CHARACTERISTICS

Abstract

The main objective of this dissertation work is to study the variation in characteristics of ground motion caused by surface topography of various shapes and size. The main concern in our research work is to quantify the variation of ground motion characteristics in different valley models and how the shape and height to width ratio is going to affect the amplification pattern. A Finite Difference numerical simulation will be used. From the past studies it has been brought out that for valley topography maximum deamplification is observed at the trough of valley while the maximum amplification occurs at edges and flank of the valley. Our numerical analysis results hold a fair validation to the past results and also to the analytical results. To study the effect of shape and shape ratios of valley we have analyzed three different valley shape models that are Triangular (TRV-model), Trapezoidal (TPV-model) and Elliptical (ELV-models) valley models. All the three models are analyzed for four different shape ratio (H/L) that are 1.5, 2, 2.5, 3. The results of the analysis shows that the amplification is maximum at the edges and minimum at the base and as the shape ratio is increasing there is a marginal decrease in amplification at the edges. We have also considered the same model with a top weathered rock layer and it was observed that due to presence of weathered layer at the top there is a considerable increase in the amplification and DGM. We have further carried out our work to study effect real surface topography of Chenab railway bridge site of Jammu and Kashmir. A similar pattern for amplification and DGM is observed there. But due to presence highly top weathered layer and huge impedance contrast between the different rock formations there sudden increase of amplitude at the model edges is being observed. Also at the flanks amplification is much larger and approximately same throughout the span of flank. The basement suffers the maximum deamplification of the order 0.8 Although the study of ground motion characteristics with undulating ground profile or surface topography is a complex phenomenon. The amplification of waves also depends on many other factors such as slope ratio, slope angles and geological conditions.