Canyon Topography Effects on Ground Motion

Abstract eng:
It is broadly known that topographic irregularities effect ground motions, with a particular enhancement of the ground response close to convex topographic features such as ridges and slope crests. Although there are many studies investigating the ground motion in the vicinity of slope crests, the response at the toe has not been studied in great detail, as the toe ground motion is normally considered to be smaller than that of the crest. However, for canyon topographies further investigation of the ground motion at the slope toe, where a more complicated response is expected due to the interaction of the canyon sides, is needed. The response of semi-circular and semi-elliptical canyons has been previously examined; but mainly focusing on valleys filled with soft materials. This paper considers a fully weathered canyon (i.e., without any in-fill material) aiming to investigate the influence of a canyon’s width on the surface ground motion through a parametric timedomain finite element (FE) study. A two-dimensional plane-strain model of an idealised canyon is considered for vertically propagating SV waves, using wavelets as input excitation. The model consists of two step-like slopes with slope height (H), in a homogeneous linear elastic soil layer overlying rigid bedrock. The analyses focus first on the canyon slope areas, where the ground motion is altered depending upon the proximity to the topographic irregularity, identifying the main parameters that effect the response. Results are also presented for several points along the canyon ground surface showing that the distribution of topographic aggravation varies significantly with canyon width.

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