Valley amplification of horizontal ground strain: Fid-Bau Portal

Valley amplification of horizontal ground strain

Li, Hongjing / O’Rourke, Michael J.

Abstract It is recognized that seismic damages to segmented buried pipelines depend in part upon transient ground strain due to seismic wave propagation. Such wave propagation damage seems to be larger at sites with variable subsurface conditions, because of drastic changes in seismic wave characteristics as they propagates in heterogeneous rock and soil layers. This paper intends to investigate the amplification of horizontal ground strains in a valley subjected to vertically incident SH waves. A 2D model with an inclined soil-rock interface is established to simulate conditions of the valley subject to seismic wave propagation. A procedure for evaluating the ground strain amplification is developed by consideration of travel path effects. Three amplification/de-amplification mechanisms are specifically considered, the ground velocity amplification, ground strain amplification due to the change in the propagation direction, and de-amplification due to a lack of total reflection at the soil-rock interface. The analysis results show that the maximum amplification factor is mainly affected by the interface inclination angle and shear wave velocity ratio between the valley soil and the base rock. For a given number of wave cycles, the amplification factor grows with the increment of the inclination angle and declines with the growth of shear wave velocity ratio. The de-amplification at inclined interface is likely to nullify the amplification generated by travel path effects.

Highlights • There are three amplification/de-amplification mechanisms related to ground strain in a valley. • The amplification is a function of the interface inclination angle and shear wave velocity ratio. • A simplified procedure for evaluating ground strain amplification was developed. • Extensive numerical results involving different material classes were proposed.