Determination of seismic compression of sand subjected to two horizontal components of earthquake ground motions

The objective of this Technical Note is to investigate the ratio of seismic compression of sand subjected to two mutually perpendicular horizontal components of earthquake ground motions simultaneously to its counterpart for single component of horizontal motions. By using a verified, fully coupled and inelastic finite element procedure, sand specimens with various relative densities (Dr=45%, 60% and 100%) are subjected to each of the horizontal components of motion separately, and then simultaneously, with the vertical strains and corresponding ratio computed for each case. In total, 296 shallow crustal horizontal motions (i.e. 148 sets of horizontal motions) with various earthquake magnitudes, site to source distances, durations, and site conditions recorded in active tectonic regions are used in the analyses. The results showed that the ratio generally ranges from 1.52 to 2.32, and it increases with earthquake magnitude and relative density of sand but decreases with epicentral distance. These results can be used in conjunction with seismic compression correlations for single component of motion to estimate its counterpart for multiple components of motion, thereby increasing the accuracy in predicting the severity of seismic compression under multi-directional seismic motions.