Anisotropy and heterogeneity of gravelly soil layer in Hualien, Taiwan

The Hualien Large-Scale Seismic Test program is under way to investigate Soil-Structure Interaction during large earthquakes in the field of Hualien, a high seismic region in Taiwan. In this report, the ground of the test site, which consists of a sand layer and a hard gravelly layer of Pleistocene origin, was characterized and modeled for accurate dynamic simulation analysis. The following conclusions were drawn. (1) It was revealed that anisotropic behavior of the gravelly layer observed in earthquake observation and forced vibration tests could be expressed by the orthotropic elastic body model. (2) For sands, the shear wave velocity measured by cyclic triaxial tests was almost the same as that by the velocity logging, whereas shear wave velocity of gravelly soils measured by cyclic triaxial tests was much smaller than that by the velocity logging. This difference is attributable to the effect of heterogeneity in the gravelly soil layer.