Earthquake Geotechnical Engineering for Protection and Development of Environment and Constructions

Abstract

Actual earthquakes apply horizontal shear forces on soil in a multi-directional manner. The effects of multi-directional seismic loading on the undrained behaviour of medium dense Hostun sand was recently studied with stress-controlled undrained cyclic multi-directional simple shear tests. The development of shear strain in several tests with uni-directional, oval and circular loading paths is compared and the preliminary results are reported here. The general geometry of the strain paths resembles that of the loading paths. But strain paths are diverted when excess pore pressure ratio exceeds a certain threshold (0.6-0.7 in this study). The existence of static shear stresses further complicates the development of shear strain. Downhill shear strain happens no matter what direction the cyclic shearing is applied in. The shear strain in the perpendicular direction is limited if the static shear stress is large enough to eliminate stress reversal. The knowledge regarding the development of shear strain in multi-directional loading conditions remains scarce and more efforts are needed to advance the understanding of this topic.