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Impact of bidirectional seismic shearing on volumetric response of sand deposits

University of British Columbia

Ground motion-induced waves have a multidirectional nature when traveling through soil deposits. It is the interaction between their three components, one of vertical compression and two of horizontal shear, what drives the response of soils in the field. Experimental studies have shown that, for the case of soil liquefaction, neglecting one of the two horizontal shear components can potentially lead to an underestimation of seismic demand. However, while the deleterious effects of considering only one shearing direction for the seismic response of sand deposits are acknowledged, they are not properly addressed in engineering practice. A numerical study conducted here provides insight into the potential increased response of level ground dry and saturated sand deposits when subjected to unidirectional and bidirectional shear earthquake loading. The simulations utilized a three-dimensional finite difference computational platform which was verified using several analytical solutions of wave propagation through single and double phase medium. In addition, the analyses made use of an anisotropic bounding surface plasticity model with validated capabilities for capturing the volumetric response of sand deposits subjected to bidirectional cyclic shearing. Therefore, the results of the analyses were evaluated in terms of surface settlement for the dry cases and excess pore pressure for the saturated cases. The comparison of the response of bidirectional against the unidirectional seismic shearing analysis showed the importance of accounting for two horizontal rather than one ground motion component, as it was determined that the volumetric response under bidirectional shearing was always higher. Specifically, the dry models exhibited 80\% increase of surface settlement and the saturated models indicated up to 60\% rise of the mean values of peak excess pore water pressure ratio along the depth of the deposit due to bidirectional shearing. Moreover, in the saturated deposits studied, the bidirectional seismic shearing induced about 20\% increase on the thickness of the liquefied sand layer.

Text

2019-09-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/67143

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/