Post-Liquefaction Shear Behavior of Bonneville Silty-Sand

This paper presents the results of a laboratory study addressing the post-liquefaction undrained shear behavior of a silty-sand characterizing the main liquefiable layer within Bonneville sediments at the Farmington Siding Landslide Complex (FSLC). FSLC is located in Davis County, Utah where liquefaction flow-slides associated with past earthquake activity in the region have been documented. Undrained cyclic triaxial tests to trigger liquefaction in water-pluviated samples of Bonnevile silty-sand consolidated isotropically under various effective confining stresses were followed by undrained monotonic triaxial compression tests on the liquefied specimens. The experimental results revealed a dilative behavior of the liquefied soil element, and the post-liquefaction undrained shear strength showed an increase with increasing initial effective consolidation stress. An infinite slope analysis addressing the onset of flow-slide in a liquefied Bonneville silty-sand deposit, using the post-liquefaction undrained shear strength data from laboratory testing, resulted in required minimum slope inclinations much greater than the actual slope gradient at the FSLC.