Effect of Static Shear Stress on Cyclic Resistance of a Uniform Gravel

Sloping ground conditions, such as those found in dams and levees, as well as buildings, result in an initial horizontal static shear stress in the ground, affecting its cyclic resistance. When liquefaction triggering is a concern, the K-alpha correction factor is used to account for this initial static stress in a simplified manner. Laboratory testing was performed to assess the effects of horizontal static shear stress on saturated sands; however, limited data exists for this effect on gravels. In this study, cyclic direct simple shear tests were performed on a uniform gravel to determine the effects of relative density, confining stress, and pore pressure generation on cyclic resistance at increasing values of initial horizontal static shear stress. Tests were conducted using a large-size cyclic direct simple shear (CDSS) device in constant volume conditions on 9mm D-50 specimens of a pea gravel (PG9). The effects of relative density on the cyclic resistance of this material were analyzed for loose (47%) and dense (87%) specimens, at three significant vertical effective stresses: 100, 250, and 500 kPa. Testing results show that an increasing horizontal static shear stress has a significant effect on the cyclic resistance and pore pressure generation of both dense and loose uniform gravels, but is more pronounced for loose uniform gravels.