Experimental investigations on the effect of density, grain size, and fines content on ejecta-induced settlement

The occurrence of sand boils or ejecta following earthquakes can cause considerable ground settlement. This study aims to investigate how soil properties influence ejecta-induced settlement by conducting experimental tests that simulate the sand boil process. Three materials, namely coarse C306 sand, fine C778 sand, and non-plastic silt, were used to examine the effects of grain size, fines content, and density on the amount of sand boil and resulting settlement. The test results indicate that loose specimens with low density experience more ejecta-induced settlement, while specimens with higher amounts of coarse grains or fines exhibit less settlement even at similar void ratios or relative densities. However, the amount of ejecta produced is directly proportional to the duration of high pore water pressure (H-PWP), which is influenced by both PWP supplies and dissipation. The differences in permeability and one-dimensional stiffness among materials explain the varying H-PWP duration across the tests. Therefore, when estimating the ejecta amount, it is crucial to account for the varying stiffness and permeability during liquefaction and post-liquefaction consolidation to accurately assess the H-PWP duration.