Rotation of a Cantilevered Sheet-Pile Wall with Different Embedment Ratios and Retaining a Liquefiable Backfill of Various Relative Densities

Damage to retaining structures at the waterfront during major earthquakes can be attributed to the development of positive excess pore water pressure in the retained or foundation soils, leading to liquefaction. As part of Liquefaction Experiments and Analysis Project (LEAP), dynamic centrifuge tests of a cantilevered sheet-pile wall model floating in dense sand and retaining a liquefiable backfill were carried out. The embedment ratio (embedment depth / excavation height) and the relative density (D_r) of the backfill were varied to observe the rotation of the sheet-pile during a tapered 1 Hz sinusoidal input base motion. The D_r of the backfill affected the wall rotation during gravity loading and the initial static shear stress in the backfill; smaller D_r backfill led to a larger wall rotation and initial static shear. During seismic loading, the model with a higher initial static shear had a dilative pore pressure response which increased the wall stability. On the other hand, the model with a smaller initial static shear showed a contractive response leading to initial liquefaction in the active failure wedge, which resulted in a large increase of wall rotation. Moreover, the model with a higher embedment ratio had a smaller wall rotation during initial loading cycles, but the wall rotation increased rapidly after the soil in front of wall softened due to positive excess pore water pressure buildup. These results showed the importance of considering the initial static shear stress prior to earthquake loading and the vulnerability of wall stability due to excess pore pressure increase in front of the wall.