Centrifuge model tests on liquefaction mitigation performance of soil-cement grid-improved ground subjected to earthquake pre-shaking history

The soil-cement grid has been widely applied as an effective liquefaction countermeasure due to its capability to effectively mitigate the shear load and deformation of the enclosed soil under seismic loadings. In terms of its long service period, two dynamic centrifuge model tests are conducted to study the effects of strong shaking history on the liquefaction responses of the enclosed soil. The model ground consists of a 15 m-thick liquefiable clayey fine sand and an underlain 2.5 m-thick coarse sand layer. The liquefiable layer is improved by the soil-cement grid in one model, while the other without any improvement affording a contrast. Both models are subjected to a sinusoidal input motion with amplitude of 0.15g. Several more severe shaking events with amplitude of 0.4g are applied to the models prior to this 0.15g event as strong shaking history. The results imply that the damage patterns of the walls are mainly vertical penetrating cracks, partly accompanied by local diagonal cracks, and the outer cells show a "shielding effect" on the center cell similar to that of a group pile foundation. After the strong vibration history, the central cell of the soil-cement grid still has satisfactory anti-liquefaction effects, leading to a much lower excess pore pressure than free field. At the same time, due to the weakening of the overall stiffness of the soil-cement grid, the shear deformation between the soil-cement grid and the underlying coarse sand layer is significantly reduced.