| Loose sandy soil layers are prone to liquefaction under strong earthquakes, causing damage to civil engineering structures inside or upon the liquefied ground. According to the present Japanese design guideline, the entire layer of liquefiable subsoil below river embankments is supposed to be fully improved. However, this approach is not economical against deep liquefiable layers. To rationalize the design approach, this contribution evaluates the performance of floating-type cement treatment method, where only a shallower layer of liquefiable subsoil is reinforced. A series of centrifuge shake-table model tests are conducted under a 50g environment. The depth of improvement (cement treatment) was varied systematically, and the effect of sloping ground was examined. The experimental results revealed that settlements of river embankment can be reduced linearly with increasing the depth of improvement. Besides, the acceleration of embankment can be reduced drastically due to a vibration-isolation effect between the cemented block and the liquefied soil layer. These effects contribute to safe retention of the embankment shape even when liquefied sloping ground causes lateral flows. Towards practical implementation, discussions are extended on the effect of permeability of the cemented block. Furthermore, the stress acting on a cemented block during shaking is measured and related with the occurrence of cracks in the cemented block. |
