Centrifuge tests on river levee protection by partial reinforcement of underlying liquefiable subsoil

抄録

Reinforcement of existing river levees upon deep liquefiable subsoil is costly, and its effectiveness is often limited. For some conditions, it would be cost-effective to demolish an existing embankment and stabilize the liquefiable subsoil by means of cement-treatment. In the present Japanese design guideline, the entire layer of liquefiable subsoil beneath a river embankment is supposed to be reinforced; however, such construction cost depends highly on the depth of reinforcement. To rationalize the design approach, the present study aims to evaluate the performance of partial reinforcement immediately beneath the embankment. A series of shake-table model tests under a centrifugal acceleration of 50g were conducted where the depth of reinforcement by cement-treatment was varied systematically. The experimental results revealed that the settlement of levee crown can be reduced linearly with the depth of reinforcement relative to the depth of the initial liquefiable subsoil. Besides, the acceleration measured at the levee crown was reduced drastically when partial reinforcement was adopted due to the attenuation of ground motion that propagated through an underlying liquefied soil layer. This side effect would contribute to safe road operation immediately after an earthquake event, and enables prompt repairment of river levees to prepare for aftershocks.