Centrifuge shaking table tests on saturated reinforced soil walls

This paper discusses effects of saturation of backfill on seismic stability of reinforced soil wall by using the centrifuge shaking table tests. Before the shaking table test, static stability of reinforced soil wall with saturated backfill was investigated by raising the water level under the centrifugal gravity. As a result, the wall showed sufficient stability statically. The wall with unsaturated backfill showed higher seismic stability and deformation was not observed in the centrifuge shaking table test. On the other hand, large residual displacement was observed in the case of fully saturated case. The cause of the low seismic stability of the saturated reinforced soil wall was due to the decrease of stiffness of back fill soil following increase of pore water pressure, although no liquefaction occurred. In order to clarify the decrease of stiffness of backfill, relationships between shear stress and shear strain of backfill during earthquake were determined using response acceleration time histories. As a consequence, shear stiffness of backfill wall was about 25% smaller than that of unsaturated one. Additionally, it is considered that the decrease of pullout resistance between soil and reinforcement due to the decrease of effective confining pressure of the reinforcement was also one of reasons too.