Abstract
Soil improvement area as liquefaction countermeasures is determined considering the strength reduction of a portion adjacent to the unimproved area. The strength reduction is caused by the transmission of the excess pore water pressure from the unimproved area to the portion. Therefore, the improvement area is designed widely enough to keep the stability of structures ignoring the strength of the strength reduction area. However, the consideration of the strength reduction may not be necessary if the soil contains many fines, because the permeability is low and the excess pore pressure transmission may be small. In this paper the effect of the permeability of the improved area on its strength reduction is investigated by shaking table tests. The tests are conducted on a caisson type quay wall and the behavior of the backfill and the caisson are investigated. In the tests cellulose solution is used to control the permeability of soil. The test results show the caisson displacement is smaller in the case of low permeable backfill without consideration of the strength reduction area than in the case of high permeable backfill with consideration of the strength reduction area. However, the pore pressure behavior does not clearly show the difference.
