A steel-slag-mixed dredged soil is used to improve a backfilling soil of quay walls. In that case, interface shear properties between the steel-slag-mixed dredged soil and different materials contacting with it such as an originally deposited soil or an existing concrete wall can be an important issue in a design. Therefore, the authors experimentally investigated the interface shear properties between the steel-slag-mixed dredged soil and some different materials. In this study, s small-scale box shear test and a large-scale model shear test were conducted using the steel-slag-mixed dredged soils with four different materials, which are gravel, sand, clay and concrete. The box shear tests were conducted under various testing conditions in terms of vertical stress, curing time of the steel-slag-mixed dredged soil etc. using all kinds of materials. The model shear tests were conducted under a single testing condition for three kinds of materials excluding the clay. This study also describes an influence of interface friction coefficient on earth pressure at earthquake acting on a model quay wall calculated by the slice method. Based on results of the above, this study proposed the interface friction coefficient under various testing conditions and a methodology to choose it in a design.

Key Words: Steel-slag-mixed dredged soil, gravel, sand, clay, concrete, shear test, friction coefficient, interface of different materials