Flexible bulkheads, such as anchored sheet pile walls, are often employed as earth retaining structures for port facilities in Japan. In recent years, existing anchored sheet pile walls have required reinforcement for maintenance and functional enhancement for large ships. To meet these requirements, a reinforcement method called dual-anchored sheet pile wall, in which additional anchorage work is attached to the existing anchored sheet pile wall, has been developed. The additional anchorage work has the same role as braces of an earth retaining wall, and is installed after deformation of the existing anchored sheet pile wall. However, braces are placed before deformation of the earth retaining wall. Therefore, the loading histories of backfill of the dual-anchored sheet pile wall and the retaining wall are different. The additional anchorage work cannot be designed in the same manner as earth retaining wall braces. In this study, model tests of the dual-anchored sheet pile wall were conducted to understand its behaviours. This paper describes the effects of the additional anchorage work to reduce the load acting on the existing anchored sheet pile wall, such as the bending moment of the sheet pile.