A lot of paper sludge is generated during the process in which recycled papers are reproduced from used papers every year. Recently, paper sludge is often utilized effectively at construction works such as improvement of liquid mud (Kato et al., 2005), application to base course materials of road (Saito et al., 2002; Takeda et al., 2001) and treatment of discharged soils in shield tunneling constructions (Nakanan et al., 1994). Even if paper sludge is mixed with poor soil, it does not solidify chemically like cement or lime. However, it absorbs much water contained in the soil and stabilizes the poor soil ground quickly. In the case of earthworks at the poor ground (high water content state) such as diatomaceous earth, peat and volcanic cohesive soil etc., the trafficability goes down remarkably by machine-based construction, as shown in Fig 1. This paper examines the improvement effect of poor soil by paper sludge mixing.