When track irregularities have increased in that track settlement occurs on ballasted tracks by cyclic loading for trains, track maintenance is generally performed by repairing method with tie tamper. The repairing method impairs the density of the ballast compacted, and track irregularities therefore tend to increase immediately after the track maintenance in the case of ballast including fine-particles at high-mix ratio. This is due to the density change range of the ballast including fine-particles at high-mix ratio is larger than the sound ballast. The authors are under development of a repairing method by filling under sleepers with the composite filling material consisting of water glass and polymer for the ballasted tracks under which ballast includes fine-particles at high-mix ratio. It is conceivable that it is possible to make the growth of track irregularity decrease in that the track maintenance is performed without impairing the density of the existing ballast. In this study, the authors performed a box shear test to confirm the strength property of the composite filling material. Consequently, the authors confirmed that the material had a necessary performance as a material filling under the sleepers. The authors then developed a construction device adaptable to substantial construction, and performed the test with a full-scale ballasted track model. The results of the test clarified that track maintenance was effectively performed by this method. In addition, the in-situ test was performed due to confirm the effect of this method. Consequently, a growth of track irregularity could be decreased by this method.