The authors have proposed a simple design method of the VD using PBD materials for horizontal drainage. This design method is based on the comparison of the required flow volume qA calculated from a Barron type equation and the drainable amount qV computed by solving simultaneous equation of the flow network. In order to prove the validity of proposed design method, the model experiment and site observation have been conducted. As the results of this research, the followings were obtained; 1) As a result of model experiment, it was shown that the consolidation characteristics of VD is similar to the predicted value by the proposed design method. 2) As a result of observation at the actual construction site, the measured value of the flow quantity in PBD was close to the predicted one especially for a vertical drain part. 3) However, the flow quantity in a horizontal drain was measured only immediately after the loading. This means the use of PBD material as a substitute of sand mat might be practical at least at the early stage of loading.