A new type roadbed using the slug materials is adopted in the tunnel under the Shiras ground water level on Kyushu Shinkansen under construction. The roadbed is designed to decrease the ground water pressure. This paper describes the designing and construction methods of the new type roadbed. Permeability and durability tests were performed under cyclic load. Roadbed settlement was very small under a 2 × 10⁶ times cyclic load. A test on the method to construct the roadbed was performed by using a real construction machine in site. The coefficient of roadbed permeability is in the order grade of 10^-3cm/s for the slag materials added with cement to 10%.

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