THE MULTIPLIED TUNNEL SUPPORT SYSTEM APPLIED TO SQUEEZING GROUND CONDITION

To deal with the large deformation due to squeezing ground at the Iiyama Tunnel of the Hokuriku Shinkansen, the placement of the tunnel supports were taken into two phases. The idea of the different stages is based on two phenomena according to NATM theory. The first is the tendency of the earth pressure which allowing the lining to displace. The other is the effect of the closed shotcrete lining on the large earth pressure. From the trial excavation, we confirm that the displacement of the lining could be controlled by performing the thin secondary shotcrete layer, even after the first lining was yielded. The numerical analysis results show that the support system could be kept stable by placing the secondary lining at the distance of 3.5 times of the tunnel diameter from the tunnel face.