The ground condition of the Kongo-gawa Tunnel from its entrance to the 100m-depth is severe, i.e., the earth covering is thin (15m), the upper layer of the ground consists of talus, and besides the clay layer under the tunnel is short of bearing power.
To cope with this site condition, the silot tunnel method, the chemical grouting method, and the shotcrete method were adopted.
As a large amount of settlement arose after excavation of silot tunnels, it was feared that the settlement would increase much more in excavating the upper half section. But by using the shotcrete method in excavating the upper half section, the settlement could be held down to a comparatively little amount.
This paper reports the construction outline. Furthermore, the results of elastic FEM analysis for the upper half section excavation showed that the settlement of ground surface using the shotcrete method model became half as large as that of using the conventional method model.