ABSTRACT
When building tunnels beneath riverbeds where very large quantities of groundwater inflow exist due to high water head and the soil supporting conditions are very poor because the soil consists of sand and silt, it is necessary to get grouting and pipe roof installed in the region where ground reinforcement is in need to decrease permeability. According to this result of horizontal boring and laboratory soil testing, ground reinforcement was achieved by L.W grouting for range of 3.0 times the tunnel radius, to increase stability of the tunnel we used the ring cut method, 0.8m for one step excavation, shotcrete with 25 cm thick, steel lib with H-125 × 125, and a temporary shotcrete invert 20cm thick was installed to prevent deformation of the tunnel.
