ABSTRACT
Two parallel shield tunnels with 12.3m in diameter were constructed in very close proximity to each other over long distance in Osaka Japan. The clear spacing distance between both tunnels was about 0.1D where D is the outer diameter of tunnel. These tunnels were constructed by EPB machines in alternating ground with gravelly dense sand and stiff clay layers under varied overburdens with alignments including sharp curvature. In one junction, four parallel tunnels were constructed including two ramp tunnels with D=8.8 m. To know the impact on the existing 1st tunnel caused by the newly-built 2nd tunnel, the behavior of the 1st tunnel was monitored at five sections under the different construction conditions. The vertical expansion in the tunnel under large overburden was observed during the 2nd TBM passing. After the 2nd TBM passing, the 1st tunnel deformation returned to original point in the vertical direction, where it increases in the horizontal direction due to the decrease of lateral pressure. The axial compressive force at the spring line (SL) of the 1st tunnel lining increased at the close side to the 2nd tunnel due to the stress release of the 2nd tunnel construction. The ground settlement and impact on the 1st tunnel were controlled due to the careful construction of the 2nd tunnel, which indicates the proposed design method is appropriate for close proximity large diameter parallel shield tunnels.
