Construction of shaft tunnel by slurry pipe jacking through sedimentary ground under high water pressure

Abstract

A shaft tunnel driven by pipe jacking was adopted in order to provide ventilation to the Imaigawa underground reservoir tunnel under the national highway in Yokohama, Japan, which has been temporarily in service since 2001. Downward excavation of the 2000mm ID ventilation tunnel starts from ground surface and reaches to the crown of the existing 10800mm ID reservoir tunnel, which is located 87.8m deep, through the stiff clay layer. Depression angle of the tunnel is set as 75.6 degree, and pore water pressure at the arrival is 0.66MPa. This project is one of the largest in this type of tunnels in Japan.