A total of seven vertical shafts were installed on the Bandai~Hannan Sewer Tunnel, which is about 2km long and has a finished inner diameter of 3.25m. These vertical shafts are for the purpose of draining water from existing sewer mains, for ventilation and for inspection of the sewer tunnel. Three of the vertical shafts are located adjacent to a narrow heavily trafficked road within a residential area of low-rise timber houses. The traditional method of constructing vertical shafts from ground level downwards disrupts traffic flow and affects the daily activities of local residents. An "Upward Shield Construction Method" which excavates upwards from the tunnel was adopted. Since most of the work operations of the Upward Shield Construction Method were conducted underground, the overall work schedule was shortened by one third and surface operations by one sixth compared with traditional construction methods. In addition, noise pollution and vibration resulting from work activities, as well as disruption to the traffic and daily activities of local residents were minimised.
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