关键词: 迂回隧道, 崩积层, 钢管棚, 桁型钢支护, 钢纤维喷射混凝土

Abstract: On August 8, 2009, Typhoon Morakot hit southern Taiwan. It carried huge accumulated precipitation of 2,500 mm in 72 hours at Alishan area, and caused catastrophic erosion and landslide. Thus, the hundred-year historic Alishan Forest Railway was suspended due to serious embankment collapses. The rehabilitation principle for these two large embankment collapses followed the natural doctrine. Therefore, the D&B/Mechanical bypass tunnel was adopted to overcome the geological changes and groundwater problem in these two huge landslide areas. The lengths of west portal section colluviums of two tunnels were up to 99 m and 109.8 m, which were the crucial sections of tunneling engineering. The tunnel supporting system design was based on PCCR-system (Rock mass classification of Public Construction Commission) & NATM, and steel pipe roofing, lattice girders, and steel fiber reinforced shotcrete, as well as self-drilling anchors were adopted for increasing the safety and shortening the working days during construction. Currently, two tunnels have been driven through, and the amount of deformation was under control and in accord with safety level. This result indicates that implementation of pre-supporting system in drilling through the crushing colluviums section is effective, and can be used as a reference for the relevant engineering design.

Key words: bypass tunnels, colluviums, steel pipe roofing, lattice girders, steel fiber reinforced shotcrete