Slurry type shielded TBM for the alluvial strata excavation in downtown area

摘要

The soil and rock types relevant of construction lot 9 of Seoul subway line number nine ofYeoi Island area show a distinct difference between the eastern and western part of the alignment especially in the eastern part. The tunnel is expected to be located entirely in alluvial deposits, predominantly in sandy gravels with low strength of alluvial soils with presence of groundwater. For the western part, the geological conditions are considerable more complex, varying between hard rocks, residual soils and alluvium, with the higher proportions in weathered rocks. The alluvial deposits probably dominated by sandy gravels including some boulders are expected to be favorable for the application of a slurry shielded TBM with the higher underground water levels. For a more detailed assessment, reliable grain size distribution curves of the alluvial deposits along the tunnel alignment are investigated to select the optimal selection of separation plant and suitable advance rate of the slurry type shielded TBM. Along the whole alignment closed mode tunneling with active face support will be required, due to the low strength of the alluvial soil and the presence of groundwater. There are two basic options for the machine type to be applied: A Slurry type shielded TBM or Earth pressure balanced shielded TBM. For specific details concerning the technical machine operation and the safety precautions of the tunnel construction on this alluvial deposits are described in this paper.