Abstract
In the case of application of the mountain tunneling method in the urban areas, the method which the shotcrete and steel rib are installed at the invert to perform the early crosssection closure is mainly adopted in some tunnels to restrain the occurrence of ground surface settlement.
In this paper, the effect of the invert closure distance from tunnel face on ground surface settlement is examined based on the three dimensional numerical analyses, focused on the small ground covering tunnels. The results of investigation show that the invert closure distance from tunnel face has a remarkable impact on the restraint of occurrence of ground surface settlement due to excavations in the soft ground conditions and in the comparatively stable ground conditions. It is clear that the restraint effect on the ground surface settlement is very great if the invert closure distance from the upper half face is within 20m. Furthermore, comparing analysis results with measurement results of two tunnels which adopted the early invert closure method, the validity of the proposed numerical analysis approach is verified, and it is also confirmed that the early invert closure could restrain significantly the occurrence of ground surface settlement.
