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Numerical analysis of effects of weakness zones on tunnel stability - 2D versus 3D


Numerical simulation is a powerful tool in rock engineering planning and design, particularly when difficulties
and uncertainties are expected in underground excavation. For tunneling through major weakness zones or faults
where the geometry is complex, three-dimensional programs have been widely applied. Two-dimensional programs are fast and very convenient to use, but simulation results may considerably deviate from reality if a two-dimensional program is improperly used. This is discussed in the paper based on two popular used numerical programs in rock engineering, Phase2 and FLAC3D. Scenarios with varied widths of weakness zone, different sets of ratios of horizontal stresses to vertical stress and different strengths of weakness zones have been assumed in the analysis. Areas of yielded zones and vertical displacements at the crown and invert are compared, and deviation in simulation results illustrated. It is concluded that for analyzing the effects of a weakness zone perpendicular to the tunnel alignment, the thickness of the zone has to be much wider than the tunnel span for Phase2 to be realistically used. This is, however, quite unusual for “normal” tunnel excavation spans. In addition, it is difficult to define the deformation before the installation of rock support when using Phase2 for tunneling through weakness zones.


Academic chapter/article/Conference paper




  • Dawei Mao
  • Bjørn Nilsen


  • Norwegian University of Science and Technology
  • SINTEF Community / Infrastructure




Research Publishing Services


Advances in Underground Space Developmnet




388 - 398

View this publication at Cristin