ABSTRACT

Theoretically, the state of stresses and displacements around an underground opening is three dimensional. Ideally, therefore, three-dimensional (3-D) methods should be used for the proper analysis of stresses and displacements occurring around openings. Even with today’s powerful numerical methods and friendly computer programs, 3-D stress analysis is complex and requires experience for implementation and interpretation. In tunneling, nevertheless, this complicated analysis can be, and usually is, replaced by a much simpler, cross-sectional plane-strain analysis when one of the principal components of in situ stresses is acting (or assumed to be acting) parallel to the longitudinal axis of the opening. However, the result of this kind of analysis corresponds to the deformed (i.e. final) state of the tunnel. Also, it does not tell us how the stresses and displacements develop along the tunnel length.