Estimates of stress reduction factors for the tunnel design

摘要

Tunnel design methods should consider the stress reduction occurring before the installation of a liner in some way. An estimate of the ground displacements can lead to an evaluation of the stress release because the stress release is closely related to the ground displacements. Various authors have suggested various stress reduction factors. Negro (1988) observed that the problem could be manageable if the presence of the lining and the non-linear stress-strain relationship of the ground were disregarded. Stress reduction factors can be found by combining the radial displacements and a full range of diagrams in a variety of geometric and geotechnical conditions, as presented by Negro (1988). However, obtaining stress reduction factors using the table and diagrams can be tedious and time consuming even though it is not difficult. Therefore, using the table and diagrams, three final tables were obtained for the stress reduction factors (α) as a function of the support delay length X for three different in situ stress ratios by the current authors. The final values of the stress reduction factors for different soil strengths, tunnel depths, and in situ stress ratios were presented as a table.