Back-analysis of viscoelastic displacements in a soft rock road tunnel

The theological behavior of the rock proximate to excavations is of importance and practical interest for engineers in the design of soft rock tunnels. In situ theology tests may be conducted to determine the appropriate parameters of the rock masses and the ground stress component; however, this can cost a great deal in both expense and time. Hence, it is useful to study back-analysis of viscoelastic displacements induced by the excavation of tunnels. Taking four theological models, namely, Kelvin body, Maxwell body, Poynting-Thomson body and Kelvin-Voigt body as examples, this paper presents the basic finite element equations for such back-analysis, and the associated calculation methods for practical applications. A trial calculation method for the different models is adopted so as to obtain the most suitable rheological model and corresponding parameters. Furthermore, the authors have successfully applied the back-analysis method in a test section of a road tunnel excavated in soft rock. Compared with the direct in situ rheology tests, the back-analysis method presented by this paper is more concise and involves less money and time. (C) 2001 Elsevier Science Ltd. All rights reserved.