| To develop a rapid and easy method for recognizing time-dependent deformation from field data that has been measured as a part of the daily management of tunnel construction, we focus on the displacement rates of horizontal displacement measured while excavation is halted to eliminate the effects due to stress release. Simultaneous measurement of the displacement rates in several sections enables us to rapidly identify the creep phase and determine tunnel stability. An exact solution to express transient creep behavior in horizontal displacement rates on the basis of the viscoelastic theory is derived. This model assumes that a circular tunnel exists in the ground of the three elements model before supports are set and the four elements model (which has an elastic spring corresponding to the tunnel supports connected in parallel to the three elements model) after setting the supports. Each parameter of the transient creep behavior in this model is optimized to minimize the error between the exact solution and field measurements. The validity of this method is confirmed by applying it to some actual cases. This simple method is useful for extracting the coefficients of the ground property related to transient creep, although estimation of total displacement tends to have some dispersion because only the displacement rates are used as the identification factor. Furthermore, the analysis using those coefficients enables to accurate estimation of the amount of time-dependent deformation in the future. |
