A study on the application of the distributed optical fiber sensing monitoring technology in the process of dismantling temporary tunnel shoring

摘要

Temporary shorings are necessary for the stabilization of the tunnels with large cross-sections that are excavated using the New Austrian tunnelling method. The dismantling of the temporary shoring during the process of secondary lining construction would be a very serious threat to the safety of the tunnel. Therefore, in this work, a field observation was made based on distributed optical fiber sensing monitoring technology in order to determine the deformation behavior of the tunnel and to identify the most influential steps of dismantlement. The study is carried out during the tunnel's temporary shoring dismantling stage. The performance of the tunnel during every dismantling stage was analyzed based on the monitoring results using the finite element numerical simulation method. Based on the analysis results, the settlement of the tunnel was estimated through the strain curve that was obtained by using optical fiber. Furthermore, the study results showed that the continuous removal at the bottom of the shoring of the tunnel weakens the vertical support force at the bottom of the tunnel and thereby resulting in large settlement variation in all the dismantling steps. The highest value of the settlement variation obtained during the analysis is 5.7 mm, and the corresponding tensile strain variation of the crown is 50 mu epsilon. Furthermore, the results showed that it is feasible to use the optical fiber to estimate the settlement of the tunnel. The max deviation obtained was 0.9 mm and the results were compared with the results of a total station. The study results of this research are applicable to the tunnels that were excavated using the New Austrian tunnelling method and have temporary shorings.