Methodology for the ovalization monitoring of newly built circular train tunnels based on laser scanning: Liefkenshoek Rail Link (Belgium)

Abstract The ovalization monitoring methodology based on laser scanning, developed during two recent tunneling projects in Belgium, elaborates a clear processing workflow and easily interpretable deliverables with sub-millimeter accuracy. The extensive and systematic monitoring coverage during the first three months after construction of a circular tunnel structure delivers an important contribution to the understanding of the tunnels' behavior between the construction phase and the final stabilized shape. The observed differences of the average radius values generally show a decrease in the first week after ring erection and a stabilization of the tunnel structure during the following weeks. The results of such a systematic monitoring program allow the contractors or engineers involved to validate the theoretical models and to compare with the actual behavior of large diameter shield tunneling in soft soil. This is highly valuable, because very few measurements are available at this early stage of a tunnel construction to evaluate the performance and accuracy of such theoretical models.