Quantification of Stratigraphic Transition Location Uncertainty for Tunneling Projects

Abstract

Stratigraphic transitions within the tunnel envelope cause a rapid change in tunnel boring machine (TBM) operating parameters and impose a significant challenge to TBM tunnel projects. This paper presents a geostatistical modeling–based probabilistic approach to quantify the stratigraphic transition location uncertainty in the longitudinal direction of tunneling and at the tunnel face. Geotechnical data from a soil tunneling project were used to elucidate the capability of the approach. A deterministic soil profile and TBM operation data from the project were examined to evaluate the results of the approach. The results revealed that the stratigraphic transition location uncertainty (for 90% confidence interval) in the longitudinal direction, for the two stratigraphic transitions within the tunnel envelope, extended over a longitudinal distance of 28 rings and 130 rings. The occurrence of the stratigraphic transitions in the longitudinal direction at Ring 275 and Ring 550, for a 95% occurrence probability (P95), matched the locations of the change in rate of dissipation of chamber pressure from recorded TBM data. The stratigraphic transitions (P95) occurred 15 rings before and 30 rings after the locations suggested in the ground profiles suggested in the geotechnical baseline report (GBR). At the tunnel face, the probability of encountering stratigraphic transitions was the highest between Ring 200 and Ring 300, and varies between 60% and 90%.