Notice of RetractionRisk analysis of shield tunnel segment failure based on Fuzzy Fault Tree method
Through analyzing and summarizing the types of shield tunnel segment failure and the relevant causes of the accident, Fuzzy Fault Tree Analysis (FTA) was employed to study the failure risk of segment and the Fuzzy Fault Tree system model of segment and segment-related systems were established. The potential failure modes of risk accidents and their influencing factors were discussed through qualitative and quantitative analysis. With its application on practical project, some effective control measures were proposed. This research could be valuable reference for the design, construction and control of shield tunnel segments.
Geological risk in the use of TBMs in heterogeneous rock masses - The case of "Metro do Porto" and the measures adopted
The highly variable nature of the deeply weathered Oporto granite posed significant challenges in the driving of the 2.3 km long C line and the 4 km long S line of the Oporto Metro project. Two 8.7 m diameter Herrenknecht EPB TBMs were used to excavate these tunnels and early problems were encountered due to over excavation and face collapse. Three collapses to surface occurred in the first 400 m of the C line drive and the last of these collapses resulted in the death of an occupant of a house on the surface. This resulted in a delay of almost 9 months to the project and the difficulty was finally resolved by the introduction of an Active Support System which involves the injection of pressurized bentonite slurry to compensate for deficiencies in the face support pressure when driving in mixed face conditions. Both the C and S lines have now been completed with minimal surface subsidence and no face instability.
CHALLENGING SOIL CONDITIONS AT PORTO
Poor geotechnical conditions combined with budgetary constraints and operational constraints posed by nearby old buildings with shallow foundations to create a number of challenges in the tunneling elements of the expansion of the light metro system for the Portuguese city of Porto. The tunnel was required for a 7 km portion that passed directly through the town center, which is a protected historic site. It is a bi-directional tunnel, single bore with a tight turning radius of 200 m in order to match the planned alignment. Ten underground stations will be built, six by mining methods and four by cut and cover. The tunnel face is mixed; there is a great deal of underground water activity, including man-made wells connected by drainage galleries, which has resulted in destabilizing the surrounding soils. This article reports on the experiences of the first line, line C. After an incident resulted in a nine-month delay, tunneling was resumed with very strict boring control measures including a real-time system for weighing slurry to detect changes in volumes and pressure at the EPB. Integrated alarm systems were used to control activities in relation to pressure drops. Emphasis was also given to ground monitoring, including a sophisticated system of monitoring settlement. Multi-point grout injection systems were set up to protect older buildings whose foundations were close to the tunnel. The tunnel was completed without any damage to the buildings. Techniques learned on Line C should help with future lines in the system and elsewhere.