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Experimental investigation of pressurized concrete tunnel linings

Kalaycıoğlu, Münci Tunç
Behaviour of pressurized tunnels are determined by the mechanical and geometrical properties of lining, mechanical properties and overburden pressure, and the quality of contact zone between rock and lining. These factors form the backbone of the designprocessoftunnelswithinternalpressure. Estimatingcrackwidthsanddamage patternsischallengingdueto thenonlinearinteractionofnaturalandartificiallayers. Inthisstudy,influenceofkeyparametersandFRP-fabric-wraprepairingmethodwere experimentally investigated. Eight specimens which were %40-scaled replicas of typical cross-section used in Topçam Dam, a reinforced concrete tunnel built into weak rock were tested. 1)No confinement, 2)No confinement fiber reinforced concrete, 3)Low confinement (rock present) 4)High confinement (stressed rock), 5)High confinement and imperfect contact, 6)FRP-repaired high confinement imperfect contact, 7)High confinement and imperfect contact with FRC, and 8)High confinement and improved contact. Mechanical properties of weak rock was simulated with a special light weight concrete composite. Loading of the specimens was done by applying pressure in two orthogonal directions with hydraulic jacks and pressure transmitting sections. Experimental data collection was confirmed with digital image correlation results. The study demonstrated the behaviour of horse-shoe shaped pressurized tunnels using a novel experimental approach, a first in the literature, with the key variables of: in-situ state of stress, contact of lining and mechanical properties of lining. Results showed that the level of confinement strongly affects the behaviour, soffit voids are critical and infringe the assumption of continuous load distribution, FRC does not improve the capacity of the section but distribute crack locations and control crack widths.