Ground-lining interaction and longitudinal joint capacity in TBM-built segmental tunnel ring: Hybrid analysis based on strain monitoring and viscoelastic shell theory

Ring 1945 in the north tube of Koralm tunnel construction lot KAT3, situated in the south of Austria, is equipped with 38 vibrating wire strain sensors. They are mounted on the inner and outer circumferential wire mesh of the precast concrete segments making up the tunnel ring, two each along one shell generator line. Corresponding uniaxial strain histories enter viscoelasticity theory, so as to deliver the evolution of mechanical stresses in the concrete next to the sensor positions. Outside the “Saint-Venant disturbance zones” close to the longitudinal joints, circumferential stresses associated with 14 sensors follow thin shell theory. Hence, they are converted into bending moments and normal forces associated with seven shell generator line positions. Spline-based interpolation between these seven locations evidences normal forces which are uniformly distributed along the ring, while bending moments exhibit a heart-shaped distribution. Insertion of corresponding functional relationships into the equilibrium conditions of shell theory yields quasi-uniform ground pressures along the tunnel shell circumference, while the ground shear patterns vary over time. During the first year, shear forces act from the spring-line to the top of the tunnel ring; and later, they act from top and bottom, respectively, towards the spring-line. Multiaxial stress states resulting from force-moment combinations at the longitudinal joints utilize 30 to 60% of the system’s load-carrying capacity. • Pairs of vibrating wire sensors lie on generator lines of segmental tunnel ring. • They record circumferential strains which enter viscoelastic shell theory. • This evidences uniform normal forces and heart-shaped moment distributions. • These internal forces arise from ground actions in terms of pressure and shear. • The longitudinal joints are utilized between 30 and 60% of their loading capacity.