Monitoring data-based viscoelastic analysis of a 640 m long segmental tunnel lining: The stress-regulating role of longitudinal joints

Abstract

The structural behavior of a 640 m long stretch of the segmental lining in the north tube of the Koralm tunnel’s construction lot KAT3 is analyzed. Over a period of 3.5 years, circumferential normal strains were measured in nine measurement rings, each consisting of seven tubbings equipped with a centrally located strain sensor pair. A hybrid analysis combines the monitoring data with (visco)elastic modeling of concrete and steel as well as kinematics of slender circular arch theory. This allows for computing circumferential normal forces and axial bending moments at longitudinal sections through the measurement tubbings containing the strain sensor pairs. Cubic splines are used for circumferential interpolation between sensor positions and longitudinal interpolation between measurement rings. The obtained fields of internal forces are translated into fields of utilization degrees of both the reinforced concrete tubbings and the longitudinal joints consisting of plain concrete. The utilization degrees are illustrated in interaction diagrams. All computed pairs of normal force and bending moment – including those transmitted across reinforced tubbing sections – fall within the ultimate capacity boundary of the longitudinal joints. This is consistent with the interpretation that the longitudinal joints play a role in controlling lining stresses. This is particularly the case in highly utilized joints, where concrete exhibits nonlinear creep. This amplifies the overall deformability of the segmental tunnel ring, and thus provides a possibility for the lining to follow the deformation of the surrounding ground mass without activating overly high internal forces.