Realistic long-term stress levels in a deep segmented tunnel lining, from hereditary mechanics-informed evaluation of strain measurements

• Published in: Tunnelling and underground space technology 2024-03, Vol.145, p.105602, Article 105602
• Main Authors: Razgordanisharahi, Ali, Sorgner, Maximilian, Pilgerstorfer, Thomas, Moritz, Bernd, Hellmich, Christian, Pichler, Bernhard L.A.
• Format: Article
• Language: English
• Subjects: Degree of utilization; Non-asymptotic creep; Service life assessment; Structural analysis; Thermo-viscoelastic modeling
• ISSN: 0886-7798; 1878-4364
• DOI: 10.1016/j.tust.2024.105602

Realistic estimation of stresses in segmented tunnel linings is a challenge tackled herein by means of a hybrid, i.e. computational-experimental, approach. Thermistor-equipped vibrating wire strain gauges were installed (i) into concrete samples undergoing one year-long uniaxial creep tests under the environmental conditions of the tunnel site, and (ii) into the tubbings making up the tunnel lining of the Koralm tunnel. The data obtained from the creep tests allow for calibration and validation of an integro-differential thermo-viscoelastic model. The creep function combines a power-law for short-term creep with a logarithmic law for long-term creep. The corresponding relaxation function is determined by means of Laplace-Carson transformation, inversion, and back-transformation. This is the basis for translating the circumferential strain histories measured in the tubbings of Ring 2013 in Koralm tunnel KAT3 into circumferential and longitudinal stress evolutions. They are mainly due to mechanical ground-shell interactions. The corresponding degree of utilization increases during the first four months after ring installation, and remains virtually constant thereafter. Stress fluctuations due to seasonal temperature variations play only a minor role. With regards to a long-term prognosis, it is very interesting to note that the strain measurements recorded in the tubbings, when plotted as function of the logarithm of time, follow bi-linear trends. These trends can be extrapolated to 150 years, the targeted service life of newly built tunnels in Austria. Throughout this period, the viscoelasticity-based estimates of the stresses in the vicinity of the strain sensors stay temporally constant, at some 40% of the strength of concrete. •A tubbing ring was monitored over 3 years by means of 38 embedded strain sensors.•Logarithmic trends of measured strains are extrapolated 150 years into the future.•1 year-long on-site uniaxial creep tests provide viscoelastic properties of concrete.•They allow for converting measured tubbing strains into stresses close to the sensors.•Tubbing stresses increase during the first four months, and remain constant thereafter.