[Back]

R. Lackner, H.A. Mang:
"Modeling of Early-age Fracture of Shotcrete: Application to Tunneling";
in: "IUTAM Symposium on Analytical and Computational Fracture Mechanics of Non-Homogeneous Materials", B.L. Karihaloo (ed.); Kluwer Academic Publishers, Dordrecht, 2002, ISBN: 1-4020-0510-5, 197 - 210.

Shotcrete tunnel shells are mainly loaded by the inward moving soil masses and the temperature rise during the hydration process, both resulting in compressive loading of the shell. The decrease of temperature during the cooling process, however, leads to tensile loading which, favored by chemical shrinkage, may cause cracking of the early-age shotcrete. In this paper, the influence of temperature changes during the hydration process on cracking in shotcrete tunnel shells is investigated. The required temperature profiles through the tunnel shell are computed by means of a thermochemical analysis on the basis of an axisymmetric finite element (FE) model. The comparison of numerically-obtained temperature histories with respective in situ temperature measurements provides new insight into the composition of shotcrete after its application on the tunnel wall. For the first time, the loss of aggregates in consequence of rebound during shotcreting, causing an increase of the cement content, is quantified in the course of the presented analysis. In fact, the cement content strongly affects temperature changes during the hydration process. Hence, it has a strong influence on the loading of the shell. The obtained temperature profiles serve as input for the chemomechanical analysis. The chemomechanical analysis is based on a hybrid method recently developed at Vienna University of Technology. The term hybrid refers to the combination of in situ displacement measurements and a thermochemomechanical material model for shotcrete. The chemomechanical analysis provides the stress state in the tunnel shell, thus, giving insight into the load-carrying behavior of the shell.

Keywords: cracking, shotcrete, tunneling, fracture energy, Sieberg tunnel