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M. Lechner, Ch. Hellmich, H.A. Mang:
"Short-term Creep of Shotcrete - Thermochemoplastic Material Modelling and Nonlinear Analysis of a Laboratory Test and of a NATM Excavation by the Finite Element Method";
in: "Proceedings of the International Symposium on Continuous and Discontinuous Modelling of Cohesive Frictional Materials - Lecture Notes in Physics", P.A. Vermeer, S. Diebels, W. Ehlers, H.J. Herrmann, S. Luding, E. Ramm (ed.); Springer, Berlin, 2001, 47 - 62.

Embedded in a thermochemoplastic material law set up in the framework of thermodynamics, the focus of the work is on the creep characteristics of shotcrete. Short-term creep, with a characteristic duration of several days, turns out to be a fundamental feature for realistic modelling of the structural behaviour of tunnels driven according to the New Austrian Tunnelling Method (NATM). Its origin is a stress-induced water movement within the capillary pores of concrete. This process is related to the accumulation of hydrates, which are initially free of micro-stress. Hence, an incremental formulation for aging viscoelasticity turns out to be a proper tool for modelling this kind of creep. The usefulness of this formulation is tested by re-analyzing a relaxation test with non-constant prescribed strains, showing quantitatively correct results for concrete and qualitatively correct results for shotcrete. The latter results indicate the necessity of classical creep tests for shotcrete.

Keywords: shotcrete, incremental creep formulation, relaxation test, return map algorithm, short term creep