Visco-Plastic Behaviour around Advancing Tunnels in Squeezing Rock |
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| Authors: | D Sterpi G Gioda |
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| Institution: | (1) Department of Structural Engineering, Politecnico di Milano, P. Leonardo da Vinci 32, Milan, Italy |
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| Abstract: | Summary The visco-plastic behaviour of rocks plays a relevant role in the tunnelling works, especially for deep tunnels subjected
to large initial stresses for which squeezing conditions may develop. A rheological model is discussed that accounts for visco-elastic
(primary) and visco-plastic (secondary) contributions to rock creep. The effects of tertiary creep are included in the model
by way of a gradual mechanical damage governed by the cumulated visco-plastic strains. The parameters of the intact rock are
first identified based on laboratory test results presented in the literature. Then, after scaling them to those of the rock
mass, the potential applicability of the model is tested through axisymmetric and plane strain finite element analyses of
the full face excavation of a deep circular tunnel. The results are discussed with particular reference to the short term
redistribution of stresses around the opening and to its convergence. The analyses show the relevant influence of tertiary
creep on the tunnel closure. In addition, those based on an axisymmetric scheme turn out to be crucial for the correct long
term prediction of the interaction between the rock mass and the supporting structure of the opening. |
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| Keywords: | : Creep squeezing rock mass behaviour deep tunnels tunnel face finite element analysis |
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