Discuss the phenomenon of Plastic behaviour around tunnel.
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The Khimti headrace tunnel experienced instability related to tunnel deformations in several tunnel stretches through mica schist and schistose mica gneiss rock mass. The monitored convergence pattern indicated that the tunnel deformation continued for a long period of time after excavation. This paper aims to analyze plastic deformation behavior of the selected four headrace tunnel sections with considerable deformation where extensive deformation monitoring was conducted
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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