Abstract

Chemical reaction between anhydrite and water results in the formation of gypsum followed by a significant increase in the volume of the rock mass. Tunnel excavation enables increase of water conductivity around the underground opening which, superimposed to the impact of unloading on rock mass, forms sufficient conditions for the transition of anhydrite to gypsum. Suppression of the volume change caused by the primary support results in the build-up of swelling pressure in the rock mass causing damage to the tunnel lining. In the long-term anhydrite reacts to a slow change of moisture of the rock mass, which can affect functionality of the tunnel both due to swelling and sulphate aggression on concrete. Caverns filled with gypsum concentrated solutions can be encountered during tunnel excavations at transgressions between anhydrite rock mass and different geological strata due to abrupt change in rock mass transmissivity and consequent water retention. Experience gained from the construction of tunnel Ivan is presented in the paper to demonstrate the key technical aspects of tunnel construction in anhydrite containing rocks.

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