G. Poscher
Zur Umweltverträglichkeit von Spritzbeton im Tunnelbau. Erfahrungen mit Maßnahmen zur Verminderung der Spritzbetoneluation

GPM 19, p. 71-92

Zusammenfassung:
Nach der derzeitigen Gesetzeslage wird in Österreich Tunnelausbruch nach dem Abfallwirtschaftsgesetz (1990) und Tunnelabwasser nach der Allgemeinen Abwasseremissionsverordnung (1991) verhandelt. Spritzbetonarbeiten sind dabei hinsichtlich der Zusatzstoffe, der Spritzbetoneluation und der Rückprallanteile ein zunehmend kritischer Verhandlungspunkt.
Über Erfahrungen mit spritzbetontechnologischen Maßnahmen zur Verbesserung der Umweltverträglichkeit, insbesonders zur Reduktion der Eluationsneigung, wird berichtet. Methodik und Umfang der hydrogeologischen Dokumentation werden dabei erörtert.

Abstract:
Current Austrian law sets down definitely that tunnel excavation material is treated according to the 'Abfallwirtschaftsgesetz (1990)' and sewage from tunnels according to the 'Allgemeine Abwasseremissionsverordnung (1991)'.
Critical matter of negotiations are shotcrete works because of dust emissions, additional basic chemicals for acceleration, shotcrete eluation and shotcrete rebound.
Experiences with measures designed to reduce shotcrete eluations in order to improve environmental acceptance will be explained in detail. The experiences were gathered during construction of four twin track tunnel tubes of the Verbindungskurve Nantenbach / BRD totalling approx. 6.3 km in length.
Several different dry shotcrete mixtures were used. In the case of two tunnels dry shotcrete mixed with microsilica were applied under different constructional framework conditions.
Documentation of pH-values and conductivity as well as analyses of the water seeping through the primary lining revealed that no major changes in the chemistry of the groundwater occur due to shotcrete eluations until the secondary lining is installed. Independent of whether microsilica slurry is added or not, only slight differences are observed between the individual mixtures when using Hochofen cement and liquid accelerators.
Eluation tests performed on samples taken from the tunnel provided qualitatively similar results.
As the installation of the secondary lining progressed, pH-values and alkali content increased as compared to the excavation phase and a clear dependence on groundwater flow into the tunnel was found. By the time the construction works were completed, the hydrochemical conditions encountered at the side wall drainages of the secondary lining had already largely stabilized.
The readings collected so far indicate that a remarkable reduction in the pH-value and the eluate content of the tunnel water has been achieved as compared to the Mühlberg tunnel which is situated in the same mountain massif and which is constructed by shotcrete of minor quality.


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