ABSTRACT:

Severe problems with swelling rocks in the Belchen tunnel have lead to several field and laboratory investigations concerning this problem in relation to reconstruction of parts of the tunnel. The latest investigations include theoretical considerations concerning the maximum swelling stress of the "anhydrite swelling", drillings, laboratory measurements of swelling strain and stress, petrographical and mineralogical investigations. The conversion of anhydrite into gypsum in the anhydrite containing shale is of special interest.

ZUSAMMENFASSUNG:

Ernsthafte Probleme mit quellfahigen Gesteinen im Belchentunnel haben zu mehreren Feld- und Laboruntersuchungen in Verbindung mit Sanierungs- und Erneuerungsarbeiten gefuehrt Die neuesten Untersuchungen betreffen theoretische Ueberlegungen bezueglich des maximal möglichen Quelldruckes der "Anhydritquellung", gekernte Bohrungen, Labormessungen des Quellmasses und Quelldruckes, petrographische und mineralogische Untersuchungen. Von speziellem Interesse ist die Umwandlung von Anhydrit in Gips in den sulfathaltigen Tongesteinen.

RESUME:

Des problèmes considerables avec des roches gonflantes dans le tunnel Belchen ont mene à plusieures recherches sur place et au laboratoire en connexion avec des traveaux de renovation. Les dernières investigations concernent des reflexions theoriques au sujet de la pression maximum du "gonflement anhydrite", des sondages, des analyses de laboratoire sur la deformation et contrainte de gonflement, des investigations petrographiques mineralogiques. La conversion de l'anhydrite en gypse dans les schistes contenant du sulfate est tout particulièrernent interessante.

1
INTRODUCTION

The Belchen tunnel is a 3.2 km long highway tunnel in the northern part of Switzerland, consisting of two parallel 2-lane tubes. The tunnel which is located in marl, shale, and anhydrite containing marl was finished in 1970. The tunnel was constructed by excavating two invert drifts in each tube and then enlarging to the full cross-section. After the enlargement to the full cross-section in the Keuper formation, severe problems with swelling in the anhydrite containing marl caused heave of the invert level in parts of the tunnel of up till about 0.9 m within a few months during the construction phase (Grob, 1975, Einstein, 1979). As a consequence an invert arch was built with a radius of 10.4 m and a thickness of 45 cm. However, shortly after construction this invert arch was sheared off and a further 0.6 m of invert heave occurred. This required the construction of a new invert arch with a smaller radius and a larger thickness. Stress cells at the rock-concrete interface below the new invert arch showed maximum contact stresses of 3.5 MPa about 200 days after placement Laboratory measurements (Huder & Amberg, 1970) produced swelling stresses in the same order of magnitude. The maximum swelling stress (Aegerter & Bosshardt, 1988) measured in 1984 at another location in the tunnel was 12 MPa (average value of 15 pressure cells was 2.9 MPa). In the last 25 years swelling of the anhydrite containing marl has, in combination with sulfate containing water - Werder (1989) reports sulfate contents up till 1290 mg/liter - caused damage to the tunnel structure. In 1985 a survey of the whole tunnelled to major investigations and repair of parts of the tunnel (Werder, 1989). Since 1970 discussions about the role of the "anhydrite into gypsum conversion swelling" versus pure "clay swelling" in these rocks have never reached a conclusion (Steiner, W., 1993; Anagnostou, G., 1992; Madsen and Nueesch, 1991). The present paper deals especially with the problem of the anhydrite/gypsum swelling and is a contribution to above mentioned discussion. At present time a four years research program dealing with the geological and geotechnical problems around the repair of the mostly damaged parts of the tunnel is carried out. The preliminary investigations consist of 12 cored drillings, petrographical and mineralogical investigations of selected specimens from the cores, studies of the interaction between clay and anhydrite/gypsum, swelling strain and stress measurements in the laboratory, and theoretical considerations about the maximum possible swelling stress which may result from the conversion of anhydrite into gypsum. The measurements of the swelling stress in the laboratory have produced values up till 5 MPa after about 2 years of testing time. As a complete swelling test may take far more than 6 years (Madsen & Nueesch, 1989, 1990, 1991) a further increase in swelling stress is expected.

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