ABSTRACT

The paper describes the characterisation studies of Tectonised Clay Shales at laboratory and in situ scale. The interest relates to tunnelling under squeezing and swelling conditions, in Italy, along the Apennines. The results of monitoring during full face excavation are presented in conjunction with numerical modelling.

RESUME

Cet article presente la caracterisation, à l'echelle du laboratoire et in situ, des Argiles Chaotiques. L'attention est portee sur le creusement, dans ces milieux gonflants, des tunnels, dans les zones montagneuses des Appennini, en Italie. Enfin, on presentera les resultats de la modelisation numerique et la comparaison de ces derniers avec les mesures effectuees in situ.

KURZFASSUNG

Die Arbeit beschreibt die Charakterisierungsstudien von tektonisierten Schiefertonen, sowohl im Labor als auch vor Ort. Das Interesse gilt dem Tunnelbau unter Quetschund Schwellbedingungen in Italien entlang der Apenninen. Die Überwachungsergebnisse des ganzflachigen Ausbruchs werden mit numerischen Modellen prasentiert.

Introduction

Tunnelling through the Apennines is presently under way in Italy, in connection with the construction of the high speed railway line between Bologna and Firenze. A significant length of large size tunnels is being excavated under difficult conditions, within the Tectonised Clay Shales of the "Chaotic Complex" (CCTCS), which are shown to exhibit squeezing and swelling behaviour.

(Figure in full paper)

From North to South (Figure 1), the 10,450 m long Raticosa tunnel crosses the CCTCS formation (through a 5.5 km length), marly and arenaceous formations. A landslide, involves approximately 500 m of the tunnel length from the northern portal. The landslide is active with rates of displacement ranging from more than 4 mm/year to 0÷1.5 mm/year. Cubic samples were taken at chainage 116 m (22 m depth) in the Raticosa tunnel (landslide area) and at chainages 590 and 620 m (140 m depth) in the Osteria access adit.

The geotechnical characterisation was carried on both Raticosa and Osteria samples. The CCTCS of the landslide area (Raticosa) have undergone softening and/or weathering processes which have modified both the structure and properties of the rock material. The recent geological history and the variable structure of the CCTCS are likely to have originated a very different mechanical behaviour in terms of time dependence.

Geotechnical characterisation of the Chaotic Complex Tectonised Clay Shales

The cubic samples obtained at the tunnel face were taken to the laboratory, where cylindrical specimens (to be adopted for triaxial tests) were cut with great difficulty, also because of the presence of inclusions. The material in excess was used for the determination of physical properties and mineralogical content and for oedometer tests.

According to the Plasticity Chart, the CCTCS are classified as "inorganic clays of low to average plasticity". From the geological point of view, the CCTCS are turbidites, with structure heavily modified by tectonic events. The CCTCS structure is scaly, with polished surfaces, oily at a touch. Irregular striping is present, with folds of various sizes due to superimposition of a more recent wavy pattern to the original one.

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