The problem of the tunnel excavation in a swelling rock is frequently encountered in many places. Expansive formations include many different rocks such as anhydrite, marls, shales and so forth. Mineralogical analyses and geotechnical property tests can be used to predict swelling behaviour, and special tests carried out in oedometer cells to quantify the swelling deformation of a given rock. These parameters can be used to compute the forces acting on the lining. This paper studies the expansive properties of some marly rocks in Algeria and Spain correlating them with some geological and mineralogical factors. The method of calculation of forces on the lining is also described, showing some representative results.
Il s'agit d'un problème qu'on rencontre souvent. Les formations gonflantes comprennent plusieurs sortes de roches tels que l'anhydrite, les marnes et les ardoises. Pour mettre en relief le caractère gonflant, on peut employer des analyses mineralogiques et des essais dans des cellulles oedometriques. Ces paramètres peuvent être utilises pour definir les forces agissant sur le revêtement. Ce rapport etudie les proprietes gonflantes de quelques roches marneuses en Algerie et en Espagne en liaison avec quelques facteurs geologiques et mineralogiques. On presente egalement la methode de calcul des efforts sur le revêtement avec quelques resultats representatifs.
Die Konstruktion von Tunneln in blahendem Fels ist ein haufiges Problem. Von Laboratoriumsversuchen kann man dieMaterial- Kennwerte erhalten. Dann ist es möglich, die Spannungen an der Auskleidung zu berechnen. In diesem Beitrag werden geotechnische Kennwerte fuer Merge1 von Algerien und Spanien mit geologischen und mineralogischen Faktoren verbunden. Es wird die Berechnungsmethode fuer die Spannungen an der Auskleidung beschrieben.
Within the works of the second track of the rail way line Martorell-Castellbisbal (Barcelona, - Spain), the Spanish Railway Company (RENFE) is - constructing a 850 m long tunnel, with a maximum rock cover of 100 m. The survey of ground conditions established that approximately one half of the tunnel alignment is bored through Miocene - claystones and marls, with fine interbeddings of dolomies, limestones and gypsum: being the remaining half bored through Ordovician shales. The - Miocene strata, which are discordantly bedded against the ordovician substratum, dip gently (less than abour 15°) parallel to the tunnel axis. Figure 1 shows a geological profile along the tunnel alignment. Preliminary surveys showed the expansive properties of Miocene marls, so it was a mayor concern during the design stage to - account for the forces on, the lining due to swelling phenomena. An also important tunnelling design involving swelling rock was studied by the Authors in Algeria for the Bou-Roumi hydraulic scheme. It consists of the design of three tunnels for the diversion of the waters of the rivers Oued Chiffa, Oued Djer and Oued Harbil (see figure nr. 1). The three tunnels are 12,5 Km, 3 Km and 4,5 Km long, with maximum rock cover of 500 m, 200 m and 80 m respectively. This geological province is located south of the Telliennes Chains, with Cretaceous and Miocene materials. The Cretaceous rocks are schists and calc-schists and the Miocene rocks are a thick series of marls with a - basal level of limestones and sandstones. The Cretaceous formation is the northern bank of a great anticlinorium and the Miocene materials - rest discordantly on it with a gentle northward dip. The Miocene marls show swelling behaviour, and are the subject of study in this paper.
In both cases,the swelling rock belongs to the lithological group of marls. However, there are significant differences between the rocks of - the two projects. Plates nr. 1 and nr. 2 show the main geotechnical characteristics of these rocks. It can be seen that the Algerian marl contains less carbonates and is much more plastic than the Spanish one. From the mineralogical standpoint, the latter has less proportion of - clayey minerals, only a 20% against the 50% of the former. In both cases, a major clay-mineral constituent is montmorillonite. Compression laboratory tests show a great dispersion in both rocks, partly because of some calcitic or dolomitic interbedding in very thin layers which appear somewhat randomly.
As both marls have a high amount of clay, they behave more or less plastic under the tectonic stress fields. Therefore faults are neat, with smooth surfaces filled with calcite or, in the Spanish project, with gypsum. No breccia materials are found along those faults. Stratification is slightly apparent, except for the case of sandstone layers interbedded in the Algerian formation. Joints, that are well developped in the more calcareous materials, don't seem to - break the marly formation. From this study it is concluded that discontinuities are not significant for the behaviour of the marls.