The planning of long deep-lying base tunnels through the Alps highlights the problem of tunnelling in squeezing rock conditions. After a brief description of the constructional experience gained to date and a retrospective look at the first scientific attempts to explain the various forms of rock pressure, the main aspects of the project for the 57 m long Gotthard Base Tunnel are presented. Following this a description is given of the results of the planning work for the construction lot Sedrun, for which long stretches of squeezing rock conditions have been predicted. The concept is based on full face excavation with systematic support of the face and control of the convergence using a steel lining with yielding joints after Toussaint-Heintzmann as well as systematic rock bolting.
La planification de longs tunnels de base sous les Alpes fait ressortir Ie problème de la construction de tunnels dans des conditions de roche poussante. Les aspects principaux du projet pour le Tunnel de Base du Gotthard, de 57 km de long, sont abordes après une brève description de l'experience acquise à ce jour dans la construction et un regard en arrière sur les premiers essais scientifiques pour expliquer les differents types de pression des roches. Ensuite, on fournit une description des resultats de planification du lot de Sedrun pour lequel on a predit de long tronçon de roche poussante. Le concept d'excavation est base sur une attaque à pleine section avec un soutènement systematique uniforme du front et un contrôle de la convergence estimee par un revêtement en acier selon la methode de Toussaint-Heintzmann ainsi que l'utilisation de grilles d'ancrages radiaux.
Die Planung langer, tiefliegender Basistunnel durch die Alpen verleiht dem Problem des Tunnelbaus in druckhaftem Gebirge hohe Aktualitat. Nach einer kurzen Schilderung der Bauerfahrung und einem Rueckblick auf die ersten wissenschaftlichen Ansatze zur Erklarung der mannigfaltigen Äusserungen des echten Gebirgsdrucks wird das Projekt des 57 km langen Gotthard Basistunnels in groben Zuegen dargestellt. Anschliessend werden die Ergebnisse der Projektierungsarbeit fuer das Los Sedrun erlautert, wo Iangere Strecken druckhaften Gebirges prognostiziert sind. Das Konzept beruht auf dem Vollausbruch mit systematischer Sicherung der Ortsbrust und der Kontrolle einer eingeplanten Konvergenz mit Stahlausbau nach Toussaint-Heintzmann sowie radialer Systemankerung.
The term "squeezing rock" originates from the pioneering days of tunnelling in the Alps. The various descriptions of rock pressure were already in the early days classified into three groups, namely loosening rock pressure, swelling pressure and squeezing pressure. Thus the observed rock behaviour was often described using terms like spalling, swelling and squeezing. As long ago as the last century one already understood that these three types of rock pressure were caused by fundamentally different physical mechanisms (Kovari 1975)., They may also act in a superimposed way; and thus it is for example conceivable that in a rock of low strength containing clay minerals the failure processes are accompanied by the swelling phenomenon. Squeezing rock is characterised by the tendency to reduce the cross-section of the opening (Figure 1). The reduction in size of the opening in course of time is called "convergence". The actual creep potential of the rock under the given stresses is a basic requirement for the occurrence of squeezing rock. Since the lining resists the convergence, the pressure acts as a reaction, so that rock pressure and rock deformation are directly related to one another. With respect to the lining the, rock pressure is regarded as a loading, and with respect to the rock it acts as a lining resistance; thereby, two distinct aspects (action and reaction) of the same phenomenon are expressed. If the rock pressure exceeds the bearing capacity of the lining it will be damaged or even destroyed.
