The problem of swelling rock in tunnel design is introduced with an overview of swelling phenomena and swelling mechanisms in general, and swelling in anhydrite, marl and shale in particular. It is then possible to show how swelling characteristics can be measured and what factors affect swelling. This serves as a basis for the testing-analysis-design procedure which is described in detail including several design features that reduce swelling in tunnels. Several case histories illustrate the swelling effects and the application of the design method.
Les problèmes associés avec la construction souterraine en roche gonflante sont in- troduits avec un aperçu des phénomènes et mécanismes de gonflement en général et du gonfle- ment dans 1'anhydrite et dans la marne en particulier. Ensuite il devient possible d'expli- quer comment les caractéristiques du gonflement sont mesurées et de déterminer les facteurs qui influencent le gonflement. Ceci crée la base pour un mê'thode de dimensionnement qui est décrite en détail et qui comprend les dispositions constructives réduisant le gonflement dans les tunnels. Finalement quelques cas pratiques sont présentées pour illustrer les effets du gonflement et l'application de la mê'thode de dimensionnement.
Die Probleme, die mit quellendem Fels im Tunnelbau verbunden sind, werden mit einer Uebersicht über Quellerscheinungen und Quellmechanismen im allgemeinen und über Quellen im Anydrit und Mergel im speziellen eingeführt. Daraufhin werden die Messung der Quel- leigenschaften beschrieben und es wird gezeigt, welche Faktoren das Quellen beeinflussen. Damit ist die Grundlage für eine Dimensionierungsmethode, welche eingehend beschrieben wird, geschaffen; in dieser Beschreibung eingeschlossen sind die baulichen Massnahmen mit denen Quellauswirkungen in Tunneln vermindert werden können. Anschliessend werden anhand einiger Beispiele die Quellerscheinungen und die Anwendung der Dimensionierungsmethode illustriert.
Swelling ground causes major problems both during construction and during the operational life of an underground opening. Invert heave of up to 25 cm/year has been observed. Even if the swell rate decreases with time, rates of between 0.5 and 1.0 cm/ year in 75-100 year old tunnels are not un- common, resulting in total invert heave in the order of several meters. Consequently, repair of invert covers and reexcavation of the invert become regular maintenance operations, or invert arches frequently between one and two meters thick have to be built to reduce the displacements to acceptable levels. At least as significant as these phenomena during the operational life of a tunnel, are the effects of swelling during construction. Swelling rates of 1 cm/day or greater do occur and buckled steel sets and broken drainage pipes are all too familiar under such circumstances. In this paper, a design-method for tunnels in swelling rock will be described that was developed for tunnels in swelling shale, marl and anhydrite. The method is based on a testing-analysis-design procedure that is rigorously conceived inspite of the presently still-limited knowledge of several aspects of swelling rock behavior. Following this introduction to the paper will be a short review of swelling phenomena and their possible causes which will set the stage for a more detailed discussion of swelling in shale (marl) and anhydrite. Once the swelling mechanisms and the particular circum- stances of swelling in underground openings have been established, it will be possible to determine how swelling can be influenced. This knowledge provides the basis for the testing-analysis-design procedure which will be described in detail. Several design options that reduce swelling effects will then be discussed. The paper will conclude with several case histories that illustrate the swelling phenomena in tunnels driven through shale (marl) and anhydrite and that show the practical application of the design procedure.
Swelling can be defined as a time dependent volume increase of the natural ground caused by stress changes, increase in water content or by a combination of both. Depending on the interaction and sequence of causes, several typical swelling phenomena result:
Phenomenon 1: A change in the stress state, particularly in the form of stress relief or stress rotation, e.g., due to erosion, of overburden, valley cutting or excavation of an underground opening can lead to volume increase with time. A similar phenomenon can be observed on a much smaller scale due to particle rebound.
Phenomenon 2 : Adsorption or absorption of water due to differences in concentration, unsaturated or partially saturated bonds and differences in potential is frequently associated with a time-dependent volume increase.
Phenomenon 3: The stress changes lead to adsorption and/or absorption of water and further volume increase. Volume increase due to stress change and volume increase due to water adsorption or absorption can occur simultaneously or sequentially.
