This paper presents a laboratory study concerning shotcrete as a tunnel lining applied on irregular tunnel surfaces. The problem concerned is first presented. A description of the model test is given and major findings from the study are presented. The main conclusion gained from the study is that the irregularities of tunnel surfaces are unlikely to have negative effects on the general safety of a tunnel.
Ce document presente une etude laboratorie en ce qui concerne beton de spray comme un revêtement du tunnel, applique sur des surfaces irregulières du tunnel. D'abord on introduit Ie problem. Ensuite une description de I'essai du modèle est presentee. Des resultats majeurs de l'etude sont exposes et la conclusion principal est la suivante: Des irregularites des surfaces d'un tunnel n'ont pas (ou peu probable) d'effects sur la securite generale du tunnel.
Der vorliegende Bericht beschreibt eine Laborstudie bezueglich der Anwendung von Spritzbeton zur Tunnelwandverstarkung an unebenen Oberflachen. Zuerst wird das Problem dargestellt. Danach werden die Modellversuche beschrieben und die wichtigsten Ergebnisse beschrieben. Der Hauptschluβsatz dieser Studie ist, daβ es unwahrscheinlich ist, daβ Unebenheiten an der Tunneloberflache einen negativen Eintluβ auf die allgemeine Sicherheit des Tunnels haben.
When a tunnel is excavated by the drill and blast method, tunnel surfaces are usually uneven and waved, sometimes there is substantial overbreaking due to the nature of the rock mass or unfavourable blasting performance. The unevenness or irregularities of the tunnel surfaces make tunnel sections deviate, sometimes significantly, from designed sections which are often of perfectly circular, elliptical, horse-shoe shaped or rectangular in shape. When shotcrete is used as tunnel lining, the shotcrete will follow the irregularities of the constructed tunnel. Because tunnel support analysis and design are performed based on those perfect design sections, the following questions are often raised in tunnelling practice: i. how much does a shotcrete lining applied in a tunnel behave differently from the design ? ii. is it necessary to fill the overbreakings with shotcrete ? iii. is it necessary to have a smooth finished tunnel surface to meet the condition of design ? Answering those questions has significant importance to an economical and fast tunnelling performance, since filling over breakings with shotcrete is costly and time-consuming. By careful blasting the roughness of the tunnel surface can be reduced. But it can never be guaranteed that over breaking can be avoid. Moreover, smooth blasting in tunnels can be time-consuming and expensive.. In the past, some work concerning this problem in hard rock have been done (e.g. Holmgren, 1975; Fernandez, et al, 1976), whereas little has been found in the literature with reference to weak rock. This paper, with focus on weak rock, presents a study on the interaction between a shotcrete lining and uneven tunnel surfaces by laboratory model testing. The model testing is aimed at gaining overall information on the behaviour of shotcrete linings applied on waved tunnel surfaces. Numerical calculations are also carried out in order to study the rock behaviour around an uneven tunnel by means of ground reaction curve concept. The study was done at the Division of Soil and Rock Mechanics, Royal Institute of Technology, Sweden.
In order to relate the results of a model test to an actual tunnelling practice, similitude laws must be derived. This is done by dimensional analysis based on Buckingham's -theorem (e.g. see Langhaar, 1951). For the purposes of the model test of this study, the tunnel lining problem is treated as a static and non body force problem. Therefore velocity, acceleration and density are not taken into account.
