ABSTRACT:

Standard laminar roof protection and liner concepts like the application of shotcrete, steel arches or lattice girders are based on the concept of countering radial and tangential displacements with the build-up of axial compressive stiffness together with the ability of retaining rock material from falling off the roof. Additionally, they reduce the size of the plastified zone around the profile compared to non-lined excavations. Well established in mining, the concept of "Thin Sprayed Liners" (TSL) is not commonly used in the field of excavation of tunnels and caverns due to the fact that it is acting as a roof protection only. This liner concept interacts with the surrounding rock material with adhesion and tensile stiffness. The main goal is not to diminish displacements but to retain single blocks from falling off the roof using a membrane effect. One approach to assess the effectiveness of TSL is to introduce the behaviour into standard numerical models where different liner concepts can be compared directly in various environments e. g. rock mass consistence and mean stress. For this study, one modelling concept is used: The discontinuum mechanics through the software UDEC of ITASCA. This modelling concept is well established for representing the behaviour of laminar liners interacting with detached single blocks. Results of the parameterized analysis are discussed. The approach shows valuable information which is applicable to tunnelling design.

1 INTRODUCTION

Ground support materials known as "Thin Sprayed Liners" or "Thin Spray-on Liners" are alternatives to mesh/bolts or shotcrete. Initially developed for the mining industry, TSL provide a rapid support during excavation of underground mines and caverns. Common TSL material mixtures consist mainly of polyurea, polyurethane or the combination of both. All systems have in common a rapid tensile resistance and stiffness build-up which allows for immediate block retention after application.

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