The use of fibreglass nails in tunnel construction for the reinforcement, as well as the placement of a steel tube umbrella, also known as forepole umbrella, for the protection of the excavation face, are two well known and extensively applied methods. They can be used solely or in combination, which is the most common case when adverse tunnelling conditions are expected. As the application criteria and design of these methods are still mainly based on experience and some simplified analytical methodologies, 3D finite element analyses provide a very useful optimization tool. The paper presents a series of analyses of circular lined tunnels in three dimensions, to show how such analyses can be used for tunnel face reinforcement and protection design. The analyses demonstrate the effectiveness of each method and the way it changes the stress and strain distribution around and in front of the tunnel. Fibreglass nails keep the advance core under compression and minimize extrusion, enhancing the stability of the tunnel face seriously, especially when placed in frictional soils. Forepole umbrella on the other hand does not minimize face extrusion significantly, but limits the extent of the plastic zone above the tunnel face. Finally, special attention is given to the interaction between these two methods. Taking the effects of this interaction into account can lead to a more rational and economic design, as these methods are not only quite expensive but also time consuming within the tunnelling process.
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