Face reinforcement in deep tunnels

The practice of introducing and grouting reinforced fiber glass pipes or bar into the core that has to be excavated in order to keep a tunnel face stable during excavation has been applied to many tunnels excavated in difficult geotechnical conditions, with good results in terms of safety and speed of works. This reinforcing technique, initially developed to be used together with mechanical precut in clay, has been widely used with other geotechnical conditions as the only type of reinforcement or joined with other ground reinforcement techniques (such as steel pipes or jet-grouting umbrella). The effect of a systematic tunnel face bolting has been studied using a three-dimensional FLAC code, to compare different reinforcement layouts and different geomechanical ground properties. The obtained results, compared with the measurements of a real case, are able to identify the main peculiarities of the intervention and the importance of some aspects of the ground behaviour.