Assessment of blasted excavation inaccuracy at tunnel face and influences on tunnelling effectiveness

Abstract

Blasting has been the most effective solution for tunnel excavation in hard rock. The accuracy of the blasting works is demonstrated by the similarity between the design and the actual excavation boundary. Hence, the overbreak and underbreak of the tunnel boundary are used to evaluate the tunnel excavation. Widely applied for rock tunnelling, New Austrian Tunnelling Method (NATM) has been used for almost all highway tunnels in Vietnam. The assessment of the previous projects is essential since it provides learnt experiences and enriches the knowledge to handle the tunnelling technology. With this aim, the paper studied the case of a 500m NATM tunnel located on the N01 national highway in Central Vietnam. The practical excavation zone was examined, and the overbreak and underbreak of the tunnel boundary during the excavation by explosive was investigated. The dependences of the overbreak and underbreak on the geological and technical conditions were indicated. The tunnelling effectiveness was then assessed through the additional materials and works for the face correction activities.

Keywords

• tunnel engineering
• rock engineering
• construction engineering