Role of brittle fracture on swelling behaviour of weak rock tunnels: hypothesis and qualitative evidence / Sprödbruch in wenig festem Fels als Auslöser von Quellvorgängen: Beobachtungen und Analysen

Underground construction in rock prone to swelling behaviour may result in long-term problems, especially in the invert, if the structure cannot resist swelling pressures. Swelling phenomena are not only a consequence of ground conditions but are strongly influenced by excavation and construction procedures. Evidence of brittle failure observed in the field will be presented and analyzed to prove that brittle failure is the trigger effect of swelling phenomena in shale and clay-anhydrite rocks. Brittle fractures have also been observed in laboratory swelling tests. Brittle failure can create cracks that form pathways for water, leading to changes in the stress-state, and as a consequence trigger swelling phenomena. In clay-anhydrite rock, the swelling pressure is caused by the crystallization pressure of gypsum. The excavation and construction procedures used for the tunnel are a decisive factor for controlling swelling behaviour.