The risk analysis applied to deep tunnels design—EL teniente new mine level access tunnels, chile

Abstract

El Teniente Mine, with 2,400 km of tunnels excavated since the beginning of the last Century is the largest underground copper mine in the world. El Teniente Mine production plan has a thin overlap between the exhaustion of the current production level and the activation of the New Mine Level, located at almost 1,000 m depth, planned for 2017. The infrastructure system involves the construction of 24 km of access tunnels, consisting of two adits, a tunnel for vehicular access of personnel and a twin conveyor tunnel for the transport of the ore. The definition of geological and geomechanical scenarios, as predicted on the basis of the reference models, and the related hazards identification and mitigation (following a risk analysis based design), are cornerstones along the production chain. Tunnel alignment intersects a complex geological environment characterized by rock variability: from igneous (effusive and intrusive) to sedimentary volcanoclastic rocks, with sectors of intense hydrothermal alteration. Due to high overburden and variability of rock mass properties, geomechanical hazards such as squeezing and rockburst are expected, together with caving and flowing-ground conditions crossing fault sectors associated with high hydraulic pressures. This paper synthesizes the design methodology, focused on risk management (Risk Analysis-driven Design, Geodata 2009). The construction of the tunnel is actually in process and then also a preliminary comparison “predicted versus observed” is anticipated.