Numerical modelling of the formation and instability of blocks around the Monte Seco tunnel excavated in a discontinuous rock mass

Abstract

Geotechnical analysis of tunnels in complex geostructural environments requires an advanced understanding of the inter-block structure effect on rock mass behaviour, such as joints and fractures systems, bedding and foliation planes, among other discontinuity types. The conventional approach for preliminary geotechnical analysis of tunnels is based on a continuous-equivalent system representation of rock mass, i.e. without explicit consideration of systematic discontinuity systems. However, to obtain a closer to reality results of the rock mass expected behaviour, geostructural data should be included from the initial stage of numerical modelling for geotechnical analysis. The Monte Seco tunnel in Brazil, is used as a case study to analyze the implications of the discontinuity systems inclusion and degradation of mechanical properties, on the underground excavations stability. Based on the valuable geological engineering information from the TUNELCON project, numerical models with twodimensional DFN systems were developed. The case study demonstrates the importance of considering in detail the geo-structural data in numerical models from early stages of the project, thus achieving results that resemble in a better way to the actual behaviour that have the excavations during the construction and operation stages.