Geotechnical instrumentation in high seismic risk tunnels and support replacement criteria

Authors: Moraga, C; Bahamondes, C; Pulgar, D; Romero, D; Muñoz, A Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2465_34

Cite As:
Moraga, C, Bahamondes, C, Pulgar, D, Romero, D & Muñoz, A 2024, 'Geotechnical instrumentation in high seismic risk tunnels and support replacement criteria', in P Andrieux & D Cumming-Potvin (eds), Deep Mining 2024: Proceedings of the 10th International Conference on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth, pp. 575-588, https://doi.org/10.36487/ACG_repo/2465_34



Abstract:
The Andes Norte project is developing a tunnel located in a high seismic risk zone with two excavation faces. This access tunnel will be used to transport future production from sectors of Division El Teniente de Codelco via a conveyor belt. Both development faces are located in a complex environment dominated by high stress and anisotropy in rock masses with fragile behaviour, in addition to complex geological and structural conditions. This produces an unfavourable seismic response, with high event frequency, high local magnitude and different types of focal mechanisms. The unfavourable seismicity recorded through tunnel construction has resulted in the consumption of support capacity which could result in the development being unfit for service in a worst-case scenario. This has driven Codelco to implement support systems with higher energy dissipation capacity, which currently makes this tunnel that with the highest installed support capacity in Division El Teniente. In order to understand the behaviour of the reinforcement system installed and its consumed capacity after a seismic event, a monitoring system has been deployed that includes load cells and dataloggers capturing data at a high frequency rate. In addition, topographic data has been collected on a regular basis using a laser scanner, allowing the deformation measured in the tunnel due to seismic events to be recorded and analysed. This paper will describe the installation methodology, information analysis and the resulting support replacement criteria, and present two case studies.

Keywords: geotechnical instrumentation, load cells, deformation, seismicity, reinforcement, energy dissipation

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