Seismic Rock Mass Response to Tunnel Development with Destress Blasting in High-Stress Conditions

The main infrastructure tunnels of the Andes Norte Project, New Mining Level (NML) of CODELCO's Chilean mining division El Teniente, are constructed in a complex environment from a geological and geomechanical perspective. The geological structural conditions and the stress field of the surroundings play an important role in the seismic activity induced by the excavations. Preconditioning techniques applied to rock masses can be applied on a massive scale to alter a significant volume of rock and/or on a local scale around the excavation. The latter approach has been implemented in the Andes North Project incorporating explosive charges confined and detonated simultaneously or with a time delay with tunnel development blasting. This paper describes the design and operational implementation of the destress blasting technique in the personal access tunnels (TAP) and conveyor belt tunnels (TC). The geological, geomechanical design and operation of the tunnels are analyzed in terms of the seismic response of the rock mass to tunnel development with and without destress blasting. One benefit measured after applying destress blasting is the response of post-blasting seismicity. Results demonstrate a higher speed of decay and an opportunity for reducing re-entry time when the destress blasting technique is used.

Automated summary

This study describes the design and implementation of the destress blasting technique in the Andes Norte project, and its impact on the seismic response of the rock mass during tunnel development. The results demonstrate that the use of destress blasting leads to a faster decay in post-blasting seismicity and reduces re-entry time.