Kittilä Hoisting Shaft Geotechnical Investigation
SRK was commissioned to conduct a rock mechanics stability investigation and shaft development options appraisal for a 6.1 m diameter production hoisting shaft to 1,050 m deep, to be developed in various sections from surface.
The remit included SRK conducting detailed rock mass characterisation incorporating geotechnical and geological core logging, rock strength testing, interpretation of borehole geophysics, and hydrogeological testing of the entire shaft profile. This assessment was applied in empirical and analytical stability analysis with the aim of identifying the areas of potential instability, possible failure mechanisms, methods of ground improvement, and perimeter ground supporting systems to suit the planned service life.
A key element applied was to calibrate the analysis with review of the existing 4 m diameter raises at Kittilä in similar rock mass and stress conditions down to 850 m depth. SRK established the rock characterisation and identified zones of weaker wall and face conditions as well as water inflow areas to inform the shaft construction methods.
Development options identified included large diameter raise boring or primary raisebore with bench stripping to full diameter. These options were assessed based on potential stability risks during both shaft construction and long-term shaft service life. In 2018, Kittilä commenced development of the various shaft legs based on SRK’s findings and recommendations.
