Geological Mapping of ONKALO

Geological mapping is used in collecting information for adjusting a geological model as well as for the use of experts who design the strengthening measures and grouting. On the basis of mapping, forecasts are also drafted concerning the characteristics of the rock deeper down.

The geological mapping of ONKALO is divided into two parts: mapping performed in the constructed tunnel immediately after excavation, and a more precise systematic mapping.

The first phase mapping proceeds simultaneously with excavation work so that the mapped area is located at 10 to 15 metres from the rear end of the tunnel. Geologists determine, among other characteristics, the main rock type in the area, and collect versatile information on the fracturing and quality of the rock.

The systematic mapping follows the excavation work from a distance of some 100 to 200 metres. The most significant difference between the first and second mapping phase is the precision and the amount of detail involved. Almost all geological phenomena that there are to be observed and measured are then determined on the basis of the fractures and the surrounding rock.