Rock-Mechanical Studies

The purpose of the rock-mechanical studies is to determine the conditions prevailing inside the rock, such as the direction and intensity of the stress field as well as the strength of the rock. In order to determine these mechanical characteristics of the rock, various types of measurements are performed before the excavation proceeds to the zone in question. The methods can be used both in drillholes and on the excavated surface.

During and after the excavation, the mechanical characteristics of the rock can still be measured. For instance, after raise boring, the shaft profiles experience a minor transformation from round to slightly oval (this cannot be visually detected). The measurement result can then be used to determine the direction and intensity of the stress field prevailing in the area.

Rock mechanical studies are associated with the inspection of an excavation damage zone (EDZ). The development of the excavation damage zone is affected by several factors such as the force of the excavation, the geological characteristics of the rock and the rock-mechanical conditions. The excavation damage zone can be studied with various methods. Of these, boring and sawing off rock sections, as well as geophysical measurements, have been used in ONKALO.