In-situ experiment concerning thermally induced spalling of circular shotcreted shafts in deep crystalline rock

A thermally induced shotcrete spalling in-situ experiment will be carried out during 2013 in the ONKALO rock characterization facility on the west coast of Finland. In the technical areas of the planned spent nuclear fuel repository there will be shotcreted rock spaces which will be subjected to thermally induced deformations and stresses. In this heating experiment, we are attempting to establish the failure strength of shotcrete on a pre-stressed rock surface, when the stress state in both the rock and shotcrete are increased by heating. The in-situ strength can be used to evaluate the safety of the shotcreted structures. The interaction between the shotcrete and the rock mass will be observed as the rock approaches its strength limit. Posiva’s Olkiluoto Spalling Experiment niche is ideal for such an experiment due to the amount of supplementary data from preceding experiments. The area is already built, instrumented and contains running experiments. The test arrangement is described and a prediction of the expected results is provided. Similar research has been carried out using fire-induced thermal actions, but this is the first test to use heaters in the surrounding rock mass in the sub-boiling thermal range.