Main achievements and outstanding issues
The computer model and code calibration against the measured properties and failure mechanisms of the Äspö Diorite during Stage 1 was completed successfully by most of the teams. The final modeling results of Stage 2 matched measured data well but there was a general over estimation of the rock temperatures in the results. For Stage 3, the estimation of spalling strength by back calculations shown a close agreement with teh measured data, with a small standard deviation of 7 MPa, compared with the spalling strength of 120 MPa of the pillar, based on elastic models. These results are comparable with earlier findings on the spalling strength of granitic rock masses.
Modelling mechanical behaviour of crystalline rocks is a difficult challenge, as shown by the past experience of the earlier Decovalex project phases, when the rocks contain fractures of varying sizes, shapes, water-bearing status, mineral filling status, and displacement/damage histories. The main difficulty, and the outstanding issue, lies with the challenge of characterization of the rock volumes that are required to be modelled, since the details of the fracture system geometry and their mechanical behaviour cannot be known before, or even after the tests. This challenge is understood as a general feature of fractured crystalline rocks in the international rock mechanics community, not a special issue limited only to Task B.