ABSTRACT
APSE was located at the 450 m depth. The experimental layout consisted of a 7.5 m high, 5 m wide tunnel with arched roof and floor, two 1.75-m-diameter (6.5 and 6.3 m deep respectively) boreholes separated by a 1-m-thick pillar of Äspö diorite. Because of the relatively low stress magnitudes of the insitu stresses, compared with the intact rock strength, specially designed excavation-induced and thermallyinduced stresses were introduced to ensure stress magnitudes sufficient to induce spalling of the rock mass. This meant that the experiment was able to track both the elastic and non-elastic rock mass response as
the excavation-induced and thermally induced stress magnitudes were gradually increased.
