Abstract
A unique set of true-triaxial experiments have been used to mimic the loading path that the in situ rock is
exposed to during excavation, heating, cooling and unloading through the Posiva’s Olkiluoto Spalling Experiment
(POSE), at the proposed deep geological repository at Olkiluoto, Finland. Results from testing of rock specimens
prepared with their foliation planes oriented with respect to σ1, under true-triaxial conditions, show that 0o, 30o
and 60o gneiss samples fail whereas 90o gneiss and isotropic pegmatite specimens do not fail under the same
loading path. The pegmatite specimen shows numerous acoustic emission (AE) activities but does not fail during
the final stages of the stress path. Temporal and spatial analysis of AE events show that fracture initiation and
propagation are sensitive to foliation plane orientation with respect to σ1 and that failure planes coincide with
foliation planes in failed specimens. Variation of seismic wave velocities measured along three orthogonal axes
as a function of the loading path show that compressional and shear wave velocities measured parallel to
foliation planes are higher than perpendicular to such planes characterizing the transversely isotropic nature of
Olkiluoto gneiss. The true-triaxial POSE experimental loading and unloading path is complex and results in
strength and behavioural characteristics that are not replicated with conventional triaxial testing where σ2 = σ3.
exposed to during excavation, heating, cooling and unloading through the Posiva’s Olkiluoto Spalling Experiment
(POSE), at the proposed deep geological repository at Olkiluoto, Finland. Results from testing of rock specimens
prepared with their foliation planes oriented with respect to σ1, under true-triaxial conditions, show that 0o, 30o
and 60o gneiss samples fail whereas 90o gneiss and isotropic pegmatite specimens do not fail under the same
loading path. The pegmatite specimen shows numerous acoustic emission (AE) activities but does not fail during
the final stages of the stress path. Temporal and spatial analysis of AE events show that fracture initiation and
propagation are sensitive to foliation plane orientation with respect to σ1 and that failure planes coincide with
foliation planes in failed specimens. Variation of seismic wave velocities measured along three orthogonal axes
as a function of the loading path show that compressional and shear wave velocities measured parallel to
foliation planes are higher than perpendicular to such planes characterizing the transversely isotropic nature of
Olkiluoto gneiss. The true-triaxial POSE experimental loading and unloading path is complex and results in
strength and behavioural characteristics that are not replicated with conventional triaxial testing where σ2 = σ3.
| Original language | English |
|---|---|
| Title of host publication | 7th International Symposium on In-Situ Rock Stress |
| Subtitle of host publication | Symposium Proceedings |
| Editors | Erik Johansson, Ville Raasakka |
| Place of Publication | Tampere, Finland |
| Publisher | Suomen rakennusinsinöörien liitto RIL |
| ISBN (Electronic) | 978-951-758-606-1 |
| Publication status | Published - 11 May 2016 |
| MoE publication type | A4 Article in a conference publication |
| Event | International Symposium on In-Situ Rock Stress - Tampere Hall, Tampere, Finland Duration: 10 May 2016 → 12 May 2016 Conference number: 7 http://www.ril.fi/en/events/rs2016/home.html |
Publication series
| Name | RIL |
|---|---|
| Publisher | Suomen rakennusinsinöörien liitto RIL |
| ISSN (Electronic) | 0356-9403 |
Conference
| Conference | International Symposium on In-Situ Rock Stress |
|---|---|
| Abbreviated title | RS2016 Symposium |
| Country | Finland |
| City | Tampere |
| Period | 10/05/2016 → 12/05/2016 |
| Internet address |