Abstract
In-depth knowledge of the in situ stress state at the Olkiluoto site is critical for stability assessment both prior to and after deposition of spent nuclear fuel in order to understand and avoid potential damage to the rock at the site. Posiva's Olkiluoto Spalling Experiment (POSE) was designed specifically for this purpose with three primary goals: establish the in situ spalling/damage strength of Olkiluoto migmatitic gneiss, establish the state of in situ stress at the -345 m depth level and act as a Prediction-Outcome (P-O) exercise. Phases 1 and 2 of POSE are outlined in WR 2012-60. The objectives of the third phase of the POSE experiment are the same as the original objectives outlined above. This report outlines the execution and results of the third phase of the POSE experiment. The third phase of the experiment involved internally heating the third experimental hole (ONK-EH3) of the POSE niche in order to cause a symmetrical thermal stress increase around the hole due to the thermal expansion of rock. This thermomechanically induced stress increase, coupled with the estimated existing in situ stress state, should cause the maximum principal stress around the hole to exceed the predicted spalling strength of the rock
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Valli, J.;
[1]
Hakala, M.;
[2]
Wanne, T.;
[3]
Kantia, P.;
[4]
Siren, T.
- Poeyry Finland Oy, Vantaa (Finland)
- KMS-Hakala Oy, Nokia (Finland)
- Saanio and Riekkola Oy, Helsinki (Finland)
- Geofcon Oy, Rovaniemi (Finland)
Citation Formats
Valli, J., Hakala, M., Wanne, T., Kantia, P., and Siren, T.
ONKALO POSE experiment. Phase 3: execution and monitoring.
Finland: N. p.,
2014.
Web.
Valli, J., Hakala, M., Wanne, T., Kantia, P., & Siren, T.
ONKALO POSE experiment. Phase 3: execution and monitoring.
Finland.
Valli, J., Hakala, M., Wanne, T., Kantia, P., and Siren, T.
2014.
"ONKALO POSE experiment. Phase 3: execution and monitoring."
Finland.
@misc{etde_22286181,
title = {ONKALO POSE experiment. Phase 3: execution and monitoring}
author = {Valli, J., Hakala, M., Wanne, T., Kantia, P., and Siren, T.}
abstractNote = {In-depth knowledge of the in situ stress state at the Olkiluoto site is critical for stability assessment both prior to and after deposition of spent nuclear fuel in order to understand and avoid potential damage to the rock at the site. Posiva's Olkiluoto Spalling Experiment (POSE) was designed specifically for this purpose with three primary goals: establish the in situ spalling/damage strength of Olkiluoto migmatitic gneiss, establish the state of in situ stress at the -345 m depth level and act as a Prediction-Outcome (P-O) exercise. Phases 1 and 2 of POSE are outlined in WR 2012-60. The objectives of the third phase of the POSE experiment are the same as the original objectives outlined above. This report outlines the execution and results of the third phase of the POSE experiment. The third phase of the experiment involved internally heating the third experimental hole (ONK-EH3) of the POSE niche in order to cause a symmetrical thermal stress increase around the hole due to the thermal expansion of rock. This thermomechanically induced stress increase, coupled with the estimated existing in situ stress state, should cause the maximum principal stress around the hole to exceed the predicted spalling strength of the rock around the hole. ONK-EH3 is located almost completely in pegmatitic granite. Four fractures near the top of the hole were mapped after boring ONK-EH3, and a tensile failure located at the contact between mica-rich gneiss and pegmatitic granite was observed 18 months after boring, prior to the experiment. Based on predictive calculations and the estimated in situ state of stress, the maximum principal stress magnitude should reach ca. 100 MPa when the temperature was just below 100 deg C after 12 weeks of heating. There were problems with the heater control unit at the beginning of the experiment, after which heating proceeded according to plan. The crack damage threshold of pegmatitic granite has been determined to be 85 ±17 MPa at Olkiluoto and the current maximum principal stress magnitude at the end of the experiment was estimated to exceed it. Upon emptying the hole, no clear damage was evident. No spalling had occurred. Strain gauge adhesions had failed and their results were disqualified. Acoustic emission and ultrasonic monitoring results pointed to events located in the immediate vicinity of a band of foliated gneiss, distributed in a N-S trend, although this could not be corroborated visually. Water loss measurements conducted in the hole indicated that the extent of damage was constrained to the first 100 - 200 mm of the hole wall. Based on these results, POSE Phase 3 was determined as inconclusive, although the heterogeneous and anisotropic nature of the Olkiluoto rock indicated that spalling type damage may not be a factor at Olkiluoto: failure in Olkiluoto conditions may be governed more by the relationship of the in situ stress state, the local geology and weakest component than by in situ stress, excavation geometry and mean strength. (orig.)}
place = {Finland}
year = {2014}
month = {Jan}
}
title = {ONKALO POSE experiment. Phase 3: execution and monitoring}
author = {Valli, J., Hakala, M., Wanne, T., Kantia, P., and Siren, T.}
abstractNote = {In-depth knowledge of the in situ stress state at the Olkiluoto site is critical for stability assessment both prior to and after deposition of spent nuclear fuel in order to understand and avoid potential damage to the rock at the site. Posiva's Olkiluoto Spalling Experiment (POSE) was designed specifically for this purpose with three primary goals: establish the in situ spalling/damage strength of Olkiluoto migmatitic gneiss, establish the state of in situ stress at the -345 m depth level and act as a Prediction-Outcome (P-O) exercise. Phases 1 and 2 of POSE are outlined in WR 2012-60. The objectives of the third phase of the POSE experiment are the same as the original objectives outlined above. This report outlines the execution and results of the third phase of the POSE experiment. The third phase of the experiment involved internally heating the third experimental hole (ONK-EH3) of the POSE niche in order to cause a symmetrical thermal stress increase around the hole due to the thermal expansion of rock. This thermomechanically induced stress increase, coupled with the estimated existing in situ stress state, should cause the maximum principal stress around the hole to exceed the predicted spalling strength of the rock around the hole. ONK-EH3 is located almost completely in pegmatitic granite. Four fractures near the top of the hole were mapped after boring ONK-EH3, and a tensile failure located at the contact between mica-rich gneiss and pegmatitic granite was observed 18 months after boring, prior to the experiment. Based on predictive calculations and the estimated in situ state of stress, the maximum principal stress magnitude should reach ca. 100 MPa when the temperature was just below 100 deg C after 12 weeks of heating. There were problems with the heater control unit at the beginning of the experiment, after which heating proceeded according to plan. The crack damage threshold of pegmatitic granite has been determined to be 85 ±17 MPa at Olkiluoto and the current maximum principal stress magnitude at the end of the experiment was estimated to exceed it. Upon emptying the hole, no clear damage was evident. No spalling had occurred. Strain gauge adhesions had failed and their results were disqualified. Acoustic emission and ultrasonic monitoring results pointed to events located in the immediate vicinity of a band of foliated gneiss, distributed in a N-S trend, although this could not be corroborated visually. Water loss measurements conducted in the hole indicated that the extent of damage was constrained to the first 100 - 200 mm of the hole wall. Based on these results, POSE Phase 3 was determined as inconclusive, although the heterogeneous and anisotropic nature of the Olkiluoto rock indicated that spalling type damage may not be a factor at Olkiluoto: failure in Olkiluoto conditions may be governed more by the relationship of the in situ stress state, the local geology and weakest component than by in situ stress, excavation geometry and mean strength. (orig.)}
place = {Finland}
year = {2014}
month = {Jan}
}