Mechanical Stresses Affecting Deep Borehole Disposal of High Level Nuclear Waste
Bibliographic record
Abstract
While extensive stress field data are available from crystalline rock boreholes drilled in France (Soultz), Germany (KTB), and the USA (Cajon Pass, Monticello Reservoir), Canada and Sweden, the data and methods used to analyze them have yet to be applied to very deep geologic disposal facilities. Typically, to alleviate the stress fields that are intensified in a borehole, muds (mixtures of clay and water) are a critical component and are widely used in the drilling industry. In the first portion of this paper, we review the available mechanical data and analysis methods. Based on the most applicable measurements (in Canada and Germany), we propose values of stress fields and rock properties to be used for generic assessment of deep borehole disposal. The minimum horizontal stress can be approximated as Sh=23.2D, the maximum horizontal stress as SH=43.1D, and the vertical stress as SV=27.5D, where the stresses are in MPa and D is depth in km. This analysis also incorporates the effect of thermal stresses (relieved) by the cool drilling mud. Using an average uniaxial compressive strength results (C=212 MPa) and conservatively neglecting the increase in strength of crystalline rock under polyaxial conditions, a stable borehole can be drilled to 4.55 km with mud density of 1020 kg/m3. This is based on a stability limit such that at the bottom of the hole, a significant portion of the wall (180°/360°) reaches a critical state of stress (i.e., experiences spalling). Using relations developed for shallow mines (which may be overly conservative) the spalled zone is estimated to have a radius that is approximately twice that of the borehole. To reach 5 km, the mud density should be raised to 1420 kg/m3, or be actively cooled (90°C) below the ambient temperature of the rock (∼135°C) at that depth.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".