Mechanism of roof presplitting in nonpillar coal mining technology and its reasonable parameters in hard roof and longwall top-coal caving face
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Bibliographic record
Abstract
This article presents an integrated approach for theoretical analysis and numerical modeling to investigate the mechanism of roof presplitting and its reasonable parameters in the hard roof and longwall top-coal caving face. The test site is located in the city of Jinzhong, Shanxi Province, China. The theoretical analysis results indicated that when the presplitting angle remains constant, the tensile stress at the unpenetrated surface is approximately exponentially distributed with the presplitting height. When the presplitting height remains constant, the variation curve of tensile stress at the unpenetrated surface with the presplitting angle is parabolic. As the presplitting height increases, the presplitting angle required for the tensile stress at the unpenetrated face to exceed the ultimate tensile strength of limestone first increases and then decreases. The ground response of retained entry obtained with numerical modeling confirmed the theoretical analysis results. Meanwhile, numerical modeling results also showed that presplitting height affects the volume of the collapse gangues and the structure of the overlying strata above the retained entry. The presplitting angle is effective in reducing the frictional resistance between the collapse gangue and roof structure of retained entry. Moreover, based on the ground response of the retained entries, the reasonable parameters of the roof presplitting were determined at 17 m and 15°. The field application showed that reasonable roof presplitting parameters could achieve satisfactory effects at pressure relief and retained entry in the longwall top-coal caving panel. Furthermore, the proposed design principle of the roof presplitting technique can be applied to other projects.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 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 it