Development of a Weak But Brittle Analog Sediment Rock for Experimental Study
Bibliographic record
Abstract
ABSTRACT Laboratory-tested results in rock mechanics have played a crucial role in understanding rock behavior and failure mechanisms. This paper outlines the development of an analog rock, similar to sandstone, for an experimental study that yields a low unconfined compressive strength yet exhibits brittle failure characteristics. The F-75 Ottawa sand, Type I/II commercial grade Portland cement, air entrainment admixture, and water constitute the raw mixtures of the developed analog rock. The result is a reproducible homogeneous and isotropic rock. The effect of the air entrainment admixture and freezing-thawing cycle on the analog rock are investigated. This study amplifies the notable macroscopic fracturing after a limited post-yield strain. The unconfined compressive strength has been bounded at around 1.5 MPa, and the material continues to exhibit brittle behavior at a range of confinement. A set of Brazilian indirect tensile tests was used to assess the tensile strength, including the brittle failure analysis governed by the ratio between the unconfined compressive strength and tensile strength. In addition, the material physical properties were obtained, along with the thin-section-based porosity analysis. The synthetic sandstone is developed for a scale-model experimental study of brittle failure in tunnels using a true-triaxial apparatus that include spalling, dog-earing, and rockburst. INTRODUCTION Brittle failure in the underground excavation can be sudden and catastrophic, resulting in large cracks and fractures such as spalling and rockburst. This stress-induced failure is typically encountered in sparsely fractured or massive rocks at deep underground excavations (Martin et al., 1997). Therefore, understanding the nature of undesirable rock mass brittle failure is essential to provide mitigation plans for the associated risks. One approach to enhance the understanding of behavior and failure mechanisms of rocks is through laboratory testing. However, it is challenging to collect natural, homogeneous, and undisturbed rock specimens of varying sizes from the field. Additionally, the natural specimen may introduce alterations to the variables that could differentiate the investigation plan in terms of reproducibility (Johnston & Choi, 1986). Hence, developing a repeatable analog rock mix can be considered with a flexibility range of controlled properties. In this case, the prepared analog rock specimens must have the characteristics of the investigated phenomenon (i.e., brittle behavior).
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".