Journal
ROCK MECHANICS AND ROCK ENGINEERING
Volume 49, Issue 4, Pages 1479-1495Publisher
SPRINGER WIEN
DOI: 10.1007/s00603-015-0843-6
Keywords
Confining stress; TBM cutter; Biaxial state; Breaking groove morphology; Indentation efficiency
Funding
- National Basic Research Program of China [2013CB035401]
- National Natural Science Foundation of China [51174228]
- Hunan Provincial Innovation Foundation for Postgraduates [71380100003]
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The influence of confining stress on rock breakage by a tunnel boring machine cutter was investigated by conducting sequential indentation tests in a biaxial state. Combined with morphology measurements of breaking grooves and an analysis of surface and internal crack propagation between nicks, the effects of maximum confining stress and minimum stress on indentation efficiency, crack propagation and chip formation were investigated. Indentation tests and morphology measurements show that increasing a maximum confining stress will result in increased consumed energy in indentations, enlarged groove volumes and promoted indentation efficiency when the corresponding minimum confining stress is fixed. The energy consumed in indentations will increase with increase in minimum confining stress, however, because of the decreased groove volumes as the minimum confining stress increases, the efficiency will decrease. Observations of surface crack propagation show that more intensive fractures will be induced as the maximum confining stress increases, whereas the opposite occurs for an increase of minimum confining stress. An observation of the middle section, cracks and chips shows that as the maximum confining stress increases, chips tend to form in deeper parts when the minimum confining stress is fixed, whereas they tend to formed in shallower parts as the minimum confining stress increases when the maximum confining stress is fixed.
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