Strength of rocks
Qualitatively, strength can be defined as the resistance to permanent deformation by flow or fracture. In a more precise, quantitative sense, strength is the stress level that is required to produce a certain type of permanent deformation, fracture or flow, under well-defined experimental conditions. When used in its more precise sense, the term strength is usually qualified. Thus, the ultimate strength is the greatest stress difference that a test sample can support under given conditions of effective pressure, temperature, and strain rate (Handin, 1966; cf. Rock Deformation, Experimental; Rheology of Rocks). Breaking strength or fracture strength , is the stress difference at fracture, and crushing strength is the uniaxial compressive stress required to break the sample under atmospheric conditions (Handin, 1966). Under the present definition, the yield stressis also a strength although it is not normally called that; it is the differential stress necessary to produce permanent...
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