Compressive Strength and Griffith Criterion

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The University of Hong Kong Department of Civil Engineering CIVL2002 M – Geology & Rock Laboratory Report Brazilian Test A. Introduction As shown by the Griffith criterion, tensile strength of brittle materials is theoretical 1/8 of the compressive strength. Typically, tensile strength of rock materials is about 1/10 to 1/8 of the compressive strength. Hence, rock fails easily under tension. In design, rock should be subjected to minimum tensile stress. Several methods are commonly used to test the tensile strength of rocks: 1. Direct tensile test: Metal caps are cemented to the end-surfaces of the samples so that tensile load can be applied to the samples until failure. 2. Brazilian test: Compressive…show more content…
2. The test specimens were wrapped around its periphery with one layer of the masking tape. 3. The diameter and thickness of were measured 3 times, once at every 120 for each specimen. 4. The test specimens were numbered (1-8), and a line across the diameter was marked on each specimen. 5. The test specimen (no. 1) was mounted into the loading jaws such that the curved platens load the specimen diametrically with the axes of rotation for specimen and apparatus coincident. The assembly was then mounted into the loading machine. 6. The test specimen was loaded continuously at a constant rate such that failure in the weakest rocks occurs within 15-30s. A loading rate of 200N/s was recommended. 7. The failure compressive load was recorded for each specimen, and the corresponding tensile strength was calculated. 8. Steps 5-7 were repeated for the remaining 7 specimens. F. Results and Calculation Lithologic Description of Rock Figure 6: Features of Rock Specimen 8 rock specimens have

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