Study of rock deformation by a non-intrusive imaging technique

• Main Author: Surya, Henry
• Other Authors: School of Civil and Environmental Engineering
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Civil engineering::Geotechnical
• Online Access: http://hdl.handle.net/10356/61265
• Institution: Nanyang Technological University

Strain and deformation measurements are common properties measured using traditional equipment, such as extensometer. But, it has limited measuring range. Because of that, the idea of using digital image correlation has been raised. However, the accuracy of this method for practical application is not well researched. This project aims to study this method thoroughly with StrainMaster software to calculate strain and deformation. Specimens were molded into cylindrical and rectangular shape. They are made from molded Hydrocal B-11 gypsum. The prepared specimens were then painted with white color. Both shape of the specimens were then treated with different speckle patterns and different measurements. All of the specimens were tested with unconfined compression test. The measurement results on cylindrical specimens with a constant step size showed that the larger subset sizes were better at measuring circumferential strains than the smaller subset sizes were. But, the accuracy of larger subset sizes might be affected by the average deformations calculated inside their subsets. On the measurements using a constant subset size, the largest two step sizes were more accurate in measuring specimens with a lot of deformation activities. On the other hand, the smallest two step sizes were more accurate in measuring specimens with little deformation activities. It was also found out that if the specimen has constant deformation rate, measurements with different step sizes produced little differences. Finally, there was no link found on the effect of density of the speckles on the accuracy of the test. The test results on rectangular specimens showed that speckle characteristics do show effect on the consistency of the results obtained using different subsets and calculation modes. Using fast mode, the effect was more pronounced on anisotropic specimens than it did on isotropic specimens. The test also found out that different mode can produced different results on the same specimens with different contrasts. This project showed that digital image correlation technique should be used with prior knowledge of deformation trend and brittleness of a specimen. The choice of calculation mode depends on the tradeoff between time and accuracy. Finally, isotropic and non-repetitive speckle pattern is a better choice than anisotropic patterns.