The Application of Distributed Optical Sensing to Measure the Full-Field Strain Response of Uniaxial Compression Test Specimens
The uniaxial compressive strength (UCS) test is crucial in determining the strength and stiffness behaviour of intact rock and is frequently utilized by industry to determine project site characteristics. A fundamental component of UCS testing is measuring the strain response of test specimens. Conventionally, discrete strain measuring devices such as extensometers and/or electric foil strain gauges are used to measure the strain response at the mid-height of a specimen. However, this ultimately limits the ability to capture the full-field strain of UCS tests which has led to a gap in knowledge related to the complexities of the strain response caused by factors such as specimen heterogeneity and the influence of platen friction effects. This research integrates a novel distributed optical strain sensing (DOS) technology with UCS testing to develop a DOS-UCS technique for measuring the full-field strain response of UCS specimens. Unlike conventional discrete strain measurement methods, the optical technique captures a distributed strain profile along the length of a standard, low-cost single mode optical fiber with a resolution of 0.65 mm. In this regard, the following research has been devoted to developing a technique whereby optical strain sensors are installed on the surface of UCS specimens in order to measure the dynamic full-field strain response during UCS tests. The development of such a technique is a non-trivial undertaking as it has never before been implemented within the geomechanics community. To optimize the DOS-UCS technique a comprehensive laboratory testing program was carried out. The results from the testing program demonstrates the capability of the DOS-UCS technique to capture complex full-field strain profiles of UCS specimens, agreeing well with traditional strain measurement techniques. The results also demonstrate the non-uniformity of strain and deviation from continuum behaviour that takes place in UCS tests, particularly after yielding begins. Overall, it was determined that the DOS-UCS technique can capture the complexities of the strain response during UCS testing at an unprecedented level, overcoming the limitations of conventional strain monitoring.