Measuring the Full-Field Strain Response of Uniaxial Compression Test Specimens Using Distributed Fiber Optic Sensing

The uniaxial compressive strength (UCS) test is crucial in determining the strength and stiffness behavior of intact rock and is frequently utilized by industry to determine project site characteristics. A fundamental procedure of UCS testing is strain response measurement. 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 full-field strain of UCS test specimens. This has led to a gap in knowledge in terms of the complexities of UCS test strain responses caused by factors such as specimen heterogeneity and the influence of platen friction. Within this context, a novel distributed optical strain sensing (DOS) technology has been integrated with UCS testing (DOS-UCS technique). Unlike conventional discrete strain measurement methods, the optical technique captures a distributed strain profile along the length of standard, low-cost single mode optical fiber with a spatial sampling resolution of 0.65 mm. By wrapping an optical strain sensor around a UCS specimen, continuous full-field strain profiles along the length and circumference of UCS specimens can be realized. This paper presents a laboratory investigation that illustrates the potential of this technology to provide an in-depth look into the strain response of heterogeneous nodular limestone during UCS testing.