Quantitative Evaluation of Optical Fiber/Soil Interfacial Behavior and Its Implications for Sensing Fiber Selection

Abstract

An adequate understanding of the interface between optical fibers and geomaterials is a prerequisite for applying distributed optical fiber sensor systems to strain monitoring in geoengineering. This contribution reports a quantitative investigation of the fiber/soil interfacial behavior regarding the influence of fiber types and normal pressures. A simplified model describing the progressive failure of a fiber/soil interface was briefly illustrated. Results of a series of pullout tests on three different soil-embedded optical fibers under various normal pressures were interpreted by this model, through which the fiber/soil interfacial behaviors were quantified. The results showed that the mechanical properties of the three fiber/soil interfaces were similar. Optical microscopic images indicated that the soil particles and the fibers were merely loosely contacted. This led to the formation of a fiber/soil interface susceptible to the normal pressure: 1) the interfacial bond was tightened and 2) the deformation measurement range was widened under high normal pressures. Moreover, the criterion for selecting a strain sensing fiber for geoengineering applications was discussed in terms of interfacial bond, deformation measurement range, ratio of peak to residual interfacial shear strength, Young's modulus of fiber, and so forth. An assessment of the three fibers reveals that, for ground deformation measurement, each fiber has its own advantages as well as limitations. In field or laboratory applications, a combination of different types of fibers may obtain the best measurement results.

A field study on distributed fiber optic deformation monitoring of overlying strata during coal mining

“…8, 9, and 10, while the working face passed through the monitoring borehole, the compressive strain of the sensing fiber increased gradually at the drilling depth of 450-580 m. It indicates that the advanced support pressure of the overlying strata increased gradually as well. The strains of the three sensing cables were relatively large at the depth of 490 m, indicating that the strata behaviors induced by mining distributed between the fault zone and the depth of 490 m. Figures 7,8,9,and 10 show that, during the period from July 10 to August 30, the rock strata beneath the bottom of the lower igneous rock layer were compressed by periodic weighting of the overlying rock, and the deformation increased gradually during the mining process. Because the sensing cables have been broken, the strata deformation below the damage points could not be measured anymore.…”

“…In the recent years, optical fiber sensing technologies have developed rapidly and are being recognized as a promising monitoring method [7][8][9][10]. The Brillouin optical time-domain reflectometer (BOTDR)-based optical fiber strain sensor has emerged with a variety of advantages, such as distributed and long-distance measurement, corrosion resistance, and anti-electromagnetic interference.…”

Introduction to an FBG-based inclinometer and its application to landslide monitoring

“…Recently, the fiber optic sensing technologies have been advocated for slope monitoring by some scholars [1][2][3][4][5][6][7][8]. Different types of FBG-based in-place inclinometers have been developed, which demonstrated various features, such as small size, superior chemical resistance and stability, immune to electro-magnetic interference, and quasi-distributed monitoring capability [9][10][11][12][13]. This technology is especially suitable for automatic and long-distance monitoring in landslides.…”

Role of the interface between distributed fibre optic strain sensor and soil in ground deformation measurement

“…The interaction between optical fibre and soil has therefore attracted considerable interest111927282930. Recently an integrated DFOSS- and photogrammetry-based performance evaluation of a small-scale model of sand foundation under surcharge loads has brought our attention to this issue (Supplementary Fig.…”

“…suggested that pull-out tests can be an effective method to understand the interaction between optical fibre and soil. Subsequent research performed by our group has shown that the overburden pressure (OP) can effectively tighten the fibre–soil interfacial bond, thereby extending the measurement range of the optical fibre272829. However, this phenomenon was discovered in pull-out tests on small soil samples and the strain distribution along the optical fibre was not obtained during the failure process of fibre–soil interface.…”