Interfacial behavior of soil-embedded fiber optic cables with micro-anchors for distributed strain sensing.

Accurate deformation monitoring of geotechnical infrastructures using distributed fiber optic sensing requires a strong interfacial bond between strain sensing cables and surrounding soil. Micro-anchors provide a straightforward solution to enhance the interlocking effect at the cable–soil interface, but their anchorage mechanism remains unclear. This paper presents an experimental study on the interfacial behavior of anchored strain sensing cables embedded in soil. A series of pullout tests were conducted to investigate the effect of various factors on interfacial performance, including anchor spacing, anchor diameter, and confining pressure. The test results indicate that the anchor spacing and confining pressure substantially influenced the pullout resistance of anchored cables, while the anchor diameter had a minor effect. In contrast with unanchored cables, anchored cables exhibited strain hardening behavior during the pullout process instead of strain softening. The micro-anchors on cables played a reinforcing role sequentially with increasing pullout displacements, and those closer to the cable head exerted reinforcing effect earlier. Due to the pullout resistance of micro-anchors, the anchored cables have unique step-like strain profiles throughout the pullout tests, and they are not prone to interface decoupling under large deformation conditions. However, for closely spaced micro-anchors, the overlapping of interfacial shear zones led to a loss in the pullout resistance, which becomes insignificant with increasing anchor spacing. This study not only provides improved insight into the interpretation of fiber optic strain measurements but also sheds light on soil–inclusion interaction mechanisms in geotechnical analyses. [ABSTRACT FROM AUTHOR]