Numerical investigation on interfacial behavior of soil-embedded fiber optic cables for distributed strain sensing

The application of distributed fiber optic sensing (DFOS) technology to geotechnical and geological stability monitoring faces a key challenge: ensuring deformation coordination between embedded fiber optic (FO) cables and the surrounding soil matrix, which is critical for evaluating implementational feasibility and sensing accuracy. This study investigates the interfacial behavior of soil-embedded FO cables for distributed strain sensing using a series of numerical simulations on laboratory pullout tests. A three-dimensional (3D) finite element (FE) model was constructed to analyze the progressive failure mechanisms at the cable-soil interface. The pullout force-displacement relationships, shear stress evolution, and strain distribution were explored to gain insights into the interfacial behavior under various test conditions. The results demonstrate that increasing overburden pressure significantly enhances interface shear strength and extends the effective displacement range, thereby improving the cable-soil deformation compatibility. Stiffer soils were found to narrow shear band development, promoting coupling, while shear dilatancy had a minor effect on the peak and post-peak behavior of the interface. Parametric studies reveal that thicker cables improve the sensing range due to higher residual pullout forces, whereas cable stiffness primarily influences the strain transmission efficiency rather than interface shear properties. Notably, numerical simulations visualize the transition from elastic to residual interface states and associated soil plastic zones, overcoming testing limitations. Findings provide guidance for the design of strain-sensing cables by clarifying interfacial mechanics and coupling efficiency under diverse geotechnical conditions.