Enhancing strain transfer efficiency of fibre optic sensors for geo-structural health monitoring through 3D-printed packaging

Effective monitoring of geo-structures is essential to ensure their long-term stability and safety. Fibre optic sensing technology has emerged as a promising solution, offering precise and real-time data on structural performance. However, despite increasing use in geotechnical engineering, a key challenge remains the optimisation of sensor packaging, particularly in minimising strain transfer loss from the surrounding soil to the sensor core. The three-dimensional (3D) printing has recently gained significant attention as a promising method for manufacturing components. This study presents the first investigation into the optimisation of fibre-optic strain sensor packaging for geotechnical applications. The aim is to minimise strain loss between the soil (host medium) and the sensing core while improving soil–sensor interface performance. The research includes the design and mechanical characterisation of different 3D-printed materials and geometries for sensor packaging, alongside direct shear testing to assess the interaction behaviour between the soil and the packaging. The influence of material type, printing method, mechanical properties, infill configuration, and surface texture on strain transfer and interface behaviour is examined. A bare fibre is subsequently embedded within an optimised 3D-printed housing, and the performance of the strain sensor with the new packaging is evaluated. Results show that soil particle size, the Young’s modulus of the packaging material, and surface characteristics play critical roles in strain transfer efficiency. The findings provide new insight into the design of effective 3D-printed housings for fibre-optic sensing systems and establish a practical framework for improving strain sensitivity, reliability, and long-term performance in geo-structural health monitoring applications.