Interfacial Behavior of Soil-Embedded Fiber Optic Cables for Desiccation Crack Monitoring

Desiccation cracking in surface soil presents significant risks to earthen structures by compromising their stability and integrity. Despite advances in distributed fiber optic sensing (DFOS) technology within the geotechnical field, a critical gap remains in improving the coupling between drying soil and fiber optic (FO) cables, which are essential for accurate monitoring and predicting crack development. To address this knowledge gap, we conducted systematic soil evaporation experiments across multiple soil types utilizing optical frequency domain reflectometry (OFDR) technology coupled with surface-treated FO cables. Experimental results demonstrated that OFDR systems integrated with sand-treated FO cables exhibit superior sensitivity in detecting and measuring strain distributions associated with desiccation crack formation, enhancing applicability to monitoring complex crack networks. The enhanced strain transfer efficiency achieved through surface treatment enables high-precision monitoring of both crack initiation and propagation processes. To validate the superior characteristics of sand-treated FO cables in monitoring, we designed a pullout test and microscopic observation experiments. The results indicated that FO cables with roughened surfaces, particularly those treated with sand particles, exhibited an average 195% increase in peak pullout force and over 300% enhancement in surface roughness compared with untreated FO cables. This surface treatment significantly improved FO cable–soil coupling, reducing slippage and enhancing strain sensitivity. These enhancements enable the precise detection of microdeformations within the soil, greatly increasing the accuracy of crack monitoring. Overall, the study presents an innovative approach for improving FO cable–soil interaction and provides a more reliable method for monitoring soil desiccation cracks. This study not only provides new insights into the monitoring mechanisms of soil desiccation cracking by DFOS technology, but also offers novel technical support for assessing the stability of cracked earthen infrastructure under drought conditions.