Application of distributed optical fiber sensing in detecting potential slip surfaces of high slopes: a case study

High slopes associated with large hydraulic infrastructures are prone to progressive deformation and instability, posing significant risks to engineering safety. This study presents a field application of distributed optical fiber sensing (DOFS) at a high rock slope of a hydropower project located in Northwest China, where ongoing deformation of a joint intake slope has been observed since 2022. A multi-orientation monitoring system comprising six boreholes (vertical, inclined, and horizontal) instrumented with distributed strain-sensing fibers was deployed to capture internal deformation. The monitoring results reveal time-dependent and depth-localised displacement patterns, with horizontal displacement magnitudes of approximately 1.5–2.0 mm within 2 months and multiple potential slip surfaces identified within a depth range of 20–50 m. The deformation localisation is consistently captured across different borehole orientations, demonstrating the capability of the DOFS system to detect small-scale deformation relative to its spatial resolution (0.255 m). These observations indicate the presence of complex multi-level deformation mechanisms within the slope. The inferred slip surface locations were further validated against independent engineering evidence, including borehole core observations, anchor drilling records, and adit crack mapping, showing strong agreement with zones of fractured and weakened rock mass. The results demonstrate that DOFS provides continuous, high-resolution, and reliable monitoring of internal slope deformation, enabling both slip surface identification and quantitative deformation assessment. This study highlights the significant potential of DOFS for early warning, hazard mitigation, and the design of reinforcement measures in large-scale slope engineering.