Application of Spread-Spectrum Induced Polarization for Seepage Pathway Identification and Risk Assessment in an Earth Dam: A Case Study of the Youyi Reservoir, Hunan, China

Leakage in earthen dams is characterized by high concealment and complex structures, making it challenging to identify. In particular, the seepage pathways of the dam foundation are often governed by the coupled effects of geotechnical structures and long-term hydraulic erosion, rendering their spatial connectivity difficult to locate precisely. Existing detection technologies generally suffer from insufficient spatial resolution, low coverage efficiency, or poor environmental adaptability, which hinders the detailed characterization of leakage pathways under complex engineering conditions. To address this issue, this paper focuses on the earth dam of Youyi Reservoir as the research subject, introducing spread spectrum induced polarization (SSIP) for high-resolution leakage pathway detection. This method utilizes pseudo-random signals as excitation field sources, offering both non-invasiveness and strong interference resistance. Based on data despreading and frequency fusion processing, combined with low-frequency approximate finite element forward modeling theory, a stepwise inversion imaging strategy for resistivity and polarizability is implemented to suppress parameter coupling and enhance inversion stability. The results reveal a continuously distributed low-resistivity and low-polarizability anomaly zone at the dam body-foundation contact zone, which is highly consistent with known seepage points and subsidence areas, indicating it as the primary seepage pathway. Localized high-resistivity and high-polarizability patches observed in the shallow subsurface primarily indicate material heterogeneity with weaker seepage connectivity. This study validates the effectiveness of SSIP in precisely identifying seepage pathways and conducting risk zoning for earth dams, providing reliable geophysical technical support for the safety assessment and seepage control of hazardous dams.