A reliable lithological characterization of earthen dikes constitutes an important asset by virtue of enhancing a good diagnosis, which is of immense value in preventing dike breakage. Ruptures of hydraulic works can lead to disastrous consequences (loss of life, severe environmental and economic impacts). Recognized methodologies for characterizing earthen dikes include complementary geophysical and geotechnical investigation methods. This article explores a fusion methodology to combine data from these two types of information sources in considering actual datasets from a canal dike investigation campaign. This campaign involves electrical resistivity tomography as well as a multi-channel analysis of surface waves and a particle size analysis derived from laboratory testing. Our fusion methodology is based on the use of belief masses to enhance the characterization of lithological sets within earthen structures. While taking into consideration the particularities of each method (spatial distribution, data imperfection), this approach provides information on the conflict level between information sources and moreover displays a confidence index associated with the results. This work contributes several improvements to the fusion methodology (including the fusion of two distinct geophysical datasets and the implementation of K-means clustering algorithms) in addition to new application possibilities (larger area of investigation, more complex structure and lithological variability). It also offers fusion results and dike characterization whether considering zero, four or seven boreholes. Fusion results highlight the ability of this enhanced methodology to identify the position of lithological sets (fine and coarse fill materials with limestone breccia, marls and limestones) as well as specify the interface positions and associated levels of confidence, ensuring consistency with available knowledge on the geological setting and presence of a fault. These results also display good consistency between the geoelectrical and seismic characterizations for this specific investigation site despite the inability to characterize each material individually.