Although it has been studied for more than 30 years, the large clayey Avignonet landslide (western French Alps) exhibits a heterogeneous kinematic pattern which is still poorly understood. Conducting electrical resistivity tomography profiles over the whole landslide has allowed the presence of a superficial coarser layer to be detected in its upper north-western part. The extension of this more permeable layer matches the zone exhibiting low slide velocities values (lower than 2 cm/yr),suggesting a lithological and hydrogeological control on the landslide activity. The presence of this coarser layer was not detected before, because investigation efforts concentrated on the southern inhabited areas where displacement rates are the highest (10 cm/yr to 50 cm/yr) and the slope is only composed of laminated clays. Combined interpretation of seismic reflected waves and geological data has also evidenced the presence of a 10m thick sandy alluvial layer interbedded in the clayey sequence. Comparison between reflectors and slip surfaces detected in boreholes suggests a significant role of this coarse layer on the location of the deepest slip surface at about 40m. This study highlights the control of both vertical and horizontal lithological variations on the Avignonet landslide process and the necessity of combining various investigation techniques for understanding the complexity of large landslide mechanism.