The research and development work carried out on internal erosion led to an innovative assessment of Cameroon’s largest dam, the Lom Pangar dam, which was impounded in 2016. The 57 m high dam stores 6 billion m3 of water for hydroelectricity. The Coyne & Bellier1/ISL Ingénierie consortium commissioned INRAE in 2014 to carry out laboratory tests on the dam’s foundation soil in order to provide information on the risk of internal erosion. More than 30 HET (Hole Erosion Test) tests were carried out in Aix-en-Provence on materials taken in Cameroon during the geotechnical reconnaissance campaign in April 2014. Specific procedures were deployed to carry out tests on intact samples, and to incorporate the effects of dam construction (increased density) and reservoir filling (saturation). The results obtained made it possible to quantify the influence of important parameters on erodibility: dry soil density, water content and above all the fraction of fine clay, making it possible to distinguish between silts (weathered gneisses) and lateritic clays. These results were then used to diagnose the risk of internal erosion of the foundation. This would be the first analysis of this level carried out on the foundation soil of a large dam before its construction.