In view of the electrical difference between the riprap layer and the argillaceous clay layer, the authors used

synthetic methods of ground penetrating radar and highdensity resistivity to detect the riprap layer in an inning dam. The

result shows that the limits and thickness of the riprap detected by the synthetic methods are quite coincident with those

detected by the drilling. This indicates that synthetic use of ground penetrating radar and high density resistivity method is

very effective in riprap layer detection.