Investigation of the coarse alluvial foundation for the Pichi Picun Leufu embankment dam is described and evaluated. Direct and indirect investigation methods are compared and an assessment is made of their relative adequacy in order to gain a realistic understanding of foundation conditions. Indirect methods—dynamic cone penetration testing and shear wave velocity measurement—calibrated by comparative testing in a test embankment, have been found to provide a satisfactory means of evaluating the density of thick alluvial deposits below the water table. Relationships of relative density, penetration resistance, and shear wave velocity are discussed. Dynamic penetration resistance normalized for effective overburden pressure appears to be the more sensitive indicator of changes in material density. Key words: coarse alluvium, relative density, dynamic penetration, shear wave velocity, test embankment, overburden pressure.