Growth in production rate in large-scale metallic mines has resulted in an increasing demand for larger tailings disposal capacity. In the case of mines located in mountainous regions these larger tailings deposit frequently require the construction of high dams. Tailings deposits operating in Chile three decades ago required dams of about 150m maximum height. In the last decade dams more than 200m high have been designed and built [1][2] and even higher dams are now being considered in South America. Most of the tailings dams that started operation in the last decades are downstream or center line tailings sand dams with sand been deposited as hydraulic fill, with a limited maximum percentage of fines in the sand to guarantee an adequate permeability. Usually, hydraulic deposition of soils and specially of tailing sands leads to a variation of the particle size distribution along the downstream slope of the dam, the coarser particles being deposited at shorter distances. This hydraulic segregation depends mainly on the flow volume of the sand pulp been deposited, on the solids concentration of the pulp, and on length and slope of the dam [3][4]. In general, particle size segregation in tailings sand dams has not been analyzed in enough detail, since it did not have a great impact for the most common range of dam heights. Nevertheless, the impact of this segregation could become important in higher dams since an increase in the percentage of fines in the sand could cause a reduction in its permeability, shear strength, and cyclic resistance, which in turn could affect the stability of the dam.