We present the results of an experimental study of granular segregation on a large number of rectangular grain piles built by dropping simultaneously glass beads of two different sizes. During the construction process, we control the height of the injection point, the amplitude and velocity of its displacement and the injection flow rate for each kind of grain. The final spatial distribution of the grains is determined by a quantitative image analysis. A phase diagram of the mixing state as a function of the experimental parameters is presented along with a quantification of the different types of segregation patterns. Contrary to the assertions of other authors, we clearly demonstrate here, that stratification phenomena may be observed even for beads with the same round shape but a different size. We also find that the free fall height of the grains, the ratio between the discharged masses of the different types of grains and the amplitude of the horizontal motion have the greatest influence on segregation. (C) 2012 Elsevier B.V. All rights reserved.