Effects of randomness and spatially dependent relaxation on sandpile models

We investigate two types of randomness in the relaxation of sandpile models when the slope at some point becomes over critical. In one type of randomness, the number of particles nf, falling to its nearest neighbors in the resulting relaxation, is not constant but random, even though an equal number fall in each direction. We find that this kind of randomness does not change the universality class of the models. Another type of randomness is introduced by having all nf particles to fall in one single direction, but with the direction chosen randomly. We find that this type of randomness has a strong effect on the universality of the models.