We study asymptotic limit of random pure dimer coverings on rail yardgraphs when the mesh sizes of the graphs go to 0. Each pure dimer covering correspondsto a sequence of interlacing partitions starting with an empty partition and ending inan empty partition. Under the assumption that the probability of each dimer covering isproportional to the product of weights of present edges, we obtain the limit shape (Law ofLarge Numbers) of the rescaled height function and the convergence of unrescaled heightfluctuation to a diffeomorphic image of Gaussian Free Field (Central Limit Theorem); an-swering a question in [6]. Applications include the limit shape and height fluctuations forpure steep tilings ([8]) and pyramid partitions ([20, 35, 36, 37]). The technique to obtainthese results is to analyze a class of Mcdonald processes which involve dual partitions as well.