The aim of this article is to study some asymptotics of a natural model of random ramified coverings on the disk of degree N . We prove that the monodromy field, called also the holonomy field, converges in probability to a non-random continuous field as N goes to infinity. In order to do so, we use the fact that the monodromy field of random uniform labelled simple ramified coverings on the disk of degree N has the same law as the S(N )-Yang-Mills measure associated with the random walk by transpositions on S(N ).This allows us to restrict our study to random walks on S(N ): we prove theorems about asymptotics of random walks on S(N ) in a new framework based on the geometric study of partitions and the Schur-Weyl-Jones's dualities. In particular, given a sequence of conjugacy classes (λN ⊂ S(N )) N∈N , we define a notion of convergence for (λN ) N∈N which implies the convergence in non-commutative distribution and in P-distribution of the λN -random walk to a multiplicative P-Lévy process. This limiting process is shown not to be a free multiplicative Lévy process and we compute its log-cumulant transform. We give also a criterion on (λN ) N∈N in order to know if the limit is random or not.