The Rosetta mission escorted comet 67P/CG from August 2014 to September 2016, allowing to follow the onset of activity during its perihelion passage. The spacecraft was equipped with a high-resolution camera (OSIRIS/NAC) which allowed to monitor the morphological changes occurring around perihelion. One of these changes was the motion of very large boulders (> 50 m) which moved by several tens of meters. In this internship, I modelled the motion of a boulder assuming that it is controlled by the recoil force produced by the outgassing of an icy patch. I showed that very small icy areas (< 10 cm2) are able to explain the observed motion.