Abstract : This thesis is about the study of nuclear reactions at intermediate energies. A dedicated phenomenological model has been developed and compared with experimental data collected within the INDRA collaboration. The model is detailed in the first part of the work. Largely based on experimental facts, it uses geometrical assumptions by considering both the degrees of freedom of the nucleons and of the nuclei. In a second part, the assumptions of the model are tested and validated. After a presentation of the phase space explored during the reaction, a global comparison between the model and the experiment is performed for the system Xe + Sn from 25 to 80 MeV/u bombarding energy. Before concluding, two specific studies, one dedicated to central collisions and the other to the decay modes of the quasi-projectile in peripheral reactions are presented.