Abstract: The fibrous assembly (1) is intended to constitute a fibrous reinforcement for a composite part. It comprises at least two preforms (11, 13, 15, 17), each of which includes stacked fibrous cloths. Each preform includes at least one structure (111, 131, 151), the structure (111) of a first preform (11) being substantially complementary to the structure (131) of the second preform (13). The first and second preforms are adapted to be fitted one into the other by engagement of their respective structures, then firmly connected by the injection of polymer resin.