A screw conveyor system for a compaction apparatus can be adapted on a material transportation vehicle. The compaction apparatus is characterized by having a hopper receiving materials and a container storing the materials in a compacted fashion. The compaction apparatus comprises a screw conveyor system that can include a screw conveying the materials from the hopper to the container, a passageway structure traversed by the screw, located between the hopper and the container and allowing passage of the materials. The passageway structure can define an asymmetrical aperture and the passageway structure can include a main passageway and a by-pass passageway allowing passage of materials from the hopper to the container.