Separation
They prevent migration and mixing of coarse materials with fine materials.
Reinforcement and Stabilization
They add tensile stress to soft soils, thereby increasing their bearing capacity.
Filtration
They retain soil particles with diameters larger than their pores, allowing water to pass through.
Drainage
They evacuate water and gases from the underlying soil through their plane, preventing damage from the pore pressure they generate.
Protection
Buffers/avoids direct contact with a surface.
