The four basic functions of geotextiles:
The function of filtration is to restrict the migration of fine soil particles from the soil clumps while maintaining water movement permeability greater than or at least equal to the permeability of the protected soil.
Due to its construction, water is transported along the path of the geotextile and then reaches the outlet. Water can be transported vertically or horizontally. Drainage is related to the role of filtration and is a function of the permeability of the geotextile and its pore size or porosity.
Separation is the function of preventing the mixing of two different soils of different materials. The key factors for geotextiles to fulfill this function are porosity, toughness and strength.
This function involves stabilizing soil quality by providing tensile strength to the soil fabric system.
The choice of geotextile can be expressed as the relationship between these four basic functions and the attributes that design engineers need to meet certain specific requirements.