When there is seepage in the soil, it is often accompanied by seepage deformation, such as piping and flowing soil. This should be paid attention to in the excavation of dams and foundation pits. On the one hand, the hydraulic gradient can be reduced by means of anti-seepage, precipitation or increasing the seepage diameter, and on the other hand, the seepage flow can pass smoothly and a reverse filter layer is set at the outlet to prevent soil erosion. Grain loss, such cases include drainage consolidation of soft soil foundations and other underground drainage facilities.
Different products of geosynthetics have good drainage and reverse filtration (infiltration or filtration) functions, so they can replace traditional sand and gravel to build drainage and filtration structures. When the geotextile is in contact with the soil and there is seepage, the drainage and filtration effects of the geotextile are two inseparable and coexisting functions. When water seeps out of the soil and flows into the geotextile, the geotextile must not only drain the amount of infiltrated water, but also protect the soil from harmful seepage deformation. Therefore, drainage and reverse filtration are often contradictory. For example, for the pore size of the filter layer, it is better to have a larger pore size in terms of drainage, but it may be more appropriate to want it to be smaller in terms of reverse filtration.
In practical projects, non-woven fabrics are often used, because non-woven fabrics can not only drain water inside the fabric along the plane, but also filter back in the direction perpendicular to the plane, so it can better take into account both the functions of water drainage and back filter. Sometimes in order to take into account other functions, textiles are also used. When the drainage capacity is high, geocomposite drainage materials can be used, such as plastic drainage belts, drainage nets, flexible drainage pipes and drainage mats and other materials and structures.
