Geotextiles used in filtration

Federal Waterways Engineering and Research Institute, Karlsruhe, Germany 

Hydraulic loads acting on a soil either internally or externally will dislodge the soil particles when their resistance against these loads is exceeded. Therefore, a filter is needed to retain the particles without altering the drainage capacity of the system. A filter is not mandatory only if the hydraulic load at the subsoil—filter interface is permanently so low that no grains will be eroded. 

The design approaches to filters are usually grouped into geometticaT and hydraulic criteria. Geometrical criteria define limit values for void diameters to hinder the transport of finer particles through them. Hydraulic criteria define a limit value for the hydraulic gradient at which the transport of particles begins. In most cases. 

Geotextilcs. http //dx.d Lorga0Ll01 ai978. MH-10a221.6.00012-7 Copyiight 2016 Elsevier Ltd. All rights reserved. 

Filter rules are predominandy developed for drains and other applications with unidirectional flow. Filters in coastal and riverine training and protection stmctures often experience much heavier loads with high gradients and turbulent and reversing flow. Therefore, tests are recommended to prove the filtration capability of geotextile fabric in such cases. 

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In each case, these composites are used to ease installation and create synergistic effects among the materials used in their production. For more information about the design, the reader should refer to chapters Geotextiles used in filtration and Geotextiles used in drainage. 

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