Filters and drains

• 3.1.

  Filters

• 3.2.

  Geotextile filters

• 3.3.

  Geotextile filtration mechanism

• 3.4.

  Factors affecting geotextile filter behaviour

• 3.5.

  Laboratory filtration performance tests

• 3.6.

  Filtration design

• 3.7.

  Filtration of high water content geomaterials with geotextiles

• 3.8.

  Drains

• 3.9.

  Summary of main points

• 3.10.

  Common questions and answers

• References

Geosynthetics are composed of plastic polymers, and have been commonly employed in civil and environmental engineering projects for the last 30 years to prevent erosion of soils without impeding the flow of water seeping through the soils. Geotextiles are increasingly being used to replace graded granular filters in many applications, because of their economy, consistent properties, ease of placement and comparable performance. Various different geosynthetics can also provide lateral drainage of percolating water in a construction application, and prevent the build-up of excess pore-water pressure in the soil. Several empirical criteria incorporating varying factors of safety are available for selection of geotextile filters; however, they are not directly applicable to high water content geomaterials. An extensive literature review has been made to gather information pertinent to filtration of natural soils and high water content geomaterials using geotextiles. Factors affecting the behaviour of filtration processes are presented. This chapter also provides a step-by-step methodology for designing filters and drains.