Filterlaget

Filterlaget, or the filter layer, is a term used in civil and geotechnical engineering to describe a granular layer placed between a drainage medium and surrounding soil. Its primary function is to prevent migration of fine soil particles into the drainage system while allowing water to flow freely. The layer works together with other components such as geotextiles or drainage pipes to control seepage and reduce the risk of piping and clogging in drainage applications.

In design terms, the filterlag is selected to achieve compatible hydraulic and mechanical properties with both the surrounding soil and the drainage media. Materials commonly used for the filterlaget include well-graded sand or gravel, sometimes with a geotextile separator on one or both sides. The specific grain size distribution and the permeability of the layer are chosen to balance filtration efficiency with adequate drainage capacity. Design criteria are typically based on local standards or guidelines, taking into account soil type, anticipated loads, groundwater conditions, and the required drainage performance.

Applications of the filterlaget include foundation and roadway drainage, slope stabilization, retaining wall drainage, and landfill leachate systems, where it helps maintain effective drainage while preventing soil migration. It is often part of a broader drainage assembly that may incorporate geotextiles, filter screens, and perforated pipes.

Construction considerations focus on proper placement and compaction to maintain uniform thickness, preventing contamination during installation, and ensuring continuity with adjacent drainage components. Proper inspection and testing help verify that the layer meets the intended filtration and drainage objectives.