| abstract |
A separator material for sub-grade, e.g. containing clay and/or silt, comprises a composite (60) formed of at least one layer of a geotextile material (52,54) and at least one layer of a nonwoven fabric (50) formed of polymeric fibres. The nonwoven fabric (50) is calendered so as to achieve a material that can filter out particles of clay/and or silt but is normally permeable to liquid. The nonwoven fabric (50) has a maximum pore size between 5 and 20 µm or between and 40 µm. |