Mirafi® X Series are slit tape (a.k.a. slit film) geotextiles made from flat, tape‐like yarns woven into a fabric. Geotextiles made from slit tape construction create fabrics with very low hydraulic permittivity (0.05 sec‐1, ASTM D4491). The use of slit tape geotextiles as purely a separator geotextile in dry conditions can perform well. However, all geotechnical applications will have moisture intrusion at some point during the service life of the structure, whether environmental, seasonal, or introduced by manmade forces (i.e. utilities). As an alternate to low permittivity slit tape geotextiles, a geotextile separator with a minimum permittivity greater than or equal to 0.2 sec‐1 should be considered.
There are several types of geotextiles with a hydraulic permittivity ≥ 0.2 sec‐1, including nonwoven geotextiles and woven monofilament/multifilament geotextiles (not made from slit tape yarns). When following AASHTO M288‐17 specification for Separation/Stabilization, TenCate Geosynthetics recommends considering products that have a permittivity ≥ 0.2 sec‐1; this includes nonwoven geotextiles that have >50% elongation properties outlined in AASHTO M288.