Filter opening size of geotextile related to adjacent soil (following R. Veldhuijzen Van Zanten)

Calculation method

H.J.M. Ogink developed the concept of using the geotextile as a sieve and defined in 1972 the O x (geotextile), as well as its relation with the D y (soil). The criteria for soil retention by a geotextile, in contact with a sandy soil, were as follows:

O₉₀ / D₉₀ =< 1 (laminar flow, woven geotextiles)

0₉₀ / D₉₀ =< 1.8 (laminar flow, nonwoven geotextiles)

O_max/ D_min =< 1 (dynamic situation, wave impact)

Experience learned that the retention of particles also took place thanks to the formation of arches between particles, interlocking in the openings of the geotextile, and the formula, still often used today, became:

O₉₀ / D₉₀ =< 2 (laminar flow)

The calculation method used in the Texion Applet, takes also in account the uniformity coefficient (Cu = D₆₀/ D₁₀) of the soil and distinguishes applications: (1) with laminar flow (e.g. drainage, road building) and (2) submitted to dynamic wave impact (e.g. river bank protection).

Water permeability and retention of soil particles

Those two properties are in conflict to each other. The greater the openings, the more water flows through, but the fewer particles are retained. An optimum should be sought to reconcile the two conditions.

If there is a choice to be made between water permeability and retention of soil particles, it is the experience of Texion that an 0₉₀, that is theoretically too large, can be chosen. The passage of small soil particles, through the geotextile, allows a natural filter to build up. This graded structure of particles ensures that blinding, clogging and blocking will be avoided.