Protrusion/particle shape—geotextile cushions

Flammability? Zip ties? MARV? Ponds? GT specs?
Questions and answers from the GMT Techline.

Our landfill liner project specifications require the use of rounded to subangular gravel to be placed as a leachate drainage layer or leachate collection pipe bedding. The gravel is separated from the geomembrane liner by a nonwoven geotextile cushion.

During bidding, the question has come up about the quantity or percentage of gravel particles with fractured faces that is acceptable while still meeting the rounded to subangular requirement. The local materials lab says that bankrun gravel deposits typically contain approximately 15% gravel particles with one or more fractured faces.

Do you know if there is a reference that provides a quantitative definition particle shape (rounded, subrounded, subangular) that might take into account a limited percentage of fractured particles?

Thank you,

Deb | Washington

Deb,

The question of gravel angularity (and sphericity) is a common one insofar as geomembrane puncture is concerned.

Soil property textbooks as well as geology books classify both of these terms. Sphericity is how close the particles are to spheres and angularity is how sharp are the edges. James K. Mitchell’s Fundamentals of Soil Behavior book has a nice treatment in this regard.

How important are these different shapes? This is embodied in the geomembrane puncture design I give in the Designing with Geosynthetics textbook—on pages 645–648 of the sixth edition we see that modification factors range from angular at 1.0 to subrounded at 0.5 to rounded at 0.25. These values are in the denominator of the geotextile mass equation indicating that an angular particle is four times as severe as a rounded one. Stated differently, the characteristics of the particle shapes are
very significant.

Bob Koerner | GMA Techline