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Geotextile cushion design

October 1st, 2007 / By: / Geotextiles, GMA Techline

Subject: Geotextile cushion design— Using the geotextile cushion calculator on landfilldesign.com, and according to your research report, we should be using a factor of safety of 3 for cushion geotextile and the size of the protrusion height at half the height of the largest particle of gravel used for the Linear Containment Remediation System (LCRS).

The one question we are still puzzled about is the MFA for arching of solids. The [report] seems to suggest that arching may not be proportionally more effective for “deep” gravel.

Based on that, we used a shallow MFA of 0.75 rather than a deep MFA of 0.50. The LCRS gravel is 12in. and there are 3ft of operations layer made from sandy material for a total height of aggregate material that could arch 4ft.

The problem is, if we use an MFA of 0.75, then we need a 14.7 oz geotextile for 0.75in. gravel. If we use an MFA of 0.50, then a 10oz geotextile is sufficient for 0.75in. rock

What is the correct MFA for 4ft of aggregate above a geotextile cushion? (Mark, California)

Reply: Thanks for the question, however it is really beyond the lab experiments that we performed. That is, the extension from the truncated cones that were used to real soils/gravels are best-estimate values. I have done work on angularity and thought those MFs were OK. But the arching MF values are not as well-founded.

In the end, you seem to be in a decision between a 10osy and a 14.7osy nonwoven geotextile. The difference in cost is so small that I would use the larger value, and then you would have to specify a 16osy geotextile, which is the closest value typically manufactured.

Bob Koerner | GMA Techline

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