Puncture strength measures a geotextile’s ability to resist damage from the stresses associated with the installation process. Until recently, ASTM D4833, “Standard Test Method for Index Puncture Resistance of Geomembranes and Related Products,” also known as “Pin Puncture,” was used to determine a geotextile’s puncture resistance. This test was adopted from standard textile testing and the ability to withstand the puncture of an 8mm, beveled pin was more relevant to a shirt or pair of pants than a geotextile.
As such, the geotextile industry determined Pin Puncture was an insufficient method for measuring a geotextile’s performance and have replaced it with ASTM D6241, “Standard Test Method for the Static Puncture Strength of Geotextiles and Geotextile related Products Using a 50-mm Probe.” This test utilizes a 50mm diameter, flat-ended probe (plunger) that is pushed slowly through the geotextile. The relatively large size of the plunger provides a multidirectional force on the geotextile and simulates the stress of big stones being pressed onto a geotextile laying on a relatively soft sub-base.
PIN PUNCTURE CBR PUNCTURE
Unfortunately, it will take many years for specifications requiring Pin-Puncture to filter out of the specifying community. Additionally, some current products may not currently have the CBR testing included in their data. This creates a problem for those in charge of approving geotextiles. How does Pin Puncture and CBR Puncture correlate, if at all?
Many studies have passively compared ASTMs D-4833 and D-6241 or determined a trend, but a correlation of Pin Puncture and CBR Puncture testing methods, independent of manufacturing or material type, has not been attempted.
A May 2014 Thesis by Stacy Van Dyke of the University of Milwaukee-Wisconsin undertook determining a correlation. Her final formulas allow one to estimate a decent ball-park CBR value (and vice-versa) when only one set of data is available. Below are the two formulas for woven and nonwoven geotextiles. This is only offered as a way for an engineer to get a feel for the CBR puncture of a fabric when Pin Puncture is the only available value submitted (or vice-versa). The formulas tend to run a little high in our opinion, but give a good estimate regardless.
Pin Strength x 5.27 = Estimated CBR for Nonwovens.
Pin Strength x 7.378 = Estimated CBR for Wovens.
I hope this is helpful!