Geogrid evaluation - Break Elongation 1

[Geoman1965]

Two biaxial polypropylene geogrids each have about the same ultimate strength but one has a lower break elongation. I'm told that the grid with the lower break elongation is superior because it confines the aggregate quicker and thus stabilizes the reinforced layer quicker. Is this a correct explanation and is it better to have the grid with the lower break elongation?

Looking at the two grids we are comparing the data is:
Type A
Strength at 2% strain 21.0kN
Strength at 5% strain 32.6kN
Ultimate Strength (at break elongation) 33.2kN (5.3% strain)
Type A
Strength at 2% strain 12.0kN
Strength at 5% strain 23.0kN
Ultimate Strength (at break elongation) 31.5kN (10% strain)

 

[Ron]

The lower elongation is a positive factor in your application, given essentially the same ultimate tensile strength. This means that its strength is mobilized quicker and with less displacement than if the elongation were longer. The downside is that if you are close to failure, failure will occur quicker because of the reduced ductility.

Also...don't cross post in multiple forums. Against the rules. I red flagged your same post in the "Foundations" forum.

 

[Geoman1965]

Thanks Ron. I think I'm missing something. About failure, isn't failure caused if the force exerted on the gird exceeds the ultimate strength? If that's the case, wouldn't both grids break at the same time once that strength was reached?...also, isn't the difference only that the grid will the higher elongation will move more before it breaks.

 

[Ron]

They would break at the same stress level, but the displacement of the one with greater elongation could give some failure warning. With the lower ductility, failure could occur without warning. In either case, there might not be enough warning to do anything about it.

 

[JML4TCM]

What test method are you using to test tensile strength? I ask because you are showing units as kN, for geogrid testing the proper test would be a wide-width test that would give you kN/m values (ASTM D6637). 21 kN at 2% strain does not sound right for a biaxial geogrid.

Also, are both geogrids polypropylene (PP)?

 

[Geoman1965]

Tensile strength as per ASTM D 6637, method b (wide width). The units are kN/m and both grids are polypropylene. The strengths indicated are for only the Transverse direction. The Machine direction strengths are similar in that the strength at 2% strain is very high.