Performance Properties of Geogrids - Reinforced Soil Engineering: Advances in Research and Practice - page 32

Geosynthetic sheet reinforcement: F * ¼ 2/3·tan f.

Geogrids: F * ¼ 0.8·tan f.
f

¼ peak friction angle of the soil.

For reinforced soil slopes (RSS) as lower bound value f ¼ 28 8 is advised;

for mechanically stabilized earth walls (MSE) walls f ¼ 34 8 in case granular

backfill is used.
This document contains requirements for geogrid pullout such as

Quick, effective stress pullout tests and through-the-junction creep testing
of the geogrid per GRI-GG3a Test Method, or
Quick, effective stress pullout tests of the geogrid with severed transverse
ribs, or
Quick, effective stress pullout tests of the entire geogrid structure if the
summation of the strengths of the joints occurring in a 300-mm-(12 00 )
long grid sample is equal to or greater than the ultimate strength of the
grid element to which they are attached, or
Long-term effective stress pullout tests of the entire geogrid structure.

Research on the long-term effective stress pullout of four flexible grids and
one stiff grid, Wilson-Fahmy and Koerner (1995), showed that, “For practical
purposes the pullout strength of the geogrids tested is independent of time within
the observed 1000 hours test duration.”
Whenever a safety factor is required for pullout, it should be related to the
anchor length or grid length in the embankment and not to the allowable strength
as suggested and used in the United States (AASHTO-AGC-ARTBA,1989;
Washington FHWA, 1997).
In the design method developed by Jewell (1990b), the effect of the junction
strength or anchor length is taken into account in the calculation of the bond length.
Even with very low values, it shows that the effect is minimal. The bond factor has
a very limited effect on the anchor length. Together with the findings of recent
research work, Oostveen et al. (1994), especially the extra safety in the anchor
length due to the fact that the design is for an allowable strength compared to the
available rupture forces, it is concluded that a separate factor of safety for junction

Table 1 Availability of Load/Strain/Time Data

Load/strain/time data Flexible Stiff

Stress-strain curves Available Available

Long-term stress-rupture Available Sherby-Dorn plots

Stiffness (strain vs. time) Available Sherby-Dorn plots

Junction strength Minimum strength Unlimited strength