Performance Properties of Geogrids - Reinforced Soil Engineering: Advances in Research and Practice - page 31

valid requirement in this case is a bond coefficient (C.O.I.) or an anchor length
requirement based on performance testing (Voskamp, 1992).
Further, the junction strength has no influence on the strength of the geogrid
and should therefore not be related to a safety consideration for the strength of the
geogrid as was suggested by Task Force 27 in “Design guidelines for the use of
extensible reinforcements,” AASHTO-AGC-ARTBA (1989). Later design
guidelines, such as that published by the FHWA (1997), no longer specify this.
FHWA (1997) describes that the stress transfer mechanisms in pullout are
by friction and/or passive resistance.
The pullout resistance is given by

F*·a·s z v ·L e ·C

P r ¼

where

F * is the pullout resistance factor.
a is the scale effect correction factor, for a nonlinear stress reduction over
the embedded length of highly extensible reinforcements (a

¼ 0 : 6-1 : 0

for geosynthetics).
s z v is the effective vertical stress at the soil reinforcement interface.
L e ·C is the total surface area per unit width of the reinforcement in the
resistive zone behind the failure surface.
L e is the embedment length in the resistive zone.
C is the reinforcement effective unit perimeter (C ¼ 2 for strips and

grids).

F * can be obtained from laboratory or field testing. Alternatively, F * can be
estimated:

F* ¼ F q ·a b þ tan r

where

F q is the embedment bearing capacity factor.
a b is the bearing factor for passive resistance based on the thickness of
the bearing member.
r is the soil reinforcement interactive friction angle.

Default values are given for geosynthetic geogrids:

a 1.

In case F 1 is derived from tests: tan r is not applicable.
In case tan r is derived from tests (in case grid mesh/d 50 ,

¼ 0 : 8 ; in case grid opening size/d 50 .

1): F q is not

applicable, use tan ronly).

Long-term pullout tests are advised to determine F * . As default values are
mentioned: