using the Giroud and Noiray method with a 100
ing capacity failure from local (near the elastic
kN/m modulus geotextile and the Army method
limit, see e.g., Whitman and Hoeg 1965) to gen-
(0.12 m vs. 0.13 m, or essentially 5 in. for each case).
eral (plastic). Thus, they applied the same soil
If a geotextile with a modulus of 300 kN/m
mechanics principles as did Barenberg et al. (1975).
(1,715 lb/in.) is used, however, Figure 6 indicates
However, Giroud and Noiray (1981) extended this
that no aggregate is required since ∆h = 0.2 m (8
concept to account for the "membrane effect" of
in.). However, a minimum 0.10 to 0.15 m (4 to 6
the geotextile. Membrane effect refers to the fact
in.) aggregate cover over a geotextile is recom-
that the material contained by the concave side of
mended at all times. The aggregate protects the
a stretched, flexible membrane is at a higher pres-
geotextile from damage imposed by construction
sure that the material on the outside of it. As bear-
traffic as well as degradation due to exposure to
ing capacity failure deforms the subgrade, the
ultraviolet light (sunlight). It also helps anchor the
geotextile undergoes deformation that puts it in
geotextile to allow it to develop the required ten-
tension. The tensile strength of the geotextile then
sion.
helps to both support the load and confine the soil
above the geotextile, making it stronger (Fig. 8).
The modulus, K, of the geotextile is increasingly
Theory
Giroud and Noiray (1981) assumed a soft, satu-
influential as the rut depths increase (membrane
rated cohesive subgrade in undrained loading, and
action occurs at large strains).
that the effect of the geotextile placed between the
Like that of Barenberg et al. (1975), this theory
aggregate and the subgrade will change the bear-
and the design technique is based on the assump-
Aggregate
Geotextile
Subgrade Soil
e
2a
2a
2a
β
β
(P ) β
β
t
t
t
t
B
A
B
A
s
r
s
(P)
Initial Location
Geotextile
e
of Geotextile
Figure 8. Diagram of "membrane effect" of geotextile reinforcement of thawing soil (top),
and shape of deformed geotextile (bottom). (After Giroud and Noiray 1981.)
9
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