TM 5-818-8/AFJMAN 32-1030
strength and solve for
, the length of geotextile
This can be solved for the length of overlap,
required. Thus, the expression would be:
required:
(eq 7-11)
(eq 7-7)
where
The minimum length of overlap should be 3 feet to
= fabric tensile strength
ensure adequate contact between layers.
F.S. = safety factor of 1.5 to 1.75
h. External Wall Stability. Once the internal
stability of the structure is satisfied, the external
The minimum length of the fabric required is 3
stability against overturning, sliding and founda-
feet.
tion bearing capacity should be checked. This is
g. Length of Fabric Overlap for the Folded
accomplished in the same manner as for a retain-
Portion of Fabric at the Face. The overlap,
,
ing wall without a geotextile. Overturning loads
must be long enough to transfer the stress from
are developed from the lateral pressure diagram
the lower section of geotextile to the longer layer
for the back of the wall. This may be different
above. The pullout resistance of the geotextile is
from the lateral pressure diagram used in check-
given by:
ing internal stability, particularly due to place-
(eq 7-8)
ment of live loads. Overturning is checked by
= depth to overlap. Tension in the
where
summing moments of external forces about the
geotextile is:
bottom at the face of the wall. Sliding along the
base is checked by summing external horizontal
(eq 7-9)
forces. Bearing capacity is checked using standard
foundation bearing capacity analysis. Theoreti-
Since the factor of safety can be expressed as:
cally, the fabric layers at the base could be shorter
than at the top. However, because of external
(eq 7-10)
stability considerations, particularly sliding and
bearing capacity, all fabric layers are normally of
uniform width.
7-5
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