TM 5-818-8/AFJMAN 32-1030
1.3 against rotational slope failure. There are
L =
= 2,800
many slope stability procedures available in the
287
literature for determining the required tensile
L = 9.8 ft; approximately 10 ft
strength T . Computer programs are also available
e. Prevention of Sliding. Calculate
to pro-
that will determine the critical slip surface with a
vide an FS of 2 against sliding failure across the
search routine. Assume that an analysis was
geotextile.
conducted on the example embankment and an
(1) Calculate lateral earth pressure,
active moment of 840,000 foot-pounds per foot of
width was calculated and a resisting moment of
820,000 foot-pounds per foot of width calculated for
a slip circle having a radius of 75 feet. This would
result in a safety factor of 0.98 which is not
satisfactory. Using equation 4-1, the tensile
strength of a geotextile necessary to provide an FS
PA = 8 1 7
of 1.3 can be calculated as follows:
(2) Calculate
AM - RM
FS = Resisting Force
FS
T=
Active Force
R
8 4 0 , 0 0 0 - 20,000
8
FS =
1.3 = 2,800 pounds per
T=
foot of width
75
d. Pullout Resistance. Pullout resistance of the
geotextile from the intersection of the potential
failure plane surface is determined by calculating
where X = ratio of the vertical and horizonal slope
the resistance and necessary geotextile embedment
(i.e., 10 horizontal to 1 vertical).
length. There are two components to geotextile
pullout resistance-one below and one above the
geotextile. Resistance below the geotextile in this
example is 50 pounds per square foot, and resis-
tance above the geotextile is determined by the
average height of fill above the geotextile in the
affected areas. In this example, the resistance
above and below the geotextile is determined as
follows:
(eq 4-13)
f. Prevention of Geotextile Splitting. Calculate
required geotextile tensile strength
to provide
where
an FS of 1.5 against splitting.
= moist weight of sand fill, 100 pounds per
FS = 1.5 against splitting
cubic foot
= 817 pounds per foot width
h = average height of sand fill above geotex-
tile in the affected area, 6.5 feet
Calculate
= sand-geotextile friction equal to
= remolded strength of foundation clay
= (1.5)(817)
soil beneath the geotextile, 50 pounds
= 1,226 pounds per foot width or
per square foot
= 102 pounds per inch width
g. Limiting Spreading and Rotation. Calculate
= 287 width
the tensile modulus
required to limit embank-
The required pullout length is determined from
ment average spreading and rotation to 5 percent
the ultimate tensile strength requirement of 2,800
geotextile elongation.
pounds per foot width. Therefore,
(1) Spreading analysis:
4-9
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