1.3 against rotational slope failure. There are

= **2,800**

many slope stability procedures available in the

literature for determining the required tensile

strength T . Computer programs are also available

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

of 1.3 can be calculated as follows:

(2) Calculate

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)

required geotextile tensile strength

to provide

where

an FS of 1.5 against splitting.

= moist weight of sand fill, 100 pounds per

cubic foot

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

soil beneath the geotextile, 50 pounds

per square foot

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:

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