with the soil and geotextile chosen, then the

as the average strain, then the maximum strain

which would occur is 5 percent.

embankment side slopes must be flattened, or

additional berms may be considered. Most high-

strength geotextiles exhibit a fairly high soil-

geotextile friction angle that is equal to or greater

tensile resistance is instantaneously developed to

than 30 degrees, where loose sand-size fill material

prevent rotational slope/foundation failure and is

is utilized. Assuming that the embankment sliding

inherently included in the slope stability limit

equilibrium analysis. But for the geotextile to

analysis results in the selection of a geotextile

develop tensile resistance, the geotextile must

that prevents embankment fill material from slid-

strain in the vicinity of the potential failure plane.

ing along the geotextile interface, then the result-

To prevent excessive rotational displacement, a

ant force because of lateral earth pressure must be

high-tensile-modulus geotextile should be used.

less than the tensile strength at the working load

The minimum required geotextile tensile modulus

of the geotextile reinforcement to prevent spread-

to limit or control incipient rotational displace-

ing or tearing. For an FS of 1, the tensile strength

ment is the same as for preventing spreading

would be equal to the resultant of the active earth

failure.

pressure per unit length of embankment. A mini-

mum FS of 1.5 should be used for the geotextile to

prevent embankment sliding. Therefore, the mini-

evaluated and specified for both the transverse

mum required tensile strength to prevent sliding

and longitudinal direction of the embankment.

is:

Stresses in the warp direction of the geotextile or

(eq 4-6)

longitudinal direction of the embankment result

from foundation movement where soils are very

where

= minimum geotextile tensile strength.

soft and create wave or a mud flow that drags on

the underside of the geotextile. The mud wave not

Geotextile tensile forces necessary to prevent lat-

only drags the geotextile in a longitudinal direc-

eral spreading failure are not developed without

tion but also in a lateral direction toward the

some geotextile strain in the lateral direction of

embankment toes. By knowing the shear strength

the embankment. Consequently, some lateral

of the mud wave and the length along which it

movement of the embankment must be expected.

drags against the underneath portion of the geo-

Figure 4-3 shows the geotextile strain distribution

textile, then the spreading force induced can be

that will occur from incipient embankment spread-

calculated. Forces induced during construction in

ing if it is assumed that strain in the embankment

the longitudinal direction of the embankment may

varies linearly from zero at the embankment toe

result from the lateral earth pressure of the fill

to a maximum value beneath embankment crest.

being placed. These loads can be determined by

Therefore, an FS of 1.5 is recommended in deter-

the methods described earlier where

mining the minimum required geotextile tensile

and

= 20

at 5 percent strain. The geotextile

modulus. If the geotextile tensile strength

strength required to support the height of the

determined by equation 4-6 is used to determine

embankment in the direction of construction must

the required tensile modulus

an FS of 1.5

also be evaluated. The maximum load during

will be automatically taken into account, and the

construction includes the height or thickness of

minimum required geotextile tensile modulus may

the working table, the maximum height of soil and

be calculated as follows:

the equipment live and dead loads. The geotextile

strength requirements for these construction loads

(eq 4-7)

must be evaluated using the survivability criteria

discussed previously.

where

= maximum strain which the geotex-

tile is permitted to undergo at the embankment

mary purposes of geotextile reinforcement in an

center line. The maximum geotextile strain is

embankment is to reduce the vertical and horizon-

equal to twice the average strain over the embank-

tal deformations. The effect of this reinforcement

ment width. A reasonable average strain value of

on horizontal movement in the embankment

2.5 percent for lateral spreading is satisfactory

spreading modes has been addressed previously.

from a construction and geotextile property stand-

One of the more difficult tasks is to estimate the

point. This value should be used in design but

deformation or subsidence caused by consolidation

depending on the specific project requirements

and by plastic flow or creep of very soft foundation

larger strains may be specified. Using 2.5 percent

materials. Elastic deformations are a function of

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