(2) For thickness design using geotextile.

thickness design that would perform with very

little rutting (less than 2 inches) at traffic vol-

umes greater than 1,000 equivalent 18-kip axle

loadings.

thickness design that would rut 4 inches or more

under a small amount of traffic (probably less than

100 equivalent 18-kip axle loadings).

a 24,000-pound-tandem-wheel load on a soil having

a CBR of 1. The road will have to support several

thousand truck passes and very little rutting will

be allowed.

(1) Determine the required aggregate thick-

ness with geotextile reinforcement.

value of 4.20.

little rutting will be allowed.

sign loading, normally the maximum axle loads.

obtain a value of 14 inches as the required

aggregate thickness above the geotextile.

Determine the required thickness of aggregate

(e) Select geotextile requirements based on

survivability requirements in tables 2-2 and 2-3.

above the geotextile using figures 2-4, 2-5, and

(2) Determine the required aggregate thick-

2-6. These figures relate the depth of aggregate

ness when a geotextile is not used.

above the geotextile to the cohesion of the soil (C)

and to a bearing capacity factor (NC). The product

tile is not used and only a small amount of rutting

of C and NC is the bearing capacity for a rapidly

will be allowed.

loaded soil without permitting drainage. The sig-

nificance of the value used for NC as it relates to

11.8.

the design thickness using figures 2-4, 2-5, and

2-6 is as follows:

obtain a value of 22 inches as the required

(1) For thickness design without using geotex-

tile.

aggregate thickness above the subgrade without

the geotextile.

thickness design that would perform with very

(3) Compare cost and benefits of the alterna-

little rutting (less than 2 inches) at traffic volumes

tives. Even with nearby economical gravel sources,

greater than 1,000 equivalent 18-kip axle loadings.

the use of a geotextile usually is the more econom-

ical alternative for constructing low volume roads

thickness design that would rut 4 inches or more

and airfields over soft cohesive soils. Additionally,

under a small amount of traffic (probably less than

it results in a faster time to completion once the

100 equivalent 18-kip axle loadings).

geotextiles are delivered on site.

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