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characterization of existing subgrade soil is done via
laboratory tests and/or nondestructive testing. Laboratory
tests can include the determination of gradation, soil type
(clay, silt, gravel, etc.), AASHTO soil classification, liquid
limit, plasticity index, R-value, and resilient modulus.
The resilient modulus is defined as the slope of the
stress-strain plot within the plastic range. The resilient
modulus is a measure of the materials stiffness and is not a
measure of its strength. |
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Resilient Modulus Laboratory Test |
Quality construction
materials must be readily available. Selection of design
options may be influenced by the cost of materials.
The environment has a significant impact on
pavement performance. Some of the environmental
considerations are frost (design total pavement thickness to
withstand the effects of freeze-thaw), rainfall (requirements
for drainage), temperature (concern with asphalt rutting and
joint spacing in concrete pavements) and location of groundwater
table (requirements for drainage). |
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loads are estimated and characterized according to equivalent
single axle loads (ESAL). This method is used to convert
wheel loads of various magnitudes and repetitions to an
equivalent number of "standard" or
"equivalent" loads for design purposes. An ESAL
is equivalent to an 18,000-lb single axle load. |
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Non Destructive Testing using the Falling Weight
Deflectometer
The design period is the length of time that a new or
reconstructed pavement structure will last before reaching its
terminal serviceability. WSDOT has established the
following periods based on functional class for new pavement
design:
- Interstate and principal arterial: 40 years
- Minor arterial and collectors:
ESAL > 100,000 per year use 40 years
ESAL < 100,000 per year use 20 years
Economic analyses are required for interstate and principal
arterial highways with project lengths of two or more center
line miles. |
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