United States Department of Transportation
i
Consideration of regional variations in climatic and soil conditions in the modified triaxial design method.
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2008-11-01
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[PDF-2.57 MB]
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Edition:Technical report; Sept. 2002-Dec. 2005.
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Abstract:The Texas Department of Transportation (TxDOT) uses the modified triaxial design procedure to check
pavement designs from the flexible pavement system program. Since its original development more than
50 years ago, little modification has been made to the original triaxial design method. There is a need to
verify the existing load-thickness design chart to assess its applicability for the range in pavement materials
used by the districts and the range in service conditions encountered in practice. Additionally, there is a
conservatism in the current method, which assumes the worst condition in characterizing the strength
properties of the subgrade. While this approach may apply to certain areas of the state such as east Texas, it
can lead to unduly conservative assessments of pavement load bearing capacity in districts where the climate
is drier, or where the soils are not as moisture susceptible. Clearly, there is a need to consider regional
differences to come up with a more realistic assessment of pavement thickness requirements for the given
local conditions. To address this need, researchers characterized the variation of climatic and soil conditions
across Texas to develop a procedure that accounts for moisture effects and differences in moisture
susceptibilities among different soils. Researchers incorporated this procedure in a computer program for
triaxial design analysis that offers greater versatility in modeling pavement systems compared to the limited
range of approximate layered elastic solutions represented in the existing modified triaxial design curves.
This program permits engineers to correct soil strength parameters to values considered representative of
expected in-service conditions when such corrections are deemed appropriate for the given local climatic and
soil conditions.
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