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ESTIMATING SUBGRADE RESILIENT MODULUS FOR PAVEMENT DESIGN | ||||
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Norman Dennis, Ph.D., P.E.
August 15, 1999 - January 31, 2005
The Arkansas State Highway and Transportation Department (AHTD) designs its pavement
structures in accordance with the 1986/1993 American Association of State Highway and
Transportation Officials (AASHTO) Guide for the Design of Pavement Structures.
These procedures include an evaluation of the support characteristics of a subgrade soil in
terms of resilient modulus, Mr, and it has been used almost exclusively in
design practice over the past 20 years.
The resilient modulus parameter is not measured
by the AHTD, but rather it is typically estimated from R-Value test results. This
convention was accepted primarily to avoid equipment and labor expenses that would be
associated with the resilient modulus test.
Previous research sponsored by the AHTD
suggests that current pavement designs are conservative and basically no fundamental
relationship exists between the R-Value and the Mr parameter for subgrade soils.
This project aims to improve the resilient modulus prediction method by developing a material
model for subgrade soil based on correlation of soil index properties with the resilient modulus
parameter. Index properties for soils are measured by tests that are relatively simple, inexpensive,
and repeatable, unlike either test to determine the resilient modulus or R-Value. Correlation of
index properties to resilient modulus of a soil has the potential to provide a more accurate and
cost effective means for estimating the Mr parameter used for pavement design.
Development and implementation of the proposed methodology and pavement design guidelines
will emphasize mechanistically-based design criteria, generate savings in areas including soil
testing and material/construction costs, and contribute to improving pavement performance and design life.
TRB Keywords: Resilient modulus, subgrades, pavement design, moisture content.
Product: In Progress (MBTC-2007)
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