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Abstract:Subgrade soil characterization in terms of Resilient Modulus (MR) has become crucial for pavement design. For a new
design, MR values are generally obtained by conducting repeated load triaxial tests on reconstituted/undisturbed cylindrical
specimens. Because the test is complex and time-consuming, in-situ tests would be desirable if reliable correlation equations
could be established. Alternately, MR can be obtained from correlation equations involving stress state and soil physical
properties. Several empirical equations have been suggested to estimate the resilient modulus. The main focus of this study is to
substantiate the predictability of the existing equations and evaluate the feasibility of using one or more of those equations in
predicting resilient modulus of Mississippi soils. This study also documents different soil index properties that influence
resilient modulus.
Correlation equations developed by the Long Term Pavement Performance (LTPP), Minnesota Road Research Project,
Georgia DOT, Carmichael and Stuart Drumm et al., Wyoming DOT, and Mississippi DOT are studied/analyzed in detail. Eight
road (subgrade) sections from different districts are selected and soils tested (TP 46 Protocol) for MR in the laboratory. Other
routine laboratory tests are conducted to determine physical properties of the soil. Validity of the correlation equations are
addressed by comparing measured MR to predicted MR. In addition, variations expected in the predicted MR due to inherent
variability in soil properties is studied by the method of point estimates. The results suggest that LTPP equations are suited for
purposes of predicting resilient modulus of Mississippi subgrade soils. For fine-grain soils, even better predictions are realized
with the Mississippi equation.
A sensitivity study of those equations suggests that the top five soil index properties influencing MR include moisture content,
degree of saturation, material passing #200 sieve, plasticity index and density.
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