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Estimation of Subgrade Resilient Modulus Using the Unconfined Compression Test
Wan Soo Kim
M. Shabbir Hossain
M. Shabbir Hossain
Year: 2014
VTRC No.: 15-R12
Abstract: To facilitate pavement design, the new proposed mechanistic-empirical pavement design guide recommends the resilient modulus to characterize subgrade soil and its use for calculating pavement responses attributable to traffic and environmental loading. Although resilient modulus values could be determined through laboratory testing of actual subgrade soil samples, such testing would require significant resources including a high level of technical capability to conduct the test and interpret results. For smaller or less critical projects, where costly and complex resilient modulus testing is not justified, correlation with the results of other simpler tests could be used.

The Virginia Department of Transportation (VDOT) uses a simple correlation with the California bearing ratio (CBR) to estimate the resilient modulus in their current pavement design procedure in accordance with the 1993 AASHTO design guide. As this correlation with CBR is considered to be poor, a simpler unconfined compression (UC) test was explored for better estimation of the resilient modulus of fine-grained soils. Several models were developed in this study to estimate the resilient modulus of fine-grained soil from the results of UC tests. The simplest model considers only the UC strength to predict the resilient modulus with a fair correlation. The more detailed models with stronger correlations also consider the plasticity index, percentage of materials passing the No. 200 sieve, and modulus of the stress-strain curve from the UC test. These models are recommended for implementation by VDOT.