United States Department of Transportation
i
Development of Stiffness-Based Specifications for In-Situ Embankment Compaction Quality Control
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2007-08-01
[PDF-3.44 MB]
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TRIS Online Accession Number:1076669
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Abstract:Compaction of embankment soils is a key factor influencing premature pavement distresses and bridge approach settlement. The current specifications of the Kansas Department of Transportation (KDOT) address embankment compaction in terms of density and moisture content. However, the implementation of performance-based specifications would require measuring mechanical properties of soil, such as stiffness, in addition to density. This is needed because soil stiffness is the parameter used to characterize the embankment soil in the design of pavement structures. The objectives of this study were to investigate the use of the Light Falling Weight Deflectometer (L-FWD) to measure in-situ soil stiffness and to investigate the feasibility of developing a stiffness-based specification for embankment soil compaction quality control. To achieve these objectives, soil stiffness values were measured at multiple locations along nine KDOT embankment projects using the Prima 100 L-FWD. Concurrent density and moisture measurements were also taken at select locations. Bulk soil samples were collected and remolded soil samples were used to measure the resilient moduli of the soils in the laboratory at varying density and moisture contents. For each soil, and at each combination moisture content and dry density level used in the laboratory tests, a constitutive model was derived from the laboratory resilient modulus data to capture the stress-dependent behavior of the soil. The constitutive model was then implemented in a finite element model of a semi-infinite soil half-space to compute the deflection at the surface of the half-space for a circular load. An equivalent elastic modulus for the soil half-space was back-estimated with the Boussinesque formula, for each combination moisture content and dry density. A regression model was then developed to relate the equivalent elastic modulus of the soil half-space to the dry density and moisture content of the soil. The regression model was used to predict the equivalent elastic moduli for the in-situ moisture contents and dry density values recorded during the field L-FWD tests. The predicted equivalent moduli were then compared to the moduli measured by the L-FWD. It was found that the equivalent moduli predicted from the results of the laboratory resilient modulus tests do not correlate with the in-situ soil stiffness measured with the L-FWD. This prevented the development of a quality control scheme based on laboratory measured resilient moduli. The high degree of spatial variability obtained for the in-situ moduli measured with the L-FWD prevented the development of a quality control scheme based on a control test strip
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