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Swell, stiffness and strength of expansive soil-rubber (ESR) mixtures at various scales: effect of specimen and rubber particle sizes




Heyer, Lance C., author
Carraro, J. Antonio H., advisor
Shackelford, Charles D., committee member
Butters, Gregory, committee member

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Expansive soils and stockpiled scrap tires present unique constructability and environmental challenges to the Front Range of Northern Colorado, respectively. Swell, stiffness and strength parameters of expansive soil-rubber (ESR) mixtures were systematically evaluated in the laboratory under one-dimensional and axisymmetric boundary conditions. ESR mixtures tested contained highly plastic, swelling clay from the Pierre shale formation and scrap tire rubber (STR) with nominal maximum particle sizes equal to approximately 6.7 or 19.0 mm. Compaction parameters were determined using standard Proctor compaction procedures (ASTM D698). Mixtures were compacted to relative compaction levels equal to 90, 95 or 100% and water contents varying by ± 2% around the optimum water content. Rubber contents used were equal to 0, 10 or 20%. Specimen and rubber particle sizes were also studied to assess differences in mechanical behavior of 6.7- and 19.0-mm ESR mixtures tested in one-dimensional compression employing three specimen sizes (small-scale, large-scale and field-scale) and in undrained axisymmetric compression employing two specimen sizes (small-scale and large-scale). Swell-compression results indicated the swell percent and swell pressure of specimens subjected to one-dimensional compression with lateral confinement were most impacted by initial water content, followed by relative compaction and rubber content. Compressibility parameters, including the constrained and elastic moduli, are most impacted by rubber content, followed by relative compaction and initial water content. Small-scale one-dimensional specimens demonstrated a minimal increase in swelling and insignificant variations in compressibility in comparison to large-scale one-dimensional and field-scale specimens. ESR specimens subjected to axisymmetric boundary conditions exhibited volumetric swell during flushing and back pressure saturation and swelling magnitudes were similar for nominal rubber particle sizes equal to 6.7 and 19.0 mm. Normal compression line parameters, λcs and κcs, were equal to 0.10 and 0.05, and 0.11 and 0.04 for large-scale 6.7- and 19.0-mm ESR specimens, respectively. Critical state parameters, Mcs, Γcs, and λcs, were equal to 1.20, 2.23 and 0.14, and 1.04, 2.15 and 0.13 for large-scale 6.7- and 19.0-mm ESR specimens, respectively. Scalability results indicate similar swell, stiffness and strength of ESR mixtures compacted to various specimen sizes with the inclusion of either 6.7- or 19.0-mm scrap tire rubber particles. Results indicate reasonable predictions of the mechanical behavior of ESR mixtures including tire chips can be made using conventional laboratory specimen sizes and testing techniques employing similar host expansive soils and rubber contents used to create ESR mixtures including granulated rubber.


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expansive soil
scrap tire rubber


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