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- All Subjects: Asphalt
- All Subjects: Foundations
- Creators: Houston, Sandra L.
Description
The primary objective of this study is to understand the effect of soil cracking on foundation performance for expansive soil profiles. Two major effects of cracks were studied to assess the effect of cracks on foundation performance. First, the effect of cracks on soil volume change response was studied. Second, the effect of cracks on unsaturated flow properties and extent and degree of wetting were evaluated. Multiple oedometer-type pressure plate tests were conducted to evaluate the effect of cracks on soil properties commonly used in volume change (heave) analyses, such as swell pressure, soil water characteristic curve (SWCC), and swell potential. Additionally, the effect of cracks on saturated and unsaturated hydraulic conductivity was studied experimentally to assess the impact of cracks on properties critical to evaluation of extent and degree of wetting. Laboratory experiments were performed on both intact and cracked specimen so that the effect of cracks on behavior could be benchmarked against intact soil response. Based on laboratory observations, the SWCC of a cracked soil is bimodal. However, this bimodal behavior is only observed in the very low suction ranges. Because the bimodal nature of the SWCC of cracked clays is only distinguishable at extremely low suctions, the bimodal behavior is unlikely to have engineering significance when soils remain unsaturated. A "lumped mass" parameter approach has been studied as a practical approach for modeling of cracked soils for both fluid flow and volume change determination. Laboratory unsaturated flow experiments were simulated using a saturated-unsaturated flow finite element code, SVFlux, to back-analyze unsaturated hydraulic conductivity functions for the subject soils. These back-analyzed results were compared to the results from traditionally-applied analyses of the laboratory instantaneous profile tests on intact and cracked specimens. Based on this comparison, empirical adjustments were suggested for modeling "lumped mass" cracked soil behavior in numerical codes for fluid flow through cracked soils. Using the empirically adjusted flow parameters for unsaturated flow modeling, example analyses were performed for slab-on-grade problems to demonstrate the impact of cracks on degree and extent of wetting under unsaturated and saturated flow conditions for different surface flux boundary conditions.
ContributorsAbbaszadeh, Mohammad (Author) / Houston, Sandra L. (Thesis advisor) / Zapata, Claudia E (Thesis advisor) / Welfert, Bruno D (Committee member) / Houston, William N (Committee member) / Arizona State University (Publisher)
Created2011
Description
The trend towards using recycled materials on new construction projects is growing as the cost for construction materials are ever increasing and the awareness of the responsibility we have to be good stewards of our environment is heightened. While recycled asphalt is sometimes used in pavements, its use as structural fill has been hindered by concern that it is susceptible to large long-term deformations (creep), preventing its use for a great many geotechnical applications. While asphalt/soil blends are often proposed as an alternative to 100% recycled asphalt fill, little data is available characterizing the geotechnical properties of recycled asphalt soil blends. In this dissertation, the geotechnical properties for five different recycled asphalt soil blends are characterized. Data includes the particle size distribution, plasticity index, creep, and shear strength for each blend. Blends with 0%, 25%, 50%, 75% and 100% recycled asphalt were tested. As the recycled asphalt material used for testing had particles sizes up to 1.5 inches, a large 18 inch diameter direct shear apparatus was used to determine the shear strength and creep characteristics of the material. The results of the testing program confirm that the creep potential of recycled asphalt is a geotechnical concern when the material is subjected to loads greater than 1500 pounds per square foot (psf). In addition, the test results demonstrate that the amount of soil blended with the recycled asphalt can greatly influence the creep and shear strength behavior of the composite material. Furthermore, there appears to be an optimal blend ratio where the composite material had better properties than either the recycled asphalt or virgin soil alone with respect to shear strength.
ContributorsSchaper, Jeffery M (Author) / Kavazanjian, Edward (Thesis advisor) / Houston, Sandra L. (Committee member) / Zapata, Claudia E (Committee member) / Arizona State University (Publisher)
Created2011