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Austin, Texas consists of highly expansive soils that have caused failures in many structures. Minimizing the detrimental effects of expansive soils on structures requires that the swelling of these soil(s) is quantified accurately, efficiently, and timely. A testing procedure was developed to directly measure soil swelling using centrifuge technology by Plaisted, 2009. This testing procedure was developed in order to reduce the test duration while generating more swelling data relative to conventional tests that directly measure swell. However, the new procedure was incapable of obtaining in-flight swell data, resulting in the need to develop a procedure to directly measure swell during centrifugation. The objectives of this study were to update the testing procedure developed by Plaisted, 2009 by incorporating the use of an in-flight Data Acquisition System (DAS) that would produce accurate and repeatable results; and use the updated testing procedure to quantify the effects of compaction conditions on swelling for three expansive soils in the Austin area (Eagle Ford Shale, Houston Black Clay, and Taylor Clay). A DAS consisting of linear position sensors, analog to digital converters, JeeNode Arduinos, and an accelerometer was developed and installed within the centrifuge. Specimens were compacted at various water contents, and densities, and subjected to different g-levels. The effects of g-level, compaction water content, compaction dry unit weight, and soil type were determined by comparing the 34 hour swell percentages for the compacted specimens. The results of this study showed that in-flight monitoring of clay swelling could be successfully implemented in a comparatively small centrifuge, and that the data collected from the DAS was accurate and repeatable. Swelling of tested soils was found to be sensitive to changes in water content around optimum, with specimens compacted wet of optimum swelling less than specimens compacted dry of optimum. A 6% increase in relative compaction was found to negligibly affect the swelling. Finally, variations in confinement and compaction conditions were found to have a greater effect on swelling for soils that are more expansive in nature compared to soils less expansive in nature. / text

Expansive soils are characterized as having high amount of clay minerals such as smectite, which lead to swelling during wet seasons by absorbing water and shrinking during dry seasons owing to moisture loss by evapotranspiration. The soil volumetric changes due to moisture fluctuations cause extensive damage to civil engineering structures, namely pavements, retaining walls, low rise buildings and canals founded on such soils. The primary swelling portion of the swell curve has been studied in significant details in previous studies. However, there is a dearth of literature concerning the secondary swelling phenomenon in expansive clays, which has also been observed in experimental studies. While it may be argued that the magnitude of secondary swelling is significantly less as compared to primary swelling, the characterization of the rate of secondary swelling is relevant for fully characterizing the swell potential of the soil. The rate of secondary swelling has been used to predict the long-term swelling of expansive soils. Conventional laboratory swell tests may take over a month for specimens to demonstrate secondary swelling behavior. A centrifuge based method has been recently developed at The University of Texas at Austin to achieve this objective in multiple specimens, and within less than a day. The effects of soil fabric, soil type, relative compaction, molding water content, gravitational gradient, and infiltrating fluid, on the rate of secondary swelling, are thoroughly investigated in this thesis. Four different expansive clays found widely in and around Texas, namely – Eagle Ford Clay, Tan Taylor Clay, Black Taylor Clay and Houston Black Clay, have been used in the study. Based on this extensive experimental evaluation, it may be concluded that secondary swelling behavior could be explained by flow processes associated with the bimodal pore size distribution in expansive clays. The rate of secondary swelling was found to increase with increasing molding water content and increasing compaction dry unit weight. The experimental results revealed that clays with a flocculated structure (compacted dry of optimum) demonstrate rapid primary swelling but exhibit less swelling in the secondary region, as compared to clays with a dispersed structure (compacted wet of optimum). The slope of secondary swelling showed a decline with increasing gravitational gradient. The rate of secondary swelling showed evidence of upward trend with an increase in the plasticity index and clay fraction of the soil. It was observed that soils which exhibit higher primary swelling also demonstrate higher secondary swelling. / text

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / n this article, the geotechnical behavior of the reinforced soil is studied through additions of polypropylene fiber and recycled glass powder, this in order to obtain a homogeneously reinforced soil matrix to reduce possible structural failures, differential settlements and increase capacity bearing. The sample used was classified as a clay soil with low plasticity (CL) and with moderately expansive characteristics, based on the values of the Liquid Limit, Plastic Limit and Plasticity Index. The effect of the 1% polypropylene fiber and different amounts of recycled glass powder (0%, 4%, 5%, 6.5%), with respect to dry weight is analyzed in this soil. The purpose of varying the quantity of these materials is to find a trend of the strength parameters and obtain the optimal percentages that provides improvements in geotechnical behavior. Modified Proctor and Direct Shear tests were carried out, this latter to obtain the shear strength parameters of the mixtures and compare them with the clay soil. Finally, the optimal result for soil improvement was the mixture made by 1% polypropylene fiber and 4% glass powder, which achieved an increase of the angle of friction and cohesion.