Clay mineralogy effects on long-term performance of chemically treated expansive clays

In this research study, an attempt is made to address limitations in soil stabilization. Incorporation of the clay mineralogy aspects of the soils into the stabilization design process was first addressed, followed by durability studies to address the long-term effectiveness of the stabilization and leachate studies. All these are the main focus of this dissertation investigation.;The first task was to develop a simple procedure to identify the dominating clay mineral in a given soil as the current procedures of mineral quantification are expensive and highly skill oriented. Hence, properties such as Cation Exchange Capacity, Specific Surface Area and Total Potassium were used and statistical regression equations were developed to predict the dominating clay mineral in a given soil. Prediction models were developed using the test results' database. Tools such as regression analysis and artificial neural networks (ANN) were utilized to develop different prediction models. These clay mineralogy prediction models were validated using the artificial soil data. Predictions by both methods were compared and it was observed that the regression based prediction model showed better prediction capabilities than ANN based model. However, the differences between predictions are small and practically negligible. Hence any of these models could provide realistic prediction of clay mineralogy in a given soil.;The second task was to assess the effects of clay minerals on the long-term durability of stabilized expansive clays by conducting wetting/drying (W/D) studies replicating moisture fluctuations expected during summer and winter seasons in the field. A total of eight soils were selected for studying the long-term performance of stabilized expansive soils by conducting wetting/drying studies. An accelerated curing method was developed and followed in this study for curing and moisture conditioning of the treated soil specimens. The effect of curing methods is studied on four select soils and it is observed that both the curing methods including old and longer curing (Tex 121-E) for 17 days and the present accelerated curing methods of 3 days yielded similar UCS and volume change test results. It has been interpreted from these results that there was no considerable effect of curing on the long-term performance of these treated soils except for an initial strength since soil was partially saturated.;The third task was to assess the performance of the stabilization under severe rainfall conditions where heavy amounts of rain water infiltrates into the soil and causes leaching of the stabilizer and thereby reducing the life time of the stabilization. To understand this behavior leachate studies were conducted on all the eight soils selected to replicate moisture ingress and digress in the field during rainfalls and to study the effect of these moisture infiltrations on the long-term performance of stabilized soils. Leachate samples were collected after 3, 5, 7, and 14 cycles of leaching to address the chemical changes occurring due to leaching of the additive from the soil specimen. Also, unconfined compressive strength tests were conducted on soil specimens after 3, 7 and 14 cycles of leaching to address the strength changes from leaching.;Finally, an attempt was made to highlight the effect of the loss of strength in the treated soils due to the above mentioned climatic changes on the performance of a flexible pavement. Four different flexible pavement sections with varying asphalt concrete layer and base course layer thicknesses were altogether analyzed. The effect of treated base modulus deterioration on the pavement performance was assessed by obtaining the compressive strains on the subgrade top. (Abstract shortened by UMI.)...