Novel stabilization methods for sulfate and non-sulfate soils.

摘要

Expansive soils are commonly found in arid and semi-arid climate zones. These soils typically exhibit moderate to high plasticity, moderate to high strength, and high swell and shrinkage characteristic. They also undergo large amounts of swelling and shrink related volume changes when these soils are subjected to moisture fluctuations from seasonal changes. These volumetric movements weaken the subgrade soils, which in turn lead to structural distresses on pavements. Another type of expansive soil is chemically treated expansive soil with high amounts of sulfates, which undergo heaving due to the formation of Ettringite mineral.;This dissertation project was conducted to develop stabilization methods for both natural and chemical treated sulfate rich expansive soil types. Both soils are prevalent in Arlington, Texas and these soil types were hence locally collected and used in the present research. The performance of stabilization methods considered in this research were evaluated in both laboratory and field conditions in order to select ideal stabilization method(s) for modifying expansive soils to minimize heave and shrinkage induced distresses. Four types of chemical treatment methods including Type V Cement, Ground Granulated Blast Furnace Slag (GGBFS), Class F Fly Ash with Type V Cement and Lime with Polypropylene fibrillated fibers were considered for sulfate soil stabilization studies and a combined lime-cement treatment was considered for stabilization studies for non-sulfate expansive soils.;Laboratory testing programs were also conducted to assess properties relating to volume change behavior, strength and resilient properties. The experimental programs included other basic soil property tests, chemical and mineralogy tests to assess strength improvements in the treated soils. Based on the laboratory studies, stabilizers and their dosages were selected and used for field treatments to support pavement infrastructure.;Field monitoring studies were also conducted through instrumentation studies, elevation surveys, Dynamic Cone Penetrometer (DCP) tests and visual field inspection studies to monitor the performance of pavements built over the stabilized expansive subgrades. Site investigation with an array of sensors and appropriate data acquisition in pavement instrumentation and elevation surveys provides valuable data that were utilized to assess the performance of pavement layers in real field conditions. Based on the field studies, type V cement and type V cement and fly ash treatment methods are considered effective whereas combined lime-cement treatment provided better enhancements to soil properties.;Life cycle cost analyses (LCCA) were also performed on all treatment methods considered for both sulfate and non-sulfate soils. Design recommendations and summarized specifications for the construction of stabilizer treated subgrades for both sulfate rich and non-sulfate soils are presented.