Improvement of engineering properties of tropical soils using admixtures.

摘要

Tropical soils commonly present difficulties in field compaction, display significant decrease in strength once the soils are disturbed, provide inadequate subgrade strength for highway applications, and contain highly expansive clay. The current practice of resolving these problems is to excavate these suboptimal soils and replace them with imported select materials. This can be very costly however and could aggravate landfill burden for regions with limited-land-resources, such as Hawaii. Use of admixture(s) to stabilize poor quality soils may provide an economical way to fully utilize local materials while meeting required design criteria as well.; This project, sponsored by the State of Hawaii, Department of Transportation (HDOT) and Federal Highway Administration (FHWA), was undertaken to evaluate the feasibility of using admixture(s) as tropical Hawaiian soil additives. This research was to study different combinations of stabilizing agents and tropical soils and build a database suitable for a first evaluation of the potential effectiveness of stabilizing a variety of tropical soils with admixture(s).; Engineering properties of both untreated and treated soils were assessed through comprehensive laboratory testing. Five common types of local soils were selected for this investigation. Admixtures used in this study include hydrated lime, quicklime, municipal solid waste (MSW) ash, cement and combinations of hydrated lime and ash, as well as concentrated liquid additives. Test results demonstrated improvements such as: increase in workability and constructibility due to the drying effect and significant reduction of plasticity; reduction in swelling potential; increases in unconsolidated/undrained (UU) strength and California bearing ratio (CBR); and significantly improved stress-strain relations and dynamic properties. X-ray diffraction (XRD) and scanning electron microscope (SEM) examinations indicate that the laboratory test results reflect formation of cementing materials with weak to strong intensities. A small-scale field application undertaken as a side project demonstrated that locally available equipment and admixture is more than adequate to perform the field application, and engineering properties of some poor quality tropical soils can be upgraded and enhanced through admixture stabilization.