The inclusion of randomly distributed short virgin polypropylene fibers (C3H6) in clay has proven to significantly improve the geotechnical properties of clay such as shear, compressive, and tensile strengths, ductility, volume change, and so on. Those improvements have triggered great attention on the possibility of mixing fibers with clay to form a desirable composite. Because the percentage of fibers used is arbitrarily chosen by the users, the purpose of this study is to determine if there is an optimum fiber content and if it is a function of the type of fiber used. Compaction properties of clay-fiber composite using commercially available synthetic polypropylene, synthetic polypropylene fibers (monofilament and fibrillated) and kaolinite were determined. It was found that for a clay-fiber mix, there is an optimum fiber content and it is different for different types of fiber.

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One of the causes of heavy damage due to earthquake motions is the role of soft clay in amplifying bedrock ground motions. Improving the soil conditions using polypropylene fibres at a site in order to mitigate earthquake damage could be one of the methods to modify site conditions. In this study, the optimum fibre contents were obtained for mixtures of clay with two different types of fibre. Then the dynamic properties of polypropylene fibre reinforced clay with different fibre contents were determined using resonant column testing. The study showed that the inclusion of fibre at optimum fibre content can improve the dynamic properties of clay at the low shear strains used. Test results indicated that both the shear modulus and damping increased. Hence, the inclusion of fibre in clay can provide a double benefit for the dynamic response of a site by increasing the stiffness of the site and reducing its amplitude of vibration.

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Fiber products can co-exist with natural system and can provide safe, economical, and long-lived composites. Researchers have added polypropylene fiber to soil and determined that it can improve the geotechnical behavior of the soil. However, they followed the same approach currently being used in concrete. In concrete, the amount of fiber added is usually an arbitrarily specified percentage to improve a specific property of the concrete. The percentage usually varies with the intended use of the concrete.Recently, there has been extensive research performed on the benefit of fiber addition to soils. But none has explained why the fiber content (FC) plays a role in improving the geotechnical properties of the fiber-soil composite. In this research, different approaches, i.e., a concrete approach and metallurgical (micro mechanics) approach are described and a sustainable soil approach is introduced. Using the soil approach, two different fiber types with different lengths were added to Kaolinite clay and the optimized fiber contents were determined for the composites. The soil approach explains why the amount of fiber added improves the geotechnical properties.

Piedmont residual soils form a strip that extends from Alabama to New Jersey and comprise much of Virginia, Georgia, and the Carolinas. Thus, a better understanding of their strength properties is of paramount importance. One of the hallmarks of the soils within the Piedmont region is its silty nature. Although it is usually a common practice to use lime treatment for highly plastic clayey soils, no such agreement exists on the type of soil stabilization when dealing with fine-grained silty soils. Hence, the effects of cement stabilization on the strength of residual silt were studied. California bearing ratio (CBR) and unconfined compressive strength (UCS) testing was conducted. The study showed that cement can react with the silty soil and the addition of cement can lead to further increase in strength. Equations were developed correlating liquid limit to CBR as well as cement content to UCS. A multi-variable model function was also proposed correlating CBR and cement content to UCS of treated soils, and equations were developed for silty soils with standard proctor CBR samples and 95% degree of compaction as well as modified proctor CBR samples and 97% degree of compaction. The accuracy of the proposed function was validated using data developed for cement treated lateritic sandy soils.

The Coastal Plain soils of Virginia generally comprise recent marine and fluvial deposits. It is widely accepted that grain size, plasticity, and water content of the soil are indices that can be used to geotechnically characterize fine-grained soils. The objective of this study was to determine whether the soils from a specific geologic formation have consistent or similar index properties. The data from a previously performed extensive field exploration in the Coastal Plain soils of Virginia were used in the study. The data were divided by local geology and subdivided into separate groups based on the soil fines content (FC) and density. Mean values for water content, Standard Penetration Test N-Value, Atterberg limits, FC, and pocket penetrometer tests were then determined for each geology. The statistical analysis of soil index properties was performed for soils in different formations. The results allow better identification of soils in different formations from index property testing.

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