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Collaborative Research: Strength of Clay Shale in Relation to Mineralogy, Micromorphology and Pore Water Chemistry

Researcher(s)

Principal investigators:

Project status

Completed

Start date: 01/01/03
End date: 04/30/04

Sponsor(s)/partner(s)

Sponsor(s): National Science Foundation

About the research

Abstract: Overconsolidated clays and clay shales provide engineers with some of their most challenging geotechnical problems, generally involving landslides and expansive behavior. It has been estimated that the average annual direct and indirect economic cost of landslides to public and private entities in the United States is over $3 billion in 2000 dollars. The areas most affected by landslides and expansive soils in the continental United States coincide with locations of overconsolidated clays and clay shales, including the Appalachian Mountains region, much of the prairies of the Midwest from Texas to North Dakota, and the front range of the Rocky Mountains. In recent years considerable advances have been made in understanding the role of mineralogy and system chemistry on the behavior of overconsolidated clays and clay shales. In particular, it has been observed that weathering of the materials combined with changes in the pore water chemistry of the soil system can lead to significant reductions in the soil?s strength. In this study a fundamental investigation of the physiochemical changes associated with the weathering of clay shales will be undertaken, using the Pierre shale of South Dakota as the test material. The objective is to identify changes in mineralogy, micromorphology, and pore water chemistry that accompany the weathering processes of the Pierre shale and to correlate these changes with the reduction in shear strength. If these processes are better understood, it is likely that materials susceptible to strength loss can be more readily identified and that more effective means of mitigation can be devised. Based on the conceptual understanding developed in this research, it is anticipated that recommendations for improved construction and mitigation procedures for shale slopes can be developed. Shale is one of the most commonly encountered earth materials in civil construction works. Hence, the results of this research may have a significant impact on society in terms of reduced costs associated with public works including dams, bridges, and highways, as well as private projects such as housing developments and commercial properties.