The condition, composition, depth, moisture content and density of subgrade soils directly influences the design and performance of roadways. For example, expansive subgrades create a challenging scenario for road designers and, if not properly addressed, swelling and shrinkage of subgrade soils can create situations that range from annoying to dangerous, depending on the level of severity.  In an effort to improve the quality of service to road users in South Dakota, the South Dakota Department of Transportation is interested in refining their process for designing and constructing roads in areas containing subgrade soils with high potential for expansion and/or shrinkage. The department seeks to update its specifications and construction guidelines to assist design and construction staff to manage these types of soil deposits more efficiently.

The objectives of this project are to:

1. Determine the effectiveness of common soil stabilizing agents for mitigating localized faults and heaves of clay shale in South Dakota
2. Determine construction guidelines and specifications for using stabilizing agents that include recommended construction methods, addition rates, density and moisture requirements
3. Determine the cost-benefit of using stabilizing agents to mitigate localized areas of faults and heaves in clay shale

The objectives of this research will be accomplished through a comprehensive literature review, laboratory testing, benefit–cost analysis, and synthesis of recommendations. From these efforts, recommendations for mitigating expansive clay shale will be developed to include construction specifications, optimal additive blend and application rate, and general guidance of the acceptable range in in-situ moisture content of the subgrade.