Soil Suction Surrogates for Advancing Complete-Stress-State Solutions to Expansive Soils

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Approximately 320 million hectares of the world's land is covered with expansive clays that are subject to shrinkage and swelling in response to changes in soil moisture conditions. Damage to U.S. public infrastructure from expansive clays is estimated to be $15 B/yr. For every billion dollars in damage from unconservative design, perhaps $10B is lost from overly conservative design. Expansive clays are unsaturated soils in that the void space between clay particles is filled partly with air and partly with water. However, common approaches to dealing with expansive soils do not fully consider the unsaturated soil aspects that drive infrastructure damage. This award supports the development of an innovative approach to bringing unsaturated soil mechanics theory into wide use in dealing with infrastructure development on expansive clay profiles. Due to the magnitude of expansive soils problems, and the involvement of 10s of thousands of practitioners addressing these problems, this study will provide societal benefit through saving billions of dollars annually on U.S. infrastructure. The project has numerous outreach components, including cross-training between researchers and practicing engineers that will improve engineering education. Participation of underrepresented students and returning-veteran students will broaden the impact of this study through development of more diverse and well-trained work force. A dual approach will be taken for estimation of expansive soil swell-shrinkage movements, wherein a fundamentals-based soil suction and net normal stress approach will be linked to a surrogate-based approach. The method will embrace principles of unsaturated soils theory, yet expand applicability through well-founded yet commonly-measured soil suction surrogate parameters. Climatic effects (including site-specific 'microclimate') will be incorporated into surrogate parameter determination, consistent with recent research on soil surface-atmosphere interactions. This research fills a gap between theory and the vast amount of available field data. A fundamentally-based soil suction surrogate will facilitate use of the huge database of soil parameters available from past expansive soil investigations. Simple functions of water content and index properties will be used - in lieu of soil suction - to evaluate expansive soil movements for partial wetting or drying under field net normal stress conditions. The primary goal is to develop a soil suction surrogate approach that yields exactly the same, or essentially the same, expansive soil movement results as the complete-stress-state based suction approach, and which allows geotechnical engineers to take advantage of their vast experience from a more fundamental perspective.