Expansive Soil Behavior

National Science Foundation

PI: Amy Cerato (OU)


Project Summary

Expansive unsaturated soils cover one-fourth of the United States and undergo large amounts of heaving and shrinking due to seasonal moisture changes. These movements lead to cracking and buckling of the infrastructure built on expansive soils and result in billions of dollars of damage annually (e.g., Wray & Meyer 2004).  Although not life-threatening or cataclysmic as compared to other natural events, expansive soils are certainly a natural hazard.  Even though expansive soils have been studied for several decades, all of the idealized models presented to date to predict shrink-swell potential of expansive soils have failed to predict actual soil movement under real conditions where the presence of several cations and clay minerals can influence soil behavior (Hillel 1998).

The research goal is to advance the understanding of and prediction methods for macroscopic unsaturated expansive soil behavior through microscopic fundamental soil surface phenomena, such as specific surface area (SSA) and cation exchange capacity (CEC).  This will be achieved by improving existing 1-D empirical models and extending the application of a physicochemical discrete element method (DEM) computer model to incorporate expansive soil movement.   Understanding expansive soil behavior under various environmental conditions will allow the design of robust foundation systems using life-cycle performance as the driving factor in choice of design.  This innovative unsaturated soils research program will be woven into several important high-impact educational components in order to bridge the gap between geotechnical theory and geotechnical practice.

 

Intellectual Merit

Understanding expansive soil behavior using microscopic soil surface phenomena will advance the state-of-knowledge and practice in geotechnical engineering by allowing researchers and practitioners to accurately and repeatedly predict macroscopic expansive soil behavior in a way that is not currently available.  The improvement on existing empirical models for expansive soil movement prediction using microscopic soil parameters, such as SSA and CEC, is an immediate practical necessity for our profession.   It is also essential to develop a physically meaningful mathematical model that utilizes a microlevel understanding of particles and interparticle forces to further advance our fundamental knowledge of expansive soil behavior. Merging physicochemical and unsaturated soil mechanics theories into a DEM will provide insight into observed laboratory and in situ behavior and help our profession and society progress toward a solution to a complex and expensive problem.

Broader Impacts: The topic of expansive soils is not only compelling from a scientific perspective, but a social perspective as well.  The microscopic, particle-particle understanding of expansive soil behavior will help to predict the macroscopic shrink-swell behavior that causes an estimated $15 billion dollars in annual damage to infrastructure.  To initiate this improvement, students will be taught about the important role that geotechnical engineer’s play within our society to broaden their career path opportunities as well as increase, enhance and diversify our undergraduate civil engineering population.  This enhanced undergraduate student population will feed a more talented and diverse graduate student population which will produce a more educated workforce.  In time, this extensive network of civil engineers can dispel the poor public perception of engineers and increase their status in society. Similar to current practices and successes, the PI will focus on the recruitment and retention of women and minorities in order to enhance and diversify the engineering experience.

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