Behavior of Swelling Clays: A Molecular Dynamic Study

While swelling of certain clay types is an old geotechnical engineering problem, the fundamentals governing swelling still remain poorly understood. It is known that interlayer (crystalline) and double-layer (inter-particle) forces are responsible for the overall swelling. One could study the combined behavior using a particle-based modeling technique such as the discrete element method. A suitable constitutive law (in this case, the relationship between inter-particle force-displacement) is needed for this purpose. There is inadequate information available for developing a forcedisplacement relation for the interlayer force. Furthermore, the transition from interlayer to double-layer swelling has not been studied in the past. In the present study, analyses are performed using a molecular-level analysis technique known as the molecular dynamics. The molecular dynamics is used to study the interlayer force-displacement relation for selected particle separations. The study is limited to a montmorillonite-water-NaCl system. Based on the results of the present study, and those from past molecular studies, the force-displacement relation needed for discrete element analysis is developed. The details of the discrete element study is reported in a companion paper.