Flexibility of Clay and Cracking of Earth Dams

An approximate theory is formulated to calculate the critical tensile strains in an earth dam that result from differential settlements along the axis of the dam. Laboratory apparatus and procedures are developed to estimate the limiting tensile strain at which compacted clay will crack. Comparisons between predicted and observed behavior of five dams indicate that the theory and laboratory tests can be used to predict cracking potential with an accuracy that is satisfactory for practical purposes. The ratio of tensile strain at cracking to compressive strain at failure is a small fraction (approximately 0.01 to 0.1) that shows no evidence of any consistent pattern. Accordingly, it is hazardous to assess the flexibility of compacted earth dams on the basis of stress-strain relations obtained from compression tests. The effects of molding water content and compactive effort on the flexibility of clay was investigated. No consistent relationship between flexibility and plasticity characteristics of the clay was found.