Expansive soil behavior: Property measurement techniques and heave prediction methods

Expansive soils swells (heave) upon wetting and cause distress to civil infrastructure. A soil heave analysis requires laboratory determination of the soil response to water content (suction) and net normal stress changes. However, laboratory determination of expansive soil properties is sensitive to sample disturbance. In this study existing heave prediction methods and testing procedures are evaluated, and a new method of heave prediction using conventional testing equipment and which considers partial wetting, is considered. This method, to a large extent, represents a merger of and a modification to existing methods.;The effect of sample disturbance on the response of expansive soils was studied, including effects of: (1) specimen preparation, (2) apparatus compressibility, (3) sampling method, and (4) adopted testing technique. Best practices for laboratory testing of expansive soils were determined. Empirical correlations between properties and characteristics determined from common testing methods were developed to account for disturbance effects.;The use of an "equivalent" net normal stress path was explored via an extensive laboratory program in which matric suction and net normal stress were controlled. Undisturbed samples of soils from Arizona, Colorado, and Texas were used to study "equivalent" net normal stress values for expansive soils.;A new heave prediction method capable of predicting both partial and full wetting heave was proposed and compared to existing heave prediction methods and tested against laboratory-determined volume change data over a wide range of net normal stress and soil suction conditions. The new model allows the soil suction to become zero without resulting in numerical difficulties in obtaining a heave estimate. This is accomplished using a net normal stress surrogate path approach wherein the surrogate stress does not go to zero at zero matric suction. The proposed method requires routine laboratory oedometer tests and measurements or estimates of soil suction.