Physical dispersivity is a phenomenon, which causes soil grains to be dispersed in presence of water and carried away by the flow. This phenomenon can cause many problems in hydraulic structures founded on the soils of such property. Many parts of the country may face this problem especially in places where wind blown sand and silt prevails. The main objective of this research is to investigate the dispersivity potential of such soils and to determine the parameters which have the most influence on the phenomenon. For the purpose of investigation, samples were taken from Saveh plain as well as Chamran project area in Khoozestan province. The samples were tested thoroughly for determination of their physical properties, including dispersivity. Some specimens were also prepared using physically dispersive soil plus cohesive soils to determine the grain size distribution range of the stabilized samples. All samples taken from the field as well as specimens made in the laboratory were tested for grain size distribution, compaction, and Atterberg limits as well as in pinhole apparatus. Based on the overall results, the two major factors affecting the dispersivity potential were found to be the portion by weight and plasticity of the fine grain material in the samples. The average size of the sand particles in the samples was also found to be an important factor regarding dispersivity. The greater the percentage of the finer portion of the soil and its plasticity, the less is the dispersivity potential. Based on these factors a relationship was found for evaluation of physical dispersivity potential. Another testing method was also developed based on the time necessary for collapse of a compacted, standard size specimen, which is placed in water. This experiment resembles the Crumb test somehow, but can be quantified easily.
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