Factors Influencing the Swelling Potential of Clay-Bearing Rocks

Lithologic characteristics and engineering properties, such as clay content, clay mineralogy, texture, Atterberg limits, absorption, adsorption, specific gravity, density, compressive strength, slake durability, amount of swelling, swelling pressure, and pore size distribution, were determined for 36 samples of clay-bearing, argillaceous, rocks (shales, claystones, mudstones, siltstones) collected from across the United States. The amount of swelling for individual samples was correlated the corresponding values of all other properties, using bivariate and multiple regression analyses. The purpose was to identify those properties that exhibited a significant correlation with the swelling potential and, therefore, could be used to predict the amount of swelling and the associated swelling pressure. The results indicated that swelling was not restricted to those clay-bearing rocks that contained expansive clay minerals. The texture, in some cases, was found to be more important in influencing the swelling potential than the mineral composition. The results also showed that, because of the complex nature of swelling, a single property could not be used to predict the amount of swelling for all types of clay-bearing rocks. The prediction capability significantly improved when different combinations of lithologic characteristics and engineering properties were used for different types of clay-bearing rocks.