A rational method for determining the swelling pressure of expansive soils: Paired swell test (PS-test)

Experimental investigations on the expansion behavior of clayey soils are of great importance to correctly understand the response of the soil–foundation. In this context, numerous statistical approaches and experimental techniques have been suggested to understand the swelling behavior of expansive soils, but most of these are unsatisfactory. The swelling characteristics of the soil are estimated by using the conventional consolidation apparatus, and the soil pressure is very sensitive to load increments during tests, especially in the zero swell tests. To provide reliable swelling pressure values for expansive soils, the existing methods are not based on refinements of load steps during the test. Ensuring the optimal swelling readings during the test is quite difficult unless the observations about the expansion response of specimens in different load steps have not been addressed in binary test pairs. The scope of the investigation is to assess the reliability and accuracy of oedometer testing methods and to propose a rational method based on a one-dimensional oedometer with a smaller degree of uncertainty for swelling pressure. A total of 252 remolded soil specimens were tested with commonly used oedometer methods to estimate the swelling pressure. The swelling pressure values were also measured using a specific design in which the swelling pressure under constant volume conditions is measured by an S-type load cell. The reliability and accuracy of the paired swell test (PS-test) in assessing the swelling pressure indirectly seemed to be higher than those of the conventional oedometer methods. The PS-test is proposed as a rational method for any engineering project that requires the prediction of swelling behavior of expansive soils.