Estimation of soil-water retention curve for expansive soils

Expansive soils are a challenge for engineers because they can generate movements and cracks in light structures. Therefore, its study is essential to achieve foundation designs suitable for this type of structure. The variable that directly affects the behavior of expansive clays is suction. This variable generates additional contact forces between soil particles that are known as cohesion. These forces can be known through the determination of the soil-water retention curve. The most widely used method of suction measurement for expansive soils is the filter paper technique, which requires special care for its correct execution. This is mainly due to the sensitivity and precision required for the measurement of paper moisture. In this article, the results of the measurement of the characteristic curve of an expansive clay are presented, using variations and considerations additional to the standard. The result is a comparison between the values obtained when weighing the filter paper before and after the 7-day equilibrium, using a metal container and without it, and considering an immediate measurement and another when the balance has stabilized. It was determined that the weight of dry paper is affected when it is left exposed to a desiccator and when a metallic container is not used to avoid moisture changes to the filter paper. Depending on the way in which the measurement is made, the suction values obtained for a dry expansive clay are so high that they exceed the maximum limit of the filter paper test.