The Geotechnical Engineering Department of the Polytechnic University of Valencia is currently doing a research program on swelling materials (soils and soft rocks) and the long time effect of swelling on tunnels. In this program several swelling oedometric tests, by the Huder-Amberg technique, have been carried out. The usual Huder-Amberg test takes a lot of time, so it is frequent that they are finished before the actual end of the swelling of the probes. In this research some of the tests have been maintained during more than a year, with almost continuous expansion of the samples (argillite with some gypsum inclusions) in each one of the deloading steps. This paper describes the testing techniques, and the special testing challenges and problems derived from the extraordinary time length of the tests; discusses some simple numerical models to forecast the end of each swelling step (in order to reduce as much as possible the testing time); and gives some preliminary results of the expansion parameters for clayey materials, (comparing them with other published data) which can be useful in tunnel design.