The Huder-Amberg swelling test is a laboratoty testing method used to determine the swelling characteristics of geomaterials, specially of swelling rocks, in contcat with water. The test is carried out according to the method proposed by Huder and Amberg (1980) [1].

In general, the two main swelling characteristics that can be determined by laboratory testing are the swelling strain and the swelling pressure. There are different types of swelling tests which are used to determine either one or both of these characteristics. The Huder-Amberg swelling test is a combined swelling straing and pressure test [2].

The Huder-Amber swelling test is used for different geotechnical appilications in swelling rocks. In particular, this test gives useful information for design of rock support and lining for tunneling in swelling rocks to prevent major unexpected damages due to swelling.

The Huder-Amberg swelling tests is carried out following to the method proposed by Huder and Amberg (1980) [2]. It is often carried out is a oedometric cell, i.e. contraint lateral deformation with axial loading.

The dry samples - at its natural water contenet - is first subjected to a full cycle of (i) loading (ii) unliadng, and (iii) reloading to the maximimum applied vertical stress. The samples is then soaked with distilled water while maintaining the maximum vertical stress. There is usually a small immediate strain (volume decrease) due to soaking. After that the tes vertical stress is subsequently decreased in different unloading steps. At each step, the immediate strain due to unloading and the final strain due to swelling after equilibrium is recorded.

When unloading under water, the sample first shows no swelling strain because of constant volume maintained by the applied pressure. At a given stress, however, the swelling strains can be observed. This pressure corresponds to the swelling pressure of the material.

The results of the tests are often presente in the stress-strain space, e.g oedometric plane of vertical strain versus logarithmic vertical stress. When unloading continues below the swelling pressure, the sample strain follows a swelling-unloading curve which is loacted above the dry unloading curve in a stress-strain space. In other words, the swelling-unloading strains for swelling material are much higher that dry unloading strains. The difference between the swelling-unloading and immediate unloading strain corressponds to the swelling strain of the material at the given pressures.

The results of the test are usefull for many geotechnical engineering applications such as tunnels and shafts in swelling rock. In such condition, major damages to the lining and tunnel geometry can be expected if the swelling characteristics are not considerethe design procedure.