Laboratory tests in rock mechanics, like the uniaxial compressive strength test and the triaxial test are important techniques for determining the properties of rock and have been subject of research for some time. By recreating the conditions prevalent in nature for laboratory tests, these methods attempt to predict the behaviour of rock when approaching failure. For a better understanding of the failure process it is important to recreate the actual conditions in rock as close to reality as possible. While the uniaxial stress state is actually prevalent in the sidewall of an excavation, certain differences between the triaxial stress situation in a rock mass and the laboratory test can be observed. Most testing methods rely on applying the confining pressure by means of externally applied forces. Contrasting this, the triaxial stress state in a rock mass is often the result of a three dimensional spatial restriction. In the thesis at hand, testing procedures have been reviewed and examined regarding their correctnes in recreating the triaxial stress state. Special attention was paid to the means of application of the external forces on the specimen and to restrictions in the lateral direction. The experimental part of the thesis included the developement of a testing procedure to emulate the triaxial stress state of an enclosed volume. Thereof conclusions can be drawn about the impact of restricted lateral expansion on different rocks. Lateral deformation of rock specimen has been restricted by pre-stressed wire of different spacing. By evaluating the measured data the effect of restricted lateral expansion on the maximum compressive strength and the lateral, as well as the volumetric deformation have been determined. Additionally, the stress path in the sigma 1 vs sigma 3 diagram and the deformation work have been evaluated. By generating confining stresses of up to 6.0~MPa it was possible to calculate the mi-Values of Sandstone and Granite to 15 and 19 respectively.