The most important parameters for the design and numerical modeling are deformability modulus, cohesion, friction angle, Poisson's ratio and coefficient of stress ratio, among which the rock mass modulus of deformability is of paramount importance. Dilatometer test is not applicable in the sections of borehole containing open joints or cavities due to the flexible packer. The required section for conducting the test is at least one meter. Because of existing cavities and open joints in majority of the boreholes of Karun2 dam site and mostly in the left galleries (LG1 and LG2), sections with one meter length of rock mass without any fractures were not found for executing Dilatometer test. Therefore, it was not wise the tests to be performed regarding the high price of borehole drilling and executing the tests. As the effect of the pressure in these tests is extended at most 30 cm, some sections with 60 cm or more of length, with only one open joint or cavity was chosen with the aid of borehole camera for the test so that they filled with grout and re-drilled again for conducting the tests. The results were compared with the similar tests performed in undisturbed rock mass with the same material mostly in the right galleries (RG1 and RG2) and showed a good conformity.
The deformation parameter indicates the extent of rock mass deformation in response to any loading. This parameter is particularly important in the design of underground excavations and rock foundations and for all projects that are sensitive to even minor deformation. Many of the rocks are considered elastic in laboratory scale but in the desert scale due to the presence of joints and cracks, layering plates, metamorphic zones and clay layers have plastic properties. The rate of irreversible deformation (plastic) of the rock mass is of great importance in the design.