In elements whose coarse grain size prohibits taking samples large as much as necessary to test in the laboratory, the only method of getting test results is by testing in situ. In rocks, whose mass characteristics are known to be a lot influenced by the presence of discontinuities, reasonable assessments of geotechnical parameters can only be obtained by testing in situ. Access to the body of ground to be tested, the in situ sample, is via a borehole or trial excavation. It should be noted that the excavation that gives access to the ‘sample’ itself disturbs the ground and may alter its properties.