Experience gained in rock mass deformability testing by large flat jacks

Authors carried out in situ deformability testing on different locations using the plate load tests (PLT) and the large flat jacks. As to the testing procedure and measurement technique, each of these tests proved quite reliable in practice. However, each of them is burdened by significant problems related to the interpretation of measurement results. Our experience in relation to the testing performance and difficulties in the interpretation of results obtained by LFJs and PLTs are described in the paper. Test results in rock masses of different classes (determined by RMR classifications) are presented as well as the correlation between the deformability determined by empirical methods and the deformability established by the large flat jack testing.