Rock mass deformability is of fundamental importance for a safe and economical design of rock structures, along with the initial state of stresses act on rock mass and its strength characteristics. The rock mass deformability is currently evaluated by means of different types of in-situ loading tests, i.e. the Plate Loading Test, the Flat Jack Test, the Radial Jacking Test, the Water Chamber Test, the borehole loading test and so on. The in-situ tests are presently employed in major rock engineering projects, to provide more rational data for design of rock structures which are available for the prediction of rock mass behavior when we construct them. The Plate Loading Test is a mostly familiar in-situ experiment on rock mass. In general, this is taken place in a test gallery to measure the deformation modulus (E) of rock mass surrounding it. The Plate Loading Test appears deceptively easy in principle, but the interpretation of the test results meets with many difficulties. The modulus of deformation were obtain from each horizontal and vertical plate-loading test and the data obtained by loading the opposite faces, should of course, be comparable. It will be seen that the scatter of the results is very marked although the tested surfaces were at a distance of not more than 3 m. It is shown that the test result are effected by many factors including the presence of damaged region surrounding the gallery, non-uniform geological conditions, the test set-up and so on. Additionally, discussed that there are uncertainties associated with all the in-sit
One of the basic problems in rock mechanics is the assessment of the deformability of rock masses. Knowledge of the deformability of rock masses, notably in-situ modulus of deformation, is essential for the safe and economical design of such large underground excavations as powerhouse chambers as well as important surface structures such as foundations for large dams. The rock mass deformability is currently evaluated by means of different types of in-situ loading tests, i.e. the Plate Loading Test, the Flat Jack Test, the Radial Jacking Test, the Water Chamber Test, the borehole loading test and so on. Although, these conventional loading tests, intended to measure the rock mass deformability, seek to cover a representative part of rock mass including the matrix rock and some geological discontinuities, there is a considerable variability in results obtained from different loading tests. Thus the reliability and accuracy of the in-situ loading tests are still being discussed. The main source of variability in results obtained from different testing methods are the state of stress created inside the rock mass dependent on the method of testing, different in the volume of rock subjected to loading, homogeneity and isotropy of the rock mass, preparation of a proper test surface, resolution of the monitoring system and the method of calculation [1], [2], [3], [5].
