ROCK JOINT COMPLIANCE TESTS FOR COMPRESSION AND SHEAR LOADS

Abstract A series of compression and shear tests were conducted at large scale on joint surfaces in granite and slate specimens, with special equipment being used to isolate the deformations of the joints from those of the rock material. The matrix of compliance components for a rock joint is discussed in relation to these standard tests and it is shown that one pair of compliance components can be determined from a compression test and a second pair from a shear test. Any attempt to base predictions of rock mass behaviour on the combined use of these two pairs of components should take into account the different stress paths to which they relate. The nature of the contacts between the asperities on adjacent joint surfaces is considered as a means of suggesting the form of the stress-deformation relations, both in compression and shear. This approach is shown to be of great assistance in helping to explain the test results and fit the observed compliance characteristics. For the compression tests, the test results indicate a pattern of decreasing compliance with load, an increase in compliance with initial apeture, and high levels of recoverability of deformation. In the shear tests, the curves for the relative displacements indicate there are three zones of different behaviour, elastic, transition and sliding. There appear to be links between the way in which forces are transferred at asperities and the typical patterns of observed compliance.