Normal stiffness of fractures in granitic rock: A compilation of laboratory and in-situ experiments

摘要

Results from linear regression analysis of 115 different laboratory and in-situ normal closure experiments in granitic rock showed a very large range of stiffness characteristic values, even for well-defined laboratory tests within the same rock type. This was not unexpected because fracture normal stiffness is highly affected by several, extreme complex interacting factors (i.e. fracture surface geometry, asperity deformability, fracture interlocking, testing conditions, etc.) which are discussed in detail in [3-8,29]. Given that under in-situ conditions most of these factors are difficult or impossible to determine, this study is intended to provide some ranges of stiffness characteristic values for practitioners involved in geotech-nical projects in fractured rock masses where site-specific normal stiffness tests are not available. It was found that the semi-logarithmic normal closure law provided a satisfactory description of the closure behaviour of these tests and therefore only the single parameter of stiffness characteristic is needed to estimate the normal stiffness at arbitrary normal stress levels.