The use of artificial joints executed in blocks of rock for the study of the mechanics of rock mass discontinuities

摘要

This paper refers to an experimental programme based on the acquisition of samples from a large 4.32 m~2 artificial joint obtained through tensile stresses in a 7 m~3 block of sound porphyritic granite. This programme allowed the outlining of some dozens of essential conclusions about the rock joint mechanics, like the possibility of the scale effects on the joint strength to be inverse (which are represented by positive exponential regressions) when its middle plane is levelled or the dependence of the joint strength on the perpendicular width to the slidings of the samples, which inhibits the stability analysis of rock discontinuities by the slice method (Leal-Gomes 1998, 1999b). These samples of an artificial joint are a bit different from the samples of natural joints due to their better mating and absence of weathering. But these artificial samples allow a great reliability of the theoretical conclusions from their experimental test programmes. This fact doesn't happen when synthetic casts of a discontinuity are tested (Bandis 1980, Hencher et al. 1993). These casts or synthetic models have several inherent difficulties. Testing of samples of artificial joints is a way of producing efficient and accurate models of the mechanical joint behaviour at a reasonable price. This means was very little used in Rock Mechanics.