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Abstract The shear strength of intermittent joints in rock masses has an important influence on the stability of blocky rock system. For a single rock joint，the surface roughness is of paramount importance to its mechanical property，such as shear strength. Many theoretical criterions have been proposed to predict the shear strength of intermittent joints，of which the Jennings criterion is the most widely used one. However，in Jennings criterion，the mechanical parameters of joint surface and rock bridge are simply averaged by a weight coefficient called connectivity rate to calculate equivalent mechanical parameters and the surface roughness isn¢t taken into account. So the direct shear tests are carried out on artificial coplanar intermittent joints with different surface undulating angles under different normal stresses to investigate the influence of undulating angle on the strength of intermittent joint and analyze the mechanism of the weakening of rock bridge mechanical parameters. Based on the direct shear test data，modifications are made to the Jennings criterion by considering the weakening of the mechanical parameters of rock bridge and the surface undulating angle during shear process. And comparisons between the results computed with modified Jennings criterion and the shear test data are made to evaluate the effect of modification；it is shown that the calculated results according to the modified Jennings criterion agree well with the experimental data；and the modified Jennings criterion is able to predict the shear strength of the intermittent joints with regular surface undulating angle well.
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Received: 28 September 2009
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