Abstract:

The bearing capacity of rock sample is determined by material strength and confining pressure together. Both axial compression and unloading confining pressure can induce the failure of rock sample, but because of different stress paths, the failure processes under two conditions are different. The tests of conventional triaxial, pre-peak unloading confining pressure and post-peak unloading confining pressure are done to the Baishan marble which comes from access tunnel in Jinping Hydropower Station lying on Yalong River. The test curve and the rock sample failure characteristics indicate that rock samples are all showing brittle failure in pre-peak and post-peak unloading confining pressure tests; and the brittle characteristics in pre-peak test is more stronger than that in post-peak test. The deformations of rock sample in loading and unloading are increasing with the increase of principal stress difference; but dilatancy in unloading is bigger than that in loading under the same principal stress difference. Rock sample fails as confining pressure unloaded to about 60 % of initial confining pressure in pre-peak unloading confining pressure test; and as confining pressure unloaded to about 80 % of initial confining pressure in post-peak unloading confining pressure test, it fails. The conclusion can be for reference in internal correlative engineering stability analysis, design and construction.

Key words: pre-peak unloading confining pressure, post-peak unloading confining pressure, unloading