Abstract：Unloading stress path resulted from underground rock mass excavation is completely different from loading stress path，for which results in difference from that of rock mass strength，deformation property and failure mechanism. The surrounding rock mass of diversion tunnel group of Jinping II Hydropower Station lies in the condition of high geostresses. Aiming at this characteristics，four various stress paths are chosen as test schemes corresponding as the uniaxial loading and unloading test，triaxial compressive test，pre-peaking and post-peaking unloading the confining pressure test under high stress conditions are carried out on the marble specimens from the diversion tunnel #3. The complete stress-strain curve，deformation properties，failure characteristics and change rule of major mechanical parameters are obtained under respective stress path. Some instructive conclusions are drawn from above experimental research as follows：(1) the turning rings for axial repeated unloading vary with gradual higher stress level in terms of area and the unloading stress at yielding stage takes the greatest effect on deformation；(2) the triaxial compressive tests performed under different confining pressures discover that strain softening attribute of marble begins to transferred to ideal plasticity when confining pressure reaches above the value of 40 MPa；so it can be considered as the transition point of brittleness and ductility；(3) by compared with the strength criteria equations under different stress paths，and regular peaking strength parameters，under the same initial stress conditions，the changed magnitude of stress required for rock failure is comparably less than that of triaxial compressive process，which reveals that marble sample is more prone to be subject to failure under unloading stress path；the pre-peaking confining stress unloading path strength are the most sensitive to confining pressure；(4) in terms of deformation property and failure characteristics of marble，its brittleness is constrained by plastic deformation；plastic deformation under post-peaking unloading path is greater than that of pre-peaking；and it has absorbed considerably elastic deformational energy after reaching peaking strength；therefore，post-peaking failure has no outburst property under this stress path；the rock failure mode transforms from tensile failure to the combination of tensile and shear failure；and (5) according to the results of SEM test performed on fractures of marble specimens in case of loading and unloading paths，fracture analysis of marble specimens under different stress paths validates the microcosmic tension and shear failure mechanisms. In conclusion，the above research reveals the differences in mechanical properties of Jinping marble under loading and unloading paths，and it can offer valuable references in solving underground rock engineering problems.
