In order to research the unloading property of the marble in the course of excavation

the different modes of the unloading experiments on marble which are come from the seepage tunnel of Liangshan Yalongjiang Dahewan Jinping Water Power Station in Sichuan Province have been done by hydraulic pressure servo rigidity rock mechanics experiment system MTS815.04. The results of the experiments show that: on condition of keeping the principal stress difference invariant

when the confining pressure decrease

the axial strain will increase after decrease

but the elastic modulus first increase before decrease; on condition of keeping the axial displacement invariant

when the confining pressure decrease

the elastic modulus of the samples first increase

then decrease after reaching the peak value; but the axial stress is always decreasing; the Poisson's ratio obtained from the unloading experiments on condition of keeping the principal stress sum invariant is greater than that obtained from the routine triaxial test; but the marble strengths obtained from two experiments haven’t a clear distinctness.