EXPERIMENTAL RESEARCH ON MECHANICAL PROPERTIES OF DEEP-BURIED MARBLE UNDER DIFFERENT UNLOADING RATES OF CONFINING PRESSURES

In order to understand exactly the influence of unloading rate on mechanical properties of rock,the unloading confining pressure tests under different unloading rates are carried out,which use new loading path and operation method.Thus the disadvantageous effect on test process of the results is reduced.And the deep-buried marble samples cored from Jinping II hydropower station are tested.Based on a new description variable presented as strain-pressure compliance,the influences of the unloading confining pressure path are analyzed on the axial and volume deformations and strengths.The results indicate that the unloading rates of the confining pressure have significant influence on the deformation of Jinping marble,and the initial confining pressure levels mainly control the corresponding influence rules.There are obvious differences in the dilatant processes between the unloading confining pressure tests and triaxial compression tests.In unloading confining pressure tests,the limited bearing loads under the range of unloading rates between 0.01 MPa/s and 1.0 MPa/s are higher than those in the conventional triaxial compression tests under the loading rate of 0.5 MPa/s.Limited bearing capacity increases along with the rise of unloading rates,and increases 10%-15% at the rate of 1.0 MPa/s.