中文摘要：

为研究卸荷岩体内部孔隙结构的细观损伤演化特征,以大理岩为岩样,分别进行初始围压为10、20和30 MPa,不同卸荷围压量的常规三轴卸荷试验和核磁共振测试实验,获得卸荷岩体的应力-应变曲线、横向弛豫时间T2分布、孔隙度及核磁共振成像图像.随着卸荷围压比的增大,岩石由弹性变形转化为塑性变形,岩样内小孔隙的孔径增大,大孔隙的数量增多且孔径增大;卸荷围压比低于90%,岩体损伤主要由孔隙数量的增多引起,卸荷围压比高于90%,损伤由孔隙数量和孔径均急剧增大引起;岩样的孔隙度随着卸荷围压比的增大而增大,且增速越来越快;核磁共振图像直观地反映卸荷岩体内部孔隙数量、孔径及结构变化情况.

英文摘要：

To investigate the meso-damage evolution characteristic of unloading rock mass,unloading confining pressure tests on marble specimens were first conducted under initial confining pressures of 10,20 and 30 MPa. Then nuclear magnetic resonance tests were performed on the unloaded specimens. The stress-strain curves,transverse relaxation time T2 distribution,rock porosity,and nuclear magnetic resonance imaging pictures of the unloaded specimens were obtained. It is found that the deformation of the unloaded specimens changes from elastic to plastic with the increase of unloading confining pressure ratio. As the unloading confining pressure ratio increases,the size of small microcracks increases,and the number and size of large microcracks also increase. When the unloading confining pressure ratio is less than 90%,the damage of rock mass is mainly caused by the increase in number of microcracks.But when the unloading confining pressure ratio exceeds 90%,the damage of rock mass is caused by the sharp increase in number and size of microcracks. The rock porosity increases with the increase of unloading confining pressure ratio,and the growth rate becomes greater. The development processes of the number,size and structure of microcracks in the rock specimens under different initial confining pressures and different unloading confining pressure ratios can be directly visualized by nuclear magnetic resonance imaging pictures.