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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.
In order to study the meso-damage evolution characteristics of pore structure in unloading rock mass, taking marble as the sample, the conventional triaxial unloading test with initial confining pressure of 10, 20 and 30 MPa and different unloading confining pressure NMR test, stress-strain curves of unloading rock mass, T2 distribution of lateral relaxation time, porosity and MRI images were obtained.With the increase of unloading confining pressure ratio, the rock transformed from elastic deformation to plastic deformation , The pore size of small pores increases, the number of macropores increases and the pore diameter increases; the unloading confining pressure ratio is less than 90%, the damage of rock mass is mainly caused by the increase of pore volume, and the unloading confining pressure ratio is higher than 90 %, The damage is caused by the sharp increase in the number of pores and the pore diameter. The porosity of rock samples increases with the increase of unloading confining pressure ratio, and the growth rate increases faster and faster. The NMR images intuitively reflect the unloading rock Body internal porosity, pore size and structural changes.