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为研究不同初始损伤下大理岩的卸荷特性,开展相同初始围压、不同初始轴压的常规三轴加-卸载试验,并进行加-卸载后岩样的核磁共振(NMR)特性试验研究,得到岩样孔隙度、应变、核磁共振图像及T2谱分布等参量。结果表明:(1)随着卸荷的进行,岩样孔隙度增大,且当初始轴压为三轴抗压强度(TCS)的90%时,其卸荷过程比80%与70%时更加平稳;(2)初始损伤可以有效促进应变的增大,尤其对环向扩容效应影响显著,同时应变的增长能促进裂隙的发育;(3)初始损伤较小时,岩样经历弹性变形到塑性变形的转化,岩石的T2图谱中小孔隙谱峰先向左移,后向右移,大孔隙谱峰不断向右扩展,反映了卸荷初期产生新的小孔隙,卸荷后期主要是大、小裂隙的扩展、贯通。当初始损伤较大时,T2图谱只向右扩展,反映岩样以扩展大孔隙为主,岩样只经历塑性变形;(4)初始损伤越大,相同卸荷围压比的核磁共振图像白斑亮度和面积越大,岩样的孔隙度就越大。
In order to study the unloading characteristics of marble under different initial damage, the conventional triaxial uniaxial loading-unloading tests with the same initial confining pressure and different initial axial compressive stresses were carried out, and the NMR test of the samples after adding-unloading was carried out. The parameters such as porosity, strain, NMR image and T2 spectrum distribution were obtained. The results show that: (1) With the unloading, the porosity of rock samples increases, and when the initial axial compression is 90% of the triaxial compression strength (TCS), the unloading process is 80% and 70% (2) The initial damage can effectively promote the increase of strain, especially for the ring dilatancy effect, and the increase of strain can promote the development of the fissure. (3) When the initial damage is small, the rock specimen undergoes elastic deformation to plasticity Deformation transformation, the rock T2 spectrum of small pore peak first shift to the left, after the shift to the right, macroporous peak continued to expand to the right, reflecting the initial unloading new small pores, unloading mainly late, small Crack expansion, through. When the initial damage is larger, the T2 spectrum only expands to the right, reflecting that the rock samples mainly expand macropores, while the rock samples only undergo plastic deformation. (4) The larger the initial damage, the same unloading confining pressure ratio The greater the brightness and area, the greater the porosity of the sample.