冻融岩石核磁共振检测及冻融损伤机制分析

以花岗岩为岩样在最低冻结温度为-40 ℃、融化温度为20 ℃的条件下对5组岩样开展了冻融循环试验，最高累积冻融循环次数为100次，并采用核磁共振（NMR）技术检测岩样内部损伤变化。试验结果表明，冻融作用会对岩石内部造成损伤，循环次数达到一定值时岩样表面产生明显裂纹；NMR T2谱图和成像结果表明，冻融作用使岩样孔隙结构重新分布，孔隙数量随循环次数增加而增加，产生裂纹后T2曲线信号幅度发生显著变化。最后使用损伤力学原理对花岗岩冻融损伤机制进行探讨，得到材料连续性与孔隙率的损伤关系、有效应力与孔隙率的关系表达式，并以岩样核磁共振结果为基础，得出其有效应力与循环次数的表达式。

Study of rock NMR experiment and damage mechanism analysis under freeze-thaw condition

Taking granite as samples,a freeze-thaw cycle experiment(with the temperature ranged from-40℃ to 20℃) is conducted.The highest cycles are 100.Nuclear magnetic resonance(NMR) technology is employed to observe the rock damage changes.The results show that freeze-thaw cycle action will produce damages to the sample.Some samples crack after a certain cycles.Both the T2 spectrum and NMR image indicate that the action of freezing and thawing cycle redistributes the inner structure of sample.The T2 curves change greatly after the cracks emerged.Finally,damage mechanism is adopted to analyze granite damage principle in condition of freeze-thaw.An equation of material continuity and porosity is obtained.Then an equation between effective stress and porosity is established.Taking N-4 for example,the relationship between effective stress and cycles is obtained.