In this paper, the nuclear magnetic resonance (NMR) measurements are carried out to evaluate the micro‐cracking characteristics of sandstones during the creep stage under the different levels of creep stresses. The variations in the parameters, including transverse relaxation time (T₂) spectra distribution, percentage of the pore distribution, incremental value of porosity and ultrasonic P wave velocity are analysed. The results show that, during the creep stage, small pores in the rocks gradually evolve into large pores, resulting in an increase in damage of rocks. With the increase of the loading ratio, the increasing rate of porosity increases sharply, implying that the damage degree becomes more serious under the high loading ratio. When the loading ratio is larger than 0.7, the increasing rate of porosity and the decreasing rate of the P wave velocity both increases rapidly. During the creep stage, the relationship between micro‐crack and macro‐creep characteristics of rocks is established based on the analysis of the deformation and the porosity evolution during creep. It is found that, as the loading ratio increases, the increasing rate of porosity is linear with the creep strain. The NMR method offers a feasible option to identify micro‐cracking process of rocks during the creep stage, which can directly reflect the damage mechanism of rock caused by creep. The porosity of rocks is an effective parameter to evaluate the damage of rocks. The damage evolution of the specimen is highly anisotropic and is heavily related to the loading ratio during the creep stage. The relationship between the damage parameter and the loading ratio is exponential.

中文翻译：

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使用NMR测量分析不同水平单轴应力下蠕变阶段砂岩的损伤。

在本文中，进行了核磁共振（NMR）测量，以评估在不同蠕变应力水平下蠕变阶段砂岩的微裂纹特征。参数的变化，包括横向弛豫时间（T ₂）光谱分布，孔隙分布百分比，孔隙率增量值和超声P分析波速。结果表明，在蠕变阶段，岩石中的小孔逐渐演变成大孔，导致岩石损伤的增加。随着载荷比的增加，孔隙率的增加速率急剧增加，这意味着在高载荷比下破坏程度变得更加严重。当负载比大于0.7时，孔隙率的增加率和P的减少率波速都迅速增加。在蠕变阶段，通过对蠕变过程中的变形和孔隙演化的分析，建立了岩石的微裂纹与宏观蠕变特征之间的关系。发现随着载荷比的增加，孔隙率的增加率与蠕变应变成线性关系。核磁共振法提供了一个可行的选择，可以识别蠕变阶段岩石的微裂纹过程，这可以直接反映蠕变对岩石的破坏机理。岩石的孔隙度是评估岩石损伤的有效参数。试样的损伤演化是高度各向异性的，并且与蠕变阶段的载荷比密切相关。损伤参数与载荷比之间的关系是指数关系。