Understanding the impact of mining disturbances and creep deformation on the macroscopic deformation and the microscopic pore and fracture structures (MPFS) of coal is paramount for ensuring the secure extraction of coal resources. This study conducts cyclic loading-unloading and creep experiments on coal using a low-field nuclear magnetic resonance (NMR) experimental apparatus which is equipped with mechanical loading units, enabling real-time monitoring the T2 spectrum. The experiments indicated that cyclic loading-unloading stress paths initiate internal damage within coal samples. Under identical creep stress conditions, coal samples with more initial damages had more substantial instantaneous deformation and creep deformation during the creep process. After undergoing nearly 35 h of staged creep, the total strains for coal samples CC01, CC02, and CC03 reach 2.160%, 2.261%, and 2.282%, respectively. In the creep stage, the peak area ratio of seepage pores and microfractures (SPM) gradually diminishes. A higher degree of initial damage leads to a more pronounced compaction trend in the SPM of coal samples. Considering the porosity evolution of SPM during the creep process, this study proposes a novel fractional derivative model for the porosity evolution of SPM. The efficacy of the proposed model in predicting porosity evolution of SPM is substantiated through experimental validation. Furthermore, an analysis of the impact mechanisms on key parameters in the model was carried out.

中文翻译：

---

初始损伤和蠕变行为诱导的煤孔隙和裂缝结构的时空演变：一种基于实时核磁共振的方法


了解采矿扰动和蠕变变形对煤炭宏观变形和微观孔隙和裂缝结构 （MPFS） 的影响对于确保煤炭资源的安全开采至关重要。本研究使用配备机械加载单元的低场核磁共振 （NMR） 实验装置对煤炭进行循环加载-卸载和蠕变实验，能够实时监测 T2 光谱。实验表明，循环加载-卸载应力路径会引发煤样内部损伤。在相同的蠕变应力条件下，初始损伤较多的煤样在蠕变过程中具有更显著的瞬时变形和蠕变变形。经过近 35 h 的分段蠕变后，煤样 CC01、CC02 和 CC03 的总应变分别达到 2.160%、2.261% 和 2.282%。在蠕变阶段，渗流孔和微裂缝 （SPM） 的峰面积比逐渐减小。初始损伤程度越高，煤样 SPM 的压实趋势越明显。考虑到 SPM 在蠕变过程中的孔隙率演变，本研究提出了一种新的 SPM 孔隙率演变分数阶导数模型。通过实验验证，证实了所提出的模型在预测 SPM 孔隙率演变方面的有效性。此外，还对模型中关键参数的影响机制进行了分析。