动静载荷作用下含孔洞硬岩损伤演化的核磁共振特性试验研究

STUDY ON THE DEGRADATION OF HARD ROCK WITH A PRE-EXISTING OPENING UNDER STATIC-DYNAMIC LOADINGS USING NUCLEAR MAGNETIC RESONANCE TECHNIQUE

为研究含孔洞的岩石在动静载荷作用下的细观结构损伤破坏规律,对含圆形和方形孔洞的花岗岩试样分别进行不同轴向预静载、相同冲击动载下的霍普金森压杆试验,并对动静加载前后的试样进行核磁共振(NMR)测试,得到花岗岩试样的弛豫时间T2谱曲线、核磁孔隙度和核磁共振图像等特性参数。试验结果表明,随着轴向预静载的增大,花岗岩受动力扰动作用后的T2谱峰值、谱面积以及核磁孔隙度均逐渐增大,岩石内部的损伤程度不断加剧,且当预静载大于10 MPa时,动力作用下岩石的损伤劣化特性表现得越来越敏感。对比分析含圆形和方形孔洞试样的核磁共振特性试验结果,发现相同荷载条件下方形孔洞试样的损伤程度均大于圆形孔洞试样,这一规律在预静载大于10 MPa时表现得更突出。核磁共振图像直观反映出孔洞花岗岩在动静载荷作用下岩石内部的孔隙结构和损伤劣化的演变规律,为揭示深部硬岩巷道的动力破坏机制提供有意义的试验指导。

To investigate the degradation of rock microstructure under static and dynamic loads,split Hopkinson pressure bar(SHPB) tests of granite specimens with a pre-existing opening under various axial pre-stresses and the same dynamic load were conducted. The crosswise relaxation time T2 distribution,porosity and nuclear magnetic resonance images were obtained with the nuclear magnetic resonance(NMR) technique. The peak spectrum of T2,the spectral area and the porosity of the granite specimens subjected to the dynamic loading all increased with the increase of static axial pre-stress. The degradation of granite under static-dynamic loads was more sensitive when the static pre-stress exceeded 10 MPa. The NMR results of specimens with the circular opening and ones with the square opening were compared. The damage of the specimen with the square opening was severer than that with the circular opening,and this phenomenon was more pronounced when the static pre-stress exceeded 10 MPa. The NMR images yielded the straightforward demonstration of the damage degradation process of pore structure of granite under static-dynamic loads.