基于NMR技术的充填体孔隙结构的冻融损伤演化特征
Characteristics of Freeze-thaw Damage Evolution of Pore Structure in Backfill Material Based on NMR Technology
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摘要: 为了研究在反复冻融循环条件下充填体内部孔隙结构的变化规律,运用核磁共振(NMR)技术对0、50、100和200次冻融循环后的试样细观结构损伤进行扫描,获得核磁共振弛豫时间T2谱,并对循环后试样进行拍照记录;在此基础上,分析了试样孔隙演化的规律和细观结构损伤的机理。结果表明:由T2分布曲线可以反映冻融循环作用下试样内部孔隙的演化和扩展特点;随冻融循环次数的增加,表征材料孔隙率大小的T2谱面积呈现初期增加速度较快,后期增速减小的规律,其中小孔隙比例随循环次数增加而减小,大孔隙比例随次数增加而增大;通过探讨孔隙结构演化机理,提出冻融循环中渗透力和冻胀力共同作用是砂浆结合面出现破坏而形成连通裂隙的根本原因。Abstract: To study the evolution rule of pore structure in backfill material under freeze-thaw cycles, the nuclear magnetic resonance (NMR) technique was used to scan the meso-structure damage after 0, 50, 100 and 200 freeze-thaw cycles to obtain the relaxation time T2 spectrum of NMR. The laws of pore evolution and the mechanism of meso structure damage were analyzed. The results show that the variation of T2 distribution curves reflects the evolution and expansion characteristics of the pores in the samples under freeze-thaw cycles; with the increase of freeze-thaw cycles, the T2 spectral area which characterizes the porosity of the materials increases rapidly at the initial stage and decreases at the later stage, and the proportion of small pores increases with the number of cycles. With the increase of cycles, the ratio of macro-pores increases with the increase of the number of times. Through the discussion of the evolution mechanism of pore structure, it is pointed out that the joint failure due to the combined action of osmotic force and frost heave force in freeze-thaw cycles is the fundamental reason for the formation of the connecting fracture.
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