摘要:
离子浓度在一定程度上会引起冻土冻融过程中其未冻水的含量变化,进而影响冻土的核磁共振响应.为了研究冻土冻融过程中离子浓度对其核磁共振响应的影响规律,笔者采用的试验样本是将不同浓度的NaCl溶液与马兰黄土混合,配制成NaCl含量不同、初始含水量相同的各样本,研究其弛豫特性.通过分析不同温度点下各样本的核磁共振响应特征,得到不同离子浓度对冻土核磁共振响应的影响规律.结果表明,核磁共振信号幅值随着离子浓度的增大而增大,但是横向弛豫时间T2不受离子浓度影响;在冻土冻融过程中,冻土中流体受温度和离子结晶物化作用的双重影响,样本的未冻水含量在不同温度区间的变化有所不同,但是在大于5℃和低于-20℃区间内,未冻水含量趋于稳定.
关键词:
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核磁共振
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离子浓度
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冻土
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温度
Abstract:
The concentrations of ions will have a certain effect on the change of unfrozen water content of permafrost in the frozen-thaw process and therefore on the nuclear magnetic resonance response signal of frozen soil.In order to study the influence of the ion concentration on NMR signal,the authors made the samples with the mixture of NaCl solution and Malan loess in which NaCl values are different and initial water values are the same.By analyzing the NMR response characteristics of the samples at different temperatures,the authors summarized the influence of the ion concentration on the NMR response of permafrost.The results show that increasing the ion concentration will lead to the increase of the amplitude of the NMR signal,but will not affect the transverse relaxation time,and that,during the frozen-thaw process,the fluid will be affected by the temperature and ionic crystals.Samples of unfrozen water content will change in different temperature ranges,but when temperature is higher than 5℃ or lower than-20℃,unfrozen water content will tend to be stable.
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