A new method for nondestructive testing of mudstone moisture migration process by nuclear magnetic resonance
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摘要: 利用传统方法测试岩土体内水分迁移时，往往要将原状土破碎和重塑，这会改变岩土体的结构，影响测试结果的真实性。利用核磁共振(NMR)技术具有无损测量材料中水分的特点，提出了一种新的测试方法。首先进行标定试验，将岩土试样放置在0~0.05 T的非均匀磁场中用不同的磁场强度测试，获得NMR信号量和试样水含量间的函数关系；然后对土样进行一维入渗试验与NMR测试，记录入渗时间、入渗水质量和不同位置条件下试样的NMR信号量；最后，根据标定试验所得NMR信号量与水含量之间的函数关系，计算获得试样中水分的空间分布。采用烘干法进行验证，试验结果与理论结果最大误差为4.05 %。Abstract: When traditional methods are used to test soil moisture migration of rock and soil, the undisturbed soil is often broken and reshaped, which will change the structure of rock and soil and affect the authenticity of the test results. In order to solve this problem, a new testing method is proposed by using the characteristics of nuclear magnetic resonance(NMR)technology for nondestructive measurement of moisture in materials. Firstly, the calibration experiment was carried out to establish a functional relationship between the NMR signal amplitude and the position of a soil sample with unit water mass in a non-uniform magnetic field of 0~0.05 T. Second, a one-dimensional infiltration experiment and NMR test were conducted to record the infiltration time, water mass increase and NMR signal under different test positions. Then, using the functional relationship obtained in the calibration experiment, approximations of the moisture mass and its spatial distribution in the sample were obtained by comparing the theoretical signal and the measured signals. Finally, the mudstone sample was cut into several parts to perform a verification experiment by oven drying, and the results showed that the error in water content was 4.05 % or less.
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Key words:
- water migration /
- nondestructive testing /
- nuclear magnetic resonance /
- mudstone
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图 3 在均匀磁场与非均匀磁场中的不同位置对试样进行测试
Figure 3. Test the sample at different positions in the uniform and non-uniform magnetic field
图 4 标定试样在磁场均匀和非均匀区的信号量实测值及其拟合曲线
Figure 4. The measured signal amplitude of the calibration sample in the uniform and non-uniform magnetic field and its fitting curve
图 5 不同测试位置的横向弛豫时间T2的分布
Figure 5. Distribution of the transverse relaxation time T2 at different test positions
图 8 试样在各次测试中的横向弛豫时间分布
Figure 8. Transverse relaxation time distribution of the sample in each test
图 9 理论信号量与实测信号量对比
Figure 9. Comparison between the calculated signal amplitudes and measured amplitudes
图 10 长条形土柱中含水率的空间分布
Figure 10. Spatial distribution of water content in long soil column
表 1 矿物X-射线衍射分析结果
Table 1. Mineral X-ray diffraction analysis
全岩矿物相对含量/% 黏土矿物相对含量/% 石英 斜长石 微斜长石 黏土总量 I/S It Kao C 33 9 6 52 80 15 3 2 注：S为蒙脱石，It为伊利石，C为绿泥石，Kao为高岭石，I/S为伊蒙混层。 
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表 2 参数a与含水率w之间的关系
Table 2. The relationship between a and w
a 5 011 4 605 4 363 4 135 w/% 10 18 25 31
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表 3 烘干泥岩试样在各测试位置的初始信号量
Table 3. The initial signal amplitude of dry mudstone samples at each test position
测试位置/mm 0 8 16 24 32 40 初始信号量 1 461 1 456 1 405 1 191 872 546
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表 4 水分迁移试验数据
Table 4. Test data of moisture migration
测试时间/h 试样总质量/g 试样中水的质量/g 0 5.988 0 0 24 6.612 0 0.624 0 48 7.085 3 1.097 3 72 7.496 5 1.508 5 120 7.816 7 1.828 7
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表 5 烘干法测试结果与NMR测试结果
Table 5. Drying method and NMR test results
土柱分层 质量/g 烘干后试样的质量/g 土柱中水的质量/g NMR信号换算的水质量/g 误差/% 1 1.544 4 0.989 8 0.554 6 0.577 1 4.05 2 1.335 4 0.998 1 0.337 3 0.346 3 2.67 3 1.263 3 0.996 0 0.267 3 0.277 0 3.64 4 1.252 9 1.006 2 0.246 7 0.249 3 1.05 5 1.196 8 1.002 9 0.193 9 0.199 4 2.85 6 1.182 0 0.995 0 0.187 0 0.179 5 -3.99
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