用NMR法验证在冻土中TDR标定曲线的可靠性

TDR技术是一种较新的测定冻土中未冻水含量的方法, 它有很多优点, 但是由于TDR技术应用于冻土中测定未冻水含量起步较晚, 其可靠性有待于进一步验证. NMR技术是一种较成熟的测定冻土中未冻水含量的方法. 通过应用NMR和TDR两种方法对不同初始含水率下的棕壤土冻融特征曲线的测定, 对TDR法的标定曲线的可靠性进行了验证. 结果表明: 采用TDR法与NMR法测得的冻融特征曲线明显不同, 在相同负温下前者的测定值高于后者, 且其差异随初始含水率增高而加大; NMR法的测定结果表明, 初始含水率对冻融特征曲线的影响很小; 而TDR法的测定结果表明, 由TDR法测得的冻融特征曲线, 受初始含水率影响很大, 随初始含水率的升高而明显加大. 这表明含冰率和温度对冻土的介电常数影响很大, 因此, 采用TDR法测定冻土的未冻水含量时不宜采用原有的标定曲线.

Reliability of Calibration Curves Measured by TDR in Frozen Soils Verified by NMR

Measuring unfrozen water content in frozen soil by TDR is a new technique. It has many advantages. However, there is less experience in using the technique, and it is necessary to verify its reliability. The NMR is a mature technique in measurement of unfrozen water content in frozen soil. In this study, the freezing and thawing characteristic curves of umber soil with different initial water content were measured by TDR and NMR methods, and the reliability of the calibration curves of TDR method was verified. The result shows that the freezing and thawing characteristic curves measured by NMR and TDR is obviously different. At the same negative temperature, the unfrozen water content measured by TDR is higher than that by NMR, and the difference increases obviously with increase of initial water content. The results measured by NMR show that the initial water content has a little effect on the freezing and thawing characteristic curves. Whereas the results obtained by TDR show that the initial water content has obvious effect on the freezing and thawing characteristic curves, and the unfrozen water content increases apparently with increase of the initial water content. These results show that ice content and temperature have obvious effect on the dielectric property of frozen soil. So the intrinsic calibration curve of TDR for unfrozen soil should not be applied to the measurement of unfrozen water content in frozen soil directly.