研究背景：在膨胀土工程问题中，准确测量土壤的湿度至关重要。然而，膨胀土中存在裂缝，会对测量结果产生影响，这是当前研究领域存在的一个问题。本研究通过使用主动加热光纤布拉格光栅（AH-FBG）传感技术来测量膨胀土的原位湿度，并通过一系列数值模拟，研究了土壤裂缝对监测结果的影响，并提出了一种修正函数来消除测量误差。
研究内容：本研究采用主动加热光纤光栅感应技术，通过数值模拟研究了土壤裂缝对测量结果的影响，并提出了一种修正函数来消除测量误差。研究结果表明，蔡氏模型能够准确描述热导率与湿度之间的关系，并被用作校准模型。在加热策略下，传感器的影响范围在径向上大约为4厘米。在该范围内的裂缝会阻碍热传输，导致湿度监测结果的低估。修正后的测量结果的均方根误差（RMSE）降低到0.030 m3·m−3，这证实了AH-FBG传感技术可以在考虑裂隙影响的前提下，可靠地测量膨胀土的湿度。
研究意义：本研究的创新点在于使用主动加热光纤光栅传感技术来监测膨胀土湿度，并通过数值模拟研究了土壤裂缝对测量结果的影响，在此基础上提出了一种修正函数来消除测量误差。这项技术的成功应用为解决膨胀土工程问题提供了可靠的监测手段，对于岩土工程领域具有重要的研究意义。 该成果发表在国际期刊《Measurement》上。
Study on actively heated fiber Bragg grating sensing technology for expansive soil moisture considering the influence of cracks
Li J.; Zhu H.-H.; Wu B.; Hu L.-L.; Liu X.-F.; Shi B.
Published：2023-08-15
Measurement 218 (2023) 113087
DOI: 10.1016/j.measurement.2023.113087
Abstract: Accurately moisture content measurement is crucial in addressing engineering problems of expansive soil with cracks. In this study, the actively heated fiber Bragg grating (AH-FBG) sensing technology was used to measure in-situ moisture contents of expansive soil. The impact of soil cracks on the measurements was investigated through a series of numerical simulations, and a modified function was proposed to eliminate measurement errors. The results show that the Cai model can accurately describe the relationship between the thermal conductivity and moisture content, and is thus utilized as the calibration model. Under the heating strategy, the influence range of the sensor is roughly 4 cm in the radial direction. Cracks within that range hinder heat transmission, leading to underestimation of moisture contents. The RMSE of the measurements after modification is reduced to 0.030 m3⋅m-3, which verifies that AH-FBG sensing technology can be extended to the reliable measurement of expansive soil moisture.
Keywords: Expansive soil, Crack, Geotechnical monitoring, Fiber Bragg grating (FBG), Moisture content, Thermal conductivity
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