Estimation of Moisture Content in Railway Subgrade by Ground Penetrating Radar
Estimation of Moisture Content in Railway Subgrade by Ground Penetrating Radar
复制标题
探地雷达估算铁路路基含水率
DOI：
10.3390/rs12182912
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发表时间：
2020-09-01
期刊：
影响因子：
5
通讯作者：
Wang, Yuanxin
中科院分区：
文献类型：
--
作者：
Liu, Sixin;Lu, Qi;Wang, Yuanxin
我国对铁路运输的依赖性很强，但寒冷地区路基的冻胀严重影响了列车的安全性和舒适性。含水率是路基冻胀的重要参数。无损、高效的地球物理方法在铁路路基含水量检测中具有巨大的潜力。在本文中，我们使用共中点（CMP）测量的探地雷达（GPR）估计电磁波的传播速度在路基应用。建立了铁路路基结构的综合模型。浅层和薄层的CMP道集受多次波和折射波的严重干扰，常规速度分析无法提供准确的速度。通过对数值模拟结果的分析发现，在CMP道集不同炮检距范围内，一次反射波、多次波和折射波均占主导地位。因此，本文提出了一种以一次反射波为主的一定炮检距范围内的最优道集解，用于计算速度谱，提取路基模型的精确速度。将叠加速度转换为层速度后，计算相应层的相对介电常数。然后，通过Topp公式获得含水率，该公式表示介电常数与含水率之间的关系。最后，我们应用最佳的收集方案和上述解释过程中获得的地质雷达数据在铁路现场，我们形成了一个长的铁路路基含水率剖面。通过与激发极化法测量的极化率对比，发现高含水率区域对应不同强度的极化率异常。通过对比，在一定程度上说明了探地雷达结果的可靠性。
China is strongly dependent on railway transportation, but the frost heaving of the subgrade in cold regions has seriously affected the safety and comfort of trains. Moisture content is an essential parameter in the subgrade frost heave. Non-destructive and efficient geophysical methods have great potential in measuring the moisture content of railway subgrade. In this paper, we use the common mid-point (CMP) measurement of ground penetrating radar (GPR) to estimate the propagation velocity of electromagnetic waves in a subgrade application. We establish a synthetic model to simulate the railway subgrade structure. The synthetic CMP gathers acquired from shallow and thin layers are seriously disturbed by multiple waves and refraction waves, which make the routine velocity analysis unable to provide accurate velocities. Through the analysis of numerical simulation results, it is found that the primary reflection waves, multiple waves, and refraction waves are dominant in different offset ranges of CMP gather. Therefore, we propose a solution of the optimal gather at a certain range of offset dominated by the primary reflection wave to calculate the velocity spectrum and extract the accurate velocities for the subgrade model. The relative dielectric constants of the corresponding layers are calculated after the stacking velocities are converted into the interval velocities. Then, the moisture content is obtained by the Topp formula, which expresses the relationship between dielectric constant and moisture content. Finally, we apply the optimal gather scheme and the above interpretation process to the GPR data acquired at the railway site, and we form a long moisture content profile of the railway subgrade. Compared with the polarizability measured by the induced polarization (IP) method, it is found that the regions with high moisture content correspond to polarizability anomalies with different strengths. The comparison shows the reliability of GPR results to some extent.