利用探地雷达精确探测铁路路基含水率

Accurate detection of moisture content of subgrade by GPR

冻胀是寒冷地区铁路运营的一个重要的安全隐患,因此必须查明铁路路基地下含水情况.对于铁路路基这种水平层状介质,利用探地雷达共中心点法测量数据,对预处理后的数据进行速度分析获取,通过Dix公式转换求取层速度后将其转化为介电常数,利用Topp公式可得到该点地下含水率.将多个共中心点的含水率进行插值,可得到地下含水率剖面.然而由于铁路路基的地层具有浅薄层状的特点,这使得速度分析中存在各种干扰.利用GPRmax软件进行正演模拟,发现随着偏移距的增大多次波及折射波的问题越来越明显.为解决这类问题进行了大量的模拟试验,分析试验结果并提出在速度分析中的采用最优化角度消除多次波及折射波影响的办法,提高了处理精度.利用该技术处理实际数据,处理结果与常规激发极化法异常位置具有很好的可比性.

In cold regions, heaving of the railway subgrade brings an important security risk to high-speed rail. Thus,it is necessary to find out the moisture content of the roadbed. Common Mid-Point （CMP） measurement using Ground Penetrating Radar （GPR） was carried out to estimate the underground moisture content. This method is only applicable to such railway embankment,which is a horizontally layered medium. At first, the data will be analyzed by velocity spectrum to get stacking velocity. Then vertical interval velocity profile can be accurately deduced by Dix can be obtained and converted into dielectric constant. So moisture content can obtain by Topp formula. Through interpolation, the moisture content profile of the underground will be got. However, the shallow and thin layers bring lots of problem to velocity analysis. With the help of GPRmax simulated results, we find that the problem of multiple waves and refracted waves are more obvious with the increase of the offset. A large number of simulation experiments has been done to solve this kind of this problem. Using the optimization angle can eliminate the effects of multiple wave and refracted waves. And in the actual process, under the guidance of the simulated result, it＇s obvious that the last result is comparable to the result of polarizability.