题目：Study on Ground-Penetrating Radar (GPR) Application in Pavement Deep Distress Detection
作者：Songtao Li1,2, Chengchao Guo1,3*
期刊：Journal of Transportation Technologies
0 Abstract
As some deep distresses exist in pavement structures,== ground-penetrating radar (GPR) reflected waves will vary at interfaces and defects==. Aimed at detecting the distresses in terms of position, severity and degree, electromagnetic forward simulations based on 400 MHz and 900 MHz antennas were conducted respectively. The dielectric models concerning homogeneous or coupling distresses of pavements were established, and the effects of various distresses on detection were analyzed through reflected wave images. Relying on GPR tests and field tests, coring and excavation data acquired before rehabilitation were compared and verified. The calculation results match the field measurement results. Thus, the detection method based on GPR was proposed for pavement deep distresses.
interfaces and defects:界面和缺陷
coring and excavation data:取芯和开挖数据
本文就是简单地通过对反射波图像进行分析，识别病害。下面重点关注他究竟如何操作。
本文将对GPR在路面深部病害检测中的应用进行数值模拟和现场试验。 此外，还将进行案例研究，为路面的设计，施工，维护和修复提供参考。
2 Numerical Simulation
首先，确认您具有正确的纸张尺寸模板。 该模板经过定制，可在自定义纸张尺寸（21厘米×28.5厘米）上输出。 时域有限差分（FDTD）方法可以归类为高频电磁场模拟方法。 它已广泛应用于GPR电磁波传播的正演模拟中。 根据Maxwell方程的原理以及James和Rosemary [10]的结果，对模型和PML吸收边界条件进行了修改。 根据不同的频率，设置了不同的时间窗口，并且对来自400 MHz和900 MHz地面耦合天线的反射波进行了前向仿真，以验证GPR在检测路面深处遇险中的有效性和可靠性。
- 首先从预设路面深层的缺陷开始.
- 然后，GPR将信号传输到异常位置，并记录反射波。
因此，与模拟光谱相反，可以检测到缺陷。
路面结构由几层组成，如表1所示。对于各种路面材料，介电常数ε，磁导率μ和电导率σ具有不同的值。通常，由于铺面材料是非磁性的，因此将磁导率μ设置为1。在Maxwell方程中，介电常数ε和电导率σ分别等于介电常数的实部和虚部。因此，可以确定ε和σ的值。由于沥青混凝土显示出相似的介电性能，因此可以将三个表面层简化为一层。表1列出了每一层的典型介电值。在此模型中，采用中位数作为介电常数。可以建立路面结构层的介电模型。在每一层内，可能存在几个不同尺寸的异常区域，分别指示缺陷。对于不同的路面结构，缺陷会导致ε和σ值发生变化。在模拟中，选择了8种典型的道路结构疾病作为代表。所选案例可能并不十分全面，但可能有助于揭示GPR在路面深部遇险检测中的可行性。此外，通过比较不同情况下400 MHz和900 MHz的仿真结果，可以展示这两种天线各自的优势。
总结：作者设定缺陷位置和对应参数，进行正演，观察反射波图像。
建立具有各种模拟缺陷的电介质模型，并且缺陷随类型，深度和尺寸而变化。 光源以一定的间隔放置在接收器的前面。 当源波在路面结构中以一定速度传播时，该波将被接收器记录下来。
- Case 1: 正常状况
==The dielectric model of pavement ==with locally undercompacted surface course is shown in Figure 1(a), and several layers are contained in the model, i.e. , air layer, surface course, base course, subbase course and subgrade. Three undercompacted zones are presented in surface course with the dimension of 1 cm × 1 cm, 1 cm × 3 cm and 1 cm × 5 cm respectively, and the corresponding reflected wave image is illustrated in Figure 1(b).
- Case 2: 存在未压实区域
The dielectric model of pavement with locally undercompacted zones in the intermediate surface course is shown in Figure 10(a). The two small undercompacted zones were contained with the dimension of 0.5 cm × 10 cm and 0.25 cm × 5 cm respectively. The corresponding reflected wave image is shown in Figure 10(b). Although the target defects became smaller, they still could be detected through the reflected wave image with higher frequency propagation.
道路的电介质模型:dielectric model of pavement
空气层，地表层，基础层，路基层和路基:air layer, surface course, base course, subbase course and subgrade
- Case 3:充满水
The dielectric model of pavement with voids in the bottom of surfacecourse is shown in Figure 3(a), and the defect dimension was 5 cm × 50 cm. Voids were filled with water, and the corresponding reflected wave is illustrated in Figure 3(b).
- Case 4:基部顶层存在三处未压实区域
The dielectric model of pavement with locally undercompacted zones in the base top is shown in Figure 12(a). Three abnormal zones were contained with the dimension of 0.5 cm × 3 cm, 0.5 cm × 5 cm and 1 cm × 1 cm respectively, and the corresponding reflected wave image is shown in Figure 12(b).
- Case 6: 基层和表面的层间不良
The dielectric model of pavement with poor bondingbetween base and surface course is shown in Figure 14(a). One distress was contained in the model with the dimension of 1 cm × 15 cm, and the corresponding reflected wave image is shown in Figure 14(b).
- Case 7: 基层和底基之间层间不良
The dielectric model of pavement with poor bonding between base and subbase is shown in Figure 15(a). One distress existed with the dimension of 0.5 cm × 15 cm, and the corresponding reflected image is shown in wave Figure 15(b).
- Case 8: 层间不良
The dielectric model of pavement with poor bonding between subbase and subgrade is shown in Figure 16(a). One distress existed with the dimension of 0.25 cm × 15 cm, and the corresponding reflected wave image is shown in Figure 16(b). As can be seen from Case 6 - Case 8, the set bonding conditions got weaker from the top to the bottom of pavement structures, while the defects still could generally be revealed through the simulation wave images.
- Case 9: 表面裂缝
The dielectric model of pavement with a crack in surface course is shown in Figure 17(a). One distress ( i.e. , a vertical crack) existed with the dimension of 15 cm × 1 cm. The corresponding reflected wave is shown in Figure 17(b), and it indicates that the vertical crack could also be identified through the reflected wave image.
总结：通过正演进行观察反射波图像。