【作者】 蔡迎春；

【导师】 王复明； 康海贵；

【作者基本信息】 大连理工大学 ， 水工结构工程， 2008， 博士

【摘要】 探地雷达(6PR)作为典型的电磁无损检测技术手段,由于其检测速度快、无破损、精度高等特点,已经广泛应用于地质勘探、考古、交通、土木、环保、水利、铁道等工程领域。随着道路建设与养护管理的不断发展,空气耦合式的6PR(即路面雷达)已经大量应用于道路施工质量控制和路况评价中。目前路面应用技术的研究主要围绕介电常数的确定来展开的,其中通过介质分界面上反射波波幅的相对大小和电磁波传播过程中衰减的人工假定来得到介电常数的研究成果较多,而通过反演算法研究介电常数的研究成果相对较少。另外,目前的绝大部分研究成果集中在半空间或层状的均质材料。而构成工程应用材料大部分是由固态、液态、气态三相介质组成的混合物,其材料本身的介电特性随着组成成分及其比例的变化表现出非均质的特性。受材料非均匀性质的影响,这种依赖于层间界面的反射波幅得到的介电常数,只能代表界面附近材料的介电特性,不能反映各层内部的材料介电特性,从而导致6PR分析厚度的误差以及应用的局限。本文针对上述雷达应用技术的相对不足,研究了基于层状非均匀介质的路面雷达应用技术,主要成果和结论如下:1、实现了电磁波在层状非均匀介质中传播的正演模拟建立了层状介质的非均匀介电模型,利用时域有限差分(FDTD)方法实现了平面波在层状非均匀介质中传播的模拟计算。将路面结构非均匀层状体系,等效成若干个均匀子层,实现了路面雷达层状非均匀正演模拟。通过与实测反射波的对比发现,非均匀模拟效果更加符合实测反射波。2、实现了层状非均匀介电特性的反演分析利用系统识别和遗传算法,实现了层状非均匀介质介电特性的反演。同时,考虑到系统识别初始值敏感性和遗传算法时效性问题,结合系统识别反演的局部快速收敛和遗传算法全局寻优的优点,提出了遗传算法和系统识别的联合反演算法。实例分析表明,联合反演算法不受初始值的影响,同时相对于遗传反演算法节省了大量时间。3、通过层状非均匀介电特性反演,结合现场相关试验,实现了结构层内部物理量的雷达检测与分析技术。非均匀的介电特性反映了结构层内部物理量变化的非均匀性,通过这些物理量与介电常数的相关试验,分别实现了路基碾压层内部含水量沿深度方向和水平方向的快速检测、水泥稳定碎石基层强度的检测分析、沥青混合料级配的快速检测分析。相对于传统的层间界面介电特性的分析,这种基于结构层内部非均匀介电特性分布的检测分析更加有效,同时扩大了路面雷达的应用范围。论文针对雷达应用技术上均匀材料假定的相对不足,从电磁波传播理论出发,建立了层状非均匀时域有限差分法的电磁波正演模拟,并利用系统识别和遗传反演算法及二者的联合算法,进行了层状非均匀介质介电特性的反演。该方法的实现,从本质上解决了路面雷达应用的共性技术问题,能够充分挖掘了雷达回波蕴含的丰富材料信息,结果更加符合实际材料的特点;并结合路基路面材料物理特性与介电特性的相关试验结论,将雷达尝试性应用于厚度、含水量、密度、级配等施工质量控制指标的检测与分析,推动了路面雷达电磁无损检测技术的发展。更多还原

【Abstract】 Ground Penetrating Radar (GPR) is used as a typical tool of electromagnetic non-destructure testing technologies. Because it is the fast, accurate and non-destructive, GPR has been widely used in geological explore, archaeology, traffic, civil engineering, environment, water conservancy, railway, etc, engineering fields. As the development of pavement in construction and maintenance, the air-launched GPR is widely used in construction quality control and pavement conditions evaluation. Currently, the research methods of GPR application focus on how to obtain the dielectric. Generally, the dielectric are calculated by the waveform amplitude reflected from the interfaces that the dielectric is obviously different between two layers. While the electromagnetic wave transmitting in pavement, it is assumed that the electromagnetic wave attenuation is fixed or ignored. A few methods that back-calculate dielectic constant are presented in half space or multi-layer system. But the model that is used to forecast the dielectric is homogeneous. In fact, many materials that are used in various engineerings are composites, which often are made up of three constituents or phases, such as solid, liquid, gas. The properties in every small space are different as the three phases mixtures vary. So the dielectric that predicted from the amplitude reflected from the interfaces can’t represent the properties of a whole layer, and only represent the properties near the interface. The homogeneous predicting model will affect the precision of layer thickness detected from GPR, and it also could restrict the GPR application fields.According to the above, it is presented that the multi-layered inhomogeneous dielectrics are inversely analyzed, and how to use the inhomogeneous dielectric in pavement engineering testing by GPR. It is concluded as the followings.1. The foreward simulation that the electromagnetic wave propagates in multi-layered inhomogeneous media has been carried out.The 1-D and 2-D model of multi-layered inhomogeneous media are established, and the foreward simulations of electromagnetic wave propagates in this media are finished by using Finite Difference of Time Domain (FDTD) method. Regarded the pavement structures which are inhomogeneous as many homogeneous sub-layers, the forward model which is applied in inversion is established. Compared the homogeneous simulation, the inhomogeneous simulation is more close to the actual reflected waveform. 2. The dielectric properties back-calculation for multi-layered inhomogeneous media has been achieved.The dielectric properties back-calculation for multi-layered inhomogeneous has been accomplished by System Identification (SID) method and Genetic Algorithm (GA). But the SID is influenced on the seed dielectrics sometimes, and GA is a time-consuming method. So the GA-SID hybrid method is presented, this new method contains some advantages that it can’t be affected on seed electric and it is high efficiency. Comparison analysis that the three methods are used to back-calculate the dielectrics from the same reflected waveform shows the hybrid method is more effective.3. Using the field correlation experiments between the back-calculated dielecteic and the concerned physics parameters, these parameters inside the layers could be detected by electromagnetic wave testing technology.The inhomogeneous dielectric properties are associated with some physics parameters’ uniformity inside the layers. If the correlation between the dielectrics and these parameters has been obtained by field experiments, some new testing technologies have been achieved, such as the subgrade moisture testing vertically and horizontally, strength analysis of cement stabilized base, grade estmation of asphalt concrete. These testing technologies are based on the inhomogeneous dielectric analysis of a whole layer, they utilize all information of the reflected waveform besides the amplitude. They can extend the application of GPR.In this paper, it is brought out that the homogeneous dielectric properties can’t describe actual material accurately. Based on electromagnetic theory, the model of FDTD that simulate the electromagnetic wave propagate in multi-layered inhomogeneous media is developed. And the three back-calculation methods that are SID, GA and GA-SID hybrid are accomplished to predict the dielectric constant of multi-layered inhomogeneous media. These works essentially find out the basic solution of GPR applications, they sufficiently apply the reflected waveform that connote the information of the material passed by electromagnetic wave. Combined the relationship bwteen the back-calculation dielectric and some physics parameters, the new testing technologies of construction quality control used by GPR are developed, such as base moisture testing, asphalt grade analysis, stabilized base strength survey. They effectively improve the electromagnetic non-destructive test technologies that detect pavement parameters by GPR.更多还原