Road Radar Subgrade Compaction Quality Control

The Ground Penetrating Radar (GPR) is an effective, speedy, continuous and non-destructive testing equipment, and its applications in pavement have been the international active subject since 1980s. At present, most of the achievements mainly focus on the measurement of pavement thickness. But the study on subgrade standards, such as compactness and moisture content, is only under exploration.The dielectric difference of material is the precondition of the application of GPR. The reflected wave that the GPR received is the function of the material dielectric properties, and the explaination, estimation and back-calculation of GPR date are all base on the analysis of the material dielectric properties. The identification of GPR to the performance standards, such as subgrade compactness, moisture content, are based on the study of pavement material dielectric.In this paper, in order to solve the problems of GPR's applied techonology, we lanch the experimental study on the subgrade soils dielectric property. In the experiment, the GPR is used in the subgrade compactness quality control, which expands GPR's applied fields and scope.The main achievements and conclusions of this paper are summarized as below:1. The basic charactristics of soil electromagnetic property from the mircoscopic polarization mechanics aspect, and elaborats soil media polarization model's classfication and media dielectric properties'measure method were analysed in this paper. And then were analysed from both macro and micro aspects the subgrade's composed ingredients' influences on the subgrade soils dielectric properties. All of these offer a reliable thoretical foundation and techonology supports for determining the relationship of subgrade dielectric properties and subgrade compaction standards;2. Doing indoor experiments which include dry density experiment, intensity experiment and age experiment, on several typical subgrade materials. Through these experiments, we establish the relationship between subgrade materials' dielectric properties and their performance standards like dry density, moisture content and modulus, we study three subgrade soils, like soil, Cement-stabilized soil, Lime-cement treated soil, and their dielectric change laws if they with different proportions, we testify the dielectric constant linear-model to subgrade soils, the results show that the model reflect well of the dielectric constant value which nears the subgrade soils' best moisture content, but once deviate it, the model's error will be obvious;3. Integrated with the construction of highway, we go along the experimental study on the correlation between the subgrade dielectric constant and spot-compaction, spot-loading plate and CBR. The experiment shows that if the subgrade fillers are equality, the correlation of them will be well. Then we can use the subgrade dielectric constant to indicate the compactness;4. Testifying the precision and reliability of the subgrade dielectric constant which the GPR measured. Integrated with the construction of highway, we can use the GPR to test the construction's compaction quality, we can analysize and evaluate the results.This paper presents the research achievement of subgrade soils dielectric properties, which provides theoretical and experimental support. According to the research results, it is feasible to apply subgrade soils dielectric properties to subgrade's compaction quality. The successful application has great significance for popularization of the GPR.