PURPOSES : The objectives of this study are to evaluate the condition of concrete bridge decks using the multi-channel ground penetrating radar (GPR) testing and compare the value of its dielectric constant value with actual concrete condition. METHODS : The reflection coefficient method was used to measure the dielectric properties of concrete bridge decks. Air-coupled step-frequency GPR testing was used to measure the time taken for reflection from the interfaces between the layers. Specimens of the asphalt mixture and concrete bridge-deck were collected by field coring. GPR testing was conducted on two bridges with different concrete bridge deck conditions on national highways. After the GPR tests, the actual conditions of the concrete bridge deck were investigated using specimen coring. RESULTS : GPR testing indicated that the dielectric constants of concrete bridge decks in good condition ranged from 8 to 10, whereas those corresponding to poor condition ranged from 4 to 6. The results of GPR testing can determine the actual condition and degree of distress of concrete bridge decks determined from the specimen coring data. Therefore, GPR testing is appropriate for nondestructively evaluating the condition of a concrete bridge deck. CONCLUSIONS : The analysis results of the dielectric constants of the concrete bridge deck obtained from multichannel GPR testing were consistent with the actual bridge deck conditions. In the near future, an additional verification process for this approach under different bridge conditions will be required to improve its precision and ensure reliability.

During and after the construction of LILW disposal facilities, the decrease of groundwater head potential has been monitored. In addition, an increase of the electrical conductivity (EC) has been observed in several monitoring wells installed along the coastal coastline. Monitoring activity for groundwater head potential and hydrogeochemical properties is important to reduce the uncertainty in the evaluation of groundwater flow characteristics. However, the data observed in the monitoring wells are spatial point data, so there is a limit to the dimension. Several researchers evaluated groundwater head potential changes and seawater intrusion (SWI) potential for disposal sites using groundwater flow modeling. In case of groundwater flow modeling results for SWI, there is a spatial limit in directly comparing the EC observed in the monitoring wells with the modeling results. In a recent study, it was confirmed that the response of the long-range ground penetraiing radar (GPR) system was severely attenuated in the presence of saline groundwater. In order to reduce the spatial constraint of the groundwater monitoring wells for SWI, the characteristics of SWI within the disposal facility site by using the the results of a recent study of the long-range GPR system were investigated and evaluated in this study.

This paper proposes a solution to the out-of band oscillation signal and in-band low transmitter power output that occurrs during the low-temperature operation test for the new mine detector GPR signal transmission and reception module. Tests were performed by applying the optimal values of capacitors and inductors through circuit analysis simulation under the limited space, as a result, it was confirmed that the gain and return loss were improved at all-band thereby preventing oscillation signal and low transmitter power output.

PURPOSES : In this study, a method for evaluating concrete bridge deck deterioration using three-dimensional (3D) ground penetrating radar (GPR) survey data and its in situ application are discussed. METHODS : Field surveys are conducted on two bridges in Yongsan-gu (Bridge A) and Seodaemun-gu (Bridge B) in Seoul using 3D GPR. The obtained survey data are used to calculate the dielectric constant map of each bridge using the extended common midpoint method. In addition, random points on both bridges are selected for the chloride content test in accordance with the KS F 2713 standard. The results from the dielectric constant map and chloride content test are compared. RESULTS : For Bridge A, it is discovered that the percentage of sections with a dielectric constant of 5.0 or less is 1.57%, whereas that above 5.0 is 98.43%; this indicates that the percentage of deteriorated sections for Bridge A is low. Meanwhile, for Bridge B, the dielectric constants calculated for the entire bridge exceed 5.0, which suggests no deterioration for Bridge B. Moreover, all the points selected for the chloride content test have less than 0.15% chloride content and have dielectric constants ranging from 5.0 to 7.0, which are favorable condition for the bridge deck. CONCLUSIONS : The analysis results of the dielectric constants of the concrete bridge deck obtained from the 3D GPR system are consistent with the actual chloride content results. Furthermore, additional verification of this method through field surveys on bridge sections with severe deterioration is highly recommended for future improvements.

PURPOSES : This study aims to evaluate the applicability of ground penetrating radar (GPR) for surveying utility pipes under sidewalks made of concrete brick and plate-stone block pavements. METHODS : GPR tests were conducted at two test sections to detect layer boundary and utility pipes under the pavements. The central frequency of the single-channel GPR was 800, 500, 250, and 100 MHz, and the central frequency of multi-channel (8) GPR was 450 MHz. GPR signals were analyzed in terms of 1-D (A-scan) and 2-D (B-scan) profiles. RESULTS: From the A-scan data analysis, the vertical resolution of the GPR ranged from 7.3 cm for 800 MHz to 133.1 cm for 100 MHz in the concrete brick block pavement and 13.9 cm for 800 MHz to 144.2 cm for 100 MHz in plate stone block pavement. From the B-scan data analysis, 250 MHz to 500 MHz GPR was sufficient to differentiate the layer boundary at a depth of 1.0~1.5 m to detect utility pipes at a depth of 0.5~2.0 m in both block pavements. In the plate-stone block pavement, GPR signal attenuation was greater because of the wire mesh in the concrete layer. Thus, the penetration depth was approximately 80% of the concrete brick-block pavement. CONCLUSIONS : The penetration depth and vertical resolution of GPR in the sidewalk paved with blocks were comparable to those of roadway pavement. Among the GPR evaluated, the 250 MHz GPR was the most desirable, and the 500 MHz GPR was affordable for the investigation of underground pipes situated up to 2.0~3.0 m under sidewalks.

PURPOSES: The purpose of this study is to compare the advantages and disadvantages of 3D multichannel ground penetrating radar (GPR) equipment, which is mainly used for road cavity detection. The optimal signal analysis method was also proposed for 3D GPR data. METHODS: Four types of 3D GPR equipment were used to detect road cavities in a pilot road section in Seoul. The obtained GPR signals were evaluated in the time and frequency domain using raw data. In addition, various types of filters were applied to time domain (B-scan) data to examine the optimal signal processing. RESULTS: The time and frequency domain analysis of raw data showed that all the equipment produced reverse and strong signal reflections owing to the low dielectric permittivity of air in the cavity compared with neighbor materials. Also, the asymmetric parabolic curve was observed as well. The optimal signal processing method was determined to detect road cavities: zero-setting and background removal should be applied to all equipment. Bandpass filtering can be optionally applied to remove high-frequency noise or direct waves. CONCLUSIONS: Despite the different specifications of GPR equipment in terms of signal generation and bandwidth, the GPR signals were appropriate in terms of zero-setting, noise level, and depth of investigation. Therefore, all the multichannel GPR devices evaluated were found to be suitable to detect road cavities located at depths of 1.0 and 1.5 m after the application of proper filtering process.

The Ground Penetrating Radar(GPR) is a typical non-destructive test equipment which is widely used in seeking a cavity or underground facility. Test results are generally expressed 2D monochrome or color images, distribution of the parabolic waveforms are used to determine the existence of cavity and facility. (Fig. 1) But, an analysis method of image may cause errors depending on the knowledge and experience of analyst. In this study, we analyzed the coefficient of correlation between A-Scan data of GPR to judge the existence of cavity located under the pavement layer. The correlation analysis was performed based on the assumption that the relationship of correlation between a number of A-Scan data passing through a non-cavity section is larger than a small number of A-Scan data passing through a cavity section, and relationship of correlation was visualized using Surfer Program. (Fig. 2) In addition, apart from the correlation analysis, we compared the Power spectrum of the A-scan data for the cavity section and non-cavity section. In other words, assuming that the size of the energy changes depending on the existence of the cavity, PSD (Power Spectrum Density) is obtained for all the B-Scan data, and the tendency of the energy size is confirmed using the 3D wireframe map of the Surfer program. (Fig. 3) As a result, the correlation coefficient shows a small tendency in the cavity section and the PSD shows a large tendency, which is intuitively recognized that the energy attenuation in the cavity section is smaller than other material. But, there are some ambiguous sections to judge the tendency clearly, this is estimated to be noise on the underground facility and it is necessary to take measure of mitigating this.

In this study, a novel method based on ground penetration radar (GPR) is proposed to categorize underground objects by using both B-scan and C-scan images. Three-dimensional GPR data obtained from a multichannel GPR system are reconstructed into a two-dimensional (2D) grid image which consists of several B-scan and C-scan images. Three-dimensional shape information of an underground object can be well represented in 2D grid image. The 2D grid images are then trained using deep convolutional neural networks (CNN) that is a state-of-the-art technique for image classification problem. The proposed method is validated through field applications on urban roads in Seoul, South Korea.

PURPOSES: The purpose of this study is to evaluate different types of Ground Penetrating Radar (GPR) testing for characterizing the road cavity detection. The impulse and step-frequency-type GPR tests were conducted on a full-scale testbed with an artificial void installation. After analyzing the response signals of GPR tests for detecting the road cavity, the characteristics of each GPR response was evaluated for a suitable selection of GPR tests. METHODS: Two different types of GPR tests were performed to estimate the limitation and accuracy for detecting the cavities underneath the asphalt pavement. The GPR signal responses were obtained from the testbed with different cavity sizes and depths. The detection limitation was identified by a signal penetration depth at a given cavity for impulse and step-frequency-type GPR testing. The unique signal characteristics was also observed at cavity sections. RESULTS: The impulse-type GPR detected the 500-mm length of cavity at a depth of 1.0 m, and the step-frequency-type GPR detected the cavity up to 1.5 m. This indicates that the detection capacity of the step-frequency type is better than the impulse type. The step-frequency GPR testing also can reflect the howling phenomena that can more accurately determine the cavity. CONCLUSIONS : It is found from this study that the step-frequency GPR testing is more suitable for the road cavity detection of asphalt pavement. The use of step-frequency GPR testing shows a distinct image at the cavity occurrences.