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- Volume 14, Issue 2, 2016
Near Surface Geophysics - Volume 14, Issue 2, 2016
Volume 14, Issue 2, 2016
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Step‐frequency ground‐penetrating‐radar array calibration requirements to estimate dielectric properties of pavements
Authors Nicolas Gagarin and James MekemsonABSTRACTDuring the past decade, ground penetrating radar has emerged as a viable non‐destructive testing technology for quality control and quality assurance during pavement construction and for the infrastructure subsurface condition assessment. Data are collected with the ground penetrating radar antenna array attached to a vehicle travelling along the road. With ground penetrating radar data, there is a corresponding need to follow strict protocols both in data collection and data processing, especially for antenna arrays. The key to successful data measurements is the application of calibra‐tion procedures appropriate to the hardware system, measurement protocols, and desired measurement statistic or parameter. This paper presents four primary calibration procedures required for ground penetrating radar antenna arrays with actual case application using an air‐coupled step‐frequency ground penetrating radar array. These calibration procedures for a step‐frequency ground penetrating radar antenna array are applied to produce the ground penetrating radar signal foundation for estimating the dielectric properties of materials in a layered highway pavement structure. In addition, a complete solution space is required to identify all layer interfaces and buried objects.
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A comprehensive approach for the assessment of HMA compactability using GPR technique
Authors Christina Plati, Panos Georgiou and Andreas LoizosABSTRACTWith the focus on quality assurance practices during pavement construction, the present research aims at investigating the compactability of hot mix asphalt using the ground‐penetrating radar technique. Thus, density as an indicator of the compactability of hot mix asphalt is predicted using three different electromagnetic‐mixing‐theory‐based density models (namely, the complex refractive index model, Rayleigh model, and Al‐Qadi, Lahouar and Leng model), and the prediction performance is also investigated. The investigations are based on experimental data acquired, both in the laboratory and field, from new full‐scale asphalt pavement sections with varying asphalt mixture compositions. The laboratory experiment, which involved the compaction of asphalt mixtures using the steel‐segmented roller compactor, indicated that compaction mode affects the compactability of hot mix asphalt, whereas the analysis of field ground‐penetrating radar experimental data revealed that the estimated electric permittivity during the compaction process could be considered a measure of the asphalt mix field compactability. The prediction performance of the three density models was evaluated using different methodological approaches with respect to the backcalculation of of the mix aggregates. The results indicated that, by utilizing the ground‐penetrating radar field measured for the assessment of the predicted Gmb values from the implementation of the above density models closely approach the ground‐truth field‐core bulk densities. Comparative evaluation of the three density models showed that the Al‐Qadi, Lahouar, and Leng model exhibits the best prediction performance, which is comparable to nuclear/non‐nuclear methods. In light of this, it could be argued that the ground‐penetrating radar methodology coupled with novel algorithms can be an effective and efficient tool to improve the asphalt mix compaction process and assessment of in situ density.
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GPR analysis of clayey soil behaviour in unsaturated conditions for pavement engineering and geoscience applications
ABSTRACTClay content is one of the primary causes of pavement damages, such as subgrade failures, cracks, and pavement rutting, thereby playing a crucial role in road safety issues as an indirect cause of accidents. In this paper, several ground‐penetrating radar methods and analysis techniques were used to nondestructively investigate the electromagnetic behaviour of sub‐asphalt compacted clayey layers and subgrade soils in unsaturated conditions. Typical road materials employed for load‐bearing layers construction, classified as A1, A2, and A3 by the American Association of State Highway and Transportation Officials soil classification system, were used for the laboratory tests. Clay‐free and clay‐rich soil samples were manufactured and adequately compacted in electrically and hydraulically isolated formworks. The samples were tested at different moisture conditions from dry to saturated. Measurements were carried out for each water content using a vector network analyser spanning the 1 GHz–3 GHz frequency range, and a pulsed radar system with ground‐coupled antennas, with 500‐MHz centre frequency. Different theoretically based methods were used for data processing. Promising insights are shown to single out the influence of clay in load‐bearing layers and subgrade soils, and its impact on their electromagnetic response at variable moisture conditions.
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Railway Ballast Fouling Detection Using GPR Data: Introducing a Combined Time–Frequency and Discrete Wavelet Techniques
Authors Imad L. Al‐Qadi, Shan Zhao and Pengcheng ShangguanABSTRACTGround‐penetrating radar has been recently used for quantifying railway ballast fouling conditions. This paper discusses two approaches for processing the railway ballast ground‐penetrating radar signal: the discrete wavelet transform method and the short‐time Fourier transform method. Ground‐penetrating radar field data collected in Wyoming in 2007 by two 2‐GHz air‐coupled antennas were used to verify both approaches. The collected ground‐penetrating radar signals were processed by discrete wavelet transform. The signal standard deviation values were fitted by linear regression of the fouling indices, which were calculated using ground‐truth sieving data. The spectrogram generated by short‐time Fourier transform was used to analyse the ballast fouling condition level by comparing the energy attenuation speed. It was observed that both discrete wavelet transform and short‐time Fourier transform approaches can be used to analyse ballast fouling conditions. The short‐time Fourier transform method is easier to visualize, whereas the discrete wavelet transform approach can more quantitatively predict the fouling level. However, the discrete wavelet transform method provides the fouling condition of the whole ballast layer, whereas the spectrogram provides the fouling condition with respect to the depth profile.
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Applications of the GPR Technique to indoor, bridge deck and pier structures: case studies in Turkey
Authors Mahmut G. Drahor, Caner Öztürk, Atilla Ongar and Meriç A. BergeABSTRACTThis paper presents the results of three ground‐penetrating radar case studies applied to indoor, bridge deck, and pier construction types in Turkey. In these studies, 270‐MHz and 1600‐MHz anten‐nas were employed to determine the ability limits for construction materials and diagnostic problems associated with the materials. In addition, the importance of the selected survey direction was tested during measurement. Analysing the significance of the migration technique during the data processing stage was another important goal of these case studies. The first case study analyses the indoor applications (e.g., house, villa, and fabric) of ground‐penetrating radar and aims to identify possible cracks, structural defects, and corrosion damage. The second case applies ground‐penetrating radar to a bridge deck. The third case investigates pier construction by establishing the layout of the construction materials. Identifying possible defects, including structural problems within the pier structure, was another goal. These case studies provide interesting results in terms of physically characterizing the concrete structure and the locations of rebar and slab conditions; the work also reveals the moisture and corrosion effects inside the construction materials on indoor, bridge and pier applications of ground‐penetrating radar.
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Ground‐penetrating radar measurement of the distribution of thixotropic slurry behind large‐diameter segments in long‐distance pipe‐jacking construction
Authors Yonghui Zhao, Jiansheng Wu, Xiongyao Xie, Kunwei Feng and Chenchao ZengABSTRACTPipe‐jacking engineering requires monitoring of the spatial distribution of thixotropic slurry behind the pipe segments, but timely thickness measurements are difficult during construction. Ground‐penetrating radar was used here during sewage pipe jacking, to evaluate the distribution of the slurry by considering its dielectric contrast with the surrounding soil. A series of circular ground‐penetrating radar data was collected along the inner surfaces of the pipe segments using an antenna with a frequency of 900 MHz. To enable accurate interpretation of the ground‐pene‐trating radar images, the dielectric parameters of the slurry were first measured by time‐domain reflectometry. Statistical analyses revealed the slurry as a special medium with extremely high dielectric constant and conductivity. Numerical simulation indicated that the ground‐penetrating radar images can be considerably improved by applying Karhunen–Loeve transformation followed by f–k Stolt migration, which facilitates identification of the reflections from the slurry–soil interface. Based on all the processed ground‐penetrating radar field data, the thickness and the distribution of the slurry at different pipe segments were calculated using the two‐way travel time and the radar signal propagation velocity in the slurry. The results show that ground‐penetrating radar is indeed effective for estimating the quality of slurry injected during pipe jacking.
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Visualization of buried anti‐tank landmines and soil pollution: analyses using ground penetrating radar method with attributes and petrographical methods
Authors Selma Kadioğlu and Yusuf Kagan KadioğluABSTRACTThis paper presents an approximation to display buried anti‐tank landmines with ground‐penetrating radar method, including physical data attributes by measuring data in a special military field and determination of soil pollution using mineralogical and chemical features of the soil obtained by confocal Raman spectrometry and polarized energy dispersive X‐ray fluorescence, which are petro‐graphical methods, before and after bursting the mine. Two‐dimensional ground penetrating radar data were acquired on parallel profiles using 800‐MHz shielded antenna on unexploded anti‐tank landmines buried approximately 10 cm–15 cm in depth. After general processing in the time domain, we employed migration, a frequency‐wavenumber (F‐K) filter, and ground‐penetrating radar data attributes with an amplitude envelope, spectral whitening, and first‐time derivative to activate anti‐tank landmine visualization. Finally, we obtained three‐dimensional half bird ‘s eye view of the processed volume with each separate attribute. We also derived the transparent three dimensional volumes by assigning opacity to the amplitude‐colour range. The results showed that the depth slices including attributes and the transparent three‐dimensional depth‐volumes could clearly image the anti‐tank landmine. In addition, migration and F‐K filter during special processing were very important in removing data noise. Ground‐penetrating radar data atthbutes—particularly amplitude enveloping— could suppress small phase shifts in the neighbouhng traces of the landmine amplitude anomalies and helped to obtain more complete results showing location and depth in the three‐dimensional volume.
The results of the analyses of the major oxide elements and heavy metal elements, such as Fe2O3 Pb, Zn, As, Mn, Mo, Co, Ni, Sb, and Sn, in the test area revealed that there were almost no major differences before and after blasting the anti‐tank landmines. This indicates that one‐time bursting of the anti‐tank landmines in the field has not polluted the soil in this area.
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Ground‐penetrating radar evaluation of the ancient Mycenaean monument Tholos Acharnon tomb
ABSTRACTThe assessment of cultural heritage requires high‐resolution and non‐destructive methodologies. Ground‐penetrating radar is widely applied in the inspection of historical buildings. However, some structures with curved surfaces make the radar data acquisition process difficult and consequently the following data interpretation. This paper describes a case study concerning a circular and buried Greek monument. This monument is a magnificent tomb buried with irregular stones. However, its structure and the internal stones arrangement are unknown. Therefore, a radar survey was carried out to achieve two main objectives: (i) identification of hidden elements and arrangement of the stones and (ii) detection of specific zones where further restoration and maintenance should be recommended. The methodology for the radar data acquisition involves the use of a laser scan in order to define accurately each radar line, covering all the internal surface of the tomb. Radar data processing was developed by converting Cartesian coordinates into polar coordinates. This procedure allows defining better the internal anomalies, improving the radar data interpretation. The main results of the survey were three: (i) the presence of a hidden target buried in the corridor access to the tomb; (ii) the description of the internal structure of the walls of the tomb, defining the stones arrangement and the position and depth to the keystone; and (iii) the existence of delimited zones where the signal is highly attenuated, probably due to a high salt content.
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Time‐varying band‐pass filtering GPR data by self‐inverse filtering
More LessABSTRACTEven though ground penetrating radar data signal processing has already been studied by many researchers, more research is needed and expected from automatic ground penetrating radar data analysis. An automatic band‐pass filtering procedure can lead to sufficient real‐time data interpretation as signal buried in noise could be amplified. Ground penetrating radar traces are highly non‐stationary, requiring time‐varying processing techniques. An algorithm, based on self‐inverse filtering, which is a special case of inverse filtering, was implemented. It is a ground penetrating radar trace filtering approach and is implemented by applying inverse filtering in each time sample in the time‐frequency domain. Applied on a synthetic trace, this algorithm performed better than a stationary band‐pass filter and empirical mode decomposition family methods, whereas its application on real ground penetrating radar data from two different sites enhanced reflections buried in noise without the need to test different high‐frequency band stops and with minimum distortion of the signal and the initial temporal resolution of the data.
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Volumes & issues
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Volume 22 (2024)
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Volume 21 (2023)
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Volume 20 (2022)
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Volume 19 (2021)
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Volume 18 (2020)
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Volume 17 (2019)
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Volume 16 (2018)
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Volume 15 (2017)
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Volume 14 (2015 - 2016)
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Volume 13 (2015)
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Volume 12 (2013 - 2014)
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Volume 11 (2013)
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Volume 10 (2012)
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Volume 9 (2011)
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Volume 8 (2010)
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Volume 7 (2009)
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Volume 6 (2008)
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Volume 5 (2007)
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Volume 4 (2006)
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Volume 3 (2005)
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Volume 2 (2004)
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Volume 1 (2003)