Water Level Detection in Silty Materials Using Ground Penetrating Radar

Ground penetrating radar (GPR) measurements have been conducted to retrace the natural course of the Obra River and changes of spatial extent of Obrzanskie Lake (western Poland). The Obra River valley was subjected to intensive anthropogenic transformation. Three artificial canals were constructed here in the beginning of the nineteenth century. The GPR surveys were done using a georadar MALA ProEx equipped with 250 MHz antenna. The measurement was verified by coring and analyses of historical maps, aerial photographs, and satellite images. The research has shown that there are at least three elongated depressions preserved in the modern land surface near the village of Solec, situated in the middle course of the valley. Several structures suggesting functioning of a multi-channel pattern in the past have been detected inside and in the vicinity of the depressions. Filling the channels with silts and peats might have been the effect of flow deceleration caused by the construction of the Obra Canals. Moreover, situation of two of the retraced depressions suggests that the landforms might be the remains of a river bed disappearing in wetlands. Further studies including groundwater flux measurements in the area between the depressions are needed to confirm such hypothesis. Furthermore, the study allowed retracing the spatial extent of Obrzanskie Lake. The sediment structures detected by the GPR measurements and calibrated with coring were interpreted to be the traces of the lake shoreline. The interpretation was supported by the findings inferred from aerial and satellite images. It was shown that Obrzanskie Lake had had at least three islands and had been directly connected with a network of braided channels before the anthropogenic intervention. The spatial extent of the lake was significantly altered by the construction of the North Obra Canal. Disconnecting the lake from the Canal resulted in more than 50 % decrease of the lake surface.

We compare the capability of ground penetrating radar (GPR) and time domain reflectometry (TDR) to assess the temporal development of spatial variation of surface volumetric water content. In the case of GPR, we measured surface water content with the ground wave, which is a direct wave between the sender and receiver through the upper centimeters of the soil. Spatial water content variation was measured on 18 d with GPR and TDR during a 30-d monitoring period. To ensure large fluctuations in the spatial water content variation, we created a heterogeneous pattern of water content by irrigation on 2 d. The temporal development of the spatial variation was studied by means of the variogram and interpolated water content maps. To compare GPR and TDR variograms, we estimated confidence intervals of the experimental variograms and the variogram model parameters with a jackknife approach and a first-order approximation of model parameter uncertainty. The results showed that the 95% confidence intervals of the GPR experimental variogram were one to two orders of magnitude smaller than the 95% confidence intervals of the TDR experimental variogram because of the larger number of GPR measurements. Consequently, the uncertainty in the variogram model parameters was also much lower for GPR, which meant that the temporal development of the fitted GPR variogram model parameters was easier to interpret. Furthermore, the larger GPR measurement volume resulted in a low spatial nugget variance of 1 × 10−6 to 1 × 10−9 (m3 m−3)2 because short distance variation was averaged. This meant that GPR accurately measured spatial correlation lengths, even in the case of low water content variation. Interpolated maps showing the increase of water content due to irrigation and the subsequent gradual drying of the soil were more accurate and reproducible for GPR. It was concluded that the noninvasive GPR measurements provide the means to accurately and consistently monitor the development of spatial water content variation in time.

Characterization of inland water is a topic of great interest due to the broad spectrum of potential applications. Applied geophysic boasts different techniques adapted to retrieve useful information about these kinds of environments. Certainly, the most common geophysical techniques used in shallow waters are the seismic methods. However, there are some situations in which seismic methods could fail. Although nowadays it does not exist a method able to solve completely this task, electromagnetic techniques are a cost efficient tool to provide useful information. Thanks to their versatility, we concentrated our attention on the possibility of the Ground Penetrating Radar (GPR) and of the low induction number electromagnetic multi-frequency soundings measurements, carried from the water surface. We started from acquisitions performed in controlled settings. We described how we reproduced the field condition of a riverine GPR survey in laboratory experimentation. We selected a 1500 MHz GPR antenna, and we studied five types of riverine bottom sediments. We developed two different approaches to interpret the GPR responses of the sediments: the velocity and the amplitude analysis. The amplitude analysis developed is particularly innovative and fit very well the field requirements. We tried to estimate the sediments porosities by some mixing rules by the electromagnetic properties founded with both the analysis performed. The comparison among the porosities provided by the GPR measurements and the porosities measured by direct methods confirm the accuracy of the velocity analysis and it highlights the poor reliability of the amplitude analysis. Successively, we tested our methodology in survey condition. We conducted an integrated geophysical campaign on a stretch of the river Po in order to check the GPR ability to discriminate the variability of riverbed sediments through an analysis of the bottom reflection amplitudes. We conducted continuous profiles with a 200MHz GPR system and a handheld broadband electromagnetic sensor. A conductivity meter and a TDR provided punctual measurements of the water conductivity, permittivity and temperature. The processing and the interpretation of both the GEM-2 and GPR data were enhanced by the reciprocal results and by integration with the punctual measurements of the electromagnetic properties of the water. The GPR measurements provided maps of the bathymetry and of the bottom reflection amplitude. The high reflectivity of the riverbed, derived from the GPR interpretation, agreed with the results of the direct sampling campaign that followed the geophysical survey. The variability of the bottom reflection amplitudes map, which was not confirmed by the direct sampling, could also have been caused by scattering phenomena due to the riverbed clasts which are dimensionally comparable to the wavelength of the radar pulse. About the multi-frequency electromagnetic sensor, we analyzed the induction number, the depth of investigation (DOI) and the sensitivity of our experimental setup by forward modeling varying the water depth, the frequency and the bottom sediment resistivity. The simulations led to an optimization of the choice of the frequencies that could be reliably used for the interpretation. The 3406 Hz signal had a DOI in the PO water (27 Ωm) of 2.5m and provided sediment resistivities higher than 100 Ωm. We applied a bathymetric correction to the conductivity data using the water depths obtained from the GPR data. We plotted a map of the river bottom resistivity and compared this map to the results of a direct sediment sampling campaign. The resistivity values (from 120 to 240Ωm) were compatible with the saturated gravel with pebbles in a sandy matrix that resulted from the direct sampling, and with the known geology

Cold-recycling treatments are gaining popularity in the United States because of their economic and environmental benefits. Curing is the most critical phase for these treatments. Curing is the process where emulsion breaks and water evaporates, leaving residual binder in the treated material. In this process, the cold-recycled mix gains strength. Sufficient strength is required before opening the cold-treated layer to traffic or placing an overlay. Otherwise, premature failure, related to insufficient strength and trapped moisture, would be expected. However, some challenges arise from the lack of relevant information and specifications to monitor treatment curing. This report presents the outcomes of a research project funded by the Illinois Department for Transportation to investigate the feasibility of using the nondestructive ground-penetrating radar (GPR) for density and moisture content estimation of cold-recycled treatments. Monitoring moisture content is an indicator of curing level; treated layers must meet a threshold of maximum allowable moisture content (2% in Illinois) to be considered sufficiently cured. The methodology followed in this report included GPR numerical simulations and GPR indoor and field tests for data sources. The data were used to correlate moisture content to dielectric properties calculated from GPR measurements. Two models were developed for moisture content estimation: the first is based on numerical simulations and the second is based on electromagnetic mixing theory and called the Al-Qadi-Cao-Abufares (ACA) model. The simulation model had an average error of 0.33% for moisture prediction for five different field projects. The ACA model had an average error of 2% for density prediction and an average root-mean-square error of less than 0.5% for moisture content prediction for both indoor and field tests. The ACA model is presented as part of a developed user-friendly tool that could be used in the future to continuously monitor curing of cold-recycled treatments.

Anthropogenic activities on soil layers contribute to reworking and eventual modification, which, in most cases, are detrimental to the soil. Going by the significance of soil to life in many ramifications, it is imperative that its consistent assessment enhances and guides management practices. This study focuses on delineating soil structure alterations using ground-penetrating radar (GPR), a geophysical survey method. The principle of operation and the simplicity of the technique have attracted the choice of the non-destructive testing (NDT) method with a view that it could circumvent the drawbacks that characterized the conventional methods hitherto used for such evaluation. Furthermore, the technique allows for the spatial investigation of the concealing sub-layer of the soil and, thus, informs its choice. A test site was selected on a plain farmland in Kraków, Poland, where some parts of the soil structure distortions were induced using tractor movement, which exerted normal stress from the soil surface layer. Subsequently, GPR measurements were acquired via pre-established profiles on the test site, and soil samples were taken for the laboratory evaluation of some of the soil’s physical properties. An analysis of the field data revealed that zones of distorted soil structures have lower attenuation effects on the GPR signal, with corresponding lower amplitude values compared with the unaltered soil structure zones. Evaluated physical properties such as bulk density and state variables like moisture water contents also show a declining trend from the unaltered soil structure zone to the altered zones. The results have revealed characteristic signatures of the zone of soil structure alterations from GPR scanning that can enhance its identification and characterization in the field and, thus, promote decision making toward the effective utilization and management of soil.

The study area is located about 110 km east of Astana, the capital city of Kazakhstan. Kurgans (barrows) that belong to the 6th–7th century Oghuz-Kipchak settlements were found in the Bronze Age and Iron Age necropolis and acropolis areas that lie within the limits of the Buyratau National Park, which is located in the Ereymentau District of the Akmola Province, in the vicinity of the Kumay Valley, along the foothills of Buyratau, to the left side of Kumay River (which has given the area its name). The district was introduced for the first time to the scientific community by the academicians and researchers of the Nazarbayev Center with the “International Kazakh-Turkish Project on the Constitution of the Kumay Archeology and Ethnography Open Air Museum” as a Bronze and Early Iron Age Turkic period and ethnography. The statues at the Kumay Archeological and Etnographic Complex (Turkic fences with Kos Bat?r statues, Bronze Age structure, Karagayl? 1 Turkic fence with statue, Karagayl? 2 Turkic fence with statue, Bronze Age Karagayl? 4 burial ground, Karagayl? 3 Turkic fence with statue, Barrows, Barrows with Mustache, Settlement-Stone statue, Karagayl? 5 Turkic fences, Karagayl? 2 Turkic fence with statue, Burial Henge, Bal?kt? 1 Barrow cluster, Bronze Age Karagayl? 3 burial ground, and Bronze Age Karagayl? 2 burial ground) are new discoveries of the common Turkic heritage exemplifying the cultural layers of different periods in Kazakhstan. Bronze Age structures represented by three types of statues, which, in terms of style, regarded as hundreds of different structures, fences, and barrows, cover the entire Bronze Age. A geophysical (GPR) project was jointly planned by the Nazarbayev Center of the Ministry of Culture and Information of the Republic of Kazakhstan and the Republic of Turkey Prime Ministry Turkish Cooperation and Coordination Agency (T?KA) in order to investigate the development of the cultural heritage during different periods in Kazakhstan through a contemporaneous and comprehensive study of the areas where above ground or partially buried structures, included in the the Karagayl? 2, 3, and 4 statue groups, are mainly localized to determine whether there are any buried structures in these localities. It was aimed that the buried statues, burial sites and settlements would be revealed using geophysical measurements by means of subsurface monitoring of the Kumay Valley statues and the nearby necropolis and acropolis areas. For subsurface monitoring in the region, two and three-dimensional images were obtained using Ground Penetrating Radar (GPR) measurements using a DGPS-supported 250 MHz shield antenna. Based on GPR measurements a new kurgan and ceremony site complex were located and suggested for further archeological excavation.

As the most widely used construction material, concrete is very durable and can provide long service life without extensive maintenance. The strength and durability of concrete are primarily influenced by the initial water-cement ratio value (w/c), and the curing condition during the hardening process also influences its performance. The w/c value is defined as the total mass of free water that can be consumed by hydration divided by the total mass of cement and any additional pozzolanic material such as fly ash, slag, silica fume. Once placed, field concrete pavements are routinely cured with liquid membrane-forming compounds. For laboratory study, concrete samples are usually cured in saturated lime water or a curing room with a relative humidity (RH) value higher than 95%. Thus, the effectiveness of curing compounds for field concrete needs to be studied. In this study, the dielectric constant value of plastic concrete was measured by ground penetrating radar (GPR). The w/c value of the plastic concrete was calculated by a mathematical model from the measured dielectric constant value. The calculated w/c value was compared with the microwave oven drying measurement determined result in AASHTO T318. A modified coarse aggregate correction factor was proposed and applied in microwave oven drying measurement to determine the w/c value of plastic concrete in AASHTO T318. The effectiveness of curing compound was evaluated by field concrete slabs by GPR measurement. It was found that GPR can be a promising NDT method for In this study, the dielectric constant value of plastic concrete was measured by ground penetrating radar (GPR). The w/c value of the plastic concrete was calculated by a mathematical model from the measured dielectric constant value. The calculated w/c value was compared with the microwave oven drying measurement determined result in AASHTO T318. A modified coarse aggregate correction factor was proposed and applied in microwave oven drying measurement to determine the w/c value of plastic concrete in AASHTO T318. The effectiveness of curing compound was evaluated by field concrete slabs by GPR measurement. It was found that GPR can be a promising NDT method for w/c determination of plastic concrete and curing effectiveness evaluation method for hardened concrete.

Ground penetrating radar for the detection of liquid contaminants

Because of different limitations, e. g. time, instrumental or economic limitations, only single-method geophysical investigations are carried out in many cases. However, a single method is often limited by the capability of the utilized physical principles to display certain archaeological patterns. Therefore, an integrated geophysical investigation technique should be applied to overcome this problem. At Kale peninsula (Jutland, DK) an integrated geophysical prospecting was carried out to detect different subsurface targets related to the old medieval castle and its surroundings. To locate houses and the position of different defense structures, four different areas were investigated using geomagnetic prospecting, ground penetrating radar (GPR), geoelectrical profiling and surveying. By means of combined geomagnetic and GPR measurements the situation at the first entrance to the peninsula was investigated. To correct the GPR data for topographic effects, the topographic map was refined by dense surveying. Because geoeletrical profiling has generally a lower resolution than the other two methods, it was applied as a first prospecting method to find the continuation of the ancient road outside the forecourt. Afterwards, anomaly regions found by this method were studied in detail using GPR and geomagnetic prospecting. The data revealed the distribution of old farm houses in the forecourt and the position of the ancient road leading from the entrance of the forecourt up to the castle. A 3Dimage of the urban plan of the area under study is finally presented. Fig. 1. Joint interpretation of total magnetic field data (a) and GPR data (b) on a profile crossing the remains of an ancient building. From the GPR time section a depth to the top of the remaining foundation of about 50 cm was estimated. Depth estimates of 45-50 cm, obtained by means of inverse modelling and from logarithmic power spectra of geomagnetic data, were in good coincidence with the former results

Integrated non-invasive sensing techniques and geophysical methods for the study and conservation of architectural, archaeological and artistic heritage

Combined application of GPR and ERT for the assessment of a wall structure at the Heptapyrgion fortress (Thessaloniki, Greece)

The primary objectives of this study are to investigate the interference of ground penetrating radar (GPR) signals with air-cavities behind concrete linings subjected to three experimental parameters (GPR antenna frequency, thickness of concrete lining, and thickness of air-cavities), and their effects on the evaluation of important engineering parameters (thickness of concrete, and length and thickness of air-cavities) for tunnel structure inspection using GPR. For these purposes, first, a concrete model specimen is fabricated in the laboratory, which simulates air-cavity defects with various thicknesses (0 mm, 30 mm, 100 mm, 200 mm, and 300 mm) behind concrete with four different thicknesses (100 mm, 200 mm, 300 mm, and 400 mm) in tunnel structures. Second, a series of GPR survey is performed on the fabricated concrete model specimen using three ground-coupled GPR antennas with nominal center frequencies of 400 MHz, 900 MHz, and 1600 MHz. Third, a practical signal interpretation method is proposed to evaluate air-cavities in concrete tunnel linings subjected to the three experimental parameters. It is demonstrated that the cross-correlation analysis is effective for identifying air-cavities behind concrete, and for characterizing the length of the air-cavities. In addition, the thicknesses of air-cavities are estimated by a new approach in this study, measuring the apparent time delay of partially overlapped electromagnetic wave reflections within air-cavities. The results in this study provide a fundamental basis to improve GPR signal interpretation techniques for the evaluation of air-cavities behind concrete tunnel linings.

A signal processing technique is developed to reduce clutter due to ground bounce in ground penetrating radar (GPR) measurements. This technique is especially useful when a GPR is used to detect subsurface antipersonnel mines. The GPR clutter is modeled using a simple parametric model. Buried mine and clutter contributions are separated through a pair of coupled iterative procedures. The algorithm outperforms existing clutter reduction approaches and also yields target features that are useful for detection and identification of these mines. The proposed technique effectively reduces clutter resulting in a significant decrease in false alarm rates.

Moisture presence in asphalt concrete (AC) pavement is a major cause of damage to the pavement. In recent decades, an increasing need exists for non-destructive detection and monitoring of the moisture content in AC pavement. This paper provides a simulated approach to quantify the effect of internal moisture content on AC pavement dielectric properties using ground-penetrating radar (GPR). A heterogeneous numerical model was developed to simulate AC pavement with internal moisture at various saturation levels. The numerical model was validated using GPR surveys on cold-in-place recycling treated pavements. An empirical formula was derived from the simulation to correlate the dielectric constant with the moisture content for non-dry AC pavement. The results validated the proposed model and, hence, demonstrated the ability of GPR to monitor moisture variation in AC pavements.

The objective of this work was to evaluate the feasibility and value of expanding the MDT's Ground Penetrating Radar (GPR) program to pavement design and rehabilitation, and to network level evaluation. Phase I of this project concluded that in order to investigate the feasibility and value of these program expansions, a Phase II field evaluation project be designed and implemented to evaluate the accuracy of GPR pavement thickness data on Montana pavements, and to correlate these findings with the accuracy requirements of the individual applications. This field evaluation began with identifying 26 pavement test section of different composition and structure located throughout the diverse climatic regions of Montana. At each site, FWD and GPR data was collected, followed by coring and augering to determine the thickness of the pavement layer structure and base moisture content. This testing was carried out both in the spring of 2010 and in the fall of 2010 to capture seasonal variations. The GPR data was analyzed for thickness, and the GPR thickness data was evaluated for seasonal changes, and compared to core and plan data to investigate thickness accuracy and the effectiveness of calibration methods. Compared to cores, the average GPR bound layer thickness error was 10.3% vs. 15.2% using plan data. A GPR data checking method was developed using FWD and plan data to identify potential analysis layer analysis inconsistencies and suggest alternative interpretation. Implementation of this method reduced the GPR error to 7.6%. A sensitivity study was carried out to investigate the impact of having the more accurate GPR data. This study showed that, on average, the use of GPR reduced the pavement life prediction error by 62% when compared to using as-built plan data.