Ground-penetrating Radar Techniques and Three-dimensional Computer Mapping in the American Southwest

There have been several recent reports of collapsed roads at the various locations throughout the Bangkok metropolitan area. Most of the problems are caused by improper construction of utility networks and poor rehabilitation work. Ground penetrating radar (GPR) technique was selected to investigate the potential presence of subsurface voids under the road surface. In geotechnical and structural applications, GPR is an excellent tool for being able to image steel reinforcing bars, voids and tendon ducts in concrete structures and, more relevantly to this study, voids beneath concrete roads. The objective of this study was to survey the area for potential voids that might exist under the road surface using ground penetrating radar technique. The GPR survey campaign was divided into two stages, which were the preliminary and detailed surveys. The objective of the preliminary survey was to quickly survey the area for potential voids that might exist under the road surface and subsequently a more detailed survey of those areas was performed to confirm the existence and determined the lateral and vertical extension of the potential void(s) identified in the preliminary GPR survey. The GPR data were collected with 400 MHz antenna mounted on a survey cart. Several void-like anomalies were detected from the GPR data and these selected anomalies were drilled to confirm the existence of a void. However, some GPR anomalies were found not to be voids, and mostly came from areas of past road maintenance or manholes with a hidden cover (asphaltic concrete overlay). One example of a large void under the road surface was detected in this study, being clearly seen in the GPR data and then confirmed by drilling. The GPR method was successfully used for void detection under a main road in Bangkok city. In this study the 400 MHz ground-coupled antenna was used to image potential subsurface voids and these were then confirmed (or not) by drilling boreholes in that area through the road surface. In the example shown in this report as a case study, the identified void was approximately 4 m long, 2 m wide and 1.5 m deep. As a result of its discovery it was subsequently treated by backfilling and a new road surface was then constructed.

The use of ground-penetrating radar in archaeology

Ground penetrating radar (GPR) is a very useful geophysical method for use in hydrogeologic and near-surface mapping studies. It can be used to study contaminants in groundwater, subsurface faulting, and underground cavities (natural or man-made), all of which pose potentially dangerous geological hazards. The GPR technique is similar in principle to seismic reflection and sonar techniques. The propagation of the radar signal depends on the frequency-dependent electrical properties of the ground.Electrical conductivity of the soil or rock materials along the propagation paths introduces significant absorptive losses which limit the depth of penetration into the earth formations and is primarily dependent upon the moisture content and mineralization present.Reflected signals are amplified, and transformed to the audio-frequency range, recorded, processed, and displayed. From the recorded display, subsurface features such as soil/ soil, soil/rock, and unsaturated/saturated interfaces can be identified. In addition, the presence of floating hydrocarbons on the water table, the geometry of contaminant plumes, and the location of buried cables, pipes, drums, and tanks can be detected. The GPR data are presented as a two-dimensional depth profile along a scanned traverse line in which the vertical axis is two-way travel time measured in nanoseconds. The location of hydrocarbon contamination in the ground using the GPR method is based mainly on information taken from reflected signals. In the cases investigated in Romania contaminated sites (Navodari area), such signals were very rarely recorded. A long time after spillage, contamination takes the form of plumes with different size and distribution, which depends on the geological and hydraulic properties of the ground. The survey discussed in this paper was carried out using the GPR system-Noggin with two antennas (250 and 500mHz) Data collected were processed using software(EKKO_Project™ GPR Data Analysis) to produce 2D radargram in time scale. The presence of contaminant plumes as well as the water table are observed in the GPR sections at depths approximately of 0.5 to 1.5 m. In the GPR section, the oil contaminated layer exhibits discontinuous, subparallel, and chaotic high amplitude reflection patterns. Promising results were also obtained in the GPR survey where three obvious reflection patterns representing the top sand-silt layer, oil-contaminated zone and, the underlying thick soft clay were detected in all 2D radargrams of the GPR traverse lines.

Identification of liquefaction and deformation features using ground penetrating radar in the New Madrid seismic zone, USA

Integrated geophysical investigation involving Electrical Resistivity (ER) and Ground Penetrating Radar (GPR) techniques were carried out around a site underlined by Basement Complex rocks of southwestern Nigeria. The study was aimed at imaging the subsurface lithological units and delineating shallow geologic structures for the purpose of characterizing the area for construction suitability. A total of twenty five (25) Vertical Electrical Sounding (VES) data using Schlumberger array, ten (10) traverses of Electrical Resistivity Imaging (ERI) using Wenner array and Ground Penetrating Radar (GPR) surveys were carried out along the established traverse lines within the area. The VES data were quantitatively interpreted using partial curve matching technique and subsequently improve upon by inversion software using IPI2Win, to obtain the layer geoelectric parameters. The ERI data was inverted and interpreted using Res2Dinv and Res3Dinv inversion software’s respectively to generate 2D and 3D resistivity image of the subsurface. The GPR data was processed into radar section using RadExplorer software. Vertical electrical sounding results delineates typically three to four geologic layers which are the topsoil/lateritic hardpan, weathered basement (consisting clay and sandy clay) and fractured/fresh basement with layer resistivity value ranges of 10-2684 Ωm, 12-242 Ωm and 229-3213 Ωm respectively and thickness value ranges of 0.5-2.1 m and 4.0-14.1 m respectively. 2-D inverted resistivity results also delineated three major geologic layers which are the topsoil, weathered basement and fresh basement and correlates well with the results obtained from the VES results. Layers 1 to 3 of 3D inverted resistivity slice results show high degree of variation in resistivity distribution at shallow depth, consisting of highly resistive material towards the eastern part with low resistivity material concentrating at the south-western part. Results of the GPR survey also delineated three to four geologic layers which include the topsoil/lateritic hardpan, weathered basement and fractured/ fresh basement. The study area was categorized to have semi-competent to competent basement rock based on the resistivity value of the underlying material within the area. Bedrock depression delineated at some location could pose threat of differential settlement to construction works within the study area. Thus, it should be ensured that foundation is designed to sit comfortably on the competent bedrock or by employing suitable foundation work, such as piling to ensure foundation stability and prevent structural failure. Thus, electrical resistivity and ground penetrating radar techniques are versatile tools in site characterization.

Twelve kilometers of ground penetrating radar (GPR) data have been collected over the Brookswood aquifer in southwestern British Columbia. The data have been analyzed to assess how GPR can be used to characterize the distribution and connectivity of hydraulic units. We have used GPR to locate the aquifer/aquitard boundary at several locations in the study area. The electrical contrast between these two materials makes the aquifer/aquitard boundary an excellent target for GPR surveys. GPR was also used to reconstruct the paleo-environment of one area of the Brookswood aquifer. This was accomplished by using a modification of the concept of architectural element analysis. Radar elements were identified in the survey and were assigned sedimentary parameters using data from trenching and drilling in the area. These elements were used to develop an interpretation of the paleo-environment that provides information about the spatial distribution of hydraulic units. INTRODUCTION Hydrogeologists require quantitative data to produce a realistic model of the spatial variabilities in hydraulic properties of an aquifer. Such data can be difficult and expensive to obtain. A possible solution is to develop geophysical techniques as a means of aquifer characterization. Ground penetrating radar (GPR), a shallow geophysical technique, is well suited for this purpose as it can be used to image to a depth of up to 30m in sand and gravel environments. However, the image produced by a GPR survey does not supply hydrogeologic parameters directly. The focus of this paper is to investigate how GPR can be used for aquifer characterization. At an aquifer scale of lo’s to 100’s of meters, the most fundamental aspect of aquifer characterization is the determination of the aquifer’s hydraulic connectivity through mapping of aquifer/aquitard interfaces. GPR can be used for this purpose due to the large contrast in electrical conductivity between the sand and gravel material of an aquifer, and the clay rich material of an aquitard. The electrical conductivity of a material affects the penetration depth of radar waves, such that radar waves penetrate well through resistive material, but poorly through conductive material. Aquifers, composed of sands and gravels, are resistive, while aquitards, composed of clay rich materials, are electrically conductive. Therefore a radar survey will show good penetration in aquifer materials and very poor penetration in aquitards. By exploiting this difference in radar response, the aquifer boundaries can be mapped. At a smaller scale of centimeters to meters, the determination of the internal structure of an aquifer is also important for aquifer characterization. For example, anisotropy within the aquifer can cause significant differences in hydraulic properties and so must be identified where present. In addition, identification of sedimentary features aids in the determination of the paleo-environment that can provide important insight into the probable arcal extent and orientation of geological units. GPR can be used to image these features because of changes in their electrical properties. GPR and Sedimentology GPR has received considerable attention as a means of imaging sedimentary stratigraphy (Jo1 and Smith, 1992; Smith and Jol, 1992; Pratt and Miall, 1993; Greenhouse et al, 1987; Rea et al, 1991; Huggenberger et al, 1994). The key question that needs addressing is exactly which sedimentary aspects of the subsurface are imaged with GPR. A GPR survey, conducted by transmitting radar waves into the subsurface and recording the reflected energy, will image changes in the subsurface dielectric constant and conductivity. If these electrical properties correspond to changes in sedimentary parameters, then a GPR survey can be said to image sedimentary features. The dielectric constant and conductivity of earth materials are dependent upon composition and geometry of the solid and liquid components. Sedimentological classification is based upon five fundamental properties from which all others can be derived: grain composition, size, shapes, orientation and packing (Blatt et al, 1980). These five properties clearly are related to the composition and geometry of the solid component of a system. It is therefore reasonable to assume that a change in sedimentological properties at some boundary will cause a change in electrical properties. If the resulting change in electrical properties is large enough, then the sedimentary boundary will be imaged in a radar survey. The complicating issue is the liquid, usually water, component which does not play a role in sedimentary

GPR technique as a tool for cultural heritage restoration: San Miguel de los Reyes Hieronymite Monastery, 16th century (Valencia, Spain)

Ground penetrating radar (GPR) surveys have been carried out at Schirmacher Oasis and Dakshin Gangotri located at Queen Maud Land, East Antarctica, during the 22nd Indian Antarctic Summer Expedition, 2002-2003. The present study confirmed the ability of the high-resolution GPR for monitoring the glaciers. It gives information about the health of the glaciers before it collapses. GPR survey over three frozen lakes near the Maitri Station provided the lakes' top ice thickness and bedrock depth. Similarly, the internal layers of the glaciers have been mapped in-situ using GPR. The results can be correlated with the results obtained by ice-core drill wells to understand the different field parameters (i.e., thickness of each layer, dielectric constant, etc.).

This study examines the application of Ground Penetrating Radar (GPR) to the detection of severe caverns and sinkholes in non-clastic rock formations. Due to the presence of vertically sloping bedrock, cavities, and sinkholes, geotechnical engineers face significant challenges when designing and constructing foundations in karstic formations such as limestone. The territory under investigation is located close to the Giza limestone plateau, the northern side of which has experienced severe stability issues. The ground-penetrating radar (GPR) method was used to identify the presence and extent of exposed caves and caverns in the studied region. The research area’s geological and geomorphological background is explored, including the creation of primary and secondary caves, as well as solution caves generated by the breakdown of soluble rocks like limestone. Data collecting, processing, and interpretation procedures used in the GPR survey are described. GPR survey findings revealed the existence of a severe cave and many minor sinkholes in the studied region. GPR has shown to be a useful and efficient tool for determining geometric karst features in the subsurface, helping to a better evaluation of the dangers associated with this geological environment.

<p>Time-lapse ground penetrating radar (GPR) surveys in conjunction with automated single-ring infiltration experiments can be used for non-invasive monitoring of the spatial distribution of infiltrated water and for generating 3D representations of the wetted zone. In this study we developed and tested a protocol to quantify and visualize water distribution fluxes under unsaturated and saturated conditions into layered soils. We carried out a gridded GPR survey on a 0.3-m thick sandy clay loam layer underlain by a restrictive limestone layer at the Ottava experimental station of the University of Sassari (Sardinia, IT). We firstly established a survey grid (1 m × 1 m), consisting of six horizontal and six vertical parallel survey lines with 0.2 m intervals between them. The field survey then consisted of six steps, including <strong>i)</strong> a first GPR survey, <strong>ii)</strong> a tension infiltration experiment conducted within the grid and aimed at activating only the soil matrix, <strong>iii)</strong> a second GPR survey aimed at highlighting the amplitude fluctuations between repeated GPR radargrams of the first and second surveys, due to the infiltrated water moving within the matrix flow region, <strong>iv)</strong> a single-ring infiltration experiment of the Beerkan type carried out within the grid on the same infiltration surface using a solution of brilliant blue dye (E133) and aimed to activate the whole pore network, <strong>v)</strong> a third GPR survey aimed to highlight the amplitude fluctuations between repeated GPR radargrams of the first and third surveys, due to the infiltrated water moving within the whole pore network (both matrix and fast-flow regions), and <strong>vi)</strong> the excavation of the soil to expose the wetted region. The shapes of the 3D diagrams of the wetted zones facilitated the interpretation of the infiltrometer data, allowing us to resolve water infiltration into the layered system. Finally, we used the infiltrometer data in conjunction with the Beerkan estimation of soil transfer parameter (BEST) method to determine the following capacitive indicators of soil physical quality of the upper soil layer: air capacity <em>AC</em> (m<sup>3</sup> m<sup>–3</sup>), plant-available water capacity <em>PAWC</em> (m<sup>3</sup> m<sup>–3</sup>), relative field capacity <em>RFC</em> (–), and soil macroporosity <em>p<sub>MAC</sub></em> (m<sup>3</sup> m<sup>–3</sup>). Results showed that the investigated soil was characterized by high soil aeration and macroporosity (i.e., <em>AC</em> and <em>p<sub>MAC</sub></em>) along with low values for indicators associated with microporosity (i.e., <em>PAWC</em> and <em>RFC</em>). These findings suggest that the upper soil layer facilitates root proliferation and quickly drains excess water towards the underlying limestone layer, and, on the contrary, has limited ability to store and provide water to plant roots. In addition, the 3D diagram allowed the detection of non-uniform downward water movement through the restrictive limestone layer. The detected difference between the two layers in terms of hydraulic conductivity suggests that surface ponding and overland flow generation occurs via a saturation-excess mechanism. Indeed, percolating water may accumulate above the restrictive limestone layer and form a shallow perched water table that, in case of extreme rainfall events, could rise causing the complete saturation of the soil profile.</p>

In this work we present a non-invasive investigation of the Amphiteatrum Flavium, executed using the ground penetrating radar (GPR) technique, with the aim to improve the knowledge of the construction materials and techniques employed for building foundation. Therefore, the main goal of this work is to achieve quantitative and reliable information for assessing the seismic vulnerability of the structure. The GPR survey was performed through the Passage of Commodus, excavated within the foundation for a length of about 60 m. GPR data were acquired on the floor and on the lateral walls, using different antenna frequencies (80, 200, 600, 900 MHz) as they combine good resolution and depth of investigation. On the floor dataset, we detected three equally-spaced anomalies related to old utilities parallel to the passageway, whose roof is located at a depth of 1 m. In addition to this, the GPR radargrams clearly highlight horizontal layers within the foundation, related to the sequential development of works at the time of construction. GPR dataset acquired on the wall allowed us to detect the thickness of the concrete covering the foundation and to locate the extensions of the structural elements underground. Outside the foundation, the passage is built using bricks, with external walls about 1 m thick. Therefore, GPR dataset revealed that the foundation of the Colosseum is a heterogeneous multi-layer element, with the presence of cavity networks and buried elements related to the plinths of the load-bearing structures. This work confirmed that foundation was built over time by means of subdivisions into small sectors, probably both in the horizontal and vertical directions.

In May of 1997, the Department of Geology and Geophysics at the University of Missouri-Rolla conducted a reflection seismic survey and a ground penetrating radar (GPR) survey for the Missouri Department of Transportation (MoDOT) along and adjacent to a 300 meter section of Interstate 44 in Springfield, Missouri. In October of 1997, a second GPR survey was conducted along the same section of interstate. The site was located approximately 1.5 kilometers west of Missouri Highway 266. The section of interstate studied overlies an active sinkhole and has experienced continued, localized subsidence. Seven 12-fold reflection seismic profiles were acquired along or near Interstate 44, using a Bison 24- channel seismograph and an EWG weight drop source. Forty-live GPR profiles were acquired along paved sections of Interstate 44 during the first survey. During the second GPR survey, the survey area was expanded to include a total of seventy ground penetrating radar profiles. A GSSI SIR-S GPR unit equipped with a 500 MHZ (megahertz) monostatic antenna/receiver was used to acquire the data. The geophysical surveys were successful. The reflection seismic data established that sinkholes, both active and nonactive are prevalent in the area. The seismic data also supports the interpretation that a sinkhole lies immediately beneath the interstate. The ground-penetrating radar data also proved to be of significant utility. Anomalous areas interpreted as voids on the GPR data were drilled and significant volumes of grout were injected. The second GPR survey established the success of the grouting program.

Mapping the spatial variation of soil water content at the field scale with different ground penetrating radar techniques

In this paper, we present the results of non-destructive integrated geophysical surveys (ground penetrating radar (GPR) and seismic sonic) performed in the crypt of the Basilica of St Nicholas in Bari, Italy. The aim was twofold, namely to investigate the consistency of restoration work performed in 1950 and the presence of features of archaeological interest. The GPR technique has also been exploited to characterize the subsurface water content under the crypt. In particular, the existence of buried anomalies, probably due to the restoration work, has been identified. Moreover, by means of an electromagnetic-wave velocity analysis, an estimation of the volumetric water content under the floor has been achieved. The results indicate the main causes of the deterioration and have provided significant information for the safeguard of this historical building. Furthermore, the GPR survey allowed us to identify some anomalies buried under the crypt that are probably of archaeological interest. Finally, both sonic tomography and a GPR survey have been performed on an important mosaic, and have enabled us to identify probable ?internal? reasons for its decay.

<p>It is a truism that pavements deteriorate due to the combined effects of traffic loads and environmental conditions. The manner or ability of a road to meet the demands of traffic and the environment and to provide at least an acceptable level of performance to road users throughout its life is referred to as pavement performance. An important indicator of pavement performance is ride quality. This is a rather subjective measure of performance that depends on (i) the physical properties of the pavement surface, (ii) the mechanical properties of the vehicle, and (iii) the acceptance of the perceived ride quality by road users. Due to the subjectivity of ride quality assessment, many researchers have worked in the past to develop an objective indicator of pavement quality. The International Roughness Index (IRI) is considered a good indicator of pavement performance in terms of road roughness. It was developed to be linear, transferable, and stable over time and is based on the concept of a true longitudinal profile. Following the identification and quantification of ride quality by the IRI, pavement activities include the systematic collection of roughness data in the form of the IRI using advanced laser profilers, either to "accept" an as-built pavement or to monitor and evaluate the functional condition of an in-service pavement.</p><p>On the other hand, pavement performance can vary significantly due to variations in layer thickness, primarily due to the construction process and quality control methods used. Even if a uniform design thickness is specified for a road section, the actual thickness may vary. It is expected that the layer thickness will have some probability distribution, with the highest density being around the target thickness. Information on layer thickness is usually obtained from as-built records, from coring or from Ground Penetrating Radar (GPR) surveys. GPR is a powerful measurement system that provides pavement thickness estimates with excellent data coverage at travel speeds. It can significantly improve pavement structure estimates compared to data from as-built plans. In addition, GPR surveys are fast, cost effective, and non-destructive compared to coring.</p><p>The present research developed a sensing approach that extends the capability of GPR beyond its ability to estimate pavement thickness. Specifically, the approach links GPR thickness to IRI based on the principle that a GPR system and a laser profiler are independent sensors that can be combined to provide a more complete image of pavement performance. To this end, field data collected by a GPR system and a laser profiler along highway sections are analyzed to evaluate pavement performance and predict future condition. The results show that thickness variations are related to roughness levels and specify the deterioration of the pavement throughout its lifetime.</p>