Ground Penetrating Radar Investigations Research Articles

Large-Depth Ground-Penetrating Radar for Investigating Active Faults: The Case of the 2017 Casamicciola Fault System, Ischia Island (Italy)

We conducted large-depth Ground-Penetrating Radar investigations of the seismogenic Casamicciola fault system at the volcanic island of Ischia, with the aim of constraining the source characteristics of this active and capable fault system. On 21 August 2017, a shallow (hypocentral depth of 1.2 km), moderate (Md = 4.0) earthquake hit the island, causing severe damage and two fatalities. This was the first damaging earthquake recorded on the volcanic island of Ischia from the beginning of the instrumental era. Our survey was performed using the Loza low-frequency (15–25 MHz) GPR system calibrated by TDEM results. The data highlighted variations in the electromagnetic signal due to the presence of contacts, i.e., faults down to a depth larger than 100 m below the surface. These signal variations match with the position of the synthetic and antithetic active fault system bordering the Casamicciola Holocene graben. Our study highlights the importance of employing large-depth Ground-Penetrating Radar geophysical techniques for investigating active fault systems not only in their shallower parts, but also down to a few hundred meters’ depth, providing a contribution to the knowledge of seismic hazard studies on the island of Ischia and elsewhere.

GPR investigation of the cause of persistent failure of a university road

We present the results of a multi-frequency ground-penetrating radar (GPR) survey over a university road in south-western Nigeria that has experienced persistent failures. The goal was to evaluate causes of failure to aid remediation efforts. Data was collected concurrently at 250, 500, and 1000 MHz using a UTSI electronic trivue system. Data were processed and interpreted using Reflex-Win. Visual observations of major features apparent on the road surface including failed sections were noted. Imaged features included possible bases of the surface course, base course and sub-base, subsurface projections of an outcropping and buried basement rocks, three deeply cut and back-filled sections that lie beneath sections of the road that have experienced persistent failure, and the ringing effects and rebar-associated reflection hyperbolae of two reinforced concrete drains. Indications of preferential wetting of the shallow subsurface beneath much of the failed sections suggest that failure is due to excessive moisture content in these sections. These failed sections generally correspond to regions of deep cut and backfill, and regions cut and filled for the construction of reinforced concrete drains. Apparently, the backfills at these locations have failed to prevent water influx into the subsurface and more effective remediation measures need to be deployed.

Ground-penetrating radar investigation of regolith thickness on a periglacial alpine summit flat, Uinta Mountains, Utah, USA

ABSTRACT Summit flats are low-relief, gently sloping landforms common in periglacial mountain environments. Apart from at their edges where summit flats are truncated by glacial headwalls and at their crests where isolated tors are occasionally present, bedrock is typically mantled on a summit flat by a continuous layer of regolith. This study applied ground-penetrating radar (GPR) to survey the thickness of regolith on a summit flat in the Uinta Mountains (Utah, USA). More than 500 m of GPR data were collected along transects extending from the edge of the summit flat to the crest, as well as adjacent to a deep soil pit. Results indicate that the regolith thickness is quite variable, with a mean of 91 ± 38 cm when calculated with an appropriate radar velocity. Because the ground surface of the summit flat is notably smooth, the variability in thickness is a consequence of irregularities in the bedrock surface at depth, which is significantly rougher. Recognition that regolith thickness can vary considerably beneath an alpine summit flat has implications for soil formation, carbon storage, and the transmission and storage of shallow groundwater, as well as evolutionary models for periglacial mountain landscapes.

Engineering Geological and Geophysical Investigations to Characterise the Unstable Rock Slope of the Sopu Promontory (Gozo, Malta)

Different engineering geological and geophysical investigations were performed at the Sopu promontory in the island of Gozo (Malta), involved in an impressive lateral spreading process due to the superimposition of a stiff limestone (ULC) on a ductile clay (BC). The applied techniques include: traditional geological and engineering geological surveys, unmanned aerial vehicles (UAV) survey, electrical resistivity tomography (ERT) survey, ground-penetrating radar (GPR) investigations, single-station seismic ambient noise measurements, and array seismic ambient noise measurements. The integration of the obtained results allowed us to reconstruct a subsoil model of the promontory that includes features related to the local geology of the slope and to the landslide process, as well as to define a conceptual model that describes the main evolution phases of the expansion process. The presence of back-tilted rock blocks with no features of polarization of Rayleigh waves evidenced the different failure mechanism of the rigid UCL plateau at the Sopu promontory with respect to the Selmun promontory, located in the close island of Malta, where the lateral spreading due to the same geological setting tends to produce unstable rock blocks with a toppling mechanism. This result encourages further future observations and analyses of this topic.

Theoretical Analysis and Practical Verification of the Worp Technique Applied for the GPR Investigation of a Flood Levee

The ground-penetrating radar (GPR) method is one of the geophysical electromagnetic methods. The standard technique of the GPR surveys is the short-offset reflection profiling (SORP) technique, which can theoretically be described in the same way as the zero-offset (ZO) measurements. During the surveys performed using the SORP technique, the offset (i.e. the separation between the transmitter and receiver antennae) is not adjusted to the depth of the objects located in an examined medium. In more advanced measurements, performed using the wide-offset reflection profiling (WORP) technique, the offset is adjusted to the supposed depth of the underground objects which should be detected using the GPR method. The theoretical background and comparison of the SORP and the WORP surveys were described in the paper. The article also presents theoretical analyses regarding to the shape of the radiation pattern generated by the GPR antennas located on the ground surface, i.e. on the border of two media (i.e. air and geological medium) with different electromagnetic properties. The variability of shapes of the radiation patterns as well as the variability of the reflection coefficients for electromagnetic waves with transverse electric (TE) and transverse magnetic (TM) polarizations for different offsets, affect the quality of GPR recordings, which was analysed in the paper theoretically as well as through the field tests. The terrain measurements were performed on a selected part of the Vistula river flood levee in Krakow (Poland), where geotechnical sounding indicated the existence of the loose zones. In order to increase the detection possibilities of the GPR method, surveys were performed after precipitation, which created a temporary two-layer medium, i.e. near-surface, water-saturated zone and deeper located, dry zone. The results of the WORP surveys confirmed the theoretical analysis and allowed to record more readable radargrams for larger offsets than in the case of the short offset, which facilitated further interpretation of the recordings.

Unveiling a hidden fortification system at “Faraglioni” Middle Bronze Age Village of Ustica Island (Palermo, Italy) through ERT and GPR prospections

We carried out a geophysical research project in the Middle Bronze Age village of Ustica (Palermo, Sicily, Italy), named “Faraglioni Village” after the stack formations which detach from the coast north of the archaeological site. The investigation, which comprised Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) techniques, allowed us to discover the buried foundations of an outwork fortification system never evidenced by previous archaeological studies, only hypothesised from the observation of aerial photography and partially outcropping boulders, which align roughly parallel to the main defensive wall of the Village.Our geophysical prospection involved the entire 250 m-long arc of the outward village defensive wall, with the acquisition of eleven ERT profiles and 27 GPR scans. The techniques were selected based on both favourable logistics and methods applicability: ERT sections allowed us to trace a series of high-resistivity anomalies arranged to form an arc-shaped structure along the perimeter of the defensive wall. GPR investigation was localised in the most accommodating patch of terrain of the site, with the effort of intercepting clear enough sections of the target, to determine more accurately its shape, depth, and overall dimensions. Our discovery paves the way for new investigations, mainly aimed at defining the timing of construction of the fortification system, as well as the function of the remains of other architectural structures identified close to the wall, which could represent the target of further geophysical investigations.

Unveiling the Hidden Secrets of Bomarzo Cathedral: New Evidence from Last Ground-Penetrating Radar Survey

The Bomarzo Cathedral, also known as the Duomo di Bomarzo, is a remarkable historical and architectural masterpiece situated in Bomarzo (VT), Italy. Constructed in the 16th century under the sponsorship of the Orsini family, the cathedral’s design is a harmonious blend of Renaissance and Baroque styles. Despite enduring numerous challenges, including damage from the Italian Wars, extensive restoration efforts were undertaken to preserve its cultural legacy. Driven by a deep appreciation of the cathedral’s historical context, a ground-penetrating radar (GPR) investigation was deployed to gain insights into its foundations and potentially uncover buried remains beneath the floor and altar. The GPR investigation focused on the cathedral’s interior, specifically the central and left naves, altar, and oratory. This revealed the presence of disclosed rectangular chambers beneath the floor and altar, along with unique foundation structures. These findings, coupled with historical insights and architectural understanding, emphasize the cathedral’s cultural importance.

Ground penetrating radar investigations of buried remnants at ancient capital cities of Panchala and Vatsa kingdoms spread along Ganga-Yamuna doab of India from 600 BCE to 1100 CE

Ahichhatra and Kaushambi, ancient settlements located in Uttar Pradesh, comprise differential cultural deposits and architectural remnants from 2500 BCE to 1200 CE. These settlements flourished as the capital cities of once-prosperous urban kingdoms known as Panchala and Vatsa Mahajanapadas but remain abandoned in the present day. To provide ancillary data for the simplification of traditional archaeological explorational practices, a few portions located in and around the fortified areas of both settlements were considered for subsurface investigations using Ground Penetrating Radar (GPR). In Ahichhatra and Kaushambi, 2D and 3D GPR survey was carried out in the open areas devoid of vegetation for the understanding of the spatial alignment of the buried features within the fortified walls. The subsurface investigations at Ahichhatra have shown high amplitude reflections referring to buried wall structures, residential complexes, raised platforms, past-used surfaces and structural continuity. Also, the partial excavation carried out at Ahichhatra has revealed walls and compacted floors validating our findings. From Kaushambi, the findings include wall structures and interconnected chambered structures. The anomalies obtained in the data collected from considered survey sites located in Ahichhatra are 1–2 m wide and 2–4 m deep whereas in Kaushambi they are 0.5–1 m wide and 2–4 m deep. These findings helped us to determine the progressive urban relics of the ancient kingdoms which were known for their second phase of urbanism in Ganga Valley that prevailed until their abandonment. For a better understanding of the cultural history, detailed mapping of the contemporary sites can be carried out using integrated survey methods.

Ground penetrating radar investigation and georeferencing without global satellite navigation systems: The case history of the amphitheatre of Lecce, Italy

AbstractIn this work, we present a case history relative to ground penetrating radar measurements performed close to the Roman amphitheatre of Lecce, Italy. We have performed a classical data elaboration with focusing of the data and slicing putting into evidence hidden details of the structure of the monument. It will be shown that the interpretation of the ground penetrating radar data is meaningfully helped by the consultation of ancient documents, which makes the final result multidisciplinary. Finally, we have georeferenced the data matching the shape of the depth slices with the shape of the investigated roads. In fact, we did not have at disposal any differential global satellite navigation systems. Indeed, this can be a method exploitable in cases when satellite data are not available, either because the area is shadowed or because the user does not have a differential global satellite navigation system. The proposed geographical matching is achieved by means of the matching between the shape of the slices and those of the physical obstacles present in the field. Therefore, it is essentially based on a continuous of points, and so it is probably more precise than a method based on the only vertexes. In particular, the proposed procedure does not require any deformation of the shape of the slice.

Testing of a GPR equipment to assess the integrity condition of a subway tunnel located under groundwater level

AbstractDetermining the condition of underground concrete tunnels is fundamental for ensuring continuity and safety of operations, as well as for deploying efficient maintenance plans. The increased traffic volumes in early infrastructures, which are characterized by outdated construction techniques and potential approximated realization, as well as rising groundwater levels due to variations in urban industrialization patterns, are among the main causes of current concerns regarding their performance. Such uncertainties and constraints push towards the use of non‐destructive techniques, rather than direct methods, to gather the required knowledge on the actual status of structures. This study presents the results of a ground penetrating radar (GPR) investigation carried out in a subway tunnel segment to characterize the thickness of its underlying concrete elements, namely the tunnel invert and the concrete filling, deemed necessary after relevant flooding events prompted the evaluation of its overall integrity condition. A preliminary step was performed to define the optimal frequency and polarimetric antenna configuration, given the resolution and penetration requirements and considering the high electromagnetic interference characterizing the site. The selected configuration was then assembled in a dedicated survey platform, and an entire 650 m long segment surveyed, producing a high resolution delineation of the concrete elements thickness. The accuracy of the estimation has been validated through nine core samples, demonstrating the reliability and consistency of the conceptualized GPR platform.

Archaeological prospection of a prehistoric lithic workshop site using ground penetrating radar with a high‐frequency antenna unit

AbstractWe surveyed in detail the Chalcolithic lithic workshop Fofanovo XIII an East Fennoscandian region by ground‐penetrating radar (GPR). A high‐frequency antenna unit was applied to map small‐scale features, mainly waste flakes. To substantiate the efficiency of the GPR technique, we performed a primary analysis of a set of equivalent models in a sandbox. The laboratory‐scale GPR investigation highlights differences in GPR patterns depending on the spatial arrangement of small features and supports the further interpretation of real‐life data. The GPR survey in the field covered 2200 m2, revealing areas with a high density of artefacts in the cultural layer and locating individual structural elements of the Fofanovo XIII archaeological site. We suggested using microdebitage samples from manual probing to verify the detected anomalous values of GPR attributes. The results point to a significant correlation between microdebitage and the envelope peak amplitude of the echo signal. Ultimately, our study confirmed the cultural layer in the Fofanovo XIII workshop site to be rich in lithic production wastes, indicating it was a place of mass‐scale production of lithic chopping tools.

A Potential Beach Monitoring Based on Integrated Methods

This study focuses on the analysis of sandy beaches by integrating sedimentological, geomorphological, and geophysical investigations. The beach represents an extremely variable environment where different natural processes act simultaneously with human activities, leading to the gathering of different methodologies of the Earth Sciences to study its evolution in space and time. The aim of this research is to propose a potential procedure for monitoring the morpho-sedimentary processes of sandy beaches by analyzing the textural and compositional characteristics of the sands and quantifying the volumes involved in the coastal dynamics. The study area includes two Apulian sandy beaches (Torre Guaceto and Le Dune beach) that are representative of the coastal dynamics of a large sector of the central/northern Mediterranean Sea involving the southern Adriatic Sea and the northern Ionian Sea. Sedimentological and ecological investigations allowed to describe the textural and compositional characteristics of the beach sands by interpreting their sand provenance and the physical/biological interactions within the beach. The topographic surveys carried out with a Terrestrial Laser Scanner and an Optical Total Station, aimed to quantify the variations of sediment volume over time, whereas the Delft3d software was applied to analyze the effects of the dominant wave motion on the sedimentary dynamics. Lastly, the geophysical techniques which included Sub Bottom Profiler procedures, Ground Penetrating Radar investigation, and resistivity models enabled us to calculate the sand sediment thickness above the bedrock.

Automatic pixel-level detection of vertical cracks in asphalt pavement based on GPR investigation and improved mask R-CNN

Non-destructive testing and characterization of internal vertical cracks are critical for road maintenance by ground penetrating radar (GPR). This paper describes a mask region-based convolutional neural network (R-CNN) that automatically detects and segments small cracks in asphalt pavement at the pixel level. Simulation using Gprmax software and field detection were performed to determine the crack features in GPR images of asphalt pavement and the relationship between the width of vertical cracks and their area in GPR images. Results showed that a 0.833 precision, 0.822 F1 score, 0.701 mean intersection-over-union (mIoU) and 4.2 frames per second (FPS) were achieved on 429 GPR images (1024×1024 pixels), and the mean error between the segmented crack width and the true values was 2.33%. The research results represent a further step toward accurately detecting and characterizing internal vertical cracks in asphalt pavement

Multi-Instrumental Approach to Slope Failure Monitoring in a Landslide Susceptible Newly Built-Up Area: Topo-Geodetic Survey, UAV 3D Modelling and Ground-Penetrating Radar

Slope failures and landslides cause economic damage and deaths worldwide. These losses can be minimized by integrating different methodologies, instruments, and data monitoring to predict future landslides. In the constantly growing metropolitan area of Cluj-Napoca, Romania, changes in land cover, land use, and build-up areas are an issue. The unprecedented urban sprawl pushed the city limits from the Somes River to hilly terrain prone to landslides and erosion. This study focuses on a landslide-prone area where a previous slope failure caused significant economic losses. It combines topo-geodetic measurements, UAV monitoring of surface displacement, GIS spatial analysis, ground-penetrating radar investigations, and geotechnical assessment. Two years of data show that the slope is undergoing surface erosion, with soil displacements of a few centimeters. Geodetic monitoring of the retaining wall’s control points indicates a small rotation. Coupled with georadar profile imaging showing changes in soil and rock layers with an uplift trend, it was deduced that the area suffers from a global instability. The findings provide valuable information about the dynamics of landslides and erosion for forecasting future movements and developing preventative strategies based on a new methodology that combines affordable and prevalent instrumentation and techniques.

Investigation and characterization of karst landform with GPR: a case study in Shandong, China

A substation is an important infrastructure for city operation and people’s life. The proposed site, 37 km northeast of Zaozhuang, Shandong province, is located on top of Cambrian limestone, most of which is directly exposed or covered by thinner Quaternary silty clay. The Karst processes on the surface contribute to the dissolution of gullies and limestone fissures in the surface topography. Directly the evidence shows that the study area is karst cave or the possibility of larger crack, the potential risk impact on subsequent substation the safety of the pile foundation installation construction. Thus led to the ground penetrating radar (GPR) investigation on the bedrock of karst development. The aim of this study was to characterize the development of karst caves in the shallow surface and delineate their locations. The 80 MHz shielding antenna was used to study and characterization of the karst features. The results of GPR method show that the application of a low-frequency antenna can satisfy a certain detection depth and well characterize the development of underground karst, which also proves that GPR method is very practical in the detection of karst landform and can be applied to identify similar geomorphic features.

GPR Mapping of buried monumental retaining walls at biblical Kiriath-Yearim near Jerusalem

ABSTRACT In 2019 a ground-penetrating radar (GPR) investigation was conducted at Kiriath-Yearim near Jerusalem, one of the largest Bronze and Iron Ages mounds in the highlands of the southern Levant. The main objective was to test an archaeological hypothesis regarding the existence of an Iron Age summit compound which was supported by monumental stone retaining walls. We used a wheeled GPR with simultaneous central frequencies of 200, 400, and 800 MHz. Despite attenuation in the topsoil, scattering by distributed rock fragments, and asphalt pavement, we were able to penetrate almost a meter and detect anomalies. Some of the GPR anomalies are consistent with the above-mentioned theory, meaning that their locations agree with data retrieved in nearby control trenches and with the plan of the site. The excavation findings, jointly with the GPR interpretation, indeed imply the existence of a rectangular monumental summit compound that dates to the 8th century BCE.

Refining Late-Holocene environmental changes of the Akko coastal plain and its impacts on the settlement and anchorage patterns of Tel Akko (Israel)

Akko/Acre, a UNESCO World Heritage site since 2001, is one of the oldest continuously inhabited sites in the eastern Mediterranean. Tel Akko was a major maritime centre of the southern Levant from the Middle Bronze to the Late Persian period. The city was then moved 1500 m to the west on the Akko promontory where the ‘Old City’ of Saint-Jean d'Acre is located. The natural and anthropogenic evolution of Tel Akko area is reflected by persistent geographical and habitation pattern changes. We combine sedimentological and faunal analyses of radiocarbon dated cores as well as identification of ceramic sherds found in the cores with ground penetrating radar investigations to propose an up-to-date palaeogeographical reconstruction of landscape/environmental changes of the Akko coastal plain in order to understand the extent to which environmental pressures have played a role on the position of anchorage and habitation patterns. We highlight how the local population make use of the natural advantages of the area and adapted to environmental pressures. Following a constant sedimentary input and simultaneous coastal progradation of the Akko coastal plain the main anchorage areas where forced to move. While the 2nd Millennium BCE anchorage was on the southern area of the tell, the late-1st Millennium BCE (Phoenician-Persian) anchorage was relocated on the western area. Vicissitudes in settlement pattern noted in archaeological excavations and surveys on Tel Akko have, most likely, been the consequence of the changes in the position of the coastline.

Ground-Penetrating Radar and Photogrammetric Investigation on Prehistoric Tumuli at Parabita (Lecce, Italy) Performed with an Unconventional Use of the Position Markers

In this contribution, we propose ground-penetrating radar (GPR) investigation performed close and on some prehistoric tumuli, locally called “piccole specchie”, in the countryside around the town of Parabita (Lecce), within the Salento peninsula (southern Italy). In order to perform the GPR investigation on the tumuli, an unconventional method of data acquisition was exploited, involving, consequently, some non-conventional data processing steps. Photogrammetric survey was also performed, and 3D digital models of the prehistoric tumuli were created. The investigations have revealed some anomalies under two out of three investigated tumuli, which were interpreted as prehistoric tombs.

Finding Mesolithic Sites: A Multichannel Ground-Penetrating Radar (GPR) Investigation at the Ancient Lake Duvensee

The shift to the early Holocene in northern Europe is strongly associated with major environmental and climatic changes that influenced hunter-gatherers’ activities and occupation during the Mesolithic period. The ancient lake Duvensee (10,000–6500 cal. BCE) has been studied for almost a century, providing archaeological sites consisting of bark mats and hazelnut-roasting hearths situated on small sand banks deposited by the glacier. No method is yet available to locate these features before excavation. Therefore, a key method for understanding the living conditions of hunter-gatherer groups is to reconstruct the paleoenvironment with a focus on the identification of areas that could possibly host Mesolithic camps and well-preserved archaeological artefacts. We performed a 16-channel MALÅ Imaging Radar Array (MIRA) system survey aimed at understanding the landscape surrounding the find spot Duvensee WP10, located in a hitherto uninvestigated part of the bog. Using an integrated approach of high-resolution ground radar mapping and targeted excavations enabled us to derive a 3D spatio-temporal landscape reconstruction of the investigated sector, including paleo-bathymetry, stratigraphy, and shorelines around the Mesolithic camps. Additionally, we detected previously unknown islands as potential areas for yet unknown dwelling sites. We found that the growth rates of the islands were in the order of approximately 0.3 m2/yr to 0.7 m2/yr between the late Preboreal and the Subboreal stages. The ground-penetrating radar surveying performed excellently in all aspects of near-surface landscape reconstruction as well as in identifying potential dwellings; however, the direct identification of small-scale artefacts, such as fireplaces, was not successful because of their similarity to natural structures.

Foundation features investigation of a heritage structure in India through noninvasive and invasive techniques

Investigation of the foundation system of the heritage site is a challenging task. The heritage site in the present study is Sun temple, Konark. The temple is a 700–800 years old stone masonry structure and world heritage site in the Indian state of Odisha. The investigation of the foundation details, i.e., type, depth, and horizontal extent, along with the soil layering below and around the temple premises, involves non-invasive and invasive techniques. The shielded and unshielded Ground Penetrating Radar (GPR) antenna, with a central frequency of 250 MHz & 500 MHz, and 100 MHz, are used for non-invasive investigation. In addition, invasive investigation, i.e., drilling at the top of the platform, at the plinth level, collection of samples, and characterization are performed to determine the soil layering below and around the temple premises. The GPR radargrams of the layering system corroborated with the bore logs obtained by performing the invasive investigation. The non-invasive and invasive study establishes the foundation system as a block type having a depth of 10.5 m from the top of the temple platform. The study demonstrates the efficacy of GPR as a support system for conventional invasive techniques. The paper in detail presents the GPR investigations, their inferences, invasive testing, and the corroboration of the non-invasive and invasive tests.