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Three-Dimensional Ground Penetrating Radar (3D GPR) detects subsurface targets non-destructively, rapidly, and continuously. The complex environment around urban roads affects the positioning accuracy of 3D GPR. The positioning accuracy directly affects the data quality, as inaccurate positioning can lead to distortion and misalignment of 3D GPR data. This paper proposed a multi-level robust positioning method to improve the positioning accuracy of 3D GPR in dense urban areas in order to obtain more accurate underground data. In environments with good GNSS signals, fast and high-precision positioning can be achieved based on GNSS data using differential GNSS technology; in scenes with weak GNSS signals, high-precision positioning of subsurface data can be achieved by using GNSS and IMU as well as using GNSS/INS tightly coupled solution technology; in scenes with no GNSS signals, SLAM technology is used for positioning based on INS data and 3D point cloud data. In summary, this method ensures a positioning accuracy of 3D GPR better than 10 cm and high-quality 3D images of underground urban roads in any environment. This provides data support for urban road underground structure surveys and has broad application prospects in underground disease detection and prevention. [ABSTRACT FROM AUTHOR]

An important geological risk to which many towns in Puglia are exposed is sinking cavities in urban areas. For urban centers, studying, mapping, providing geological and speleological descriptions, classifying, and cataloging the forms and types of cavities is essential because cavities are linked to past local anthropic and natural processes at different sites. These circumstances could lead to the enhancement of existing underground cavities in urban areas through conservation and continuous monitoring. Unfortunately, in many cases, these underground cavities have been used as landfills and subsequently abandoned. In late March 2007, one of these cavities collapsed inside Gallipoli's inhabited center, causing damage to the structures but fortunately not human lives. In the area surrounding the collapsed cavity, a series of geophysical investigations were undertaken using ground penetrating radar in an attempt to delimit the area of collapse and develop possible interventions for restoration. In the same area, these measures were repeated 16 years later in December 2022 due to another collapse. The comparison between data acquired in these two periods shows that there were no strong changes apart from an increased presence of subsoil moisture in 2022. [ABSTRACT FROM AUTHOR]

Ground penetrating radar (GPR) survey can be used to image geological hazards such as cavities, faults, fissures and also for identifying buried utilities. Sinkholes formed in the Secunderabad-Patny stretch road, Hyderabad, India were speculated to have been caused due to leaking from the sewer pipe. GPR survey using 200 MHz antenna was used in order to study the sinkholes formed in the collapsed area. GPR profiles were taken both parallel to and perpendicular to the road section to get a complete 3D visualization. Subsurface images acquired the marked position of the manholes, cavities, loose soil, different utilities, and sewer pipeline in the area. The results showed that there was no leaking in the sewer pipeline, instead, a water pipeline was damaged due to poor maintenance. Thus, GPR can be efficiently used to delineate the subsurface infrastructure and has further played an important role in identifying, delineating the zone of sinkhole in a busy street in Secunderabad. [ABSTRACT FROM AUTHOR]

Karst as an extremely complex and heterogeneous system, that presents a great challenge for the ground penetrating radar (GPR). However, properly planed GPR surveys can provide additional information about the shallow subsurface, where most karst processes take place. Due to the specific nature of the karst terrain, the introductory part presents some obstacles and adaptive approaches to karst research. An analysis of the published literature revealed that the GPR is most commonly used for detecting caves and subsidence areas and for preventing collapses in urban areas and for construction interventions. This is followed by exploration of karst aquifers, epikarst and quarry research. Some non-established applications are also presented, such as the use of a georadar in exploration of unroofed caves and cave sediments. The main purpose of this article is to demonstrate and evaluate the possibilities of using a georadar in different karst environments, to encourage its use in some new applications, and to emphasize the necessity of an interdisciplinary approach in such studies. [ABSTRACT FROM AUTHOR]

Climate change represents an important cause of subsidence, especially in coastal cities affected by changes in surface water level and water table. This paper presents a complementary study of Interferometric Synthetic Aperture Radar (InSAR) and Ground Penetrating Radar (GPR) for the early detection of subsidence and sinkhole phenomena. The methodology was applied to a coastal urban area in Galicia, northwest Spain (humid region), showing apparent signs of subsidence and building settlement during the last two years. Two different InSAR methods are compared for the period from June 2021 to March 2022: PSI (Persistent Scatterer Interferometry) and SBAS (Small Baseline Subsets), and the average deformation velocities obtained resulted in −3.0 mm/yr and −4.1 mm/yr, respectively. Additional GPR data were collected in January 2022 to validate the InSAR results, which detected subsidence in agreement with the persistent scatters obtained from the PSI method. This is crucial information to plan preventive maintenance. [ABSTRACT FROM AUTHOR]

An extensive magnetic survey has been carried out on a large part of the Roman and late antique city of Pollentia (Alcúdia, Mallorca, Spain), combined with ground penetrating radar (GPR) and electric resistivity imaging (ER Imaging) to obtain data for a better understanding of the ancient city. For magnetic measurements, the 7‐probe fluxgate gradiometer array was used. The GPR data were collected by means of a system equipped with two dual‐frequency antenna boxes of 200 and 600 MHz, respectively. The geophysical data provide some new insights into the layout of the city, with the identification of numerous structures in areas that are still unexplored by archaeological investigation. The results fill the gap of previous partial geophysical surveys and show an interesting, unseen image of ancient Pollentia. [ABSTRACT FROM AUTHOR]

The paper presents the acquisition and data processing approach for the Ground Penetrating Radar (GPR) and laser scanner surveys carried out within the SOS project (the acronym comes from 'SOtto Siena', in English 'Beneath Siena'). SOS is a program aimed to overcome some of the problems and limitations currently present in the study of cities with long-term continuity of life, responding in particular to the need for a better understanding of the city's ancient fabric and hence to improvements in its conservation by: GPR city survey full coverage (of all the public spaces, streets, squares, courtyards, gardens, etc.), GIS data entry of the historical-archaeological and geoarchaeological knowledge and the development of a 3D Archaeological WEBGIS.The paper discusses the procedure for the creation of a 3D viewer within an already active WEBGIS platform, specifically created for the visualisation and management of archaeological data. The GPR data, once acquired, were exported in 3D in the form of point clouds and subjected to a procedure of cleaning and filtering from noise, so as to eliminate geometries not referable to anomalies and therefore to the presence of buried structures or cavities, and then transformed into mesh to meet the needs of the subsequent process of semantic enrichment. The GPR survey of the underground was flanked by laser scanning of some of the most significant structures in the historic centre (e.g. the cathedral). All 3D geometries were then inserted into the new visualiser via a pipeline using open-source tools and libraries. [ABSTRACT FROM AUTHOR]

Due to the difficulty in detecting the upper breakpoint of active buried faults, high-resolution detection of active buried faults in urban areas is very important for urban planning and disaster risk mitigation. The seismic reflection technique is the most common technique used to image faults at depth, but it is difficult to precisely locate the upper breakpoint of active buried faults. Ground-penetrating radar (GPR) provides high-resolution imaging in ultrashallow exploration, but the penetration depth of traditional GPR is shallow. In this work, we conducted six GPR surveys with multifrequency (25 MHz, 50 MHz and 100 MHz) and high-power GPR antennas across the possible range of the Shuiyu fault based on seismic reflection results. We obtained the trace of the Shuiyu fault within 45 m of the surface in Datong city, and the fault was found to dip approximately 70–80° to the SE. According to the GPR results, we selected a location for trenching and excavated one trench across the Shuiyu fault. The trench results verified the accuracy of the fault imaging in the GPR profiles and helped to interpret the stratigraphic information in the GPR profiles. In the accurate detection of active buried faults in other urban areas, the seismic reflection method can be used to determine the main strike of faults at depth, and then GPR can be used to detect the near-surface distribution of the faults in detail and guide trench location selection. The application of high-power GPR antennas with different frequencies in the fast detection of the upper breakpoint of active buried faults in urban areas is of great significance to earthquake hazard analysis and urban planning in Datong city. • The GPR can quickly and effectively locate the upper breakpoint of buried faults. • The combination of reflection seismic and GPR is reliable and high resolution. • The surface location of SYF in Datong city was obtained for the first time. • The SYF was active in late Late Pleistocene, the earthquake risk cannot be ignored. [ABSTRACT FROM AUTHOR]

Recently, global urbanization and industrialization have resulted in excessive groundwater exploitation, and the occurrence and damage of land subsidence to human life and property are increasing accordingly. The present study assessed the impact of tunnel excavation on the groundwater system and potential land subsidence in a Korean metropolitan area. A numerical model was established to predict groundwater level variations with tunnel excavation, and the mechanisms and cases of land subsidence worldwide were reviewed. The established model adequately represented the groundwater system in the study area. The tunnel excavation decreased the groundwater level along the tunnel line, and significant groundwater drawdown primarily occurred up to 6.1 m at locations with high permeability, leading to the temporary development of a large depression cone. The study area has favorable conditions for land subsidence, and curved tunnel excavation may induce ground disturbance, resulting in groundwater inflow and soil loss in the region. In addition, the risk of land subsidence is expected to persist owing to the lag time caused by the creep phenomenon, even though the groundwater level recovers. Efforts to effectively reduce land subsidence damage in urban areas are crucial, requiring measures such as controlling land subsidence occurrence and implementing prevention measures through early recognition, including artificial recharge of groundwater, underground cavity observation with ground penetrating radar, land subsidence observation with a borehole extensometer, and groundwater level monitoring systems. [ABSTRACT FROM AUTHOR]

The Roman theatre of Padua stood in the area now occupied by Prato della Valle, a huge elliptical-shaped square with a central green part (Isola Memmia) surrounded by a canal, built in the second half of the 18th century and part of the modern urban city center of Padua. Some still-preserved remains of the Roman theatre stand at the bottom of this canal. Recently, in 2017, emptying and cleaning the canal and excavating these remains, which had been known in the past, new geometrical and archaeological information has been collected. To date, however, there are no specific indications about additional preserved buried parts of the Roman theatre and its overall extent between the central and the outer part of Prato della Valle. Therefore, several electrical resistivity tomographies (ERT) and ground penetrating radar (GPR) sections were collected in 2017 to gather new information. The results of geophysical prospecting with recent archaeological evidence and historical documents, even the complexity of the urban environment, provide further details on the possible extent and location of additional buried remains of the Roman theatre, opening new archaeological considerations and issues related to the use of ERT and GPR in urban contexts. [ABSTRACT FROM AUTHOR]

The density of the built environment is growing due to the migration from rural areas to urban areas. The challenges that should be addressed are therefore increased in today's built environment. In relation to this, the productive use of underground space is essential to overcome the problems on the surface. Since the built environment has complex and multi-layered buildings more than ever, the delineation and management of the cadastral rights, restrictions, and responsibilities (RRRs) are significantly difficult in two-dimensional (2D). For this reason, creating approaches for the efficient representation of RRRs in three-dimensional (3D) is a hot topic in recent years. Considering the multifaceted structure of the underground, 3D geoinformation regarding the underground is needed for managing the underground space. Regarding this, it is significant to underline that legal and administrative namely land administration considerations are integral parts of the planning of underground space. This paper thus extends the CityJSON core schema in a way that it can be used for 3D delineation of underground cadastral RRRs. [ABSTRACT FROM AUTHOR]

Road collapses pose dangerous threats to traffic safety in urban cities. Typically, these collapses result from under-road defects such as cavities, loose soil, and voids. With the development of multi-channel 3D ground penetrating radar (GPR) systems, GPR has become a routine method for inspecting the subsurface conditions of roads. However, the reflection characteristics of hidden defects in 3D GPR results have not been well studied due to the complexity of urban road structures. Consequently, accurately detecting all subsurface defects in GPR survey areas remains challenging. In this paper, numerical models of road structures with typical types of hidden defects are constructed, and their reflection characteristics in GPR B-scan profiles and C-scan depth slices are analyzed. Then, the field results obtained using a car-mounted 3D GPR system are presented to confirm the reflection characteristics of these hidden defects. Finally, the reflections of manhole covers and underground pipelines, which are the most prevalent forms of clutter in GPR images in urban environments, are compared with those of hidden defects. The findings of this paper will facilitate the accurate interpretation of field 3D GPR data for road inspections and the mitigation of road collapse accidents. • Reflection characteristics of typical under-road defects in 3D GPR images. • Numerical models of road structures with typical types of hidden defects. • Field case studies employing a 3D GPR system to detect under-road defects. • Comparison between under-road defects and other anomalies in 3D GPR images. • Under-road defects detection for mitigating road collapse accidents. [ABSTRACT FROM AUTHOR]

Ground penetrating radar (GPR) is a promising non-destructive evaluation technique for detecting buried underground objects in urban area. Deep learning technique is recently being applied into this field to automate the GPR data interpretation. However, there is no proper technique that can reflect the uniqueness of urban road pavements. In this study, an underground object detection technique suitable for urban road pavement is proposed by using a statistically determined threshold amplitude and a large amount of GPR B-scan image libraries. An automated thresholding technique is newly developed based on the statistical distribution of GPR data. Deep learning technique is then applied to the reconstructed GPR data to detect underground objects in urban area. The proposed method is experimentally validated by field data collected on urban roads in Seoul, South Korea. In addition, its application possibility is also tested with full-size GPR data. The proposed method successfully emphasises the feature of underground objects and classifies hyperbola, manhole cover, layer interface and subsoil background. [ABSTRACT FROM AUTHOR]

Geoelectrical resistivity is an excellent method to investigate the structural composition of shallow subsurfaces. However, existing commercial equipment is typically expensive and often requires proprietary accessories and software to provide full system functionality. The objective of this study was to develop a multichannel, modular, automated, and programmable geo-resistivity meter capable of user customization and programming. To this end, a conceptual prototype was built based on free software and open hardware technologies as a low-cost alternative to commercial equipment while maintaining the accuracy and quality of the data at the same level. The prototype was based on electrode multiplexing to make the switching process more efficient by reducing cabling complexity, whereas synchronous demodulation for signal detection was employed, providing strong rejection of spurious electrical noise, typical of urban areas where such equipment is frequently used. The results demonstrate the feasibility of this project and an important academic contribution to open-source instrumental research. [ABSTRACT FROM AUTHOR]

A utilidor is a 'system of systems' infrastructural solution to the 'subsurface spaghetti' problem resulting from direct burial of utility transmission infrastructure beneath the public right of way (PROW). The transition from direct burial to utilidors in older, dense American cities has generally not occurred, despite the potential to increase system performance in a long-term, financially and environmentally sustainable manner, because it would require reform of local planning practices and of utility pricing to support financing within a complex regulatory system. Utilidor adoption in New York City (NYC) would be a significant local infrastructure transition, amplifying the need for locality-based research, that would occur while each utility sector undergoes its own infrastructure transitions, thereby increasing the level of regulatory complexity. This paper applies transitions analysis, recursive collective action theory, and capacity to act analysis to NYC's experience with its PROW subsurface spaghetti problem and utilidor implementation to demonstrate a place-based methodology that identifies specific sources of resistance to innovative subsurface design and feasible pathways for resolving them. This methodology would be transferable for application to other American cities or classes of American cities to supplement the limits of generalised subsurface and subsurface resource integration research for practitioner application. [ABSTRACT FROM AUTHOR]

Featured Application: Combining of geophysical and hydrogeological surveys provides basic insights for the shallow groundwater resource evaluation in a coastal urban area. This paper conceptualizes and evaluates the groundwater resource in a coastal urban area hydrologically influenced by peri-urban irrigation agriculture. Adra town in southern Spain was the case study chosen to evaluate the groundwater resource contributed from the northern steep urban sector (NSUS) to the southern flat urban sector (SFUS), which belongs to the Adra River Delta Groundwater Body (ARDGB). The methodology included (1) geological and hydrogeological data compilation; (2) thirteen Multichannel Analysis of Surface Waves (MASW), and eight Ground Penetrating Radar (GPR) profiles to define shallow geological structures and some hydrogeological features; (3) hydrogeological surveys for aquifer hydraulic definition; (4) conceptualization of the hydrogeological functioning; and (5) the NSUS groundwater resource evaluation. All findings were integrated to prepare a 1:5000 scale hydrogeological map and cross-sections. Ten hydrogeological formations were defined, four of them (Paleozoic weathered bedrock, Pleistocene littoral facies, Holocene colluvial, and anthropogenic filling) in the NSUS contributing to the SFUS. The NSUS groundwater discharge and recharge are, respectively, around 0.28 Mm3 year−1 and 0.31 Mm3 year−1, and the actual groundwater storage is around 0.47 Mm3. The groundwater renewability is high enough to guarantee a durable small exploitation for specific current and future urban water uses which can alleviate the pressure on the ARDGB. [ABSTRACT FROM AUTHOR]

Geoelectrical resistivity is an excellent method to investigate the structural composition of shallow subsurfaces. However, existing commercial equipment is typically expensive and often requires proprietary accessories and software to provide full system functionality. The objective of this study was to develop a multichannel, modular, automated, and programmable geo-resistivity meter capable of customization and programming by the user. To this end, a conceptual prototype was built based on free software and open hardware technologies as a low-cost alternative to commercial equipment, while maintaining the accuracy and quality of the data at the same level. The prototype was based on electrode multiplexing to make the switching process more efficient by reducing cabling complexity, while synchronous demodulation for signal detection was employed, providing strong rejection of spurious electrical noise, typical of urban areas where such equipment is frequently used. The results show the feasibility of this project and demonstrate an important academic contribution to open-source instrumental research. [ABSTRACT FROM AUTHOR]

Data from geocryological studies of soil and rock massifs in permafrost zone are very important as a basis for predicting possible negative consequences associated with climate change. A promising technique for studying geocryological structures (various types of underground ice) is the ground-penetrating radar (GPR) method. This paper presents the applications of the GPR method to prospect and evaluate massive ice in a frozen rock mass. To study the features of GPR signals received during sounding of underground ice, a model of a single GPR trace for the structure "frozen rock-ice-frozen rock" was developed. As a result, regularities were established in the kinematic and dynamic characteristics of GPR signals at the upper and lower boundaries of massive ice, depending on its geometric parameters. The established features were confirmed by the results of computer and physical simulation of GPR measurements of a frozen rock mass model. The main result of the study was to obtain a set of criteria for identifying massive ice according to GPR measurements. The developed criteria will allow the use of GPR for a detailed study of the structure of permafrost rocks to prevent the development of dangerous cryogenic processes in undisturbed and urban areas of the Arctic. [ABSTRACT FROM AUTHOR]

This paper deals with the application of non-destructive geophysical techniques of investigation in the urban environment of the city of Nicosia (Cyprus). The main aim of the research was, in the frame of the Eleftheria Square redesign project, to image subsurface properties in order to reduce the impact of hazards on the old buildings (therefore preserving the cultural heritage of the place), and on the new infrastructure under construction. Since 2008, electrical resistivity tomography (ERT), ground penetrating radar (GPR) and induced electromagnetic method (EMI) were employed during the different phases of the project to provide an understanding of geological stratigraphy, the detection of buried objects (archaeological structures and underground utilities) and the solution of unexpected events (such as water infiltration in the course of works). The geophysical results proved the efficiency of the adopted methods, adding scientific value to the knowledge of the studied area. The new gathered information helped the public administration technicians to plan direct and targeted interventions and to modify the original design of the project according to the discovery of archaeological findings. [ABSTRACT FROM AUTHOR]

This paper presents the selected results of GPR (ground penetrating radar) and ERT (electrical resistivity tomography) surveys carried out on the sites in Poland where shallow karst forms were found in gypsum deposits. The aim of the surveys was the noninvasive detection of karst forms as well as weathered and fractured bedrock which may threaten the stability of the surface and, consequently, may cause damage to buildings, as well as overground and underground infrastructure. The geophysical surveys were conducted at a depth of only a few meters, i.e., to the depth of buildings foundations. GPR surveys were carried out in short-offset reflection profiling mode with standard orientation of the antennae set; however, on one site, different orientations of antennae were tested. During ERT surveys, different measurement arrays were applied in order to analyze which array was optimal for the detection of karst forms as well as weathered and fractured bedrock. Complex interpretation of geophysical surveys resulted in reduced ambiguity and revealed some regions, dangerous for surface stability. Due to the fact that gypsum deposits were investigated to the depth of maximum 10 m; therefore, hydrological processes were analyzed in the paper instead of hydrogeological processes. [ABSTRACT FROM AUTHOR]

This paper focuses on the use of the Canny edge detector as the first step of an advanced imaging algorithm for automated detection of hyperbolic reflections in ground-penetrating radar (GPR) data. Since the imaging algorithm aims to work in real time; particular attention is paid to its computational efficiency. Various alternative criteria are designed and examined, to fasten the procedure by eliminating unnecessary edge pixels from Canny-processed data, before such data go through the subsequent steps of the detection algorithm. The effectiveness and reliability of the proposed methodology are tested on a wide set of synthetic and experimental radargrams with promising results. The finite-difference time-domain simulator gprMax is used to generate synthetic radargrams for the tests, while the real radargrams come from GPR surveys carried out by the authors in urban areas. The imaging algorithm is implemented in MATLAB. [ABSTRACT FROM AUTHOR]

• Integrate the SLAM positioning and the GPR imaging. • Provide real-time positioning in Satellite-free areas. • Synchronization accurate positioning and GPR traces, with the scan-lag solved. • Improve the quality of GPR C-scans. Ground Penetrating Radar (GPR) is commonly used for detecting and locating underground utilities, as well as identifying water leakages and other buried objects without the need for excavation. To precisely depict the subsurface by GPR, an accurate geo-referencing technique on each GPR scan is also essential. Traditional geo-referencing of GPR scans requires a survey wheel to walk along a predetermined grid, or relies on the Global Navigational Satellite Systems (GNSS) to work under open sky environments where enough satellites are available (Böniger and Tronicke, 2010; Chang, 2016). In this study, we attempt to use a mobile mapping system (MMS) backpack guided by SLAM as the geo-referencing device for synchronizing GPR scans in areas with bad or no GNSS, and is free of control points. The study develops a method to synchronise the SLAM positioning and GPR measurements and then validate the proposed method's precision and accuracy with a site case. It was proved that the integrationed time and labour required in the traditional gridding are minimized for improving the GPR survey efficiency, facilitating the large-scale survey in dense urban areas where good GNSS coverage is unavailable. [ABSTRACT FROM AUTHOR]

• Develop an automatic GPR workflow for subsurface void detection. • The workflow imitates human decision-making process. • The workflow makes interpretation a lot more efficient and alleviates human biases. Countless subsurface voids in urban areas of cities threaten people's lives and property. A workflow for automatically identifying subsurface voids from ground penetrating radar (GPR) data was developed in this study. The workflow consists of 3 stages: locating voids automatically from C-scans, then verifying voids from corresponding B-scans, and finally making judgements based upon the previous 2 sets of results. This study adopted 2 (Lai et al., 2016) approaches: approach 1 quantified the GPR response of air voids using forward modelling, while approach 2 used workflow prototyping and validation with inverse modelling. Forward simulations indicated that different ratios of void size to GPR signal footprint could result in a variety of patterns in B-scans: they can be hyperbolas, cross patterns, bowl shaped patterns and reverberations. With a database of void patterns of both C-scans and B-scans established, in approach 2 the workflow uses a pyramid pattern recognition method – with pixel value or gradient being used for feature identification – to search automatically for air-filled void responses in GPR data. The workflow was tested using 2 laboratory and field experiments and the results were promising. The constraint values proposed by the 2 experiments were validated with another site experiment. Given the huge workload involved in city-scale subsurface health inspections, a standardized workflow can help improve efficiency and effectiveness of subsurface void identification. [ABSTRACT FROM AUTHOR]

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Sinkholes caused by natural or anthropogenic factors pose as potential safety hazards in urban areas. From April to May 2019, six consecutive ground collapses occurred in Beihuan New Village (Guigang City, China) that affected the livelihoods of residents and caused substantial economic losses. The present study aimed to investigate potential sinkhole areas and determine the formation mechanism of a series of ground collapses in Beihuan New Village using a combined drilling and multi-geophysical approach. Geophysical profiles collected using electrical resistivity tomography (ERT) and ground penetrating radar (GPR) revealed shallow geological structures, potential sinkholes, and karst fracture zones. We also drilled several shallow boreholes along the geophysical survey profiles to obtain accurate hydrogeological information. To precisely identify groundwater runoff zones, cross-hole electrical resistivity tomography (CHERT) surveys of deep boreholes were conducted to locate the initial boundaries of the target anomaly areas delineated using ERT and GPR. The results demonstrated that a combination of geophysical exploration and geological profile analysis could accurately delineate potential sinkholes in urban areas. The locations of sinkholes in the study area were consistent with subsurface karst and groundwater runoff zones inferred from our survey results. Additionally, comprehensive analysis indicated that a depleted groundwater table, heavy seasonal rainfall, and overlying soil characteristics were possibly responsible for sinkhole formation. These findings can assist in prevention of ground collapses in urban areas and mitigation of the damages caused by these collapses. • Potential sinkholes in an urban area were assessed using a multi-geophysical survey. • GPR revealed interfaces between different strata and the karst fissure distribution. • ERT and CHERT delineated groundwater runoff zones and potential sinkhole areas. • A 3-D geological interpretation model was created based on drilling data and CHERT. • Sinkholes are caused by depleted groundwater, heavy rainfall, & soil characteristics. [ABSTRACT FROM AUTHOR]

This paper deals with a geophysical survey carried out in some critical urban areas of the historical city of Matera (Southern Italy). Matera has a very complex shallower stratigraphy characterized by both anthropic and natural "targets" and is affected by geological instability. Therefore, Matera represents an ideal and very challenging outdoor laboratory for testing novel approaches for near-surface explorations in urban areas. Here, we present the results of a near-surface survey carried out by jointly applying Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) methods. The survey was implemented in three different critical zones within the urban area of Matera (Piazza Duomo, Piazza San Giovanni, Villa dell'Unità d'Italia). These test sites are of great interest for archaeological and architectonical studies and are affected by ground instability phenomena due to the presence of voids, cavities and other anthropic structures. The effectiveness of the survey was enhanced by the exploitation of advanced 3D tomographic approaches, which allowed to achieve 3D representation of the investigated underground and obtain information in terms of both the location and the geometry of buried objects and structures and the characterization of shallow geological layers. The results of the surveys are now under study (or have attracted the interest) of the Municipality in order to support smart cities programs and activities for a better management of the underground space. [ABSTRACT FROM AUTHOR]

The aim of COST Action TU1208 was to share and increase scientific-technical knowledge and experience of Ground Penetrating Radar (GPR) techniques in civil engineering, whilst promoting a wider and more effective use of this safe and non-destructive method in the monitoring of structures. The COST Action TU1208 started in April 2013 and ended in October 2017. We were invited to participate in 2014. Our main efforts were directed towards several areas:- Expanding the network of researchers involved in GPR technology and its applications- Joint work with other participants on research, implementation of GPR technology and its applications, as well as publishing in conferences and scientific journals- Participation in founding of TU1208 GPR Association as a follow up initiative of COST Action TU1208. Association is open to experts from all over the world, and its goals are to keep scientific network alive and cohesive, continue the work that was done in the framework of the Action, and further support of cooperation between universities, research centers, private companies and public agencies active in the GPR field. - Development of "Guideline for the detection and the mapping of underground utilities and voids using Ground Penetrating Radar (GPR), with a particular focus to urban areas". This document incorporates elements from various standards, recommendations and good practice from countries where the usage of GPR technology is regulated and is aimed to represent a basic document for development of standards in countries where GPR technology is fully recognized. - Participation in GPR antenna testing campaign. Testing was done based on "GPR system performance compliance tests" which were developed within COST TU 1208 Action. - Development of educational materials "GPR in civil engineering applications - Detection of underground utilities" and "GPR survey – Integration of GPR with other remote sensing technologies" which can be used in introducing of GPR technology to a wider audience.- Organizing 'GPR Workshop - European experiences, standards and recommendations in application of Ground Penetrating Radar', Road Show event where GPR technology was presented to stakeholders, private companies, professionals and other interested parties. [ABSTRACT FROM AUTHOR]

The role of the applied geophysics for the new scenario of the global urbanization is going to be important. In fact, a high-resolution observation point of the shallow geological subsoil and its iteration with the urban infrastructures became a fundamental point of view. The reinforced concrete (RC) technologies has become the most used technology into the engineering infrastructures. However, RC technology is affected by degradation phenomena that could reduce strongly the life time of engineering structures. This weakness is due to corrosion for flow of chloride ions, cracks, fractures or delamination induced by mechanical stresses, voids or carbonation due to water or moisture coming from the subsoil. Therefore, it is important to develop a new approach less invasive and with fast detection that taking in account not only the structure but also the "infrastructural critical zone" in order to considers the interactions between geology and foundations and the static and dynamic aspects of structures and infrastructures. A novel sub-discipline, called Urban Geophysics, has recently been developing in the field of geophysics for analyzing limits and potentialities of well-known geophysical techniques in urban and industrialized areas. Unfortunately, not all the geophysical techniques are applicable in urban areas for the strong noise due to the presence of metallic structures. However, good results are achievable with applications of electrical resistivity measurements and ground penetrating radar so much to investigate structural elements as to monitor the stability of civil structures. The work presents an experimental approach on full-scale engineering structures and some real cases where the electrical resistivity technique and ground penetrating radar were jointly applied for civil engineering issues. [ABSTRACT FROM AUTHOR]

Two critical aspects for assessing the hazard and managing the risk associated with active sinkholes in developed areas are the precise mapping of the areas affected by ground instability and the quantitative characterization of the ground displacement (kinematic style, spatial-temporal patterns, rates). However, sinkhole site investigations typically provide a static picture of the instability phenomena, and the performance of remediation measures is rarely evaluated using time-series of displacement. This work illustrates the practicality of a non-invasive approach, combining detailed mapping, ground penetrating radar (GPR), and high-precision leveling, for the characterization at different time scales of the ground deformation associated with an active sinkhole in an urban area. The selected highly-active sagging and collapse sinkhole affects four multi-storey buildings in Zaragoza city, Spain, involving direct losses higher than 15 Meuro. GPR data provided information on the internal structure of the sinkhole and the subsidence mechanisms. The boundaries of the ground-deformation zone, established with the GPR data, and especially high-precision leveling, indicate a sinkhole area two times larger than that previously proposed on the basis of airborne imagery and surface deformation features (length from 100 m to 130 m). The leveling profiles reveal an inner rapidly subsiding zone with vertical displacement rates as high as 3 cm/yr, an outer slow settlement ring, and a marginal uplifting bulge with vertical displacement rates that reach 0.6 cm/yr. This phenomenon of marginal bulging is probably a relatively common process in sagging sinkholes, which may have gone unnoticed since its identification requires the use of geodetic methods with utmost accuracy, such as high-precision leveling. Monitoring data indicate that ongoing salt dissolution significantly contributes to the active subsidence and reveal the high impact on the subsidence of water pumping from the evaporitic aquifer and the limited efficiency of a shallow compaction grouting program performed above cavities and karstification zones. • Multimethod and non-invasive investigation of a sinkhole in an urban area. • The studied sinkhole has caused direct losses higher than 15 Meuro. • Spatial-temporal deformation patterns revealed by high-precision leveling and GPR. • Quantitative characterization of marginal uplift in an active sinkhole. • Assessment of the performance of sinkhole mitigation measures. [ABSTRACT FROM AUTHOR]

Accurate assessment of damage caused by conflict can be difficult to determine from ground-based surveys, particularly in the context of violence and unsafe conditions. Earth Observation data provides a non-invasive method for rapid damage assessment over wide geographic areas. In this study we use Landsat Imagery captured between 2011 and 2017 to assess the damage in Aleppo, Syria caused by conflict during the Syrian Civil War. Extracting temporal changes in urban environments is complex and the capabilities of traditional spectral-based methodologies are limited. We examined the effectiveness of the Gray-Level Co-Occurrence Matrix (GLCM) and two texture-based metrics (correlation and homogeneity) at classifying changes in reflectance characteristics within urban environments caused by building damage and consequent changes in surface orientation. Homogeneity was a more effective texture measure than correlation (overall accuracy of 79% vs 50%). Results indicated that between 45% and 57% of Aleppo was damaged during the study period, including up to 57% of former rebel held areas and between 34% and 46% of government areas and their surrounds. We used SPOT-6 imagery for accuracy assessment. Damage to Aleppo has yet to be fully quantified and several parts of the city remain unsafe and inaccessible. The results of this study highlight the potential offered by texture analysis for mapping damage to urban areas with freely available imagery and can be readily applied to natural disasters such as earthquakes and the aftermath of extreme weather events. • Around half of Aleppo was damaged between 2011 and 2017. • Damage was primarily concentrated in rebel-contested areas and occurred between 2012 and 2013. • Homogeneity a better measure than correlation for mapping damage. • Texture-based analysis a safe, free, non-invasive method for rapidly mapping damage to wide areas. • Easily ported to assess damage from natural disasters. [ABSTRACT FROM AUTHOR]