Using InSAR and GPR techniques to detect subsidence: application to the coastal area of “A Xunqueira” (NW Spain)

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.Xunta de Galicia | Ref. ED431F 2021/08European Commission | Ref. 101036926European Commission | Ref. 101021714Ministerio de Ciencia e Innovación | Ref. RYC2019–026604–IMinisterio de Universidades | Ref. CAS21/00241Ministerio de Ciencia e Innovación | Ref. TED2021-130183B-I0

Review of InfraRed Thermography and Ground-Penetrating Radar applications for building assessment

The first appearance of concern for the good condition of a building dates back to ancient times. In recent years, with the emergence of new inspection technologies and the growing concern about climate change and people’s health, the concern about the integrity of building structures has been extended to their analysis as insulating envelopes. In addition, the growing network of historic buildings gives this sector special attention. Therefore, this study presents a comprehensive review of the application of two of the most common and most successful Non-Destructive Techniques (NDTs) when inspecting a building: InfraRed Thermography (IRT) and Ground-Penetrating Radar (GPR). To the best knowledge of the authors, it is the first time that a joint compilation of the state-of-the-art of both IRT and GPR for building evaluation is performed in the same work, with special emphasis on applications that integrate both technologies. The authors briefly explain the performance of each NDT, along with the individual and collective advantages of their uses in the building sector. Subsequently, an in-depth analysis of the most relevant references is described, according to the building materials to be studied and the purpose to be achieved: structural safety, energy efficiency and well-being, and heritage preservation. Then, three different case studies are presented with the aim of illustrating the potential of the combined use of IRT and GPR in the evaluation of buildings for the purposes defined. Last, the final remarks and future lines are described on the application of these two interesting inspection technologies in the preservation and conservation of the building sector.European Union Next GenerationEU/PRTRAgencia Estatal de Investigación | Ref. PDC2021-121239-C32Agencia Estatal de Investigación | Ref. RYC2019-026604-

Ground Penetrating Radar applied to monumental stone conservation: application to the Rock Necropolis of San Vítor de Barxacova in NW Spain

This paper deals with the application of the Ground Penetrating Radar (GPR) method in the assessment of stone monuments. Compilation of published works and a discussion of their main findings are first addressed. Next, to show the potential of the method, a case study is presented aiming to assess the state of conservation of the rock necropolis of San Vítor de Barxacova (Ourense, Spain) consisting of 56 anthropomorphic graves carved into the natural rock. Fieldwork was carried out using a GPR system equipped with a 2.3 GHz central frequency antenna. The main goal of this study is to provide an effective approach for the detection and localization of internal damages such as fractures and voids. New amplitude-based 2D and 3D imaging strategies are presented aiming to improve damage detection. A new approach was also developed to digitize the extracted information into a point cloud format, thus improving the possibilities for 3D visualization with the surrounding environment. Although a total of 39 graves were surveyed, only 13 graves are included in this paper due to their singularity and relevant results. The potential of using GPR tests for the assessment of the conservation state of monumental stone structures is also discussed.Xunta de Galicia | Ref. ED431F 2021/08Ministerio de Ciencia e Innovación | Ref. RYC2019-026604-IAgencia Estatal de Investigación | Ref. RTI2018-095893-B-C2

Multi-objective optimization-based model calibration of masonry bridges

Multi-objective optimization-based model calibration can be an intermediate solution between the computationally expensive probabilistic approaches and the single-objective optimization strategies that do not allow uncertainty quantification of the obtained solutions. This work addresses the multi-objective model calibration of two historic stone arch bridges using high-fidelity computational FE models. To implement the methodology, a five-step approach is proposed: experimental characterization through non-destructive testing techniques, non-parametric asbuilt geometric modeling, macro-finite element modeling, sensitivity analysis, and multiobjective optimization. The preferred solution among the Pareto front solutions is selected based on two different classical criteria, and the set of optimal solutions is further statistically analyzed to assess the validity of the identification process. The results show an average frequency error of 0.97 % and 0.70 % and an average MAC of 0.97 and 0.96 for each case study, respectively, thus highlighting the adequacy of the proposed methodology.Agencia Estatal de Investigación | Ref. PID2021-124236OB-C33Agencia Estatal de Investigación | Ref. PRE2019-087331Agencia Estatal de Investigación | Ref. RYC2019-026604-IXunta de Galicia | Ref. ED431F 2021/08Universidade de Vigo/CISU

Combined use of GPR and Other NDTs for road pavement assessment: an overview

Roads are the main transportation system in any country and, therefore, must be maintained in good physical condition to provide a safe and seamless flow to transport people and goods. However, road pavements are subjected to various defects because of construction errors, aging, environmental conditions, changing traffic load, and poor maintenance. Regular inspections are therefore recommended to ensure serviceability and minimize maintenance costs. Ground-penetrating radar (GPR) is a non-destructive testing (NDT) technique widely used to inspect the subsurface condition of road pavements. Furthermore, the integral use of NDTs has received more attention in recent years since it provides a more comprehensive and reliable assessment of the road network. Accordingly, GPR has been integrated with complementary NDTs to extend its capabilities and to detect potential pavement surface and subsurface distresses and features. In this paper, the non-destructive methods commonly combined with GPR to monitor both flexible and rigid pavements are briefly described. In addition, published work combining GPR with other NDT methods is reviewed, emphasizing the main findings and limitations of the most practical combination methods. Further, challenges, trends, and future perspectives of the reviewed combination works are highlighted, including the use of intelligent data analysis.Xunta de Galicia | Ref. ED431F 2021/08Ministerio de Ciencia e Innovación | Ref. RYC2019–026604-

Reliability-based structural assessment of historical masonry arch bridges: The case study of Cernadela bridge

Nowadays, several historical masonry arch bridges present a deficient state of conservation due to degradation processes induced by natural or human actions. Usually, these constructions have significant economic, cultural, and heritage value. Therefore, they shall be thoroughly assessed to verify their structural integrity and safety condition. For this purpose, reliability-based structural assessments are typically performed. However, the associated outcomes (i.e., reliability index and probability of failure) highly rely on the accuracy of the structural parameters uncertainty quantification. This work presents a study regarding the influence of the scattering of the arches' thickness dimensions in the load-carrying capacity assessment of the Cernadela Bridge, a historical stone bridge located in Galicia, Spain. The study first involved a comprehensive experimental campaign to characterize the outer and inner bridge geometry through geomatic techniques, i.e., terrestrial laser scanning and ground penetrating radar. Subsequently, a limit analysis model was developed, considering only the arches' outer (visible) data. From this initial structural assessment, a reliability index of 2.38 was obtained. The influence of the uncertain structural parameters, both geometric features and material properties, in the collapse load was investigated through a global variance-based sensitivity analysis (i.e., Sobol' indices) complemented by a surrogate modeling strategy based on the Kriging approach. Finally, the measured inner geometry of the arches was introduced in the computational model through Bayesian inference procedures. Thus, two new structural assessments were performed: first, by considering the updated distributions of all arches thicknesses, and second, by considering only the updated distributions of the non-influential ones. Reliability indexes of 1.51 and 2.33 were derived, thus highlighting the importance of a proper uncertainty quantification process and the relevance of the sensitivity analysis outcomes to identify the critical parameters on the bridge mechanical response.Ministerio de Ciencia e Innovación | Ref. TED2021-130497A-I00Ministerio de Ciencia e Innovación | Ref. RYC2019-026604-

GPR application on geothermal studies: the case study of the thermal baths of San Xusto (Pontevedra, Spain)

Geophysical studies are frequently used on the geothermal field to define and characterize deep structures. However, shallow investigations are also needed for understanding the origin and local potential structures of a promising geothermal site. In this research, it is intended to present a review of the possibilities of the application of ground-penetrating radar (GPR) on the study of geothermal resources and how this geophysical technique can contribute to improving the energy use of these thermal resources. For this, the specific case of application to the investigation of the thermal baths of San Xusto (Pontevedra, Spain) is included in this work, whose interest for the region makes it necessary to perform an in-depth analysis of the original thermal structure. A GPR survey with frequency antennas of 200 and 500 MHz was conducted. Additionally, chemical analyses were performed to characterize the thermal water in the San Xusto site. As a result, a hot spring was detected by identifying reverberation phenomena in GPR imaging due to the presence of metal compounds and silica. Locating the origin of the thermal springs could allow for a more efficient use of the thermal resources as well as the hydrothermal possibilities of the area.Xunta de Galicia | Ref. ED431F 2021/08Ministerio de Ciencia e Innovación | Ref. RYC2019-026604-

From its core to the niche: insights from GPR applications

Thanks to its non-destructive, high-resolution imaging possibilities and its sensitivity to both conductive and dielectric subsurface structures, Ground-Penetrating Radar (GPR) has become a widely recognized near-surface geophysical tool, routinely adopted in a wide variety of disciplines. Since its first development almost 100 years ago, the domain in which the methodology has been successfully deployed has significantly expanded from ice sounding and environmental studies to precision agriculture and infrastructure monitoring. While such expansion has been clearly supported by the evolution of technology and electronics, the operating principles have always secured GPR a predominant position among alternative inspection approaches. The aim of this contribution is to provide a large-scale survey of the current areas where GPR has emerged as a valuable prospection methodology, highlighting the reasons for such prominence and, at the same time, to suggest where and how it could be enhanced even more.Xunta de Galicia | Ref. ED431F 2021/08Agencia Estatal de Investigación | Ref. RYC2019-026604-

GPR analysis to detect subsidence: a case study on a loaded reinforced concrete pavement

Subsidence seriously affects the structural stability and safety of pavements and foundation soils. In heavy-loaded pavements, there is a risk of floor sinking and further construction collapse; hence, there is a need to develop efficient methodologies to detect subsidence earlier. This work proposes the use of ground penetrating radar (GPR) as a solution to non-invasively inspect the subsoil. Furthermore, as the interpretation of the GPR data is arguably subjective and highly dependent on who interprets it, different imaging techniques are herein exploited to improve the interpretability and detection of subsidence and settlement phenomena. The approach was applied to a heavily loaded reinforced concrete pavement servicing a manufacturing facility. Amplitude- and texture-based imaging methods were used to detect subsidence. The interpretation of such imaging was validated with additional geotechnical studies, which show that the proposed methods provide reliable results with good agreement between techniques.Agencia Estatal de Investigación | Ref. PID2019-105221RB-C44Ministerio de Ciencia e Innovación | Ref. RYC2019-026604-IXunta de Galicia | Ref. ED431F 2021/0

A review of GPR application on transport infrastructures: Troubleshooting and best practices

The non-destructive testing and diagnosis of transport infrastructures is essential because of the need to protect these facilities for mobility, and for economic and social development. The effective and timely assessment of structural health conditions becomes crucial in order to assure the safety of the transportation system and time saver protocols, as well as to reduce excessive repair and maintenance costs. Ground penetrating radar (GPR) is one of the most recommended non-destructive methods for routine subsurface inspections. This paper focuses on the on-site use of GPR applied to transport infrastructures, namely pavements, railways, retaining walls, bridges and tunnels. The methodologies, advantages and disadvantages, along with up-to-date research results on GPR in infrastructure inspection are presented herein. Hence, through the review of the published literature, the potential of using GPR is demonstrated, while the main limitations of the method are discussed and some practical recommendations are made.European CommissionMinisterio de Ciencia e Innovación (España) | Ref. RYC2019–026604–I /AEI / 10.13039/50110001103