1,721,036 research outputs found
Direct Current Electrical Methods for Hydrogeological Purposes
No full textThe climate change has dramatically decreased the useful freshwater resources so raising the probability of severe droughts. Near-surface geophysics uses the investigational methods of geophysics leading to their massive use in all scientific sectors (geology, hydrogeology, engineering, archaeology, environmental problems). Moreover, the increasing challenge of quantifying extractable, economically viable, potable water supplies has led to the definition of a new subdiscipline of hydrology known as hydrogeophysics. Direct current (DC) electrical methods are probably the most widely used near surface geophysical techniques for environmental investigations. DC methods are increasingly used in different approaches to cover a larger field of applications. In hydrogeological applications, the electrical resistivity distribution can provide important information that allows to characterize the heterogeneity of the aquifers and soil, to reconstruct the geometry of the aquifers and/or waterproof, to study the relationships between freshwater and seawater, or from groundwater different salinity
Real-Time Hydrocarbon Mapping by Time-Lapse Borehole Electric Tomography
No full textReal-time mapping reservoir fluids distribution during hydrocarbon production, or during injection operation, represents a crucial issue and a big challenge at the same time. In this article, we present a new approach based on single-well and cross-well electric measurements. We use electrodes permanently installed on the well casing and electrically insulated from it. We tested our approach through a two-steps workflow. In the first step, we performed forward and inverse modelling on realistic production scenarios. In the second step, we acquired, processed and inverted real data acquired in laboratory, where we tested small-scale scenarios of hydrocarbon production. We acquired and inverted DC (Direct Current) data. Our objective was to reconstruct the variations of the 3D distribution of electric resistivity during the various phases of oil production. The retrieved models reproduced properly the experimental movements of fluids observed in our lab measurements. Finally, modelling and inversion of both synthetic and real data confirm that cross-hole DC method allows mapping reservoir fluid variations even in case of predominant metallic components of the well completion
Multiscale geophysical investigation on the Budoia-Aviano thrust system (NE Italy): first results
No full textThe work group is involved in the framework of the PRIN2020 research project (NASA4SHA), which aims to identify the complexity of faults in active thrust systems in Northern Apennines and Southern Alps in Italy. The paper describes the application of a multi-scale geophysical investigations applied on the Budoia-Aviano thrust system, that is part of the Polcenigo–Montereale fault system. The investigated area, which is part of the external Plio-Quaternary front of the Eastern Southalpine Chain, is characterized by the presence of distinct WSW-ENE trending and S-verging reverse fault planes arranged in thrust systems and affecting the Quaternary succession (Poli et al., 2014). The proposed methodology included deep and shallow geoelectrical and GPR techniques to upscale the buried geological structures and to identify the site for the excavation of paleoseismological trenches. The adopted multiscale geophysical approach was applied in the studied area perpendicularly to the morphotectonic evidence of the Budoia-Aviano fault. The first step of the multiscale approach defined a Deep Electrical Resistivity Tomography (DERT). The DERT was long around 6000m, and it was able to obtain an investigation depth of about 1000m. The used DERT apparatus is a multichannel system designed and implemented by the CNR-IMAA (Rizzo et al.2004; Rizzo and Giampaolo, 2019). The acquired DERT data set was processed and elaborated through a procedure built ad hoc for this type of geoelectric surveys. While the first step highlighted the deep geological structure, several shallow high resolution geophysical surveys were planned close the morphotectonic evidence along the Budoia-Aviano thrust fault. Several shallow Electrical Resistivity Tomographies (ERT) with different electrode spacing were carried out. Three ERTs were carried out with an electrode spacing of about 5m obtaining an investigation depth of about 60m. Consequently, in order to increase the shallow resolution, a high resolution ERT with an electrode spacing of about 1m was acquired. The results of the shallow ERTs highlighted the buried geological structures in terms of subsurface faults and geological formations. Moreover, taking in account the previous results, several GPR profiles were carried out on the investigated area and the obtained results permitted to identify the site for the excavation of two paleoseismological trenches (Poli et al., at this session 1.1). The GPR results well depicted the highresolution image of the buried geological deformation, that were highlighted during the excavation phase (Poli et al., 2024). Finally, the multiscale geophysical approach allowed to improve the interpretation of previous geological and morphotectonic studies of the investigated area
Combined GPR and Self-Potential Techniques for Monitoring Steel Rebar Corrosion in Reinforced Concrete Structures: A Laboratory Study
No full textSteel rebar corrosion is one of the main causes of the deterioration of engineering reinforced structures. Steel rebar in concrete is normally in a non-corroding, passive condition, but these conditions are not always achieved in practice, due to which corrosion of rebars takes place. This degradation has physical consequences, such as decreased ultimate strength and serviceability of engineering concrete structures. This work describes a laboratory test where GPR and SP geophysical techniques were used to detect and monitor the corrosion phenomena. The laboratory tests have been performed with several reinforced concrete samples. The concrete samples were partially submerged in water with a 5% sodium chloride (NaCl) solution. Therefore, an accelerated corrosion phenomenon has been produced by a direct current (DC) power supply along the rebar. The geophysical measurements were performed with a 2.0 GHz centre frequency GPR antenna along several parallel lines on the samples, always being the radar line perpendicular to the rebar axis. The GPR A-scan amplitude signals were elaborated with the Hilbert Transform approach, observing the envelope variations due to the progress of the steel rebar corrosion in each concrete sample. Moreover, Self-Potential acquisitions were carried out on the surface of the concrete sample at the beginning and end of the experiments. Each technique provided specific information, but a data integration method used in the operating system will further improve the overall quality of diagnosis. The collected data were used for an integrated detection approach useful to observe the corrosion evolution along the reinforcement bar. These first laboratory results highlight how the GPR should give a quantitative contribution to the deterioration of reinforced concrete structure
Review of Ground Penetrating Radar Applications for Bridge Infrastructures
No full textInfrastructure bridges play a crucial role in fostering economic and social development.
However, the adverse effects of natural hazard and weather degradation, coupled with escalating
rates of traffic, pose a significant threat. The resultant strain on the structure can lead to undue
stress, elevating the risk of a critical asset failure. Hence, non-destructive testing (NDT) has become
indispensable in the surveillance of bridge infrastructure. Its primary objectives include ensuring
safety, optimizing structural integrity, minimizing repair costs, and extending the lifespan of bridges.
NDT techniques can be applied to both existing and newly constructed bridge structures. However,
it is crucial to recognize that each NDT method comes with its own set of advantages and limitations
tailored to specific tasks. No single method can provide an effective and unequivocal diagnosis on its
own. Among the various NDT methods, Ground Penetrating Radar (GPR) has emerged as one of the
most widely employed techniques for monitoring bridges. In fact, recent technical regulations now
mandate the use of GPR for bridge monitoring and characterization, underscoring its significance
in ensuring the structural health and longevity of these critical infrastructures. Ground Penetrating
Radar (GPR) stands out as one of the most highly recommended non-destructive methods, offering an
efficient and timely assessment of the structural conditions of infrastructure. Recognizing the pivotal
role of non-destructive testing (NDT) in this context, this paper aims to elucidate recent scientific
endeavors related to the application of GPR in bridge engineering structures. The exploration will
commence with a focus on studies conducted both at the model level within laboratory settings
and on real cases. Subsequently, the discussion will extend to encompass the characterization and
monitoring of the bridge’s main elements: slab, beam, and pillar. By delving into these scientific
experiences, this paper intends to provide valuable insights into the efficacy and applicability of GPR
in assessing and ensuring the structural integrity of bridges. This paper provides a concise survey of
the existing literature on the application of Ground Penetrating Radar (GPR) in the assessment of
bridges and viaducts constructed with masonry and reinforced concrete, taking into account papers
of journal articles and proceedings available on open databases. Various approaches employed in
both laboratory and field settings will be explored and juxtaposed. Additionally, this paper delves
into discussions on novel processing and visualization approaches, shedding light on advancements
in techniques for interpreting GPR data in the context of bridge and viaduct evaluation
Deep Electrical Resistivity Tomography for Geophysical Investigations: The State of the Art and Future Directions
No full textElectrical Resistivity Tomography (ERT) is a robust and well-consolidated method largely applied in near-surface geophysics. Nevertheless, the mapping of the spatial resistivity patterns of the subsurface at a depth greater than 1 km was performed in just a few cases by the ERT method, called deep ERT (DERT). Since, in many cases, the term DERT was adopted with ambiguity for geoelectrical explorations varying in depth within a range of 0–500 m, the main goal of this review is to clearly define the DERT method, identifying a threshold value in the investigation depth. The study focuses both on the purely methodological aspects (e.g., geoelectrical data processing in low noise-to-signal ratio conditions; tomographic algorithms for data inversion) and on the technological features (e.g., sensor layouts, multi-array systems), envisaging the future directions of the research activity, especially that based on machine learning, for improving the geoelectrical data processing and interpretation. The results of the more significant papers published on this topic in the last 20 years are analyzed and discussed
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