1,720,965 research outputs found
3D Electrical Resistivity Tomography to Improve the Knowledge of the Subsoil below Existing Buildings.
No full textThe impact of multiple transmitters on signal strength in Deep Electrical Resistivity Tomography data: an experiment in the Vajont valley (north-eastern Italy)
No full textElectrical Resistivity Tomography method has boosted its potentials since the development of new-concept resistivity-meters. Key improvements include a much better data quality and the reduced logistics required to operate long spreads in rough terrains. The Multi-Source (MS) resistivity-meter incorporates both these two features and, moreover, its peculiarity of transmitting and receiving with short isolated wires reduces inductive and capacitive coupling in cables and multiplexer. It is a modular system based on stand-alone units remotely controlled via radio signals. Modularity eases the use of the system but the real innovative and most important feature is its capability of injecting current simultaneously with different dipoles. The system was tested in the Vajont valley, in north-eastern Italy, with the purpose of imaging the deep sliding surface of the catastrophic landslide occurred in 1963. An array of potential loggers was laid down parallel to the MS line in order to gain full control on transmitted/received signal character and strength and finally validate the system reliability. The MS waveform was clearly recognisable up to a distance of more than 1 km in single transmitter mode, while using multiple transmitters the threshold distance is probably far beyond and it was not reached. A potential of 0.02 mV was identified as the detection threshold. A one-to-one correspondence was observed, also at maximum offset, between MS measurements and potential values recorded with the data loggers indicating the effectiveness of the tested system in removing self-potentials
Integrated geophysical methods to detect buried structures for archeological prospection
No full textLocation and determination of dimensions and shapes of buried historical evidences it is a task that generally in the last times is let to geophysics, because of the improvement of automatically measuring geophysical systems and of the inversion algorithms. In particular 2-D electrical method permits the acquisition of large measurements in short time, consequently the interpretation and inversion procedure have to be accurate
Three-dimensional Electrical Resistività Tomography to control the injection of expanding resins for the treatment and stabilization of foundation soils
No full textIn this paper we describe how time-lapse three dimensional Electrical Resistivity Tomography (3D ERT) can be advantageously integrated in the standard practice of shallow polyurethane resin injections, to improve the reliability of ground treatment and to reduce its costs. Settlement of buildings has several causes, which are generally triggered by movement of fluids in the subsurface. The goal of the injection of expanding resins is to occupy voids and displace water so that the continuity and stiffness of terrains around and below the settled foundation are re-established. In order to control the effectiveness of the consolidation beneath the building, non-invasive geophysical methods such as Seismics, ERT or GPR can be used. Among these, ultimate 3D ERT developments provide the best solution for this application because of the fast imaging capability, the extreme reliability and repeatability of the measurements and the high correlation of electrical resistivity to soil moisture, which is known to be the most common cause of settlement. Given the often limited accessibility of work sites, a successful practical approach was focused on innovative arrangements of surface electrodes (inside and outside of buildings) and acquisition geometries, combined with appropriate measurements and processing procedures, that enable the effective 3D imaging of the foundation soils, before, during and after the injection treatment. Details on the field procedures, validated by a sensitivity and resolution analysis, are introduced through the description of a case-history in which the pre-injection ERT measurements, combined with structural and geotechnical evidences, allow to investigate the status of foundations and lithological heterogeneities. Time-lapse ERT surveys control soil homogenization and fluid movements and provide a quasi real-time feedback for modifying and modulating the parameters of treatment, which would be very difficult with direct methods. The illustrated case-history has been purposely selected since it represents the most common practice occurring throughout Italy and allows to assess and to discuss the current limitations and the future developments
Valutazione dell’efficienza delle iniezioni di resine espandenti per il consolidamento dei terreni di fondazione mediante prove geotecniche e indagini di tomografia elettrica tridimensionale.
No full textTecniche di consolidamento di terreni mediante iniezioni di resina espandente sono state utilizzate con buon successo, quando le cause di cedimento differenziale verticale delle strutture di fondazione sono connesse ad alterazioni naturali e/o antropiche del terreno di fondazione e/o a una non corretta progettazione/esecuzione dell’opera. Tra le diverse tecniche di consolidamento dei terreni mediante iniezioni di resine espandenti, è stato ideato un procedimento che prevede, in abbinamento alle tradizionali prove geotecniche, l’applicazione di metodi geofisici, in particolare della tomografia di resistività elettrica 3D, per poter acquisire, anche nei volumi di terreno difficilmente accessibili, quelle informazioni necessarie al progetto del consolidamento e al suo monitoraggio in corso d’opera. E’ secondo questo approccio di intervento, e con modalità del tutto simili alle condizioni di cantiere, che vengono presentati i risultati ottenuti in un campo prove in vera grandezza, interessato da iniezioni di resina espandente poliuretanica bicomponente
Valutazione dell’efficienza di resine espandenti per il consolidamento dei terreni di fondazione mediante prove geotecniche e indagini di tomografia elettrica tridimensionale. ISBN 9788897517047,
No full textEvaluating physical and mechanical changes induced in the subsoil by expanding resins injections for consolidation purposes by means 3D Electrical Resistivity Tomography and geotechnical tests
No full textInstability phenomena in the urban environment and their consequences on infrastructures are a very topical issue in engineering practice. There are a lot of technical solutions on the market and, among these, consolidation techniques have assumed a role of primary importance. Due to the effectiveness of the intervention, the reduced invasiveness and especially the implementation and integration of monitoring techniques like the geophysical method of time-lapse 3D electrical resistivity tomography and geotechnical tests like dynamic penetration tests (Morelli et al., 2006, Santarato et al., 2011), the injections of expanding resins are one of the most established among consolidation methods. This work tries to deepen knowledge about physical and mechanical changes in the subsoil after consolidation with expanding resins. The research is divided into two main branches: experimental tests on a controlled test site and continuous data analysis on a wide archive of data, kindly provided by a specialized company operating in the market. Geological, geotechnical and geophysical test have been carried out in the test site in order to obtain a detailed picture of the physical and mechanical properties of the undisturbed state. In particular CPT tests, geotechnical laboratory testing, 2D and 3D electrical resistivity tomography, MASW were carried out. The experimental tests were carried out in three main phases. In the first one the effects induced by injections on the mechanical properties of the involved materials have been studied. In the second one the effects induced on the electrical properties and in the last one the possible relationship between the physical and mechanical properties measured after the injections have been studied. From the mechanical point of view, obtained results shows remarkable increases in load-bearing capacity of subsoils, in the ability to fill voids and the consequent migration of the interstitial water. The results also show the effectiveness of the 3D electrical resistivity tomography in the three-dimensional and temporal evolution monitoring of the phenomena taking place in the subsoil during the injections, as well as a good relationship between electrical and mechanical properties after the consolidation. Before the analysis of case histories a rigorous and careful data sorting work aims to generate datasets as homogeneous as possible. The data is classified by buildings properties (number of floors, presence of basements, topographical variations, etc..), soil properties (detected in situ by the geologist), presence of groundwater, etc.. Both 3D electrical resistivity tomography and dynamic penetration tests are performed before and after the injections. Electrical resistivity and dynamic cone resistance percentage change is then calculated. The obtained results show that there is a high percentage of cases in which the curve of the percentage change of the electrical resistivity is similar to the curve of the dynamic cone resistance percentage change. This work aims to improve our understanding on the effects induced in the subsoil by the expanding resins injections. The research has led to better understand, in quantitative terms, physical and mechanical changes that occur as a result of expanding resins injections and to increase knowledge about the response of the 3D ERT applied to the monitoring of the consolidation process. Thanks to the large amount of case histories analyzed, results clearly demonstrate a relationship between the ERT geophysical method and the dynamic cone penetration test
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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