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1st Conference on Geophysics for Infrastructure Planning Monitoring and BIM
- Conference date: September 8-12, 2019
- Location: The Hague, Netherlands
- Published: 08 September 2019
38 results
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Keynote - Geophysics in Infrastructure - An Industry Perspective
Authors M. Brough and A. VerweerdSummaryThis keynote speech will show an industry perspective of the application of geophysics in infrastructure construction and asset management projects. Geophysics is uniquely placed in this industry due to its flexibility in different targets and scales. Several examples will be used to highlight the current state of affairs, including an outlook to further integrate geophysics into the civil engineering discipline.
With the increasing need for upgrading existing infrastructure and construction of new large scale infrastructure, the industry is looking to geophysics to manage and identify risks through non-destructive techniques, reducing the costs and impact of these large construction works through proper planning and integration of various data streams into a combined deliverable model.
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Time-Synchronized Geophysical Investigations in Denied GPS-Time Spaces
Authors A. Malehmir, L. Dynesius and T. SjölundSummaryWithout doubt much more can be done to utilize underground workings for site investigations. A few years ago, we realized this offered a unique opportunity with important applications and benefits of providing synchronized surveys in underground spaces using receivers typically used at the surface. However, technical limitations were hindrances. We have now been able to pioneer a prototype system that can provide accurate GPS-time (micro-second accuracy) to an array of various sensors placed in different tunnels and in different depth levels. The solution will be useful for any deep mines, tunneling industry and anywhere that a synchronized survey is needed but accurate timing is not available directly via satellites. The system does not need extensive cabling or accessibility to mine communication and operational facilities. It is a mobile system, transportable to underground workings using a couple of small boxes, and easy to set-up. Add-on options and modularity are also possible to provide greater flexibilities. Such a solution can bring for example 3D surveys to underground. No need to revise existing sensors implies also millions of saving and possibility to dual use sensors used for surface measurements.
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Void Detection and Consolidation Filling Verification by ERT, GPR and Seismic Refraction Methods
Authors G. Vargemezis, P. Tsourlos, I. Fikos, N. Diamanti, D. Angelis and E. AmanatidouSummaryThe present work deals with the application of applied geophysical methods to voids by two different approaches. The one refers to the detection of the voids and the second to monitor the consolidation of the ground. Three different methods are tested in both these two phases, resistivity, ground penetrating radar and seismic refraction. Initial geophysical survey was based mainly on resistivity and GPR methods, which allowed the detection of possible voids who were drilled after the suggestion of the geophysical results. All voids verified by the drilling were filled by a mix of soil and cement. Just before the start of the filling procedure, ERT, GPR and seismic data have been produced and measurements repeated again after the end of it, in order to verify the complete filling of the voids.
The response of the geophysical data was very clear since all geophysical features indicating the existence of the voids, vanished and showed the success of the consolidation process
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Non-Invasive Characterisation of Cement-Based Materials by Spectral Induced Polarization
Authors J. Holzhauer, P. Dick and A. RevilSummaryIn the context of radioactive waste management, concrete is used at various levels of the radioactive waste repositories. For safety purposes, it is of fundamental importance to characterise the mechanical integrity and chemical alteration of cementitious materials. While various sensors have been developed to provide punctual information on concrete infrastructures, indirect non-intrusive methods are still scarce. Spectral induced polarization (SIP) has been considered to fill this gap, based on its sensitivity to both fluid content and specific surface area, the latter being in connection with chemical alterations and pore-fluid interface evolution.
The frequency-dependent polarization of different CEMI and CEMV cement types was investigated for various formulations determined by water/cement ratio and possible aggregate addition. SIP measurements provide complex conductivity values, both at early-age and mature stages.
First results show an increase of both real and complex conductivity components with increasing water/cement ratios, and a decrease but proportional electrical response of mortars (obtained by addition of a resistive sand aggregate) with regard to their corresponding hardened cement pastes. The proportionality coefficient seems independent from the water/cement ratio. The eventual aim is to achieve homogenous quantifiable damaging of the cement-based samples, as to test the observability of its impact on polarization measurements.
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Comparison of Reflection Seismic Data with Seismic Tomography in an Underground Environment
By T. DickmannSummarySite investigations ahead of the tunnel face by means of geophysical methods are increasingly becoming an essential part of the risk management process for the last 20 years. Seismic methods have established as the frontrunner offering a wide range of data acquisition techniques, data processing types and result visualization tools. Continuous seismic measurements look for optimising both data acquisition process as part of the operative work flow while tunnelling and the rapidness in providing reliable geological predictions for the next tens of meters ahead of the face. To cope with the scenario that no explosives are available, the use of an alternative impact source together with continuous measurements is foreseen. By comparing TSP reflection seismic results of a sporadic measurement with results of high resolution seismic tomography in a test gallery, important insights about the penetration depth and resolution of the TSP results was possible. In the shown example, reliable results were obtained until about 50 meters away from the seismic layout.
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Example of a Survey in Transition Area for Construction Purposes
Authors A. Turchkov, A. Oshkin, V. Ignatev, A. Konkov, E. Samsonov and I. DmitrievSummaryThis paper is aimed to highlight both equipment and measurement techniques that may be effectively used for studying such complex sites (in comparision with standard near-surface seismic) as transition areas. The proposed solution allowed to obtain final sections that are suitable for further interpretation and linking the marine and land data for construction purposes.
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Keynote - Use of Geophysics to Provide Input Properties to Geotechnical Calculations
By M. LongSummaryCivil and geotechnical engineers have used geophysical techniques for many decades. However more recently geophysics is being used to provide input parameters for civil / geotechnical engineering design and numerical modelling. The examples given include use of GPR to give very detailed profiles at peat sites and Vs to give very good first order estimates of soil strength and stiffness properties.
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Evaluation of Dispersion Diagrams Distances Based on Usual Histogram Analysis for the Surface Wave Difference Inversion
Authors A. Wang, D. Leparoux, O. Abraham and M. Le FeuvreSummaryIn some recent geophysical monitoring studies, researchers have proposed a method of difference inversion, which means taking the difference between data into inversion process. It overcomes the crucial problem of the initial model for local optimization and reduce the environmental or system error in the results. Until now, there has not been an application of this method in the global inversion of Seismic Surface Waves. However using directly the difference between the dispersion curves as the data to be inverted can be not robust. Here, we propose to calculate differences between dispersion diagrams, which contains a part of the measurement uncertainty. Based on histograms distances definitions, several diagram distance calculations are used and tested numerically and experimentally in order to study the impact of the distance definition on the misfit assessment in case of a small variation about 10% in a deep part of a 2-layer medium. Results show the feasibility of this method. even if the accuracy of the the inversion result of the preliminary part remains a key issue on the assessment of medium’s variation.
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Exploring and Modelling the Qanat Gallery Path Using Electrical Resistivity Tomography Data
Authors A. Najafabadipour and G. KamaliSummaryApplying different optimal methods like Semi-Newton method results in modelling as well as interpreting the acquired data. Tikhonov regulation parameter was used for minimizing the objective function. The present study was conducted to explore and model the path and depth of the qanat gallery, bedrock and water table with sufficient resistivity compared to its surrounding area using electrical tomography data. According to the deep targets, the acquisition of data was made by using Schulmberger array with 3 profiles and 12 soundings. For inverting the data and constructing a 3D model of them, IPI2WIN software and VOXLER software were used respectively. The results revealed that as the qanat was water bearing the direction of its gallery path was from the southwest to the northeast at an approximate depth of 10 meters and with the electrical resistivity of about 100-ohm meter. According to the geological information, the bedrock was dolomitic having the electrical resistivity of almost 550-ohm meter compared to the surrounding area. The water table was about 16 meters being lower than the qanat gallery. The size of grains belonging to quaternary sediments were estimated as well.
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Performance Assessment of Novel Offshore Cable Detectors Based on Synthetic Data
By T. StolzSummarySubmarine power cables are an important infrastructure in modern times to connect, for example, separate energy power grids or offshore windfarm with the mainland. The position of these buried cables is often known only roughly after installation due to several reasons. Therefore, a cable tracking system is used which can detect the cable’s position. In this thesis, a novel system is presented which is based on inverting the magnetic field measured which is created by an active signal in the cable. An array of five three-axis fluxgate magnetometers measure the magnetic flux. Two different algorithms for detection are introduced. The first method relies on a simple model of the cable and a non-linear system of equation to estimate the location by inverting the total magnetic field measured by each sensor. The second approach uses the three-axis measurements to get the direction where the cable is from each sensor. The distance to the sensor array can be than estimated by using at least three different direction measurements. Both approaches are evaluated on synthetic data obtained by modelling the magnetic response of a cable in a marine environment.
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Advanced Signal Processing Method for Detection Surface Inhomogeneities from a Reflected Signal
Authors N. Antonyuk, M. Klein Wolterink, S. Kataeva and S. KataevSummaryAbstract – The successful realisation of high performance radars requires sophisticated methods and algorithms capable of obtaining information about investigated objects.
This paper illustrates a new method to determine surface inhomogeneities and/or their shapes for centimetre, millimetre, and sub – millimetre waves based on a method for revealing structures (MRS) which is a powerful tool to analyse data by means of finding of spatial points in which signals have the greatest contrast concerning other background points.
Typical examples of such inhomogeneous (textured) areas are near-surface buried objects, snow-covered ground, water waves and many others.
The new suggested method was named as “BinREL” and can be considered a generic approach for advanced signal processing since it is not tied to the physical nature or a concrete form of probing signal.
The merits of the method has been evaluated by processing datasets obtained from Staal Technologies prototypes based on 60 GHz frequency modulated continuous wave (FMCW) radar application specific integrated circuit (ASIC): RIC60A. The inkjet - printed images were taken as an investigation example.
Index terms – signal processing algorithms, microwave imaging, FMCW, ASIC, radar measurements, radar applications.
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Beyond Locating - Resolving Unique Underground Utilities with a Handheld-Sized Stepped-Frequency Continuous-Wave (SFCW) GPR
Authors M. Kaufmann and I. TsalicoglouSummaryPulsed GPR has been the main GPR technology for more than 30 years. However, stepped-frequency continuous-wave (SFCW) GPR technology presents two documented advantages compared to pulsed GPR: a bandwidth wider than the typical definition of “UWB”, and an approx. up to 20 dB higher signal-to-noise ratio. This results in larger penetration depths and improved resolution without salt-and-pepper noise.
In late 2017, SFCW technology became commercially available for concrete, where a system with frequency range 0.2–4.0 GHz demonstrably delivers both better resolution and depth penetration without post-processing filters. Since 2018, the SFCW GPR instrument is increasingly used for locating shallowly-buried utilities, an application so far addressed with pulsed-GPR devices.
We collected SFCW GPR data in soil to investigate the reason behind this trend, revealing that the technology’s benefits extend beyond concrete.
The SFCW GPR system can not only detect closely-spaced utilities but also resolve them uniquely within a bundle as countable hyperbolas, within typical depths, even though it was not developed with this application in mind.
Thus, with SFCW GPR subsurface investigators receive information beyond a “dig / no-dig” decision and can deliver insights that improve BIM and increase clarity for all stakeholders of infrastructure planning, monitoring and maintenance operations.
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Ground Penetrating Radar for Site Investigations and Utility Locating – Case Studies from Leipzig and Dresden
Authors F. Koellner and A. SchuckSummaryEspecially in urban areas, where the survey areas are often covered by concrete or asphalt, ground penetrating radar (GPR) is an ideal, sometimes the only, geophysical method for site investigations and for locating buried utilities. In the two case studies presented, construction works for traffic infrastructure are planned at busy traffic intersections in the inner-cities of Leipzig and Dresden by the respective municipal transportation companies and it was required to explore the shallow soil stratigraphy, to locate old foundation structures as well as to verify existing documentation of pipe and cable networks. These objectives could be met by GPR surveys in a very efficient way. The structure of a completely covered historic bridge was imaged, old foundations of a theater destroyed in WW II and a former pedestrian bridge were identified, the documentation of pipes and cables was refined and an undocumented cable was found. By means of a D-GPS surveying, which is synchronized to the GPR system, the results of the GPR investigations are immediately available with a highly precise spatial reference and can easily be incorporated into a building information model (BIM).
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Detecting the Position of Impermeable Membranes Buried in the Subsurface
Authors P. Kruiver, M. Karaoulis, B. Beuving, M. De Kleine and V. HopmanSummaryPVC membranes are used as groundwater barriers in infrastructure works in situations with high groundwater levels. When reconstruction works are necessary, the position of the membrane in the subsurface needs to be known. Deltares developed a method based on Electrical Resistivity Tomography (ERT) using the high electrical resistivity of the PVC membrane. Modelling showed that the PVC membrane has a profound effect on the electrical field lines. Classical ERT employed from the surface does not have sufficient spatial resolution to locate the membrane. Electrodes need to be closely spaced and within ca. 1.5 m from the membrane. To this end, a prototype tool was developed that can be pushed in the ground and measure while approaching the membrane. This prototype was tested in the laboratory. Measurements at different distances from the membrane showed that the tool can detect the distortion of field lines. Inversion was used to pinpoint the position of the membrane within 10 cm. The next step is to develop a tool that can be used in the field.
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The Impact of Spatial Sampling and Polarisation in GPR Survey for Utility Mapping
Authors F. Lombardi and M. LualdiSummaryThe presented analysis has quantitatively evaluated the performance of different GPR survey strategy for the detection and mapping of buried utilities. Results have shown that just the acquisition of a set of sparse 2D profiles is not a reliable strategy, as detection performance drops in presence of complex subsurface geometries, for which the profile spacing might be too wide to properly reconstruct the situation. A step ahead is represented by a 3D survey, in which the increased acquisition effort is balanced by the improvements achieved in terms of reconstruction quality. Targets can be tracked out of the 2D domain, feature that is highly relevant in areas with multiple intersecting objects. However, depolarisation phenomena, critical factor for linear and elongated targets, can be efficiently neutralised by the acquisition and combination of mutually orthogonal GPR volume.
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Keynote - Geophysical Practice of UXO Detection
More LessSummaryWorld War II UXO detection is a present day subject due to the large amounts of ammunition that is still buried in the subsurface. These may pose a threat during digging activities at larger depths. Removal is a four phase process, including historical research and geophysical detection onshore and offshore. A range of geophysical techniques, including their (dis)advantages, is described. The methods selected are based on historical information, soil type, potential disturbing objects and efficiency.
Geophysical UXO detection, geotechnics and infrastructure planning are interrelated. UXO detection activities can be reduced by geotechnical information. Infrastructure planning delays can be reduced by on time initiation of UXO detection and removal and careful planning. Planning takes into account in detail the infrastructural activities that will be carried out, its phasing and possibilities for intermediate reporting of geophysical research outcomes.
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Keynote - Identifying the Research Needs for Developing a Digital Buried Infrastructure Management Practice
More LessSummaryWestern cities manage their buried utilities through a large number of distinctive owners. This current fragmentation of the utility sector, and the poor registration of utility locations in the past has created an underground puzzle containing data pieces with different formats, accuracies, and completeness. We argue that virtual technologies address this problem but require that basic modelling conditions be fulfilled first. To structure this discussion, we use literature on Building Information Modelling (BIM) technologies in construction. BIM supports construction management tasks through the use of object-based parametric design models. This enables 3D and 4D design reviews as well as multi-stakeholder scheduling and planning. Furthermore, BIM integration with geospatial data enables the on-site use of construction data for facility management. Based on the experiences from our lab, we explain that the utility sector should train engineers in 3D utility mapping, and develop 3D/4D underground data models for design, scheduling, and maintenance. Such 3D models consequently integrate with other geospatial data to support risk analysis, construction site decision making, and on-site Virtual Reality applications. Our lab currently works on these needs together with industry. It seeks collaboration with other partners that also contribute to BIM for buried infrastructure.
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BIM - the Key for Implementation of Geophysics in Infrastructure Planning
Authors M. Svensson and O. FribergSummaryTo make more use of geophysics in general and more continuously during a whole infrastructure project geophysical data and models must be more compatible with other geo related data and other design disciplines and CAD software. The way to reach this is standardization of data formats, data exchange formats, objectification and implementation of a classification system for these objects. This would also enable full BIM compatibility and make it possible to keep track on data and models in an LCC perspective. A few suggestions on how to achieve this is presented.
In this paper a case study where the GeoBIM concept is used in a large infrastructure project for efficient communication and handling of geophysical data and models is presented.
CoClass is suggested as the classification system being used for true objectification of all data and models - points, lines, surfaces, volumes - adding meta data and classifying the objects so they can be used in a true BIM manner, also in a LCC perspective. When CoClass is implemented in all systems in the industry the workflow will be independent of what tool or software one is using, no matter who is the stakeholder.
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The Use of Geophysics in Large Swedish Infrastructure Projects
More LessSummaryIn Sweden the use of geophysical investigation methods as complement to geotechnical investigations in larger infrastructure projects have increased during the last 10 years. One of the main reason’s is probably the increasing use of planning tools in 3D, which increases the need for better data coverage. However, geophysics is still not counted as a standard method in the toolbox for ground investigations and the amount of geophysical investigations carried out in Swedish infrastructure projects differ a lot, due to several reasons. This abstract will discuss how and why geophysical investigations become or not become a part of larger infrastructural projects in Sweden and also discuss what should be done in the future to promote the use of geophysical investigation techniques. The main points of actions concerns purpose and expectations, awareness, uncertainty, standards and tools.
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Keynote - Multi Source for Digital Underground Constructions
By P. DohmenSummaryUnderground constructions and tunnelling are characterised by a dynamic advancement of tunnel boring technologies, increasing TBM (tunnel boring machines) diameters and a broadening range of applicability driven by the progress of digitalisation. This development in association with the inherent heterogeneity of the underground and the uncertainty of ground parameters poses new challenges to reliable prognoses models. Digital models are a vital element for the limitation of risks, particularly if difficult conditions concerning geology or sensitive urban environments must be considered. To cooperate in teams worldwide and coordinate projects we start to combine different sources for a more holistic view to describe asset and environment.
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Application Benefits of Using Downhole Magnetic Resonance and Wireline Geophysical Logging for Geotechnical Ground Investigation Projects
Authors D. Gartner and B. RiglerSummaryGeotechnical ground investigations in nearshore conditions requires a level of precision and accuracy in the determination of subsurface parameters that is more rigorous than most applications of geophysical logs. As such, these projects demand a wealth of measurements of the subsurface by geophysical means. In the following examples for detailed interpretation of wireline logging, geotechnical data and packer test results are presented with particular interest to benefits of the DMR method and the detailed log analysis the geotechnical industry. Expansive suite of wireline logs included DMR, optical and acoustic televiewer, orientated four arm caliper, gamma-gamma density, resistivity and acoustic methods, leading to an accurate understanding of the rock strength and geo-mechanical properties. DMR measurements provided continuous total porosity and pore-size distribution data. Permeability estimations were also performed using DMR Porosity and T2 distribution data, packer test derived, in-situ permeability results were used to refine estimated permeabilities. Ability to significantly lower construction related risk by facilitating identification and detailed description of weak zones justifies the use of wireline geophysical logging and particularly the DMR method more broadly in the construction and engineering sectors.
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Satellite Based Radar Technology for Asset Management During Large-Scale Transport Infrastructure Projects
Authors R. Frauenfelder, M. Vöge, A. Pfaffhuber, C. Hauser and A. LysdahlSummaryGround settlement and associated deformation of existing infrastructure is a major risk in urban development projects. Project owners in such areas have a responsibility to document and manage settlement records before, during and after construction works. Traditionally, land surveying has been the state-of-practice tool to provide settlement monitoring data. Modern radar interferometry provides the opportunity to drastically increase the number of monitored locations, while at the same time reducing expenses for traditional geodetic survey work. We illustrate this technology for a large urban railway development project near Oslo, the capital of Norway.
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Fibre-Optic Strain Sensing: Game Changer for (Urban) Seismic Surveying?
Authors C. Krawczyk, P. Jousset and T. ReinschSummaryNatural hazard prediction and efficient crustal exploration benefit from densely designed surveys. Seismological techniques provide ground-motion data, while active seismics aims at structural imaging and increasingly on physical properties determination. Dense networks exist on some volcanoes and in exploration plays, but not in urban areas where data acquisition is more challenging.
We demonstrate that dynamic strain determination is now possible with conventional fibre-optic cables deployed for telecommunication. This is a new tool for earthquake location or for crustal exploration using unexpected sources. Thereby, this method provides key records for understanding subsurface dynamics, especially in urban areas.
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Keynote - Fibre-Optic Distributed Sensing for Infrastructure Objects and Near-Surface Monitoring
More LessSummaryFibre-optic distributed acoustic sensing (DAS) has developed into a technology that has found application in many different scientific, engineering and industrial fields, where dynamic strain measurements are used to analyze the elasto-dynamic behaviour of an object or medium. Using a highly coherent laser source, a standard telecom-grade optical fibre, usually utilized for network data transmission, can be turned into an array with tens of thousands of virtual sensors. Many of the advanced analysis algorithms, such as feature extraction, or various forms of near-surface or subsurface imaging, machine learning or AI, require spatially and temporally well-sampled wave field recordings with fine sampling intervals and large spatial coverage. Such a type of data acquisition is only possible, if the individual sensors can be deployed cheaply on a large scale; and can be operated continuously without the need for power and data storage at each sensor location. Distributed fibre-optic sensing is a sensing technology that enables such pervasive sensor networks and provides continuous data streams of high resolution and coverage to feed real-time or offline analysis algorithms. We demonstrate such possibilities with a transport system infrastructure recording of train movement while obtaining earthquakes recordings and measuring near-surface conditions.
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Using GPR at Deutsche Bahn and First Steps in Merging the Results with BIM Models
Authors J. Wolf and D. HofmannSummaryThe number of applications for the GPR method at Deutsche Bahn has grown over the last decades. Besides monitoring the substructure under railway tracks, GPR is used to detect the build-up of civil engineering structures to complete building plans, it is used to detect pipes and drains not noted in the records, as well as to detect the remnants of suspected former buildings in future construction sides.
The advance of GPR to survey a large-scale area non-destructively allows its use to inspect train platforms quickly and completely to help experts with the planning of maintenance, reconstruction and upgrades. Possible obstacles for reconstruction works such as unknown pipes, steel beams, old foundations, voids or even parts of a former tunnel were detected in the platforms of a main train station using GPR. First steps are taken to compile the results of the survey into a BIM model of the station. The aim is to help the planner get a workable view over the abundance of information gained by the different crafts. Thus supporting the time planning and budgeting of the reconstruction project.
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Spectral Analysis of Vibrations of ITU TRIGA MARK-II Nuclear Research Reactor Building, Istanbul, Turkey
Authors M. Cakman, U. Harmankaya, B. Barutcu, P. Inci Kocak, A. Ilki and A. KaslilarSummaryWe examine the spectral properties of the vibrations of ITU TRIGA MARK-II nuclear research reactor building located at the Istanbul Technical University Ayazaga campus, Istanbul, Turkey. Istanbul is located in a seismically active region, where a large earthquake is expected. The building is for the first time equipped with sensors by a government-university-industry collaboration. We installed twelve tri-axial MEMS accelerometers to the three-story building for monitoring purposes. We estimated the basic dynamic characteristics of the building, namely, modal frequencies, translational and rotational modes, and the soil structure interaction of the building by spectral methods, using a recorded earthquake and continuous vibration data. Our results are in general in agreement with the results of numerical calculations based on simple clamped model and three dimensional finite element structural analysis model. The aim of the study, in long term, is to monitor the structural health of the reactor building and involve a rapid damage assessment system as well as the earthquake early warning system to the reactor control facility.
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Cross-Correlation Analysis of Surface Waves for Group and Phase Velocity Mapping along a 2D Seismic Profile
Authors K. Leontarakis, C. Orfanos and G. ApostolopoulosSummarySurface-Wave Analysis is widely adopted for estimating S-wave velocity of near-surface, a crucial parameter appearing in geotechnical standards. In this paper two different approaches are implemented and compared for the creation of pseudo-2D dispersion images of phase and group velocity through the analysis of multichannel cross-correlation (CC) of surface waves at a Test site. The surface wave travel time tomography approach can produce precise phase and group velocity maps, since the eikonal equation is used for the inversion of the automatic estimated phase and group delays. However, when sharp lateral variations are exist near surface, an average 1D reference phase velocity model is not adequate to properly estimate them, due to cycle skipping problems at high frequencies. The implementation of the common mid-point cross correlation approach results to smoother mapping of the velocity distribution, though sensitive to near surface variations, both on group and phase velocity. In that way, a more reliable 2D reference phase velocity model can be assigned to the first approach. Moreover, the 3D velocity dispersion imaging assists in defining specific problematic areas as well as frequency bands of possible significant higher mode interference, in order to be excluded from the 2D Vs inversion procedure.
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Assessment of Reservoir Embankment Dam Condition Using Field and Laboratory Geophysical Techniques
Authors S. Donohue, A. Trafford, D. Gunn, B. Dashwood, R. Swift, D. McKillen and D. LeemonSummaryThis extended abstract briefly discusses some initial results from an ongoing collaborative research project between University College Dublin, Queen’s University Belfast and the British Geological Survey as well as industry partners Aecom, Canal & River Trust and the Environment Agency. The project, funded by the Natural Environment Research Council (NERC), is investigating the application of geophysical techniques for improving flood defence management at a number of sites in Northern Ireland and England. The expanded abstract focuses on initial results from one case study, where a number of geophysical methods have been used to forensically examine the cause of a reservoir embankment leak. Although geophysical surveys can provide useful information in isolation, when used in conjunction, or calibrated, with relevant geotechnical properties, they can be valuable tools for assessing geotechnical infrastructure condition and for identifying possible seepage pathways through reservoir embankment dams.
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Keynote - Structural Health Monitoring Meets Ambient Noise Seismology
Authors C. Hadziioannou, J. Salvermoser, R. Steinmann, L. Marten and E. NiederleithingerSummaryHow can we harness the ambient vibrations that move the ground - and buildings - everywhere and all the time? I will discuss methods that use ambient seismic noise to characterize shallow subsurface structure. How can we track changes sensed by the seismic wavefield, related to water saturation and frozen ground?
Can we use these methods on buildings, bridges, larger civil structures, to continuously monitor the structural health status, and potentially detect the effects of damage? I will present results of studies that delve into these questions.
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Long-Term Monitoring of Slopes that Affect Transport Infrastructure
Authors J. Holmes, S. Donohue, J. Chambers, P. Wilkinson, P. Meldrum, D. Gunn, R. Swift, B. Dashwood, M. Kirkham, S. Uhlemann, D. Huntley and P. BobrowskySummarySlope failures on the transport network are a growing issue as populations continue to expand, putting increasing demand on aging infrastructure, much of which is already operating at full capacity. Monitoring of such slopes is therefore necessary to maintain the serviceability of transport infrastructure, mitigating against the large social, economic and environmental costs that would emerge in the result of slope failure. Near-surface geophysics is used increasingly for the assessment of the condition of transport infrastructure. Here, the use of Proactive Infrastructure Monitoring and Evaluation (PRIME) Electrical Resistivity Tomography, which allows for continuous, near-real time monitoring of subsurface moisture conditions, is assessed in terms of its applicability to monitoring both man-made embankments and natural slopes that affect transport infrastructure. Long-term monitoring data is presented for two field sites (Old Dalby, a railway embankment in Leicestershire, UK, and the Ripley landslide, a natural slope in British Columbia, Canada). Results demonstrate the sensitivity of electrical resistivity to changes in moisture content, which vary seasonally, and highlight the advantage of resistivity imaging for monitoring slope moisture dynamics over predictions based on rainfall data alone, providing information on the spatial aspects of slope hydrogeological regimes.
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Geoelectric Modelling of Near-Surface Resistivity Distribution for the Design of Windfarm Grounding Grids
More LessSummaryThe design of grounding system of windfarms and large solar plants, which can be in the order of a few kilometres size, requires deeper geoelectric models than the usual models developed for the design of a typical electrical substation. The average apparent resistivity curves of windfarms located at the Northeast of Brazil, in the states of Bahia and Rio Grande do Norte, reveal that, in general, ground resistivity is high at these sites, resulting in high grounding resistances for the windfarm towers.
In this study we propose the use of 1D geoelectric models built from the combination of two types of geophysical soundings - the traditional Wenner.array method, which provides resistivity distribution of the shallow ground, combined with the AMT – Audio Magnetotelluric Method, which can investigate the resistivity distribution of the upper few kilometers.
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Where Geophysics Meets Asphalt - Monitoring Roads Using Fibre Optics
Authors M. Devrez, J.A. Karabacak, O. Dowd, H. Veerman and J. SingerSummaryFibre optic sensing technologies, and in particular Fibre Bragg Gratings (FBGs), are enabling high precision and detailed mapping of strain in various structures by direct integration into the material layers. Here, embedding fibre optic sensor lines in asphalt has been demonstrated to detect miniscule changes in lateral strain due to vertical deformations of road construction layers, in response to the loads in real-time traffic conditions. The spatial and temporal resolution of the system allows for very detailed mapping of the deformations due to vehicle loads, including the extraction of the viscoelastic properties of the pavement and the rigidity characteristics of the underlayers. By continuous and/or periodic monitoring of the dynamic asphalt behaviour in response to controlled loads, the long-term changes in the near-surface properties due to material aging because of weather conditions or traffic loads can be extracted. Such detailed analysis can enable monitoring of large-scale assets, literally paving the way for a new approach to asset management of roads.
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Monitoring the Effect of Artificial Dune Construction Using Multiple Geophysical Methods
Authors F. Schaars and M. GroenSummaryIn the winter of 2014/2015, the Dutch coast near Petten was reinforced by the construction of a large artificial dune. The dune was constructed next to the old sea dike that did not meet the current safety requirements. Since 2013, the Hollands Noorderkwartier Water Board has been monitoring ground- and surface water data to describe the transient effects of the construction on the groundwater quantity and quality. To keep track of the changes, a range of monitoring methods are applied. In addition to head measurements and water quality samples in monitoring wells, we use different geophysical methods to describe the reference and the current situation. We will show the pros and cons of the different methods, and how the combination of the results of all methods will get us closer to understanding the hydrological system and the consequences of the construction of the artificial dune.
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Raspberry Shake Sensor Field Tests for Unstable Rock Monitoring
Authors M. Taruselli, D. Arosio, L. Longoni, M. Papini and L. ZanziSummaryIn this work, we evaluate the performance of the Raspberry Shake 3D (RS-3D) seismometer in estimating the resonance frequencies of unstable rock blocks. In this perspective, we compared this low-cost sensor with the Nanometrics Trillium Compact 20s to assess whether RS-3D is suitable for the development of reliable rock monitoring systems. We carried out surveys on eight rock compartments located both in the Northern Italy and in the Maltese archipelago. Ambient noise recordings have been processed by computing the mean amplitude spectra, the ratio between the Raspberry Shake spectra and the Trillium ones, and the Horizontal-to-Vertical Spectral Ratio. The obtained results show that the RS-3D performs according to the vendor specifications, with slight spectral differences with respect to the Nanometrics reference. Our preliminary tests reveal that the Raspberry Shake may be a reliable sensor for estimating the fundamental frequency of unstable rock blocks provided the HV peak occurs within the RS flat frequency response, and, because of its low-cost, may promote the deployment of denser seismic monitoring networks.
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Geological Characterization and Geomechanical Parameters Assessment Using Electrical Resistivity Tomography and Seismic Methods
Authors B. Benjumea, A. Gabàs, A. Macau, F. Bellmunt, J. Ripoll, J. Ledo and S. FiguerasSummaryA broad understanding of the subsoil characteristics is required to deal with uncertainty in the infrastructure planning phase or even in the diagnosis of infrastructure damage. In this work, electrical resistivity and seismic methods have been employed for lithological characterization and geomechanical parameters assessment. The study area is characterized by high variability in geotechnical characteristics due to complex lithology. For lithological discrimination, we have used a soft clustering method to combine the independently electrical and seismic derived models. The outputs of this integration process are zonal models that help to decrease interpretation uncertainties. From single seismic profiles, both Vp and Vs information is extracted allowing geomechanical parameters to be estimated. All this information is critical for assessing the variance and inhomogeneity of the subsoil characteristics. The methodology shown in this work can be used in the infrastructure planning phase as well as to ascertain the causes of detected damage on built infrastructures.
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Quantitative Subsurface Information of Athens Basin (Greece) Derived from Urban Gravity Measurements
Authors S. Dilalos and J.D. AlexopoulosSummaryA disastrous earthquake of the past (7th September 1999) was the reason for acquiring 1.122 urban gravity measurements in order to investigate and model the deeper subsurface of Athens city basin. The aim was to gather any additional quantitative subsurface information based on the gravity survey, such as the density distribution provided by the 3D density models and depths of potential anomaly sources. The standard corrections have been applied (drift, tide, latitude, free-air, Bouguer, terrain ones) along with an additional Building Correction that was calculated based on the urban characteristics. The isolation of the residual anomaly has been accomplished with the contribution of the Fourier filters and power spectrum analysis. The Euler deconvolution has been used in order to calculate the depth solutions of anomalous sources, based on the residual maps. These solutions seem to identify with several fault zones. Some of these zones have already been mapped or proposed (covered ones) but additionally some new zones have been revealed. The 3D density model of the area provides information about the geometry of the subsurface geological bodies that can also be related to the tectonic structures of Athens basin beneath the surface.
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Field-Scale Quality Control of Lime-Cement Pillar in Conductive Clay Using Electrical Resistivity Tomography
Authors P. Olsson, S. Rejkjær and T. DahlinSummaryGround improvement with lime-cement pillars is becoming increasingly common in the Nordic countries for exploitation of areas with poor stability. However, there is no non-destructive method for quality control of the ground improvement. Significant changes in the electrical properties after mixing of the binders make electrical resistivity tomography (ERT) a potential method. In connection with lime-cement pillar trials for the Västlänken project in Gothenburg, Sweden, a series of different single borehole ERT measurements were performed. Three cases are compared in this paper: untreated ground, treated uncured ground and treated cured ground. The raw data pseudosections show a significant general drop in resistivity between the untreated and treated uncured data sets, while the curing process increase the resistivity significantly close to the borehole. Full 3D inversions have been carried out for all three cases. In model space the cured pillar is still causing a clear increase in resistivity around the borehole, while the decrease between the untreated and uncured case is less obvious than in data space. With the large contrast between the untreated and the treated uncured in data space it was expected to be visible in model space, improved inversion methods and settings could help resolve this.
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The Automated Geoelectrical Data Processing Workflow of the PRIME Infrastructure Monitoring System
Authors P. Wilkinson, J. Chambers, P. Meldrum, C. Watson, C. Inauen, R. Swift and G. CurioniSummaryPRIME (PRoactive Infrastructure Monitoring & Evaluation) is a low-cost geoelectrical ground monitoring system developed by the British Geological Survey. It is designed to integrate with standardised technologies and information delivery platforms to provide remote, near real-time, volumetric monitoring of infrastructure earthworks condition, thereby aiding asset failure prediction and timely intervention. A key recent development has been the implementation of a fully automated data processing workflow to enable regular and timely delivery of information to end-users. It is a customisable procedure, which enables each monitoring objective to have its own combination of processing steps applied to its data. The standard workflow consists of: data filtering and quality assurance; motion sensing (under development); inverse image generation; property translation via petrophysical relationships; and image analysis. The flexible implementation of the workflow will allow for new processing steps to be incorporated as they are developed.
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