- Home
- Conferences
- Conference Proceedings
- Conferences
25th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 8-12, 2019
- Location: The Hague, Netherlands
- Published: 08 September 2019
81 - 100 of 141 results
-
-
Testing ERT and Fiber Optic Techniques at the Laboratory Scale to Monitor River Levees
Authors A. Hojat, D. Arosio, I. Di Luch, M. Ferrario, V. Ivov Ivanov, L. Longoni, A. Madaschi, M. Papini, G. Tresoldi and L. ZanziSummaryIn this paper we present the results of laboratory tests using electrical resistivity tomography (ERT) and fiber optic techniques to monitor river levees. A small-scale levee was constructed with the scale of 1:12 based on the earthen levee of an irrigation canal in San Giacomo delle Segnate, Italy, where a customized ERT monitoring system has been operating since September 2015. The most important mechanisms affecting the stability of river levees were simulated during different tests. To explore the possibility of using fiber optic sensors to monitor the integrity of levee structures, Fiber Bragg Grating (FBG) technology was adopted and four Organic Modified Ceramics (ORMOCER) coated 250μm-diameter fibers were deployed at the water exit side of two leakage zones. ERT data from a miniaturized electrode spread show that changes in the water level in river and the rainfall events significantly affect the resistivity distribution in the levee. Using TDR data, the relationship between water content and resistivity values was calibrated to be able to translate the inverted ERT images into water content maps. The results of fiber optic measurements showed the feasibility of fiber optic sensors to detect the deformations of the levee body in response to water infiltration.
-
-
-
Incorporating Spatial Heterogeneity in Stability Analyses of an Unsaturated Soil Embankment - Extended Role of Integrated Geophysics
More LessSummaryExtreme climate events like frequent and heavy rainfall and extreme dry weather make slopes, dykes and embankments extremely vulnerable. The shallow subsoil in such cases are generally in unsaturated condition. In all common failure mechanisms of unsaturated slopes or embankments, the spatiotemporal distribution of water saturation and matric suction plays a crucial role. With input data from integrated geophysics, we have developed a new inversion scheme to invert in-situ soil-water characteristic curve (SWCC), linking saturation to suction. The new inversion uses total least squares to minimize the data-model residual simultaneously for water saturation, confining stress and smallstrain shear modulus. Applied to data obtained from integrated geophysics, the inversion offers quite accurate estimates for in-situ SWCC. For the first time, it has been possible to incorporate deterministically obtained heterogeneous SWCC to make reliable stability estimates for unsaturated slopes/embankments. For an embankment containing a clay layer underlying surficial silty-sand, the estimated factor of safety for Coulomb failure and internal erosion and piping can be dangerously overestimated if a mean value of SWCC is used, instead of a more accurate SWCC considering heterogeneity. For a clay-cored sand embankment, the mean value of SWCC can overestimate the safety factor.
-
-
-
Levee Characterization by Means of Data Fusion of In-Situ Geophysical and Geotechnical Information
Authors T. Dezert, Y. Fargier, S. Palma-Lopes and P. CôteSummaryTo prevent catastrophic consequences imputed to levee breakage, the identification of the subsoil constitutive materials, as well as the detection of interfaces and anomalies are crucial. During investigation campaigns, complementary geophysical and geotechnical methods are usually used. These two sets of methods provide data with very different spatial scales, levels of incompleteness, uncertainty and inaccuracy. The effective combination of these two different types of data is challenging. In this work, we propose the fusion of geophysical and geotechnical data by means of Belief Functions, implementing Smets and Dempster-Shafer rules. We demonstrate our approach on a real case study, at Saint-Clément-des-Levées (France) including one geophysical method (electrical resistivity tomography) and two geotechnical ones (cone penetrometer and grain size analysis after drilling). This work also aims at supplying a better visual representation of a levee section with related degrees of belief. Our results highlight the ability of our fusion methodology to properly characterize the considered materials as well as to indicate the positions of the interfaces and the associated levels of confidence.
-
-
-
Electrical Resistivity Tomography (ERT) Study in the Xochimilco District - Mapping the Subsidence in Southeastern Mexico City
SummaryThe district of Xochimilco is located towards the Southeast of Mexico City. The area is found within the transition zone between the basalts of the Chichinautzin formation and the lacustrine sediments of the ancient lake of Xochimilco. This paper presents the preliminary results of two electrical resistivity tomography (ERT) studies conducted in two different areas of the Xochimilco district (Mexico City). The first one is carried out in the hilly zone to identify the subsoil structures that are causing a severe affectation to the urban zone in the area, just over the transition between the igneous extrusive rocks of the Chichinautzin formation and the sediments of the ancient lake. The second study was carried out in the low-lands, where a sinkhole appeared in a pre-Hispanic canal of Xochimilco (Zacapa pier), which drained it completely.
The results obtained in both studies show the applicability of the ERT technique, and for making decisions regarding remediation. It was observed that both events are closely related to the superposition of two different phenomena, the presence of an abrupt transition zone between two materials of different mechanical properties (i.e. basalts and sediments) and the excessive groundwater extraction that exacerbates the phenomenon of subsidence.
-
-
-
Delineation of Dead-End Structure of Thin Sand Layer by ERT and Cylinder Electrode CCR Survey
Authors C. Konishi, Y. Yamashita, K. Takahashi, D. Kurata and A. ShinseiSummary2D ERT and cylinder electrode capacitively coupled resistivity (CCR) survey has been conducted to detect deadend structure of a thin sand layer that may cause piping and a river levee collapse in the worst case. The survey lines were placed at an inland side of Tokoro river where a flood occurred by unprecedented heavy rainfall in 2016. We planted electrodes with 0.5 m spacing to increase the vertical resolution for ERT, and cylinder electrode, which is equivalent to 0.5 m dipole cable, was employed for the CCR survey. As a result, high resistivity thin layer was detected at 1 m depth, and dead-end structure was observed by 2D ERT and CCR survey. Soil samples were collected by auger drilling at several places around the observed dead-end point of the high resistivity layer and lateral variations of the soil were confirmed. It suggested the sand layer was terminated and the capability of ERT and the cylinder electrode CCR for delineating the thin sand layer was verified.
-
-
-
Dynamical Changes of Foundation Displacements and Local Seismic Activity Occurred During Construction of Enguri Arch Dam
SummaryIn present research we aimed to analyze dynamical characteristics of high dam foundation displacement under the construction of large hydro power plant and during periodic changes of water in artificial lake behind the dam. We used data sets collected at international test area around Engury high dam from 1974 to 2013. We also analyzed changes occurred in the dynamics of local seismic process during the construction of hydro power plant and its functioning. Data sets of dam foundation displacements and seismic data sets have been collected in period started from the beginning of Enguri high dam construction (1974) to 2013. In our analysis we used modern methods of data analysis such as recurrence quantification analysis, algorithmic complexity testing, singular spectrum analysis as well as multivariate data analysis combined with the surrogate data testing. It was found that dynamics of dam foundation displacement is strongly influenced by process of HPP construction and especially by water level change in artificial reservoir behind Enguri high dam. It was also shown that the same factors leaded to quantifiable changes in the dynamics of local seismicity around Enguri hydro power plant.
-
-
-
Combined 3D Inversion of Ground and Airborne Electromagnetic Data over Iron Ore in Kiruna
Authors M. Smirnova, N. Juhojuntti, M. Becken, M. Smirnov, P. Yogeshwar, A. Steuer, R. Rochlitz and M. SchifflerSummaryWe present the first results of a semi-airborne survey conducted in 2018 at Per Geijer iron ore in northern Sweden (Kiruna). In our semi-airborne system, the transmitter is positioned on the ground and magnetic field receivers are airborne. To support airborne measurements, we complemented the survey with an array of ground electric field receivers, magnetotelluric (MT) stations, and SMARTem measurements. The objective of the study is to combine different types of electromagnetic (EM) data in order to derive a common 3D conductivity model of the exploration area. We process data in frequency domain using a robust processing scheme. The airborne data are additionally corrected for rotation. The final 3D model is derived using combined ground and airborne data from three source positions (Controlled-Source EM inversion). Additionally, a 3D model from MT data is obtained separately and used as a starting model for CSEM inversion. Both models match the well-known surface geology and other geophysical information yet bring new insights into the general model of the camp. The next step is a joint inversion of the MT and semi-airborne CSEM data.
-
-
-
ERT Survey for Identifying Mine Shafts in a Area of Municipality of Höganäs, Sweden
Authors J. Siikanen, E. Lindvall and A. Fouskopoulos LarssonSummaryAn ERT survey has been carried out in an area of Höganäs municipality, Sweden. The aim of the survey was to locate old mine shafts where coal was previously mined. The result should be used as a basis for facilitating the municipality's detailed planning work so that future exploitation of buildings is carried out in a safe manner. The ERT survey consist of four lines performed with gradient configuration and a electrode separation of 2 meter. The direction of the mine shafts is presumed to have a north-easterly direction. All ERT lines have been placed to measure perpendicular to the direction of the mine shafts. The result show anomalies that initially was interpreted as mine shafts and later verified with geotechnical drilling.
The inverted resistivity model of line 1, 2 and 3 indicates a low value in residuals. Line 4 indicates high residual that probably is caused by high conductive material in the ground in or close to the line. The results from this investigation have not shown clearly that the mine shaft consist of a cavity in the rock, but rather a change in the quality of the rock, probably have the mine shafts been filled and/or have collapsed.
-
-
-
Assessment of Water-Protective Sequence at the Verkhne-Kamsky Deposit of Salts from 3D Inversion Results of EMS-IP
Authors A. Belova, Y. Davydenko, A. Zhukov, D. Bogdanovich, S. Bukhalov, M. Shkirya and K. AbornevSummaryApplication of ground-based methods of electromagnetic sounding in geology-and-engineering survey allows assessment of geological structure in terms of discovering potentially dangerous low-resistivity zones. For this purpose, the method of electromagnetic sounding and induced polarization (EMS-IP) turned out to be highly efficient. The method implies excitation of transitional processes with grounded dipole and registering with receiver lines. Considering inversion within 1D model, it was feasible to specify the horizontally bedded structure of sedimentary sequence above the potassium mine, and to outline potentially dangerous objects of increased conductivity. At the next stage, the obtained model produces initial approximation for 3D inversion of transitional processes. As a result, position of the increased conductivity field was rectified both in plan and over depth.
-
-
-
Multimethod High-Resolution Geophysical Imaging of Landslides in Mountain Area - A Case Study from Cisiec, Poland
Authors A. Marciniak, S. Kowalczyk, T. Gontar, B. Owoc and M. MajdańskiSummaryThe presented paper shows a case study of Multimethod high-resolution geophysical imaging of landslide. The study area was located in the SW Poland Beskid Zywiecki Mountain range. The area is a clearance, where ski lift is located. To obtain high-resolution images, a proven combination of seismic (Surface Waves Analysis, Seismic travel-time Tomography and Reflection Imaging) methods with ERT tomography were used. The final interpretation shows the whole characteristics of the landslide with accompanying faults. The proposed methodology is cost-effective, and in comparison to a standardly used stand-alone ERT or other single method approaches, delivers the much more detailed image with minimal additional effort
-
-
-
An Overview of High Spatial Resolution Geophysical Methods for Landslide Characterisation and Monitoring
Authors J. Whiteley, M. Kendall, C. Sujitapan, C. Inauen, R. Swift, A. Watlet, M. Raines, J. Boyd, M. Cimpoiasu, J. Holmes, L. Sibbett, S. Uhlemann and J. ChambersSummaryCombining geophysical methods allows for the characterisation and monitoring of subsurface processes in landslide systems at unprecedented spatiotemporal resolutions. For high spatial resolution characterisation and monitoring of the subsurface, methods that provide maps, cross-sections and three-dimensional volumes of data are preferred. An overview of the results of various long-term monitoring campaigns using such geophysical methods at the Hollin Hill Landslide Observatory in the UK are presented. These methods include electrical resistivity and seismic tomography, self-potential mapping and cross-sections of horizontal-to-vertical ratio measurements of ambient seismic noise. Repeating these surveys over time results in the production of time-lapse data, making these approaches effective monitoring tools. Variations in these measurements show relationships to changes in environmental conditions, for example, decreases in seismic velocity and resistivity values associated with decreases in soil moisture content. Critically, the use of geotechnical-geophysical relationships can provide information between, and beyond the depth of, shallow geotechnical and surface environmental sensors. Using such time-series of high resolution spatial data can help achieve a better understanding of the moisture and kinematic dynamics of unstable slopes, and provides subsurface information for incorporation in to local landslide early warning systems.
-
-
-
Seismic Noise Polarization Analysis for Unstable Rock Monitoring
Authors D. Arosio, M. Taruselli, L. Longoni, M. Papini and L. ZanziSummaryIn this work, we discuss three different approaches to investigate the polarization characteristics of ambient vibrations collected on unstable rock slopes for monitoring purposes. We consider the Principal Component Analysis (PCA) of the time-domain covariance matrix, the Horizontal-to-Vertical Spectral Ratio as a function of Azimuth (HVSRA), as well as the Singular Value decomposition (SVD) of the Hermitian spectral density matrix. A simple test taking into account seismic noise datasets collected in two acquisition sessions on a potentially unstable rock pillar suggests that the latter method is able to provide more information with respect to the PCA and HVSRA approaches. Processing of the spectral density matrix allows to estimate frequency-dependent polarization parameters, namely the degree of polarization and four angular quantities describing the particle motion in the 3-dimensional space. Provided that processing is properly tuned, frequency-dependent polarization analysis may be able to track subtle changes of unstable rock vibration modes and so to increase our rock failure forecasting capabilities.
-
-
-
Linking Geoelectrical Monitoring to Shear Strength - A Tool for Improving Understanding of Slope Scale Stability
Authors J. Boyd, J. Chambers, P. Wilkinson, S. Uhlemann, A. Merritt, P. Meldrum, R. Swift, M. Kirkham, L. Jones and A. BinleySummaryLandslides pose a risk to both infrastructure and wider society, managing the geohazard requires and understanding of factors driving slope instability, in particular the response to moisture content. Traditional methods of slope investigation involve discrete point geotechnical measurements which are not spatially sensitive. Recent studies have shown the spatial sensitivity of geoelectrical methods to both the internal geometry of unstable hill slopes and moisture dynamics, demonstrating their value in landslide investigation and characterisation. In this study we present the use of a geoelectrical monitoring system on an active landslide in Lias mudrocks, North Yorkshire, UK. Building on previous studies of the field site, subsurface resistivity distributions determined from time-lapse electrical resistivity tomography (ERT) are converted into shear strength estimates through calibration between electrical resistivity and matrix suction. Geotechnical parameters are determined from shallow borehole samples. Shear strength distributions show agreement with field observations of the slope, relatively low shear strength values (<100 kpa) correspond to the parts of the slope which are actively moving. We suggest there is scope for further work identifying regions of potentially instability on hillslopes through coupled hydromechanical and geoelectrical modelling.
-
-
-
Imaging Near Surface Scatterers by Scattered Surface Waves - Revamping an Inverse Scattering Code
Authors U. Harmankaya and A. KaslilarSummaryWe use an inverse scattering method for imaging the near surface scatterers by scattered surface waves. The method involves three dimensional elastodynamic wave propagation and scattering in a layered medium. The scattered wavefield is due to density contrast only, and is given as an integral representation by considering Born approximation. For efficient modeling and inversion, we converted our legacy computer code, developed for the method, into a newer programming language. Also, parallel programming techniques were introduced into the code to increase its efficiency. A simple parallelization structure was implemented, which resulted in a significant decrease in program runtime. We validated the code by comparing its modeling output with a finite-difference modeling of wave propagation program. We used half space models with scatterers that have positive and negative density contrasts in both programs and compared the results. Scattered wavefields obtained from the finite-difference modeling are used in our revamped code for imaging. Inversion results for both scatterer cases show that the location and density contrasts of the scatterers are reasonably well estimated.
-
-
-
Near-Surface Geophysical Imaging of the Permafrost — Initial Result of Two High Arctic Expeditions to Spitsbergen
Authors A. Marciniak, B. Owoc, T. Wawrzyniak, A. Nawrot, M. Glazer, M. Osuch, W. Dobiński and M. MajdańskiSummaryIn presented work, authors applied multiple geophysical methods, to monitor and estimate the seasonal changes in both the active and permafrost layers. The study site, located near the Polish Polar station in Svalbard, is unique due to its location and the environmental processes occurring in this region. The two seismic lines were deigned to image the structure between coast and mountains and post galcial sediments in formt of the retreating glacier. The acquisition of the same lanes was repeated in two consecutive seasons in Autumn 2017 and Spring2018, to develop optimal acquisition and processing methodology. To image seasonal changes, multiple geophysical methods (Seismic Imaging, Travel time tomography, surface waves methods, ERT, Thermal monitoring) were used, in both seasons. As a result, the optimal acquisition was designed. The optimal processing, assumes the use of ERT, GPR, MASW, Seismic travel-time Tomography and Reflection Imaging in presented order. The interpretation of the data shows high variability of the active layer and possibly bottom of the permafrost.
-
-
-
Seismic Monitoring and Site-Characterization with Near-Surface Vertical Arrays
Authors E. Ruigrok and B. DostSummaryThe northeast of the Netherlands is covered with a dense network of seismic stations. The prime use is monitoring of induced seismicity from the Groningen field and a string of surrounding gas fields. The near-surface consists of unconsolidated sediments. After extensive testing, a standard station design was chosen with an accelerometer at the Earth's surface and geophones at 50, 100, 150 and 200 m depth. Clearly, these vertical arrays cost more than single sensors and do not add in the network coverage. However, they also bring multiple advantages. The combination of a strong motion sensor and at least one weak-motion sensor is needed to record a wide spectrum of earthquake magnitudes. The installation of weak-motion sensors at depth reduces the seismic noise up till about 30 dB. Sensors are placed at different depth levels to enable near-surface characterization and to facilitate phase identification. Furthermore, the installation of multiple buried sensors provides redundancy in case one of the geophones breaks down.
-
-
-
High-Resolution Crosshole Seismic Tomography (CST) Studies on Nuclear Power Plant Foundation Site
Authors V. Ignatev, A. Konkov, I. Polikarpov, A. Shuvalov and A. OshkinSummaryThis paper describes an example of crosshole seismic tomography (CST) fulfillment on the construction site of one nuclear power plant (NPP). The main objective was to characterize the site's subsurface condition and calculate its elastic dynamic properties. Tomographic measurements were conducted among eight borehole pairs (i.e. among one central and four side wells). Deployment of specific approach for data processing and visualization allowed us to combine the obtained data in 3D mode in order to facilitate the interpretation process. According to the CST results, a dense system consisting of intersecting velocity sections that provide detailed information on the studied structure was constructed.
-
-
-
Automated Fracture Point Calculation Procedure
Authors I. Ravimo, K. Tiensuu and E. HeikkinenSummaryPosiva Oy is responsible for preparation of final disposal of spent nuclear fuel in Olkiluoto and has done extensive research to ensure the over-all safety of the final disposal. Final disposal is scheduled to start in 2020's. Extensive geophysical survey programs have been executed in both deep boreholes and pilot holes located in the vicinity of planned disposal site. Scope of the automated fracture point calculation procedure was to automatically detect the most significant fractures from geophysical data based on known fracture locations and geophysical anomalies. This approach sets high demands for the processing and depth correction accuracy of the data. Automation was implemented using R programming language. Calculation procedure is applied to one hole at the time and processing constants were determined using existing data from pilot holes. Fracture point calculation procedure returns scaled parameter specific points and scaled total points for each fracture. Fractures are then classified based on their total points in order to determine their relevancy. The most relevant ones get the highest total points but in some cases it can also be beneficial to concentrate only on certain methods. Results are used in Rock Suitability Classification process together with geological and hydrogeological data.
-
-
-
Integrated Geophysical Studies on the Archaeological Sites without Relief Features (Ust-Tartas and Tartas-1)
Authors E. Balkov, O. Pozdnyakova, P. Dyadkov, A. Alymov, Y. Karin, G. Panin, D. Kuleshov, N. Evmenov and L. NgomayezweSummaryGeophysical survey techniques have become important tools for archaeological research. Integrated geophysical studies were conducted on two archaeological sites, Ust-Tartas and Tartas-1. The electromagnetic, electro-tomography and multiple-height magnetic survey methods were used. In these studies, the electromagnetic survey methods were used to determine the geometrical parameters of the buried objects, and also were most useful in areas of low contrast of the magnetic properties and contamination. Additional methods, the electro-tomography and multiple-altitude magnetic survey were used to carry out a more detailed study about the geometry and depth of objects. Obtained results from the electrical and electromagnetic surveys significantly complement the magnetic survey results. The integrated use of different geophysical methods is always useful for confidently identifying an anomalous object and reduce the ambiguity in the interpretation. The studies showed that the combination of geophysical data makes it possible to solve complex tasks so as to achieve the degree of information required for archaeological research.
-
-
-
Geophysical Survey at a Coastal Area of Artemida City, East Attica, Greece, with Archaeological Interest
Authors G. Apostolopoulos, G. Amolochitis, A. Sakalidi, E. Garbi, D. Karaiskos and S. KarizonisSummaryA geophysical survey was carried out at a coastal area of Artemida City, East Attica, Greece, with its main purpose to detect any anthropogenic structures of archaeological interest covered by loose sediments. The archaeological excavation has already revealed the foundation structure of the Temple of Artemis Tavropolou and southerly a small temple near the coast. Two areas have been covered with EM, ERT and GPR measurements, one in the vicinity of the Temple and the other the whole sandy coast connecting the two temples. Saline water intrusion plays the key role in the conductivity distribution in all methods which can show where dense impermeable structures exist either being anthropogenic or foredune or bedrock. Even the later can reveal the paleo-environment and exclude areas for further archaeological exploration. EM maps have provided the best position of ERT and GPR profiles which finally have indicated local structures and their continuity.
-