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24th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 9-12, 2018
- Location: Porto, Portugal
- Published: 09 September 2018
61 - 80 of 203 results
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The ERT-3D Method as a Tool to explore the Pyramid of La Luna and the Main Plaza subsoils, Teotihuacan, Mexico
SummaryThe Pyramid of La Luna is found within the archaeological site of Teotihuacan, located to the NE of Mexico City. A big Plaza is found to the south surrounded by pyramids of different ages. These two areas were restored until the beginning of the 60th’s and few archaeological investigations have been carried out in this zone. A geophysical work was performed to characterise the subsoil of La Luna and her Main Plaza. The ERT-3D method was applied in both areas. The base of the Pyramid of La Luna was surrounded by 105 electrodes and different electric arrays were applied to cover adequately her subsoil. The main Plaza was covered with 4 ERT profiles employing a special roll-along technique to obtain a 3D view of the plaza subsoil.
A very interesting low resistivity signature was determined at 8 m deep beneath La Luna, towards her central part, which may indicate the presence of a cave. Two possible passages were identified. One of them seems to be heading towards the eastern end of the pyramid. The ERT-3D study at La Luna Main Plaza did not find evidences of a buried tunnel, nevertheless several resistivity anomalies were found that are of archaeological interest.
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Seismic SH Full Waveform Inversion as New Prospection Method in Archaeogeophysics
Authors D. Koehn, D. Wilken, T. Wunderlich, D. De Nil, W. Rabbel, L. Werther, J. Schmidt, C. Zielhofer and S. LinzenSummaryA successful and efficient archaeological excavation campaign requires a high resolution seismic imaging approach to resolve small scale near surface structures. The resolution of classical first arrival traveltime tomography (FATT) is limited by the first Fresnel zone, while the inversion of surface wave dispersion spectra requires a (local) 1D medium approximation, a significant problem in 2D heterogeneous media. To overcome these limitations, we introduce in this study the seismic SH full waveform inversion (FWI) of the Love- and refracted SH-wavefield as promising archaeogeophysical prospection tool. The applicability of this approach is demonstrated for SH field data from the transect over a medieval canal structure in southern Germany. Compared to FATT, the FWI is able to improve the definition of the canal shape and resolves small scale structures within the canal. These features are qualitatively compared with sub-surface structures revealed by an archaeological excavation along the SH profile.
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Comparison of Apparent Conductivity to Ground Displacement and Surficial Geology for Continuous Permafrost
Authors G. Oldenborger, N. Short and A. LeBlancSummaryInformation on thaw susceptibility is important for predicting the behaviour of permafrost as an engineering substrate. We compare apparent conductivity surveys to ground displacement obtained from differential synthetic aperture radar and surficial geology, with the objective of improving the regional characterization of terrain stability and permafrost conditions along the western coast of Hudson Bay, Nunavut. For certain field conditions, seasonal ground displacement, conductivity, and seasonal conductivity ratio are related to surficial geology, and there is a correspondence between high displacement, low conductivity, and high conductivity ratio, inferred to be indicative of high ice content and thaw-related displacement. For other conditions, results suggest heterogeneity of permafrost conditions, thaw susceptibility and conductivity that are not easily understood in terms of surficial geology alone.
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Soil Salinity Assessment Using Electromagnetic Induction and Inversion Technique – A Case Study in Portugal
SummarySoil salinization limits agricultural productivity and can ultimately cause desertification and land abandonment. Salinity mapping represents a good contribution to control soil salinization. Recent research is revolutionizing how soil information can be obtained quickly and cheaply. By using a state-of-the-art electromagnetic (EM) instrument and inversion techniques, it is possible now to generate high-resolution EM conductivity images and, in conjunction with soil sampling, to obtain quasi 2D and 3D maps of soil salinity. In this study EM surveys were conducted in four experimental plots located in Portugal, with different levels of salinity. EM models obtained from joint inversion of EM data, collected at different heights and orientations, shows good agreement with soil sample electrical conductivity of the saturation extract (ECe) in the study area. The significant correlation between EM models and ECe permits therefore a rapid characterization of the spatio-temporal variation of soil salinity, allowing to further predict salinization risk under different conditions.
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Ebro Delta Geometry and Structure Characterization Using the Electrical Resistivity Imaging Method
Authors F. Bellmunt, A. Gabàs, A. Macau, B. Benjumea and S. FiguerasSummaryThe Ebro Delta is currently a place of interest due to the presence of zones vulnerable to subsidence. Determining the type of sediment that favours the subsidence and its identification in the subsoil is a critical task for planning protection actions in the Ebro Delta. In this point the geophysical methods can help providing subsoil information. The subsidence mainly relies on Holocene sediments (clays, silts, sands and organic deposits). All these materials are affected by salty, fresh or brackish water. For this reason, one of the best geophysical techniques to describe the geometrical structure of complex lithologies, and its spatial variation, is the electrical resistivity tomography (ERT). The used geophysical parameter is really sensitivity to the presence of ions, and efficiently detects fresh water and saline water zones. The application of ten ERT long profiles (355 m - 1km) distributed around the studied area are a well-suited way to study the different environments inside the delta and to understand its evolution, from coast to margin side. In addition, the established geoelectrical boundaries have been used as a reference to build the 3D geological model surfaces, which will be used to assess the subsidence of the whole delta plain.
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Karst Imaging Using a Fuzzy C-Means Data Clustering Approach (Montgrí Massif, Spain)
Authors B. Benjumea, A. Gabàs, A. Macau, J. Ledo, F. Bellmunt and S. FiguerasSummaryIdentification of karst zones can be critical for hydrogeological or geotechnical studies. We present a case study carried out at the carbonate coastal Montgrí Massif (Spain) characterized by a well-developed karst system. The karst is covered by Quaternary sediments in the study area. The objective of the work is to image karst structures using geophysical techniques. Both electrical resistivity and seismic tomography (ERT and SRT) datasets have been acquired on five collocated profiles. Karst filled with clays produce seismic and electrical signature difficult to interpret. The Fuzzy c-means (FCM) data clustering approach is a way of producing an integrated model that can help to constrain lithological interpretation. In this study, FCM has been applied as a first step to one of the profiles with available ground-truthing from a near borehole. The resulting zonal model and cluster distribution has been used to interpret the integrated models obtained from applying FCM data clustering to the five datasets as a group. In this way, karst areas have been identified in three of the profiles in the near surface.
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Study of Small Earthfill Dams Structure Using Seismic Refraction, ERT and Self-Potential Methods
Authors W. Malagutti Filho, J.C. Dourado, C.A. Moreira, M.M. Coura and F.A. BergonzoniSummarySmall dams are used mainly by cities, industries, mines and agro-industries as a means to discipline the use of water, for diverse purposes. The need for constant monitoring and maintenance of this kind of structure is essential to guarantee its integrity, detect fractures, infiltrations, leaks, etc and therefore helps preventing accidents which can have catastrophic proportions. This paper presents the results of seismic refraction, electrical resistivity tomography and self-potential methods, performed in an integrated manner, on two earthfill dams, located in the cities of Cordeirópolis and Ipeúna, inland São Paulo state, Brazil. The objective was to aknowledge the geophysical signature to deduce geotechnical and hydrogeological parameters such as bedrock, layer length and disposition, possible weak spots in the bodies of the two earthfill dams as well as ground water preferential flow inside them.
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Electrical Resistivity Methods with Petrophysical Analysis of their Results
Authors D.A. Kvon, V.A. Shevnin and A.A. RyjovSummarySoil resistivity can be calculated from petrophysical soil properties. That gives possibility estimate petrophysical properties on soil resistivity. Now we use forward petrophysical problem, petrophysical modeling and inverse petrophysical problem to analyze relations between soil resistivity and some petrophysical parameters. We show examples of petrophysical approach application in different situations of water resistivity, rocks composition, influence of lithology and permafrost.
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A Novel Analytical Approach to Estimate Sand Production in Unconsolidated Reservoir: Case Study in Oil Field “N”
By D. AriantiSummarySand production is the migration of formation sand caused by the flow of reservoir fluids. This paper aims to develop an analytical model to predict sand production in oil field and validate it using 4 wells in Field “N”. Coupled sand failure mechanism considering static and dynamic criteria is used to models sand production. Rock particles strength is predominantly acting by drag and buoyancy forces. To capture fluid flow and pressure drop in porous medium, Darcy’s law is applied. The result of this study is the proposed analytical equation successfully models sand prediction accurately in 4 wells at range of cavity height 12–25 ft. At oil rate 1000 STB/day, calculated sand production in Well 1 is 0.005 lb/bbl, Well 2 is 0.007 lb/bbl, Well 3 is 0.005 lb/bbl, and Well 4 is 0.002 lb/bbl. This study shows good agreement on sand production trend in the moderate production rates of 2000 STB/day and low production rate of 500 STB/day with discrepancy varies of 2–3%. Sensitivity studies resulted is fluid viscosity and sand radius very sensitive to the sand production value. This study suggests cavity height in the proposed analytical method is applied at 10–25 ft.
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Angle Dependant Interference Patterns for Blast Vibration Minimization
Authors C. Tauchner, J. Zeiß and F. BleibinhausSummaryThe project focuses on reducing blasting vibrations at sensitive targets with phased source arrays in the far field. An interference pattern is naturally created by the geometrical setup of blasting arrays and the delay time between each single blast within the array. The aim is to create focusing effects with angle dependant interference where constructive energy hits sites of lesser interest and destructive interference is directed to neighbouring infrastructure. This work applies an analytic solution, which utilizes Dirac-Delta impulses, to better understand the basic relations between certain blast configurations and the resulting frequency radiation patterns. This is important because it signifies an additional constraint to the global search for optimized patterns in a later stage of the project.
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Multimethod Geophysical Survey of a Sinkhole - The Case Study of São Mamede
Authors N. Barraca, D.R. Rodrigues, S. Oliveira, F. Almeida and M. MatiasSummaryThis paper presents a case study dealing with the characterization of an area where a sinkhole developed. Several geophysical techniques (ground penetrating radar, 3D electrical resistivity tomography and seismic refraction) were used. The geophysical survey is intended to understand the origin of that sinkhole developed under a public road in São Mamede, Batalha (Portugal).
The integrated geophysical data point out to the existence of anomalies associated with the sinkhole and local infrastructures that could contribute to the occurrence of the phenomenon. The joint data interpretation shows high-velocity anomalies on the seismic refraction data the coincide, specially, with a high resistivity anomaly in the 3D resistivity model. These anomalies can be interpreted as corresponding to a concealed underground drainage system that could originate the sinkhole visible at the road surface.
Therefore, the integrated use of the three geophysical methods allowed to propose a model to be considered for the remediation of the problems caused by local water infiltration and sinkhole development.
Only the integration of data from different methods can enhance the interpretations and models obtained from the solely use of a single method. Thus, this strategy allows to propose more complete and detailed modes to describe the area under investigation.
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Applications of Data Fusion for Estimating Water Saturation at the Basis of Seismic, GPR and Resistivity Methods
By K. CzajaSummaryThe paper presents possibilities of applications of data fusion techniques for estimating water saturation at the basis of seismic, GPR and resistivity methods. The main purpose of this works was to test few data fusion techniques in order to obtain objective rules which first of all allow to estimate the value of water saturation with as high accuracy as possible. The tests were based on the results of computer modelling for the geophysical measurements for geological layers with different thickness and petrophysical properties.
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A Seismic Reflection Signal Recognizing Algorithm Based on the Stationarity Testing
More LessSummaryIn seismic prospecting, tracking the reflection events is the pathway for getting the accurate strata information. However, the existence of the seismic random noise prevents the recognizing of the reflection signals. Recently, the properties of the seismic random noise have been comprehensively discussed, especially in the statistical properties. It is shown that the random noise can be considered as a stationary process in a short period. In contrast, the seismic reflection signals are typically non-stationary. Here, a reflection signal recognizing algorithm, which is based on the stationarity testing, is proposed. The basic idea of the recognizing algorithm is to take advantage of the differences between the reflection signals and the random noise in terms of the stationarity. The experimental results demonstrate that the proposed method can recognize the reflection signals effectively, even the signal-to-noise ratio is low. Furthermore, the proposed method also has further application in the seismic noise attenuation.
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Contribution of Deep Deposits to Estimate Site Effects in the East of Mexico City
Authors D.F. Zepeda Fernández, R. Rojas Hernández and M. RodríguezSummaryThe damages in Mexico City (CDMX) associated with September’s 1985 and 2017 earthquakes are symbolic cases of the modifications that local geology can impose to strong ground motions received by buildings in Mexico’s basin. Site effects within the CDMX are predicted considering a simplified unidimensional model, in which the amplifications of the movement are generated by a high contrast of acoustic impedance between a homogenous layer and a semi-space. In this study we advance in the discussion of the origin of the amplification within Mexico City by including the observation of shear velocity models at the east of the city, which indicates the absence of a high contrast of shear velocity in the area, even when the deep deposit formation was reached. Results show a contribution of underlying formations to the superficial deposits in the observed dominant period; this suggests that site effects are probably associated to greater shear velocity structure thicknesses, than soil thickness over deep deposits.
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Crosshole Seismic Tomography to Assess Rock Mass Foundation of Dams - Alto Ceira II Dam Case Study
Authors R. Mota and M.J. CoelhoSummaryCrosshole seismic tomography is a widespread geophysical method to estimate the elastic properties of materials in the crosshole section, for a variety of applications, including engineering site characterisation and foundation treatment evaluation.
This method was applied to Alto Ceira II dam in three phases: Phases 1 and 2 – before and after rock mass foundation treatment, and Phase 3 – after the reservoir first filling. The resulting time-lapse seismic tomographies allowed assessing the schist and greywacke rock mass foundation treatment, and the influence of the reservoir filling.
This study demonstrated that the method can be used as a management tool to evaluate the rock mass behaviour along the dam’s construction phase and during its working lifetime.
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Integration of Geoengineering Techniques to Map Hidden Qanats at Shahid Bahonar University of Kerman
Authors A. Hojat, L. Zanzi, M.H. Loke, H. Ranjbar and S. Karimi-NasabSummaryIn this paper, we present integration of remote sensing, GIS, GPR and ERT techniques to detect underground qanats at Shahid Bahonar University of Kerman, Iran. These studies were defined because of the subsidence problems and cracks of some building walls at the main campus of the university due to unknown hidden qanats. The results of remote sensing studies tracked eight qanat systems passing under the university campus. These results were validated by field visits. GPR studies performed up to now in some parts of the campus showed the depth of qanat systems to vary in the range of 8–15m. Detailed geophysical surveys including GPR and ERT measurements are still to be completed with the aim to reconstruct the maps of underground qanat galleries. Our results and observations have inspired the new idea to construct a geotechnical-geophysical test site of natural qanats at the university main campus. We propose an area in the southeastern part of the university that is not likely to be significantly included in the future construction plans and it also hosts a sequence of non-collapsed shafts which can be used to better evaluate the site.
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Geometrical and Induction Electromagnetic Soundings Resolution Capabilities for Geological Engineering Investigations
Authors I. Mendrii, I. Ingerov and A. LozoviySummaryRecently developed and currently available on the market multichannel broadband multifunction EM instruments of the generation 5+ have levelled the costs of one measuring channel as well as field survey productivity during investigations of shallow geoelectric sections (up to 200m) with geometrical and induction EM soundings methods. Hence, it raises question of comparing resolution capabilities, sensitivity, productivity of geometrical and induction EM soundings methods during investigations of shallow sections. Research carried out by the authors has shown that the control source frequency domain electromagnetic sounding method (CSFDEMS or formerly FDEMS-IP) is the most sensitive to variation of parameters in the geoelectric sections, and subsequently, the most accurate for mapping boundaries of geoelectric section’s layers. The FDEMS method was developed in former USSR in the 50s of previous century together with MT and TEM and was mainly unknown in western countries. Since then, extensive FDEMS method field application experience has been accumulated and with new capabilities of recently developed equipment and software it became sensitive, highly productive and EM noise resistant method.
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Hybrid Surface Wave Survey - A Combined Active and Passive Seismic Survey Using a Linear Array
Authors T. Inazaki, H. Kisanuki, T. Kita and K. HayashiSummaryWe developed a combined active and passive surface wave survey method and named it Hybrid surface wave survey method. The Hybrid survey method deploys a linear geophone array to measure active and passive seismic data sequentially. Surface hitting using a wooden hammer is adopted as the active seismic source. In addition, traffic noises are measured using the same linear geophone array. A number of geophones are placed along a line at 0.3 to 2 m intervals to record active and passive data. Two dispersion curves, one is for a higher frequency part calculated from active data, the other is for a lower frequency part calculated from passive data, are combined to form a single dispersion curve to a specific CMP in a survey line. The method enables us to reconstruct a dense 2D S-wave velocity profile along a line up to 50 m in depth. One of the advantages of hybrid surface wave survey is its robustness to the traffic noises or active utilization of them vice versa. We have applied the hybrid surface wave surveys to more than 30 survey lines since 2013. Our field tests demonstrated the capability of the hybrid surface wave survey method in urban areas.
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How to Detect Disorders During Tunnel Digging with a Muons Telescope Mounted on a TBM
Authors P. De Sloowere, B. Carlus, A. Chevalier, J.-. Ianigro, J. Marteau, D. Gilbert and M. Rosas-CarbajalSummaryThe fact that the earth is constantly bombarded by an isotropic flux of cosmic rays has permitted to develop a new detection method that can only look over the observation point, but powerful enough to detect anomalies in front of a tunnel boring machine (TBM) digging a gallery. To do that, a cosmic ray detector, a muons telescope is set up on a TBM, looking towards.
Cosmic radiations generate very short-lived particles in the upper atmosphere, muons, whose diameter is small enough to penetrate the ground to depths of several hundredths of meters. Muons propagate without changing direction and disintegrates when it hits a proton or a neutron. So it’s a mass detector like gamma ray, and is able to measure density variations. It is used to study volcanoes and galleries. Experiments are occurred in galleries in France and Switzerland, especially in the Croix-Rousse tunnel (Lyon). Since April 2018 a muons telescope is installed on a TBM of the “Grand Paris Express”, moving with the TBM and permanently providing results.
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How to Detect Density Anomalies in Mining Activities with Cosmic Rays Detected by a Muons Telescope
Authors P. De Sloovere, B. Carlus, A. Chevalier, J.-. Ianigro, J. Marteau, D. Gilbert and M. Rosas-CarbajalSummaryThe fact that the earth is constantly bombarded by an isotropic flux of cosmic rays has permitted to develop a new detection method that can only look over the observation point, but powerful enough to detect anomalies in front of a tunnel boring machine (TBM) digging a gallery. To do that, a cosmic ray detector, a muons telescope is set up on a TBM, looking towards.
Cosmic radiations generate very short-lived particles in the upper atmosphere, muons, whose diameter is small enough to penetrate the ground to depths of several hundredths of meters. Muons propagate without changing direction and disintegrates when it hits a proton or a neutron. So it’s a mass detector like gamma ray, and is able to measure density variations. It is used to study volcanoes and galleries. Experiments have been occurred in France at Tournemire tunnel and Switzerland in the Mont-Terri underground Laboratory, showing fault and geologic contacts. Since April 2018 a muons telescope is installed on a TBM of the “Grand Paris Express”, moving with the TBM and permanently providing results.
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