查看更多>>摘要：In the field of nondestructive inspection, ground-penetrating radar (GPR) is a widely used investigation tool, usually to evaluate quality and safety in structural engineering. However, its development has been limited due to differences in the dielectric constant in inhomogeneous media. In this study, a time-energy density analysis of wavelet transform (TEDAWT) method for GPR signal singularity recognition was proposed. In addition, a biorthogonal wavelet basis with high similarity to GPR signal waveform was innovatively constructed and added into the wavelet toolbox. A model experiment was conducted to validate the feasibility of inverse calculation of the permittivity of wet clay by the TEDAWT method. Results showed that this method offered the advantages of signal denoising, resolution improvement, singularity recognition in GPR signal processing. Subsequently, a basic flow chart was established, which could be used to inversely calculate the permittivity of inhomogeneous media, and be applied to the quantitative identification of the thickness of the reinforcement protective layer in an expressway tunnel. The calculation results showed that the inverse calculation value of reinforcement protection layer thickness was 3.74% lower than the average relative theoretical error value. That improved detection accuracy provided a new method to quantitatively identify inhomogeneous media by GPR.
查看更多>>摘要：In modern hydrogeological investigations with dense data coverage, the aim is to combine several different sources of information about subsurface structures to enable the best possible geological and hydrogeological interpretations from which a dynamic hydraulic model can be constructed. In this paper, the Egebjerg area in Denmark is used as an example of the process of combining airborne transient electromagnetic data with groundbased galvanic geoelectrical data in a joint inversion to produce a better resolution of the subsurface resistivity structure than would be possible using each of the methods alone. The joint inversion is realised by mutually constraining the inversion models of one data set with the inversion models of the other, overcoming the differences in scale and resolution power that are inherent in this type of effort.
查看更多>>摘要：The 3D inversion is a challenging task in the research of the frequency-domain airborne electromagnetic (AEM) method due to the massive amounts of data and limited computational efficiency. In this paper, we introduce the 3D FAEM inversion based on the vector finite element method (FEM). Compare with the traditional nodal FEM, the vector FEM can improve the computational efficiency by reducing the number of variables and the scale of linear equations. To tackle the computational demands, in the calculation process we apply the PARDISO solver with shared-memory distributed-memory multi-processors to solve the multi-source forward linear equations and calculate the gradient of the objective function by adjoint equations. Then typical resistivity model with the anomalous body is carried out to verify the validity of the proposed method. Meanwhile, in allusion to the multisolution problem caused by the inversion problem, we study the influence of typical initial models on inversion results. Finally, we applied our algorithm to invert field data. The inversion results demonstrate that the proposed method can obtain reliable AEM resistivity inverted results.
查看更多>>摘要：Due to the difficulty in detecting the upper breakpoint of active buried faults, high-resolution detection of active buried faults in urban areas is very important for urban planning and disaster risk mitigation. The seismic reflection technique is the most common technique used to image faults at depth, but it is difficult to precisely locate the upper breakpoint of active buried faults. Ground-penetrating radar (GPR) provides high-resolution imaging in ultrashallow exploration, but the penetration depth of traditional GPR is shallow. In this work, we conducted six GPR surveys with multifrequency (25 MHz, 50 MHz and 100 MHz) and high-power GPR antennas across the possible range of the Shuiyu fault based on seismic reflection results. We obtained the trace of the Shuiyu fault within 45 m of the surface in Datong city, and the fault was found to dip approximately 70-80 degrees to the SE. According to the GPR results, we selected a location for trenching and excavated one trench across the Shuiyu fault. The trench results verified the accuracy of the fault imaging in the GPR profiles and helped to interpret the stratigraphic information in the GPR profiles. In the accurate detection of active buried faults in other urban areas, the seismic reflection method can be used to determine the main strike of faults at depth, and then GPR can be used to detect the near-surface distribution of the faults in detail and guide trench location selection. The application of high-power GPR antennas with different frequencies in the fast detection of the upper breakpoint of active buried faults in urban areas is of great significance to earthquake hazard analysis and urban planning in Datong city.
查看更多>>摘要：Electrical resistivity tomography (ERT) aims at imaging the subsurface resistivity distribution and provides valuable information for different geological, engineering, and hydrological applications. To obtain a subsurface resistivity model from measured apparent resistivities, stochastic or deterministic inversion procedures may be employed. Typically, the inversion of ERT data results in non-unique solutions; i.e., an ensemble of different models explains the measured data equally well. In this study, we perform inference analysis of model ensembles generated using a well-established global inversion approach to assess uncertainties related to the nonuniqueness of the inverse problem. Our interpretation strategy starts by establishing model selection criteria based on different statistical descriptors calculated from the data residuals. Then, we perform cluster analysis considering the inverted resistivity models and the corresponding data residuals. Finally, we evaluate model uncertainties and residual distributions for each cluster. To illustrate the potential of our approach, we use a particle swarm optimization (PSO) algorithm to obtain an ensemble of 2D layer-based resistivity models from a synthetic data example and a field data set collected in Loon-Plage, France. Our strategy performs well for both synthetic and field data and allows us to extract different plausible model scenarios with their associated uncertainties and data residual distributions. Although we demonstrate our workflow using 2D ERT data and a PSObased inversion approach, the proposed strategy is general and can be adapted to analyze model ensembles generated from other kinds of geophysical data and using different global inversion approaches.
查看更多>>摘要：Surface electrical resistivity tomography is a non-invasive and highly competitive technique that can be used to effectively characterize subsurface sediments for different purposes: geological, geotechnical, hydrogeological or subsidence problems. However, due to the strong effect of salinity on resistivity, sediments characterization in deltas (coastal areas) becomes a challenge. In this work, the results of combining extensive surface electrical resistivity tomography measurements and limited borehole logging and geological information in the Ebro delta plain is presented. The methodology used has been critical to reduce uncertainties in the interpretation of the ERT models, allowing to characterize the sedimentary architecture of the Holocene deposits in the Ebro delta plain up to about 60 m depth. The obtained geoelectrical models have been used for the construction of the Ebro delta 3D geological model prior to the delta plain subsidence assessment. Results also highlight the feasibility and capability of the electrical resistivity tomography technique to sediments characterization in extreme environments such as coastal areas and deltas. Additionally, the water quality distribution across the delta plain is also inferred.
查看更多>>摘要：Many adverse geological structures, such as karst caves and faults, may exist in front of the tunnel face. If adverse geological structures ahead of the tunnel face cannot be detected clearly, geological hazards (i.e., the inrush of clay and water) may occur during excavation. In this study, a new ahead prospecting scheme was proposed to detect adverse geological structures during tunnel construction using probe holes. First, a new array was proposed: the potential electrodes were placed at the tunnel face, and the current electrodes were placed in the hole. The potential data were collected and used for inversion. Furthermore, a 3D resistivity multi-scale inversion method was proposed to locate and describe boundaries of geological structures with high accuracy. In this method, the 3D convolutional wavelet transform is used to extract wavelet parameter information from the resistivity model. On this basis, the inverted solution space is transformed from the spatial domain to the wavelet domain. The solution in the wavelet domain can be obtained using the inversion equation. Then, the solution in the spatial domain can be obtained from the wavelet domain using the 3D deconvolution transform. Finally, the effectiveness of the new ahead prospecting scheme was verified by numerical inversion tests. Furthermore, this paper describes the successful application of the new scheme to detect water-bearing structures in tunnel of the project "transfer water from Hongyan river to Shitou river".
查看更多>>摘要：Investigation of the foundation system of the heritage site is a challenging task. The heritage site in the present study is Sun temple, Konark. The temple is a 700-800 years old stone masonry structure and world heritage site in the Indian state of Odisha. The investigation of the foundation details, i.e., type, depth, and horizontal extent, along with the soil layering below and around the temple premises, involves non-invasive and invasive techniques. The shielded and unshielded Ground Penetrating Radar (GPR) antenna, with a central frequency of 250 MHz & 500 MHz, and 100 MHz, are used for non-invasive investigation. In addition, invasive investigation, i.e., drilling at the top of the platform, at the plinth level, collection of samples, and characterization are performed to determine the soil layering below and around the temple premises. The GPR radargrams of the layering system corroborated with the bore logs obtained by performing the invasive investigation. The non-invasive and invasive study establishes the foundation system as a block type having a depth of 10.5 m from the top of the temple platform. The study demonstrates the efficacy of GPR as a support system for conventional invasive techniques. The paper in detail presents the GPR investigations, their inferences, invasive testing, and the corroboration of the non-invasive and invasive tests.
Favacho de Freitas, Karina Lobatoda Silva, Pablo NascimentoGoncalves, Eduardo CorreaRios, Edmilson Helton...
10页
查看更多>>摘要：Reliable estimates of porosity can be obtained from different types of geophysical well logs. However, obtaining in situ permeability estimates is still a major challenge in the geosciences. This work aims to evaluate the application of data mining techniques to NMR logs for rock permeability classification, thus far tested only on laboratory data. For this study, we used a petrophysical database from two Brazilian Pre-salt wells located in the Santos Basin, a formation notoriously difficult to characterize, mainly due to its diversity and complexity. Six classification algorithms were evaluated (k-NN, NB, C4.5, RF, SMO, and MLP) according to their ability to estimate the permeability of rocks in four distinct classes (low: 1 mD, intermediate: 1-10 mD, high: 10-100 mD, and excellent: 100 mD). The predictive performance of the algorithms was compared to the behavior of two traditional permeability estimators. With an accuracy of 66%, the Naive Bayes algorithm, combined with two preprocessing steps - unsupervised discretization and attribute selection - achieved the highest predictive performance. That mark surpassed the accuracy obtained by Kenyon and Timur-Coates estimators by 154% and 106%, respectively, providing evidence for the superiority of the data mining technique to recognize permeability classes based on NMR logs. Classification experiments employing NMR logs in conjunction with conventional logs were also conducted, but this log combination was not able to best the predictive result based solely on the NMR log data.
查看更多>>摘要：The forecasting of fluid saturation changes within the reservoirs is one of the main issues of rock physics, which is often done using Biot-Gassmann theory. However, this theory demands the knowledge of the dry rock elastic moduli. Nur's (critical porosity) model is one of the theories to evaluate those dry rock properties from porosity and the mineral elastic properties of rock constituents. Therefore, that model is appropriate for estimating the dry rock bulk and shear moduli in well log analysis, especially in situations where there are no sonic logs available. In this paper, we analyzed four carbonate rock datasets reported in the literature, which consisted of measurements of porosity, mineral content and elastic velocities. Our approach focused on investigating how the misfits between the model and the experimental data varied according to porosity and pressure, through best-fitting regressions. Those observations allowed the setting of a modification on the Nur's model that can account for the pressure influence in porosity. This modified Nur's model significantly improved the accuracy of the results, exhibiting average relative errors 50% smaller than the original model estimates. The performance of that model varied for the different carbonate textures and pointed out that the siliciclastic content influences the predictability error of that modified critical porosity model. Rocks exhibiting the highest siliciclastic content showed an error reduction trend as pressure increases, while the other samples with minor siliciclastic content did not show significative accuracy variation.
NSTL
Elsevier