An investigation of finite‐element modeling for electrical and electromagnetic data in three dimensions

Pridmore, D. F.; Hohmann, Gerald W.; Ward, S. H.; Sill, W. R.

doi:10.1190/1.1441239

Cited by 176 publications

(119 citation statements)

References 6 publications

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“…Much work has been done on resistivity forward modeling in 2D and 3D using the finite-difference method ͑Mufti, 1976; Dey and Morrison, 1979a, b;Fox et al, 1980͒ and the finite-element method ͑Pridmore et al., 1981;Queralt et al, 1991;Sasaki, 1994;Zhou and Greenhalgh, 2001͒. Investigative resistivity surveys on embankments to detect structural defects or anomalous seepage are fairly widespread ͑Abuzeid, 1994; Engelbert et al, 1997;Titov et al, 2000;Van Tuyen et al, 2000;Buselli and Lu, 2001;Panthulu et al, 2001;Voronkov et al, 2004͒.…”

Section: Introductionmentioning

confidence: 99%

2.5D resistivity modeling of embankment dams to assess influence from geometry and material properties

2006

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Repeated resistivity measurement is a potentially powerful method for monitoring development of internal erosion and anomalous seepage in earth embankment dams. This study is part of a project to improve current longterm monitoring routines and data interpretation and increasing the understanding when interpreting existing data. This is accomplished by modeling various occurrences typical of embankment structures using properties from two rockfill embankment dams with central till cores in the north of Sweden. The study evaluates the influence from 3D effects created by specific dam geometry and effects of water level fluctuations in the reservoir. Moreover, a comparison between different layout locations is carried out, and detectability of internal erosion scenarios is estimated through modeling of simulated damage situations. Software was especially developed to model apparent resistivity for geometries and material distributions for embankment dams. The model shows that the 3D effect from the embankment geometry is clearly significant when measuring along dam crests. For dams constructed with a conductive core of fine-grained soil and high-resistive rockfill, the effect becomes greatly enhanced. Also, water level fluctuations have a clear effect on apparent resistivities. Only small differences were found between the investigated arrays. A layout along the top of the crest is optimal for monitoring on existing dams, where intrusive investigations are normally avoided, because it is important to pass the current through the conductive core, which is often the main target of investigation. The investigation technique has proven beneficial for improving monitoring routines and increasing the understanding of results from the ongoing monitoring programs. Although the technique and software are developed for dam modeling, it could be used for estimation of 3D influence on any elongated structure with a 2D cross section.

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Section: Introductionmentioning

confidence: 99%

2.5D resistivity modeling of embankment dams to assess influence from geometry and material properties

2006

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“…However the accuracy of such computations should not be overestimated while the corresponding costs are extremely high. The necessary improvements in the DE approach were specially considered by Pridmore and Sill (1978), Pridmore et al (1981), . The most critical aspects of these problems will be discussed below.…”

Section: Differential Equation Methods (De)mentioning

confidence: 99%

Modern trends in the solution of forward and inverse 3D electromagnetic induction problems

Варенцов

1983

Geophysical Surveys

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Abstract. The main results obtained during the last 5-8 yr in the solution of forward and inverse problems of 3D induction studies are summarized. The up-to-date status of 3D modelling is presented and prospective improvements in the formulation and numerical solution of forward problems are discussed. Approximate techniques and practical aspects of 3D modelling are specially considered.The general scheme of 3D interpretation of electromagnetic geophysical observations is outlined and realistic formalized approaches to solving 3D inverse problems, namely direct inversion and formalized model fitting, are studied. O. IntroductionThe significant progress in the development of electromagnetic (EM) array observations achieved during the last ten years made it necessary to elaborate the system of EM data interpretation in 3D environments. Theoretical studies of 3D problems have been carried out during the last twenty years or more, but not until a few years ago did these works become of practical importance and serious applied researches were begun. Now many publications concerned with 3D induction studies are well known. Still, we have no generalized reviews on this subject (except brief ones like Ward, 1980), but in many special papers meaningful discussions of the problems and outlines of 3D techniques have been presented (Weidelt, 1975a;Vasseur and Weidelt, 1977;Hohmann, 1978;Banks, 1979;Weaver, 1979;Dawson and Weaver, 1979, Fainberg, 1980;Lee et al., 1981;Stodt et al., 1981;Berdichevsky et al., 1982; etc).It looks quite unrealistic to consider in detail the significant achievements in all of the numerous branches of 3D induction studies in a single review. Therefore the subject of this paper is restricted to the study of interpretation techniques of time-harmonic EM field anomalies caused by local and regional 3D conductivity structures. Moreover, attention is paid mainly to the theoretical and computational aspects of the rational formulation and effective solution of 3D forward and inverse problems. These problems form the basis of the interpretation theory and, as it can be seen from the experience of 2D induction studies, their intensive development produces the evident progress in elaboration of the whole interpretation system. It is not surprising that these problems are prevalent in the majority of publications of recent years.It should be noted that general ideas of inhomogeneous media interpretation theory, well illustrated in 2D applications, can be expressed in the main in 3D formulations. This has been shown clearly in the last monographs of Zhdanov (1981, 1983). However, we have usually enough difficulties to overcome in the theoretical analysis and at the stage of numerical considerations. Really, in most 3D

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“…Contrary to the iterative method used by Pridmore et al (1981), the system matrix is solved directly. Over the limits of the model, we have applied a Dirichlet condition (eqn 4) in a manner similar to Pridmore et al (1981). The boundary electric potentials are calculated for an appropriate homogeneous half-space and are imposed at fixed distances from the source.…”

Section: Finite-element Numerical Modellingmentioning

confidence: 99%

Theoretical study of slope effects in resistivity surveys and applications

Sahbi

Jongmans

Charlier

1997

Geophysical Prospecting

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When electric soundings are made over an irregular terrain, topographic effects can influence the values of apparent resistivity and lead to erroneous 1D interpretation. A 3D finite-element method has been applied to study the topographical effect of a slope on Schlumberger soundings parallel to the strike. When the resistivity survey is performed at the top of the slope, the apparent resistivity values can be two times higher than in the flat-earth case, depending on the angle (a) and height (H) of the slope, and on the distance (X) between the sounding and the slope top. The results are presented as nondimensional curves which can be used for evaluating topographic anomalies for any value of the parameters a, H and X. It is numerically shown that the topographic effects can be removed from measurements on horizontally layered structures with an irregular earth surface. Real measurements were performed in different geological conditions over an irregular terrain. The correction method based on the nondimensional curves has been applied to the data and has enabled the determination of the correct layered ground configuration using 1D interpretation.

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An investigation of finite‐element modeling for electrical and electromagnetic data in three dimensions

Cited by 176 publications

References 6 publications

2.5D resistivity modeling of embankment dams to assess influence from geometry and material properties

2.5D resistivity modeling of embankment dams to assess influence from geometry and material properties

Modern trends in the solution of forward and inverse 3D electromagnetic induction problems

Theoretical study of slope effects in resistivity surveys and applications

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