Figure 6 - uploaded by Ahmed Ismail
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2-D electrical resistivity line across an excavated sinkhole located 200 m west of the emptied sinkhole at site 2.
Source publication
Two-dimensional (2-D) electrical resistivity tomography data were acquired across and in proximity to active sinkholes at two highway construction sites in Missouri. Site 1 is located in Greene County in southwestern Missouri; site 2 is located in Jefferson County in east-central Missouri. Eleven 2-D electrical resistivity tomography profiles were...
Contexts in source publication
Context 1
... during the interpretation of the resistivity data from site 2, we focused on the area around and underneath the emptied sinkhole. In order to constrain the interpretation of the resistivity data at site 2 with the absence of borehole control, a resistivity profile was completed along an excavated clay-filled sinkhole located 200 m west of the emptied sinkhole ( Figure 6). Based on the interpretation of this resistivity line, units with resistivities in excess of 1000 ohm-m were interpreted as intact limestone; units with resistivities less than 300 ohm-m were interpreted as clay in-fill (or ponded water-clay in-fill in the base of the sinkhole); and units with resistivities greater than 300 ohm-m but less than 1000 ohm-m were interpreted as transitional zones probably consisting of wet fractured and/or weathered limestone and clay in-fill. ...
Context 2
... during the interpretation of the resistivity data from site 2, we focused on the area around and underneath the emptied sinkhole. In order to constrain the interpretation of the resistivity data at site 2 with the absence of borehole control, a resistivity profile was completed along an excavated clay-filled sinkhole located 200 m west of the emptied sinkhole ( Figure 6). Based on the interpretation of this resistivity line, units with resistivities in excess of 1000 ohm-m were interpreted as intact limestone; units with resistivities less than 300 ohm-m were interpreted as clay in-fill (or ponded water-clay in-fill in the base of the sinkhole); and units with resistivities greater than 300 ohm-m but less than 1000 ohm-m were interpreted as transitional zones probably consisting of wet fractured and/or weathered limestone and clay in-fill. ...
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The paper presents results of electrical resistivity imaging and engineering geological investigations conducted at the Gereb Segen dam site and reservoir to evaluate water tightness and stability. A programme of 2D resistivity imaging, discontinuity surveying, core drilling and Lugeon testing was conducted to assess the engineering geological perf...
Citations
... ERT can identify low resistivity zones which can be related to the presence of water (allowing for the identification of aquifers, water tables, and groundwater flow patterns), reveal the presence of geological structures (faults, fractures, and bedrock boundaries), and provide valuable information about subsurface porosity and fluid saturation [7,20,25]. ERT can be interpreted in terms of possible air-or water-filled voids and highly saturated volumes, which could be zones of high seepage potential [12,15,[26][27][28]. The IP method provides complementary information to other geophysical methods like electrical resistivity, helping to enhance subsurface characterization and understanding by providing valuable information about the presence of polarizable substances and hydrogeological characteristics of the subsurface [29,30]. ...
Pensacola Dam, operated by the Grand River Dam Authority (GRDA), is a multiple-arch buttress dam constructed in 1940. The dam has little or no existing geophysical reports on the integrity of the dam foundation rock and even less knowledge at depth. Visual inspection indicated evidence of seepage at some arches of the dam. As a pilot study, we conducted a suite of geophysical surveys inside two arches (Arch-16 and Arch-17) and a part of the downstream berm to characterize the dam foundation rock, delineate seepage zones, and identify the most appropriate geophysical methods for temporal monitoring of the dam’s conditions. The geophysical methods included electrical resistivity tomography (ERT), self-potential (SP), multichannel analysis of surface waves (MASW), compressional (P)-wave refraction, and shear (S)-wave reflection. Water samples were collected for geochemical analysis to investigate the source of the seepage flow inside Arch-16. The geophysical results characterized the dam foundation rock into an unsaturated limestone and chert overlying a water-saturated limestone and chert. The ERT profiles indicated that groundwater is rising inside the arches and significantly dropping under the downstream berm, which can be due to the uplift pressure beneath the dam base. Zones of high seepage potential were detected near the buttress walls of the two surveyed arches, which may be related to previous blasting, excavation of the dam foundation, concrete placement, or improper grouting. The geochemical analysis of water samples taken from the artesian wells inside Arch-16 and the Grand Lake revealed different chemical compositions, suggesting that the source of water could be a mixture of groundwater and lake water or lake water interacting with rock and reaching the surface through fractures; however, more sampling and further analysis are required to ascertain the source of the seeps. This study showed that the ERT, SP, and S-wave reflection methods have effectively characterized the dam foundation rock and seepage zones beneath the arches. The study provided a better understanding of the conditions of the dam foundation rock, evaluated the utilized geophysical methods, and determined the optimum geophysical methods that can be used for the characterization and monitoring of the subsurface conditions along the entire length of the dam. In this study, we have demonstrated that the integration of effective geophysical surveys and geochemical analysis yielded optimum results in solving a complex dam safety problem. This strategy promotes the best practice for dam safety investigation.
... The acquired resistivity data will be processed and inverted by Res2DInv software using smoothnessconstrained least squares inversion technique (Loke and Barker 1996). Several the ERT profiles will be acquired near the available boreholes in the community, near the earlier survey locations to constrain the interpretation of the acquired ERT data as demonstrated in Ismail et al., (2012). The acquired ERT survey profiles are expected to aid the characterization of the subsurface geological features and hydrogeological conditions of the aquifers to depths of up 70 meters deep. ...
... This refined hydraulic gradient estimate can then be used to laterally locate a void at or below the depth of investigation of ERT and seismic refraction. A considerable amount of research exists on the detection of subsurface voids and associated features for defense, civil, geotechnical, archaeological, and environmental purposes using seismic refraction, electrical resistivity, and ground penetrating radar methods, including: archaeological purposes for tomb and passageway mapping (Valois et al., 2010;Abbas et al., 2012;Fischanger et al., 2019;Sambuelli et al., 2019), roadbed and concrete void detection (El-Qady et al., 2005;Ismail and Anderson, 2012;De Giorgi and Leucci, 2014), mine addit mapping for residential and commercial development (McCann et al., 1987;Bharti et al., 2016;Abdel Aal, 2017), karstic terrain with sinkholes and caves (Glaser et al., 2005a;Kaufmann et al., 2011;Negri et al., 2015;Sahu and Lokhande, 2015), civil and clandestine tunnel detection (Butler, 2008;McKenna et al., 2011McKenna et al., , 2013Sloan et al., 2015;Schwenk et al., 2016;Wang et al., 2019). However, none of these approaches consider the use of changes in secondary features for diagnostic detection criteria. ...
Discrete deep targets are a significant challenge for most surface-based geophysical techniques, even when considering high property contrasts. Generally, surface-based geophysical methods lose lateral and vertical resolution with depth as a result of poor measurement geometry and increased signal attenuation. The poor measurement geometry can be overcome through use of cross-borehole methods, but lateral localization is still needed for optimal borehole placement. As such, a relatively small, deep void located near the maximum depth of investigation is very unlikely to be detected. Yet, secondary features associated with these voids can be exploited for enhanced detection performance. When voids are located below the groundwater table a significant amount of dewatering and pumping is required to make them a functional passageway. This dewatering not only removes water from the void space but also the surrounding formation, resulting in a much larger, if more diffuse, secondary target: an induced groundwater table gradient. Many geophysical sensing methods are sensitive to subsurface moisture content. Here we implement a two-dimensional (2D) joint-petrophysical mixing-model, using inverted electrical resistivity tomography and inverted seismic refraction models to sense changes in the groundwater table gradient. Results are validated using depth to bedrock, groundwater-surface water information, ground-penetrating radar, and time-domain reflectometry methods. Our initial proof of concept is applied to a shallow area with a significant soil moisture gradient, through different surface soil types and bedrock. The 2D joint-petrophysical mixing-model results were used to generate an estimate of air, moisture, and matrix percent fractions in the investigation area, providing a clear delineation of the groundwater surface.
... These geophysical measurements can be interpreted in 2D, 3D, or 4D (time-lapse). These methods are also used in determining karstic structures, recharge, and discharge dynamics [19][20][21][22][23][24][25][26]. ...
The electrical resistivity tomography method has been widely used in geophysics for many purposes such as determining geological structures, water movement, saltwater intrusion, and tectonic regime modeling. Karstic springs are important for water basin management since the karst systems are highly complex and vulnerable to exploitation and contamination. An accurate geophysical model of the subsurface is needed to reveal the spring structure. In this study, several karst springs in the Gökova Bay (SW, Turkey) were investigated to create a 3D subsurface model of the nearby karstic cavities utilizing electrical resistivity measurements. For this approach, 2D resistivity profiles were acquired and interpreted. Stratigraphically, colluvium, conglomerate, and dolomitic-limestone units were located in the field. The resistivity values of these formations were determined considering both the literature and field survey. Then, 2D profiles were interpolated to create a 3D resistivity model of the study area. Medium-large sized cavities were identified as well as their locations relative to the springs. The measured resistivities were also correlated with the corresponding geological units. The results were then used to construct a 3D model that aids to reveal the cavity geometry in the subsurface. Additionally, several faults are detected and their effect on the cavities is interpreted.
... Nevertheless, exclusively using 2D surveys and 2D data inversions is usually inadequate in delineating laterally continuous structures such as quartz ± carbonate veins which are prevalent in the study area. As such, we posit that using multiple parallel 2D profiles to construct pseudo-3D surveys followed by 3D data inversions enables improved discerning of morphological aspects of potential mineralized zones than can be offered by using 2D data inversions in isolation (e.g., Ismail and Anderson, 2012). The aim of this study is therefore to use pseudo-3D ERI and time-domain IP methods to characterize potentially mineralized zones as well as to determine the geometry of their associated geological structures in Phitshane Molopo area. ...
We used 2D and pseudo-3D induced polarization (IP) in conjunction with electrical resistivity imaging (ERI) data inversion to identify and characterize potential zones of gold mineralization in Phitshane Molopo area. Reports on historic exploration suggest that gold mineralization is associated with quartz and/or carbonate veins that cut across the banded iron formations. The 2D IP/ERI measurements were acquired along ten 300 m long profiles trending northeast southwest, with 15 m line separation and 7.5 m electrode spacing. Thereafter, we inverted the data using the standard Gauss-Newton optimization method to produce 2D and 3D models. Based on a combination of IP and resistivity results, we identified distinct lithological units comprising the mineralized and non-mineralized zones. High chargeability (≥6.86 mV/V) and high resistivity (≥641 Ωm) anomalies were attributed to the presence of disseminated sulfides or gold-bearing quartz and/or carbonate veins that obliquely crosscut (east west trend) the banded iron formation (BIF) units and the intensely silicified BIF units, respectively. Zones exhibiting a combination of low to intermediate chargeability (1.0-6.86 mV/V) and low to intermediate re-sistivity (1.4-641 Ωm) are likely non-sulfidized zones with little/no gold mineralization in the study area. The integrated use of IP and ERI methods was successful in delineating zones that are likely to be hosting disseminated sulphides and/or potentially gold-rich zones in the Phitshane Molopo area, Kraaipan Greenstone Belt.
... A considerable amount of research exists on the detection of subsurface voids and associated features for defense, civil, geotechnical, archaeological, and environmental purposes using seismic refraction, electrical resistivity, and ground-penetrating-radar (GPR) methods, including archaeological purposes for tomb and passageway mapping (Valois et al., 2010;Abbas et al., 2012;Fischanger et al., 2019;Sambuelli et al., 2019), roadbed and concrete void detection (El-Qady et al., 2005;Ismail and Anderson, 2012;De Giorgi and Leucci, 2014), mine adit mapping for residential and commercial development (McCann et al., 1987;Bharti et al., 2016;Abdel Aal, 2017), karstic terrain with sinkholes and caves (Glaser et al., 2005a;Kaufmann et al., 2011;Negri et al., 2015;Sahu and Lokhande, 2015), and civil and clandestine tunnel detection (Butler, 2008;McKenna et al., 2011McKenna et al., , 2013Sloan et al., 2015;Schwenk et al., 2016;Wang et al., 2019). However, none of these approaches considers the use of changes in secondary features for diagnostic detection criteria. ...
Submitted to GEOPHYSICS: Special Issue on Shallow Void, Tunnel, and Other Anomaly Detection
ABSTRACT: Discrete deep targets are a significant challenge for most surface-based geophysical techniques, even when considering high property contrasts. Generally, surface based geophysical methods lose lateral and vertical resolution with depth as a result of poor measurement geometry and increased signal attenuation. The poor measurement geometry can be overcome through use of cross-borehole methods, but lateral localization is still needed for optimal borehole placement. As such, a relatively small, deep void located near the depth of investigation is very unlikely to be detected. Yet, secondary features associated with these voids can be exploited for enhanced detection performance. When voids are located below the groundwater table a great deal of dewatering and pumping is required to make them a functional passageway. This dewatering not only removes water from the void space but also the surrounding formation, resulting in a much larger, if more diffuse, secondary target: an induced groundwater table gradient. Many geophysical sensing methods are sensitive to subsurface moisture content. Here we demonstrate a multi-method geophysical sensing approach for detecting changes in the groundwater table gradient using electrical resistivity, supplemented with seismic and ground penetrating radar methods.
... The depth of investigation is a function of the spread length employed (electrode spacing times the number of electrodes) and varies as a function of subsurface electrical resistivities (Loke, 1994). The maximum depth of investigation is typically of the order of 0.2 times the total spread length (Bernard, 2003;Ismail and Anderson, 2012). In this study, a 10 m electrode separation was used in order to achieve a maximum investigation depth of approximately 100 m. ...
... The study involved deployment of equally spaced parallel 2D profiles along which electrical resistivity data were acquired to enable the generation of 2D inverse subsurface models. Consolidation of these parallel 2D profile datasets generated 3D horizontal sections to illustrate the distribution and variation of the subsurface electrical resistivity values along horizontal (x and y) and vertical (z) directions (Ismail and Anderson, 2012). The distinction of subsurface electrical resistivity values has been presented as 2D inverse resistivity model, 3D horizontal (x-y) sections and 3D volumetric isosurfaces across the study area. ...
We used 2D and 3D electrical resistivity imaging (ERI) data inversion to locate and characterize the coal seams in Mmamabula Coalfield. The 2D ERI data inversion usually assumes that subsurface geological units (e.g. coal seams) are infinitely continuous in the direction perpendicular to the profiles. However, this assumption might be violated due to the heterogeneous nature of fluvial/deltaic environments. The lateral variation of the subsurface material can be effectively determined in 3D ERI inversion models. In this study, 2D ERI data were acquired along ten parallel profiles trending north-south, then inverted to produce 2D and 3D models. From the 2D ERI inversion results, we observed that the shallower coal seam occurs around a consistent depth of 13.6 m whereas the second observable coal seam occurs at variable depths including at 50 m and 60 m along the two profiles. Discontinuities in coal seams were also identified. However, the information provided by 2D data inversion in such an environment is insufficient to determine the geometry of coal seams as well as to produce accurate and precise resource estimates for future exploitation. As an alternative, 3D data inversion gives better insight on the subsurface geology complexity and significantly resolves the geometry of coal within the study area. The presented 3D inversion results indicate that coal seams are intermittent and alternate well with other coexisting sedimentary units. We also deduced that they trend east-west and are split and adjoined in some areas along the north-south direction. Overall, 3D data inversion result resolves the elongated coal seams in Mmamabula Coalfield and reveals additional information that cannot be determined on 2D ERI inversion results.
... Geophysical methods that are commonly used for sinkhole investigation include seismic refraction [5], gravimetry [6], ground-penetrating radar [7][8][9][10], electrical resistivity tomography [11][12][13][14][15][16][17][18][19], and multichannel analysis of surface waves [20,21]. Electrical resistivity tomography (ERT) is commonly used in the state of Missouri to investigate the shallow subsurface (depths < 60 m) in karst terrain because the subsurface karst features are generally characterized by high resistivity value contrasts [22]. ...
... This implies that the intersection of the three joint sets is likely a point where water ponded and then infiltrated to the subsurface. Therefore, from the pseudo-3D ERT investigation results and other related studies in the region [4,22], a 3D model depicting the formation and development process of the sinkhole is developed (Figure 11). The formation and development of the sinkhole involved the following stages of processes: (i) the higher susceptibility for weathering and erosion along solution-widened joint sets resulted in the development of elongated depressions and saddles as a surface expression of the joint sets which in turn makes the joint sets a preferential pathway for surface water flow, (ii) ponding of water at the intersection of the three joint sets and followed by a subsequent infiltration and percolation of water, (iii) piping of clay/fine-grained soils and associated subsidence and minor collapse of residual soils. ...
Conventional 2D electrical resistivity tomography (ERT) data were acquired along 16 parallel traverses spaced at 6.1 m (20 ft) intervals across a karst sinkhole site in Greene County Missouri. The acquired ERT data were processed as both 2D data and pseudo-3D data. Based on the correlation with the available core hole control, multichannel analysis of surface waves (MASW) data and field observations, it is concluded that the subsurface structure of the sinkhole is more reliably imaged on the pseudo-3D dataset than in the 2D dataset. The interpretation results of the pseudo-3D ERT indicated that the sinkhole developed at the intersection of three vertical solution-widened joint sets.
... The L2 shows various resistivity range from 190 -300 Ωm to between 750 -1,500 Ωm among the resistivity lines. This layer was interpreted as transition layer which its composition ranges from soil (loam) to bedrock that has resistivity value between 105 -900 Ωm (Ismail & Anderson, 2012), moderate -slightly weathered limestone (Zeinab, 2013), till fresh limestone (Ismail & Anderson, 2012;Reynolds, 2011;Stepišnik, 2008;Palacky, 1987). Most of L3 pseudo-section shows Based on Gibson et al. (2004), Mitrofan et al. (2007), Chalikakis et al. (2011), Ismail & Anderson (2012), and Martínez-Moreno (2014, the near-infinite resistivity of air can display higher resistivity value compared to the surrounding. ...
... The L2 shows various resistivity range from 190 -300 Ωm to between 750 -1,500 Ωm among the resistivity lines. This layer was interpreted as transition layer which its composition ranges from soil (loam) to bedrock that has resistivity value between 105 -900 Ωm (Ismail & Anderson, 2012), moderate -slightly weathered limestone (Zeinab, 2013), till fresh limestone (Ismail & Anderson, 2012;Reynolds, 2011;Stepišnik, 2008;Palacky, 1987). Most of L3 pseudo-section shows Based on Gibson et al. (2004), Mitrofan et al. (2007), Chalikakis et al. (2011), Ismail & Anderson (2012), and Martínez-Moreno (2014, the near-infinite resistivity of air can display higher resistivity value compared to the surrounding. ...
... This layer was interpreted as transition layer which its composition ranges from soil (loam) to bedrock that has resistivity value between 105 -900 Ωm (Ismail & Anderson, 2012), moderate -slightly weathered limestone (Zeinab, 2013), till fresh limestone (Ismail & Anderson, 2012;Reynolds, 2011;Stepišnik, 2008;Palacky, 1987). Most of L3 pseudo-section shows Based on Gibson et al. (2004), Mitrofan et al. (2007), Chalikakis et al. (2011), Ismail & Anderson (2012), and Martínez-Moreno (2014, the near-infinite resistivity of air can display higher resistivity value compared to the surrounding. This anomaly can be interpreted as small air void as an open air void spaces or caves. ...
Structural pattern in Luconia, Sarawak
... Nevertheless, exclusively using 2D surveys and 2D data inversions is usually inadequate in delineating laterally continuous structures such as quartz ± carbonate veins which are prevalent in the study area. As such, we posit that using multiple parallel 2D profiles to construct pseudo-3D surveys followed by 3D data inversions enables improved discerning of morphological aspects of potential mineralized zones than can be offered by using 2D data inversions in isolation (e.g., Ismail and Anderson, 2012). The aim of this study is therefore to use pseudo-3D ERI and time-domain IP methods to characterize potentially mineralized zones as well as to determine the geometry of their associated geological structures in Phitshane Molopo area. ...
