Electrical Resistivity Tomography Results Research Articles

A Geophysical Investigation in Which 3D Electrical Resistivity Tomography and Ground-Penetrating Radar Are Used to Determine Singularities in the Foundations of the Protected Historic Tower of Murcia Cathedral (Spain)

This study presents a procedure in which 3D electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) were used to determine singularities in the foundations of protected historic towers, where space is limited due to their characteristics and location in highly populated areas. This study was carried out on the Tower of the Cathedral “Santa Iglesia Catedral de Santa María” in Murcia, Spain. The novel distribution of a continuous nonlinear profile along the outer and inner perimeters of the Tower allowed us to obtain a 3D ERT model of the subsoil, even under its load-bearing walls. This nonlinear configuration of the electrodes allowed us to reach adequate investigation depths in buildings with limited interior and exterior space for data collection without disturbing the historic structure. The ERT results were compared with GPR measurements and with information from archaeological excavations conducted in 1999 and 2009. The geometry and distribution of the cavities in the entire foundation slab of the Tower were determined, verifying the proposed procedure. This methodology allows the acquisition of a detailed understanding of the singularities of the foundations of protected historic towers in urban areas with limited space, reducing time and costs and avoiding the use of destructive techniques, with the aim of implementing a more efficient and effective strategy for the protection of other tower foundations.

Characterization and Quantification of Dam Seepage Based on Resistivity and Geological Information

Dam seepage significantly poses a serious threat to both the reservoir safety and the ecological health of the surrounding area. Characterizing and quantifying seepage zones is essential for effective risk mitigation and reinforcement measures. In this study, Electrical Resistivity Tomography (ERT) was applied to detect seepage on a reservoir dam. The ERT survey included three survey lines along the dam. The results indicated low resistivity in seepage zones, showing a distribution extending to the deep section in the middle of the dam and shallow section on both sides of the dam. The reservoir water came out to the ground surface in the downstream from seepage zones. Five seepage models were constructed to quantify seepage based on geological information. The models were further modeled based on the ERT results. Simulated results revealed the annual seepage of the reservoir is 78,880.16 m3. However, 75.5% of the total seepage is contributed by a region representing 50% of the dam. This concentrated seepage should draw the attention of future safety monitoring and reinforcement efforts. This study combines geophysics, geological, and numerical simulation to quantify dam seepage. This allows for the development of more scientifically sound solutions for preventing seepage and improving drainage ability in reservoir dams.

Investigating seawater intrusion and salinization using the integration of hydrochemical and geoelectrical techniques

Seawater intrusion poses a significant environmental threat to water resources, agriculture, and ecosystems. We investigate the extent of seawater intrusion and salinization in the eastern coastal aquifers of Saudi Arabia. Hydrochemical measurements and electrical resistivity tomography (ERT) techniques are used to assess groundwater quality and the subsurface extension of seawater intrusion. Two resistivity profiles, 475 m long each, are analyzed to gain insights into the subsurface geology and seawater intrusion. The inversion of the recorded resistivity data reveal four distinct subsurface layers. The uppermost layer consists of surficial deposits, followed by a sandy seawater intrusion layer, beneath which lies a marl layer, and at the bottom, a dolomitic limestone layer representing the brackish-water aquifer. The ERT results are integrated with hydrochemical and hydrogeologic results from 12 wells to overcome the limitations of the ERT. The findings of this study would facilitate the development of efficient mitigation strategies and sustainable management of the groundwater resources in the study area or similar coastal regions affected by seawater intrusion. Understanding and delineating the boundary between saline and fresh water is crucial for safeguarding water resources for agricultural purposes, preserving ecosystem health, and ensuring the long-term sustainability of water supplies in coastal areas.

Electrical Resistivity Changes During Heating Experiments Unravel Heterogeneous Thermal‐Hydrological‐Mechanical Processes in Salt Formations

AbstractRock salt is considered a suitable medium for the permanent disposal of heat‐generating radioactive waste due to its isolation properties. However, excavation damage and heating induce complex and heterogeneous thermal‐hydrological‐mechanical (THM) processes across different zones. Quantifying this heterogeneity is crucial for accurate long‐term performance assessment models, but traditional methods lack the necessary resolution. This study employs 4D electrical resistivity tomography (ERT) monitoring during controlled heating experiments in a salt formation to unravel the spatiotemporal dynamics of THM processes. Advanced time‐lapse inversion and clustering analysis quantify subsurface properties and map the heterogeneity of THM dynamics. The ERT results can estimate subsurface properties and delineate the damaged and intact zones, enabling appropriate parameterization and representation of processes for long‐term modeling. This approach may be used in further improving the predictive models and ensuring the safe long‐term disposal of radioactive waste in rock salt.

Thickness Estimation of the Soil‐Sedimentary Cover Inside Causewayed Enclosures to Locate an Occupation Layer: Map of the Archaeological Potential of the Neolithic Causewayed Enclosure of Le Pontet

ABSTRACTThe western centre of France is one of the richest regions of Western Europe in terms of causewayed enclosures from the Neolithic period. To date, more than 300 such sites have been identified. Most causewayed enclosures in the region range in size from some hectares to over 10 ha. Exhaustive excavation of such sites is rarely performed because such operations are both financially expensive and time intensive. Completing an exhaustive excavation of these sites is also extremely complicated due to their complexity. Recording the most complete possible site plan is a major challenge for optimizing excavation. Traditionally, aerial photography has been the primary method used for delineating causewayed enclosure plans. A magnetic survey can also provide complementary information. Magnetic imaging reveals both enclosure ditches and internal features (pits, postholes, etc.) quickly and with high spatial resolution. At some sites, occupation layers dating from the time of enclosure may be preserved and contain archaeological artefacts or small features in situ. This article proposes a protocol for locating a Neolithic occupation layer inside a Neolithic causewayed enclosure. To locate the areas where this layer is likely to be present, a map of the archaeological potential of the Le Pontet site was produced based on a thickness map of the soil‐sedimentary cover. This map was created by combining an apparent electrical resistivity map, the results of electrical resistivity tomography, an orthophotograph with contrasting cropmarks and the results of dynamic cone penetration tests. To validate the archaeological potential map, an excavation campaign was conducted in 2020 to investigate several sectors; the aim was to prove the presence of the occupation layer and study the pedo‐sedimentary stratigraphy of the site.

Exploration on electrical resistance tomography in characterizing the slurry spatial distribution in cemented granular materials

This study investigated the application of electrical resistance tomography (ERT) in characterizing the slurry spatial distribution in cemented granular materials (CGMs). For CGM formed by self-flow grouting, the voids in the accumulation are only partially filled and the bond strength is often limited, which results in difficulty in obtaining in situ samples for quality evaluation. Therefore, it is usually infeasible to evaluate the grouting effect or monitor the slurry spatial distribution by a mechanical method. In this research, the process of grouting cement paste into high alumina ceramic beads (HACB) accumulation is reliably monitored with ERT. It shows that ERT results can be used to calculate the cement paste volume in the HACB accumulation, based on calibrating the saturation exponent n in Archie’s law. The results support the feasibility of ERT as an imaging tool in CGM characterization and may provide guidance for engineering applications in the future.

Mapping Permafrost Variability and Degradation Using Seismic Surface Waves, Electrical Resistivity, and Temperature Sensing: A Case Study in Arctic Alaska

AbstractSubsurface processes significantly influence surface dynamics in permafrost regions, necessitating utilizing diverse geophysical methods to reliably constrain permafrost characteristics. This research uses multiple geophysical techniques to explore the spatial variability of permafrost in undisturbed tundra and its degradation in disturbed tundra in Utqiaġvik, Alaska. Here, we integrate multiple quantitative techniques, including multichannel analysis of surface waves (MASW), electrical resistivity tomography (ERT), and ground temperature sensing, to study heterogeneity in permafrost’s geophysical characteristics. MASW results reveal active layer shear wave velocities (Vs) between 240 and 370 m/s, and permafrost Vs between 450 and 1,700 m/s, typically showing a low‐high‐low velocity pattern. Additionally, we find an inverse relationship between in situ Vs and ground temperature measurements. The Vs profiles along with electrical resistivity profiles reveal cryostructures such as cryopeg and ice‐rich zones in the permafrost layer. The integrated results of MASW and ERT provide valuable information for characterizing permafrost heterogeneity and cryostructure. Corroboration of these geophysical observations with permafrost core samples’ stratigraphies and salinity measurements further validates these findings. This combination of geophysical and temperature sensing methods along with permafrost core sampling confirms a robust approach for assessing permafrost’s spatial variability in coastal environments. Our results also indicate that civil infrastructure systems such as gravel roads and pile foundations affect permafrost by thickening the active layer, lowering the Vs, and reducing heterogeneity. We show how the resulting Vs profiles can be used to estimate key parameters for designing buildings in permafrost regions and maintaining existing infrastructure in polar regions.

Detecting soil water redistribution in subsurface drip irrigated processing tomatoes using electrical resistivity tomography, proximal sensing and hydrological modelling

In this study, multiple soil-plant-atmosphere continuum (SPAC) monitoring methodologies, including electrical resistivity tomography (ERT), proximal thermal sensing techniques, and micrometeorological data, were combined with two-dimensional (2-D) soil hydrological modelling using HYDRUS 2-D to explore the soil water redistribution, and infer the relative crop water status in a subsurface drip irrigated (SDI) processing tomato field located in California (Yolo County, USA). Specifically, time-lapse ERT surveys were performed at two transects distributed parallel and perpendicular, respectively, to the SDI line, during an irrigation event. The ERT results were compared to HYDRUS 2-D outputs and the relative differences were explained in the form of local heterogeneities in electrical resistivity (ER) changes, as a proxy for soil water content (SWC) variations. Concurrent simultaneous soil wetting and root water uptake during the last irrigation event of the season caused negligible changes in ER in the active root zone. Slight differences in ER were observed in the top 20 cm along the dripline, confirming that the emitter spacing is small enough to create a wetted strip along the processing tomato bed. These changes were also compared to SWC values measured with time domain reflectometry soil moisture sensors. A comparison between HYDRUS 2-D and ERT confirmed negligible changes in ER during irrigation due to simultaneous wetting and root water uptake processes. In addition, a good correlation was observed between the proximal sensed and the ERT results. Finally, the findings of this study underscore the necessity of using multiple methods for improving our knowledge of the SPAC system under real field conditions.

Assessing the risk of slope failure to highway infrastructure using automated time-lapse electrical resistivity tomography monitoring

Electrical resistivity tomography (ERT) monitoring provides time-lapse images of the subsurface. These images can be used to assess spatiotemporal variation in moisture content, which is a key driver of slope failure, making ERT monitoring an effective tool to evaluate precursory conditions of failure. This work presents the results of ERT monitoring on a slope above a major highway located on the border between England and Wales. During highway construction in the 1960s the slope was subject to several large landslide events which resulted in the re-design of the carriageway and installation of engineered mitigation measures. A section of the slope known as the ‘partially slipped area’ exhibited partial displacement during this time but did not progress to full slope failure, and therefore presents an ongoing risk to the highway, even though it does not experience ongoing displacement. An ERT monitoring system was installed across this area to monitor subsurface variations in moisture content. The results show a complex pattern of subsurface moisture dynamics within the partially slipped area when compared to the adjacent area of stable slope. This is most likely a result of the uneven and hummocky terrain in the partially slipped area and its effects on rainfall infiltration, storage and drainage, combined with the displacement-induced jointing present in the underlying sandstone units. The ERT results are used to assess the volume of unstable ground, placing the volume at the upper end of estimates from previous studies. Furthermore, analysis of the ERT dataset for surface displacements shows no movement at the site, which is confirmed by analysis of differential LiDAR plots and ground motion data derived from InSAR. This study demonstrates the application of ERT monitoring on a low activity, high risk slope, highlighting the need to understand subsurface processes at the slope-scale to inform long-term slope management.

Subsurface structures of solution dolines inferred from electrical resistivity tomography: A hypothesis on the evolutionary process of solution dolines at the Akiyoshi-dai Plateau, southwest Japan

The evolution of solution dolines is regulated by carbonate dissolution mediated by water and CO2. The subsurface structure influences the evolutionary pattern of the dolines. Despite the significant effects of enlarged joints or shafts on the development of solution dolines, a few studies have identified the subsurface structures of multiple solution dolines. To this end, we utilized 2-D electrical resistivity tomography (ERT) at 15 dolines and an outcrop in the Akiyoshi-dai Plateau, Japan, which is composed of massive and fractured limestone lithology. The results of ERT exhibited the following: (i) a similar range for electrical resistivity in parallel to the topographic relief; (ii) an increase in resistivity with depth, and; (iii) a low resistivity zone characterized by <400 Ωm, at shallow areas. Some electrical resistivity distributions exhibited high resistivity zones that were vertically split by low or intermediate resistivity zones. Our results and interpretation revealed that the main shafts, which play a substantial role in the evolution of solution dolines, can be formed around the doline bottoms rather than in their central sectors. We propose a hypothesis that can better account for the subsurface structures and the development of dolines in Akiyoshi-dai. Our hypothesis suggests that the role of main shafts in the evolution of solution dolines can be superseded by another influential joint system with a potential shaft during their evolution, resulting in the ubiquity of main shafts beneath the doline bottoms. This hypothesis would further our understanding of the intricate role of shafts in the evolution of karst systems involving solution dolines.

Sub-surface configuration in the northern part of Lembang groundwater basin recharge area

Lembang groundwater basin has an area of 209 km2. Increased tourism activities in the Lembang Groundwater Basin require sufficient groundwater resources to support the sustainability of these tourism activities. The purpose of this study was to analyze the hydrostratigraphy of the groundwater recharge zone of the Lembang groundwater basin in the Cikole-Lembang. Electrical Resistivity Tomography (ERT) with dipole–dipole electrode array and seismic refraction was used to analyze the hydrostratigraphy. The results of ERT and seismic refraction inversion show that Tangkubanparahu Pyroclastic Fall 2 can be characterized as aquifers. This layer consists of low (123–292 Omega m) and intermediate (293–700 Omega m) resistivity value and also has low (300–1350 m/s) to medium (2700–1350 m/s) velocity. Tangkubanparahu lava (Tl) layer has a high resistivity value (701–3875 Omega m) and high (1350–2999 m/s) velocity. The Tangkubanparahu Pyroclastic Fall 1 has a resistivity of 300–700 ohms. Tangkubanparahu (Tl) lava deposits can be characterized as fracture aquifer and impermeable layers in the Tangkubanparahu volcanic hydrogeological system depend on the historical structural geology event.

Integrated Geophysical and Geochemical Analyses for Assessment of Potential Coal Prospects in Tirah Area, Khyber Pakhtunkhwa, Pakistan

This study presents a comprehensive investigation of the Paleocene coal in the Tirah area, District Khyber, Khyber Pakhtunkhwa, Pakistan, utilizing onsite Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) experiments combined with geochemical analyses of obtained coal-rock samples. ERT and GPR profiles, along with geochemical data, were collected and meticulously analyzed to assess the potential and quality of coal seams based on coal ranking, aiming to delineate their spatial distribution and future exploitation prospects. The study reveals a wide range of resistivity values, spanning from 8.93 Ωm to 2472 Ωm. The uppermost layer, comprising silt and clay with water saturation, exhibits resistivity values ranging from 8.93 Ωm to 50 Ωm. The subsequent stratum, characterized by wet sandstone with minor shale and clay, has resistivity values between 50 Ωm and 95.3 Ωm. Significantly, the zone with resistivity values between 95.3 Ωm and 800 Ωm is identified as the probable host of the coal seams. Based on the results, the coal seams are estimated to exist at depths ranging from 14 to 23 m, with resistivity values between 95.3 Ωm and 800 Ωm. GPR results further corroborate these findings, revealing coal-bearing strata at various depths, thus confirming the ERT results. Additionally, proximate and ultimate analysis provided insights into the quality of the coal, with average concentration values of moisture content (6.95%), ash content (22.12%), volatile matter (28.55%), fixed carbon (42.40%), carbon content (55.35%), hydrogen (4.7%), nitrogen (0.95%), sulfur (4.82%), and oxygen (10.06%). Comparative analyses of the obtained results with local coals from the Salt Range in Punjab, Pakistan, and coal from Ogboyaga, Nigeria, confirm that the studied coal ranks as sub-bituminous. This comprehensive assessment offers valuable insights into the potential and quality of Paleocene coal in the studied region and is applicable to other areas with similar geological settings.

Reconstruction of Fault Architecture in the Natural Thermal Spring Area of Daruvar Hydrothermal System Using Surface Geophysical Investigations (Croatia)

The sustainable utilization of geothermal energy mostly depends on the characteristics of the geothermal resource from which it is extracted. Among others, detailed geological modeling is a key factor for estimating the potential of a geothermal resource. This research focuses on the modeling and reconstruction of the geological setting of the Daruvar thermal spring area using geophysical techniques. An integrated geophysical approach based on electrical resistivity tomography (ERT) and both active and passive seismic (MASW and HVSR) methods was used. Based on ERT results and the stratigraphic logs of the wells in Daruvar, three resistivity layers/geological units were identified. The deepest layer with resistivity &lt; 150 Ωm is the Triassic carbonate that constitutes the thermal aquifer. Sharp lateral variations in the resistivity distributions within the bedrock were interpreted as fault damage zones saturated with thermal waters. Integrating the results of the seismic methods, the thickness of the first seismic layer that corresponds to the Quaternary cover was estimated from 5 to 20 m. Here, results of the geophysical investigations were combined into a 3D geological model highlighting the occurrence of subvertical N-S and E-W trending faults in the Daruvar spring area. The N-S-trending fault was interpreted as a fault plane parallel to the regionally mapped Daruvar fault. This fault juxtaposes the Triassic carbonate complex of the thermal aquifer with a Neogene sedimentary sequence of significantly lower permeability. Neogene–Quaternary tectonic activity further increased the fracturing and the permeability field in the Daruvar spring area, as proven by the smaller scale E-W faults and the well logs. This fracture network permits a quick upwelling of thermal fluids resulting in thermal springs with temperatures up to 50 °C. This work proves that the construction of a detailed geological model is crucial for assessing the reservoir and fault geometries in thermal systems hosted in fractured carbonate rocks.

Evaluation of ground surface deformation in discontinuous permafrost regions along the China-Russia Crude Oil Pipelines in Northeast China using InSAR and ground surveys

Adequately and timely measuring and evaluating the ground surface deformation (GSD) are keys to the prudent mitigation of frost hazards of foundation soils and thus to the safe and cost-effective operation of oil pipelines in permafrost regions. Thus, it is crucial to accurately evaluate the GSD along the route of China-Russia Crude Oil Pipelines (CRCOPs) for a better understanding of frequent and substantial (differential) frost heave and thaw settlement of pipeline foundation soils in permafrost regions. In this study, GSDs along the CRCOPs from Xiufeng town to Jinsong town, northern Heilongjiang Province were monitored in discontinuous permafrost regions in the northern Da Xing'anling Mountains, Northeast China. The Sentinel-1B images from 2017 to 2021 and the Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) technology were used in combination with the Geographical Detector (GeoDetector) for identifying the drivers for GSDs and with ground survey data for validation analysis of GSD at chosen sites (e.g., MDX304 and others). InSAR results show that most of the annual GSD rates along the CRCOPs range from −10 to 0 mm/a, with larger deformation rates in Ta’he, Cuigang, and Jinsong. GeoDetector analysis shows that latitude and soil types are the most important contributors to GSDs along the CRCOPs, and; GSDs are closely related to elevation, ground temperature at the depth of 1 m (GT1m), normalized difference vegetation index (NDVI), annual precipitation (AP), and slope aspects. Analyses of ground and oil-flow temperatures and survey results of electrical resistivity tomography (ERT) show that permafrost along CRCOPs has been degrading and thawing, resulting in thaw settlement, consolidation, and deformation of pipeline foundation soils and underlying/lateral permafrost layers and subsequently, the ground surface subsidence. This study provides key deformation data for the assessment and mitigation of frost hazards along the CRCOPs.

Application of the electrical resistivity tomography in groundwater detection on loess plateau

Agricultural irrigation of the South Jingyang tableland in Shaanxi Province, China has led to a continuous rise of the groundwater level and has triggered a series of loess landslides, thereby seriously affecting the life and property safety of local residents. Research shows that the major cause of the landslide in the loess layer of the South Jingyang tableland is the rising groundwater level. Therefore, the research on the formation mechanism of landslide in this area should include the investigation of the stratigraphic structure and groundwater level distribution characteristics. On this basis, a series of approaches, such as electrical resistivity tomography (ERT), borehole, and laboratory tests, was carried out on the South Jingyang tableland, and the groundwater level distribution and stratigraphic structure in the study area were determined. The qualitative relationship between resistivity value and water content at different depths was detected using the inversion results of ERT and borehole data. Through laboratory tests, the quantitative relationship between resistivity values under different water contents was established. The precise depth of the groundwater level was inferred by connecting the qualitative relationship with the quantitative relationship, and then a detailed 3D geological model was established by linking the inversion results of ERT with the field borehole lithology data and geological survey data. The detection results show that when the qualitative and quantitative analyses of the ERT inversion results were combined, the distribution of the groundwater level was accurately judged. The ERT is effective in reflecting the stratigraphic structure and hydrological characteristics of the Loess Plateau, and its potential as a supplementary technology for detecting the groundwater level is reasonable. This study addresses the limitation and inaccuracy in determining the stratum structure and groundwater level by solely relying on borehole information or ERT. The established 3D geological model not only provides a basis for the study of groundwater table fluctuation, but also a technical guidance for the stability evaluation of loess slope, landslide prediction, and early warning in the study area.

Subsurface Investigation on Federal Route Failure at Pengkalan Raja, Pontian, Johor

Road settlement is one of the major problems that often occurs in soft soil ground areas. The combination of destructive test method (trial pit, Standard Penetration Test (SPT) and borehole) and non-destructive method by using seismic refraction, electrical resistivity tomography (ERT) and ground penetrating radar (GPR) were performed to identify the factor causing the tension cracks and road differential settlement. The study area selected is at Section 39 to 50, Federal Route (FT005) Johor Bahru to Malacca (Pengkalan Raja, Pontian, Johor) because of the severe road condition which may cause an accident to road user. This paper presenting the result of destructive and a non-destructive test. From results of borehole, seismic, and ERT, the road was underlaid by 7-12m of a soft compressible layer. The GPR image showed the existing of concrete slab below the road has deviated from its original position and may not function as a foundation of road. In conclusion, the combination of destructive and non-destructive method is best approach in identifying the underground failure because it is the fastest solution, economical and suitable in area of high volume of traffic.

РЕСУРСЫ БАРИТА, ЦВЕТНЫХ И БЛАГОРОДНЫХ МЕТАЛЛОВ В ХВОСТОХРАНИЛИЩЕ ТАЛМОВСКИЕ ПЕСКИ: МИНЕРАЛОГО-ГЕОХИМИЧЕСКИЕ И ГЕОФИЗИЧЕСКИЕ ДАННЫЕ

The estimation of barite resources (BaSO4) as well as resources of metals (Au, Ag, Cu, Zn, Pb) was made with the help of modern precision research methods at the Talmovskie Peskitailing dump (Salair Ridge). Processed ores at the tailings dump are characterized by a large vertical heterogeneity; primary (substantially non-oxidized) and oxidized sands are distinguished with Bacontents of 39 and 35 %, respectively. Grain-size classes lower 0.25 mm are the most productive from the point of view of barite. Such occurrence forms and typomorphic characteristics as color, morphology, grain size distribution, mineral paragenesis and inclusions are described for barite and metals. Geoelectric measurements have shown a horizontally-layered structure of the tailing dump, where the values of ER (21–50 Ohm•m) corresponds to the friable oxidized matter of low humidity (up to the depth of 70 cm), 0.1–20 Ohm•m – to primary, substantially non-oxidized matter. According to the results of electrical resistivity tomography, the volumes of both media were determined (48,000 and 53,000 cu), that, in comparison with the data on the concentrations of Ba, Pb, Cu, Zn, Au, Ag in them, made it possible to calculate the resources of metals within the studied area and, in some approximation, in the entire storage.

Combined application of electrical resistivity tomography and multi-channel analysis of surface waves methods in the tunnel detection: A case study from Kocaeli University Campus Site, Turkey

In this study, two-dimensional electrical resistivity tomography (ERT) and one-dimensional multi-channel surface waves analysis (MASW) methods conducted on the surface were used to examine the location of a creek drainage tunnel constructed for the campus road and its relationship with the surrounding geological units in the Kocaeli University campus site results are presented. As it is known, geophysical studies conducted from the surface are generally applied in terms of feasibility and to determine the geological problems in the route of tunnels before the tunnel construction. Geophysical studies revealing the tunnel and associated underground characteristics in a completed tunnel are very limited. Therefore, this study aims to describe the general character of the tunnel and its surroundings in the subsurface, with measurements made by using surface geophysical methods (ERT and MASW) over the tunnel. In the ERT studies, four different arrays were examined to resolve this problem. These are, respectively; Wenner-alpha, −beta, −gamma and Schlumberger. On the tunnel problem here, a possible model similar to the geological structure dominated by the marl layers in the region was synthetically designed with these arrays. In this study, the effectiveness of all these arrays against the problem was tested. Then, by evaluating the data collected from the field, the appropriate array testing was examined for the real problem. In the context of these studies, the results of the MASW studies conducted between 24 and 46 m of the ERT line were compared with the ERT data to reveal the geological phenomena in the tunnel and its vicinity. The resistivity values (ρ) in the 2D electrical resistivity models obtained from ERT have values of ρ > 80 Ωm in the tunnel section and ρ < 55 Ωm in the materials surrounding the tunnel. The medium-high resistivity values characterize the earthfill layer. In MASW studies, it was revealed that shear wave velocity (Vs) values in the tunnel were lower (<250 m/s) and higher (250 and 500 m/s) in the materials surrounding the tunnel. Deep below the tunnel and in the northeastern part of the field, the ground has relatively higher shear wave velocities (Vs > 400 m/s). Because of the comparison of ERT and MASW results, it was revealed that both methods showed good agreement in terms of tunnel depth and size. While the different sequences used in the ERT study generally provided successful results in identifying the tunnel, different model results were revealed in the surrounding earthfill, weathered and intact marl layers. The MASW results, on the other hand, gave more successful results than expected in determining the location of the tunnel. Because of the comparison of both methods, it has been shown that the use of the ERT and MASW methods together can provide more effective results in examining the location of buried tunnels and their relationship with the surrounding geological units.

Mapping and monitoring seasonal and tidal effects on the salt-freshwater interface using electrical resistivity tomography techniques

Understanding the salt-freshwater interface (SFI) migration in the coastal aquifers is of great significance for the study of seawater intrusion (SI). The electrical resistivity tomography (ERT) method in combination with the physicochemical characteristics of groundwater were used to map and capture the SFI change in the dry and wet seasons. And the west coast of Longkou city, Shandong province, China was taken as an example. And the physicochemical characteristics of groundwater mainly analyzed Cl− concentrations, TDS and EC values. Four monitoring locations, 1200 (W4), 2100m (W3), 2600m (W2) and 3200m (W1) away from and perpendicular to the west coastline, were used to collect groundwater samples and conduct continuous ERT surveys in dry and wet seasons of 2020. The SFI was captured with continuous 24-h tidal cycle and 15-day spring-neap tidal cycle. Analysis of the groundwater samples showed that the SFI was approximately located between the W2 and W3, and the groundwater levels for the four monitoring locations were higher in the wet season than that in the dry season. The ERT results were strongly supported via the Cl− concentrations, TDS, EC values and the groundwater level in the dry and wet seasons. And the ERT results indicated that the SFIs were located about 2562m and 2558m away from the coastline in the dry and wet seasons, which means the most inland part of the interface. Due to the delay effects of the 24-h high and low tidal cycle and different tidal amplitudes in 15-day spring-neap tidal cycle, the SFI retreated to seaward in high tide and spring tide, while it intruded to inland in the low tide and neap tide. Continuous monitoring surveys using the ERT had been proven to be suitable to map and capture the SFI change in the west coast of Longkou city in this study. This study can qualitatively and semi-quantitatively evaluate the location of SFI in coastal area, and the determination of the possible farthest SFI location on neap tide and low tide is helpful for the groundwater resources management and SI prevention.

Archaeo-Geophysical Investigation of Simulated Settlement: Case Study in a Part of Basement Complex of Nigeria

We have used the 2D Vertical Electrical Sounding method and Electrical Resistivity Tomography (ERT) method to map buried artifacts in a simulated settlement, and have shown how the geographical information system could aid future research. Stones, bones, metals, cement bricks, and cement-and-sand mixtures were locally constructed to fit into an African-archaeological setting. Parameters such as the materials’ composition, width, electrical resistivity, height, age, and depth of burial were taken into account before this investigation. The integrated methods employed collected data over the study area along with a pre-calculated dense network of parallel profiles. A total of eight (8) VES points and six (6) ERT profiles were obtained. The analysis and interpretation revealed that the VES yielded poor resolution for small-scale archaeological anomalies and could only be used fractionally for prospection whilst the ERT results were more suitable for delineation due to the high spatial resolution they provided. The field values correlated with other literature values. This research suggests that rapid significant prospection information, of any area under investigation, can easily be obtained from Google Earth time-lapse images and that its results will serve as a thorough reconnaissance in the search of prehistoric activities.