Geoelectrical Imaging Research Articles

Application of Integrated Geotechnical Investigation and 2D-Geoelectrical Tomography for Engineering Site (A Case Study of Ugbomro)

The current study was designed to find a permanent solution to engineering challenges involving building cracks and associated structural failures. An integrated 2-dimensional geo-electric tomography and geotechnical investigation were carried out in Ugbomro, Effurun, Delta state to aid in unravelling the causes of frequent building collapses in this fast-developing suburb, located in the Niger Delta region of Nigeria. Soil samples obtained for geotechnical investigation were tested and analysed to complement the resistivity survey using a combination of the Wenner and Dipole-Dipole arrays. This integrated approach resulted in more comprehensive data analysis and interpretations to strengthen contemporary knowledge in the study area. Wenner array provides good resolution of vertical and lateral changes in subsurface resistivity, supporting adequate delineation of horizontal structures such as sedimentary layers while the Dipole-Dipole array aids in mapping subtle subsurface features such as faults, joints and fractures and the associated geometry which could pose a threat to structural foundations and buildings within the study area. Geotechnical investigation involved drilling two boreholes to a depth of 15 metres each with samples taken at 0.8m vertical sample rate bringing the total samples collected to 32. For the electrical resistivity surveys, a spacing range of 5-30m was used with profile lengths of 100m in three different locations for both array types. Geotechnical investigation revealed predominant clayey sand composition from the surface to depths of 14m in BH 1 and 11m in BH 2 followed by predominant sand formations at the respective depths. Shallow foundational analysis carried out on both the chosen sites revealed allowable load-bearing capacities of 54 and 77kN/m2 for footing of sizes 0.5-2.0m and founded at depths of 0.5-2.0m. For the electrical resistivity survey, the Wenner array results ranged from 6.5-1199 Ωm, 27-1199Ωm, and 52.9-1499 Ωm at locations A, B and C respectively with an average RMS error of 0.213 while the Dipole-Dipole array results ranged from 98-7560Ωm, 82-7980Ωm and 3-8503Ωm at locations A, B and C with an average RMS error of 0.39. The profile maps and resistivity profiles show similarities in the lithological structures delineated using the borehole logs and the resistivity surveys, which revealed clayey sand and sand are predominant formations within the general location.

Characterizing groundwater contamination flow-paths and heavy metal mobilization near a waste site in Southwestern Nigeria

This study investigates potential groundwater contamination near a waste disposal site in southwestern Nigeria. The area's complex geological setting, characterized by fractured rock formations, posed significant challenges for traditional monitoring methods. To address these challenges and comprehensively assess groundwater conditions, we employed a combined approach utilizing Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), and geochemical analysis of heavy metals and water conductivity. This approach enabled the investigation of groundwater levels, identification of potential contamination zones, and delineation of contaminant flow paths. GPR identified a shallow zone, termed the “shadow zone,” with conductive residues indicating contaminants with anomalous conductivity ranging from 1 to 1.5 m. An intermittent reflection zone at a depth of 1.5–3.5 m suggested the potential presence of leachate-impacted groundwater. ERT confirmed a shallow resistive layer at depths of 0–2 m, attributed to compacted waste and topsoil, around the abandoned main dumpsite. Below this layer, a zone of low resistivity, decreasing downward through a porous weathered zone, was observed. This corresponded to high water conductivity in well data, ranging from 21 to 147 mS/m (equivalent to 6.80 to 47.62 Ω-m), indicating a high conductive anomaly suspected to be a leachate plume at depths of 2–10 m in a sandy-gravelly weathered zone. Validation against ground truth data confirmed the correlation between radar signatures, geoelectrical imaging, and subsurface lithology. Analysis of well and soil samples revealed concerningly elevated concentrations of cadmium, mercury, lead, arsenic, and cobalt, ranging from 641 to 1175 ppb, exceeding established safety limits for drinking water. Additionally, soil samples showed elevated levels of nickel and chromium, generally ranging from <0 to <1 ppb. These findings highlight the significant risk of groundwater contamination due to the proximity of the leachate zone to the groundwater table in the weathered basement complex. This study demonstrates the effective integration of geophysical and geochemical methods for comprehensive mapping of contaminated zones and identification of preferential pathways for contaminant migration. The findings underscore the critical need for implementing comprehensive risk assessment methodologies in similar complex geological settings.

2D nonlinear inversion of DC resistivity measurements, a case study; southeastern part of Ras El Dabaa, Northwestern coast, Egypt

The southern Mediterranean coast suffers from limited water resources as a result of exploitation of water supply, population growth, and climate change. Spatial lineaments and Seawater Intrusion (SWI) were detected at the southeast portion of Ras El Dabaa, on Egypt’s northwest coast, using the direct current resistivity (DCR) method. The Vertical Electrical Sounding (VES) data were acquired using Schlumberger array along four profiles and inverted both independently and jointly, aiming to obtain Two Dimensional (2D) geoelectrical images. The results of the one Dimensional (1D) inversion of VES data at each profile were stitched to form pseudo-2D sections on which the resistivity values and aquifer thickness in the southwest of the region appeared to be generally increasing, indicating a potential improvement in water quality.However, the results did not fully image the lateral variation but focused on the horizontal boundaries of the subsurface. On the contrary, the results of 2D inversion of the same data sets successfully managed to provide images that depicted resistivity distribution in both lateral and vertical directions. The detected sets of lineaments and fractured zones within the oolitic limestone and fossiliferous limestone units control the occurrence of groundwater in the region. The 2D inversion scheme revealed a low resistivity zone that indicated the presence of SWI and/or the dissolution of marine salts from the marine limestone bedrock of these aquifers in the northern portions of the studied area. Additionally, analysis of the 2D apparent porosity section shows how aquifers are connected by secondary porosity, which is defined by structures that resemble channels. The current approach offers valuable structural information for future planning and development of such complex geological coastal locations, taking into consideration the vulnerability of the groundwater system.

APPLICATION OF GEOTECHNICAL AND GEOPHYSICAL RESEARCH FOR SOIL CHARACTERIZATION

In the last few decades, modern geotechnical and geophysical in situ researches have been increasingly applied because they represent methods of quickly and instantly obtaining data on the properties and structure of the soil. Exploratory drilling is a research method that only obtains one-dimensional data, and compared to geotechnical and geophysical in situ research, it is relatively expensive and time-consuming. By combining all the research methods mentioned above, the most reliable and high-quality data for soil characterization is obtained. In this paper, examples of the application of geotechnical and geophysical research at two locations, Dugo Selo and Sesvetski Kraljevac, are processed. Applied geotechnical methods include, in addition to exploratory drilling, static cone penetrometer probing (CPTu), dilatometer probing (DMT) and dynamic heavy percussive penetration (DPH). From the geophysical investigations, 2-D geoelectric tomography (ERT) and multichannel analysis of surface waves (MASW) were performed. Also, an analysis of soil parameters obtained by exploratory drilling and in situ geotechnical methods was carried out. Undrained shear strength (cu) and compressibility modulus (M) were selected for comparison. The analysis shows that exploratory drilling results in lower values of the analyzed parameters on average compared to the results of in situ testing.

Quasi-3D Geoelectrical Imaging as A New Application for Landslide Investigations: A Tunnel Case Induced by Blasting Activity

Landslides are a significant hazard in mountainous regions, especially when influenced by construction activities such as tunnel excavation. In this paper, we aim to conduct a slope stability analysis as a result of tunnel blasts using quasi-3D subsurface models based on resistivity values. The study site is a construction area for the Jakarta-Bandung High-Speed Train tunnel, located in a mountainous region undergoing drill-and-blast excavation. This excavation method makes the area susceptible to landslides, which pose a threat to settlements in the Padalarang subdistrict, West Bandung Regency, Indonesia. Data was collected along four lines in 2D, and the dipole-dipole array was used to enhance resolution. Data modeling was carried out using ResIPy v3.2.3 software to create 2D and quasi-3D subsurface models based on resistivity values. The study findings indicate that the study area exhibits three resistivity ranges: low resistivity (0-30 Ωm), medium resistivity (31-49 Ωm), and high resistivity (&gt;50 Ωm). Utilizing quasi-3D imaging, we were able to identify the dimensions and presence of slip surfaces, which can be categorized as shallow (1.5-5 m) and deep (5-20 m) criteria. This study successfully applied the quasi-3D geoelectrical approach in a susceptible environment to detect potential landslide zones.

3D Effect and countermeasure of 2D geoelectrical imaging of a subsurface linear structure

This study was prompted by a field observation of a resistivity anomaly in a 2D Electrical Resistivity Tomography (ERT) scan during a fault investigation, suspected to be an artifact from an unnoticed 3D effect. Numerical simulations explored potential 3D effects when the survey line is not perpendicular to the strike of a linear feature, violating the ideal 2D assumption. Artifacts similar to the observed field anomaly arise when the survey line is oriented at an angle <60° from the strike. This 3D effect pattern, resulting from an oblique survey line, is quite different from the known mirroring effect of off-plane objects. Previously overlooked in practical applications, this phenomenon could lead to misinterpretations. A comprehensive investigation considering various influencing factors clarified the conditions and behaviors associated with this 3D effect. Further numerical studies of pseudo-3D surveys propose a practical guideline to avoid this effect with minimal effort. When field conditions raise concerns about surveying at an acute angle to the strike, adding one more survey line on each side of the main survey line, offset by two electrode spacings, is recommended. The 3D inversion of this narrow 3-line pseudo-3D survey can accurately resolve the in-line resistivity section.

Geoelectrical image of the Sabalan geothermal reservoir from magnetotelluric studies

The magnetotelluric (MT) survey of the Sabalan geothermal zone, which includes 22 stations along three traverse profiles across the main prospect zone, was conducted in 2007. The geophysical investigation utilized sharp boundary inversion of processed MT data due to the high contrast of electrical resistivity between embedded layers. This method was preferred to suppress the smeared-out impact of the smooth inversion algorithm on retrieving geological layering. The analysis of MT data led to the use of a 2D inversion algorithm to visualize the geothermal reservoir. Additionally, the geoelectrical strike of the main geothermal target was determined, showing some inconsistency across the profiles. The simulation of synthetic numerical models is conducted to evaluate the effectiveness of sharp boundary inversion compared to a smooth algorithm in sharp gradient mediums, specifically in terms of electrical characteristics, for plausible geothermal scenarios. The Finite Element method (FEM) was employed to construct these models, followed by running the 2D forward and inversion processes. The meshing and initial parameters of the modeling were set based on information obtained from prior geological and geophysical investigations. A sharp boundary inversion can be accurately implemented by introducing layering constraints along each profile surrounding the probable sought geothermal reservoir target. These layering constraints encompass the conductive cap, topsoil, and basement rocks, which are the key components of a plausible geothermal configuration. The results of the comparison indicate that the sharp boundary inversion technique effectively restored the boundary between neighboring layers that had significant differences in electrical resistivity. This was achieved when the smoothing algorithm failed to produce an accurate representation of the layered model. Ultimately, conceptual geological models were developed to illustrate the plausible structures corresponding to each profile, focusing on the sought geothermal reservoir targets. It can be deduced that many misunderstandings in the smoothing inversion algorithm will be omitted if the sharp boundary algorithm is used in highly electrical gradient structures. Based on the outcomes, a trachyandesite, andesite, and altered andesite reservoir exists at an elevation of 1600 to −2000 m. The reservoirs were recovered precisely with sharp and discriminable interfaces. Therefore, accurate interfaces led us to determine the conductive cap, heat source, and topsoil stacking as the main components of the geothermal system.

Managing the remediation strategy of contaminated megasites using field-scale calibration of geo-electrical imaging with chemical monitoring

Groundwater contamination is a threat to drinking water resources and ecosystems. Remediation by injection of chemical reagents into the aquifer may be preferred to excavation to reduce cost and environmental footprint. Yet, successful remediation requires complete contact between contamination and reagents. Subsurface heterogeneities are often responsible for diffusion into low-permeable zones, which may inhibit this contact. Monitoring the spatial distribution of injected reagents over time is crucial to achieve complete interaction. Source zone contamination at megasites is particularly challenging to remediate and monitor due to the massive scale and mixture of contaminants. Source zone remediation at Kærgård Plantation megasite (Denmark) is monitored here, with a new methodology, using high-resolution cross-borehole electrical resistivity tomography (XB-ERT) imaging calibrated by chemical analyses on groundwater samples. At this site, high levels of toxic non-aqueous phase liquids (NAPL) are targeted by in-situ chemical oxidation using activated persulfate. It may take numerous injection points with extensive injection campaigns to distribute reagents, which requires an understanding of how reagent may transport within the aquifer. A geophysical (XB-ERT) monitoring network of unprecedented size was installed to identify untreated zones and help manage the remediation strategy. The combination of spatially continuous geophysical information with discrete but precise chemical information, allowed detailed monitoring of sulfate distribution, produced during persulfate activation. Untreated zones identified in the first remediation campaign were resolved in the second campaign. The monitoring allowed adjusting the number of injection screens and the injection strategy from one campaign to the next, which resulted in better persulfate distribution and contaminant degradation in the second campaign. Furthermore, geophysical transects repeated over the timespan of a remediation campaign allowed high-resolution time-lapse imaging of reagent transport, which could in the future improve the predictability of transport models, compared to only using on a-priori assumptions of the hydraulic conductivity field.

Traces of collisional and transtensional processes between the Carpathia and the European platform in the geoelectric image (NE Slovakia and SE Poland)

We present the latest magnetotelluric models on profiles in the northeastern part of Slovakia and the southeastern part of Poland. These models are focused on deciphering the tectonic structures at the contact of the Inner Carpathians with the European Platform in this area. For the Inner Carpathian block, we propose the term Carpathia. Profile SA-01 shows shallower structures and the parallel MT-05 profile shows deeper structures. These models are also correlated with the seismic profile CEL-05. All results are compatible and show an original subduction-collisional structure, which was later replaced by a transpressive-transtensional one. The most striking structures are thick highly conductive subhorizontal zones in the middle crust and a tectonically controlled deep vertical conductive structure—the Carpathian conductive zone. Other significant structures, which also appear in the seismic section, are back thrusting of Flysch Belt and the Klippen Belt basement (Penninic crust) uplift.

Archeogeophysical application of non-traditional geoelectric arrays. A case study in a north-east Hungary site

With the continuous development of multielectrode geoelectrical tomography (ERT) as a geophysical technique, we became able to detect small size targets. In this paper, we present ERT interpretation results obtained at an archaeological site in Szendrő village in northeastern Hungary, where a 17th century fortress once stood. Several historical notes and a collapsed entrance recall the existence of tunnels under the fortress and a water well of uncertain depth. To detect these structures, geoelectrical multielectrode measurements were carried out using conventional and quasi-null arrays. The quasi-null array applies the arrangement of the current (A and B) and potential electrodes (M and N) in a special way, i.e., the electrodes A, M, B, N follow each other in line in special distances from each other. The horizontal sensitivity of the resistivity profiling method using these types of arrays has been proven to be better than that of the Wenner or other conventional arrays. The comparative study aims not just to investigate the archeological features, but to test the sensitivity of the non-traditional quasi-null arrays to these two-dimensional inhomogeneities. As a result, the optimal array can be chosen, and the identification and delineation of shallow structures can be made more reliably. In this paper, we present the very first archeogeophysical field measurements carried out by the gamma quasi null array (γqnull).

GEOELECTRIC SIGNATURES FROM A LEACHATE PLUME MAPPED FROM A BASEMENT COMPLEX TERRAIN IN AKURE, NIGERIA

In this study, we investigated the implications of a leachate plume within an aquifer system, unravelling the intricate dynamics that govern contaminant transport and dispersion. An integrated approach of geophysical investigations is used to establish the impact of an open-waste disposal site around Aromed, in a part of Akure, in the Precambrian Basement Complex of Southwestern Nigeria. Investigations using eight (8) Vertical Electrical Sounding (VES) and Double-Dipole Resistivity Tomography (ERT) along two (2) traverses were conducted. The geoelectric interpretation and the inverted two-dimensional electrical resistivity tomography (ERT) images provided insights into the underlying geological composition, identifying three distinct units: the topsoil, the weathered column, and the fractured Basement/fresh Basement bedrock. The geoelectric tomography structures in the 2-D interpretation reveal that the dumpsite area exhibits low apparent resistivity estimated to be between 12 to 71 ohm-m in both the topsoil and the weathered column aquiferous zone. These values closely agree with results from the geoelectric sections, which range between 11 - 68 ohm-m, respectively. The relatively low apparent resistivity results are suggestive to be due to the presence of leachate’s chemical composition from the open waste disposal sites, which are suspected to be generated from the dissolution of ions of iron and other conductive minerals producing the leachate plume. The probable leachate depth of migration as revealed by the 2-D tomography structures varies from about &lt;1 – &gt; 14 m beneath the dumpsites. The leachate migration, which is structurally controlled, has a southward flow, majorly in the orientation with the observed structures. The subsurface depression-relief is also attributed to influence the direction of leachate flow. In conclusion, it is suggested that groundwater in the aquiferous zones in the vicinity of the dumpsites have entered a significant pollution level; hence water in the aquifer is not safe for consumption.

Imaging of the electrical activity in the root zone under limited-water-availability stress: a laboratory study for Vitis vinifera

Abstract. Understanding root signals and their consequences for the whole plant physiology is one of the keys to tackling the water-saving challenge in agriculture. The implementation of water-saving irrigation strategies, such as the partial root zone drying (PRD) method, is part of a comprehensive approach to enhance water use efficiency. To reach this goal tools are needed for the evaluation of the root's and soil water dynamics in time and space. In controlled laboratory conditions, using a rhizotron built for geoelectrical tomography imaging, we monitored the spatio-temporal changes in soil electrical resistivity (ER) for more than a month corresponding to eight alternating water inputs cycles. Electrical resistivity tomography (ERT) was complemented with electrical current imaging (ECI) using plant-stem-induced electrical stimulation. To estimate soil water content in the rhizotron during the experiment, we incorporated Archie's law as a constitutive model. We demonstrated that under mild water stress conditions, it is practically impossible to spatially distinguish the limited-water-availability effects using ECI. We evidenced that the current source density spatial distribution varied during the course of the experiment with the transpiration demand but without any significant relationship to the soil water content changes. On the other hand, ERT showed spatial patterns associated with irrigation and, to a lesser degree, to RWU (root water uptake) and hydraulic redistribution. The interpretation of the geoelectrical imaging with respect to root activity was strengthened and correlated with indirect observations of the plant transpiration using a weight monitoring lysimeter and direct observation of the plant leaf gas exchanges.

Late Paleozoic-Jurassic tectonic evolution of the eastern Deseado Massif in central-southern Patagonia

Previous tectonic studies have indicated that the peri-cratonic lithosphere, located away from continental margins, is sensitive to far-field stresses propagating from active plate margins, which induce variable deformation. In order to gain a better understanding of potential intraplate tectonic events associated with the geodynamic evolution of the active margin of southwestern Gondwana, we conducted a tectono-sedimentary study of the Permian-Jurassic volcano-sedimentary record in the Deseado Massif, located in southern Patagonia. Our multidisciplinary analysis includes detailed geological mapping of an area of approximately 150 km2, structural analysis, geoelectric tomography, 2D seismic data, new geochronological dating, petrographic studies, and stratigraphic loggings of the volcano-sedimentary basin record. This comprehensive data set has allowed us to establish the tectonic, sedimentary, and magmatic evolution of the eastern Deseado Massif. Specifically, we have identified major normal faults associated with the syn-extensional deposition of late Permian and Jurassic sedimentary and volcanic rocks, as well as the Late Triassic emplacement of intermediate and felsic intrusive bodies. Additionally, interspersed large-scale shortening events were recognized, which induced positive tectonic inversion events in the region, recording contrasting stress fields during the analyzed lapse. Based on this, six major intraplate tectonomagmatic events were defined: (i) a potential post-Devonian pre-late Permian exhumation of the Neoproterozoic-early Paleozoic igneous-metamorphic basement, which we tentatively link to the Gondwanide orogeny; (ii) intraplate extension in the Late Permian (255 ± 4 Ma) related to the deposition of the Dos Hermanos Member of the La Golondrina Formation; (iii) Late Triassic (231 ± 3 Ma) intrusion of andesitic bodies, tentatively linked to the inland migration of arc magmatism associated with the South Gondwana flat slab; (iv) subsequent Late Triassic positive tectonic inversion of Permian extensional faults caused by a large-scale contractional event linked to the South Gondwana flat slab; (v) the extension-related emplacement and deposition of Early-Middle Jurassic (176 ± 3 Ma; 172 ± 4 Ma) sedimentary (lacustrine and fan deltas-related deposits), pyroclastic rocks (ignimbrites and ash tuffs), and lavas (lava domes and dykes) related to the Chon Aike silicic large igneous province; and (vi) poorly-constrained post-Middle Jurassic positive tectonic inversion of Jurassic faults. Therefore, we suggest that the geological events preserved in the Deseado Massif provide a key deformational record of the distal effects associated with ancient geodynamic processes that occurred along the southwestern active margin of Gondwana.

Fluid conduits and shallow-reservoir structure defined by geoelectrical tomography at the Nirano Salse (Italy)

Abstract. Mud volcanoes are fluid escape structures allowing for surface venting of hydrocarbons (mostly gas but also liquid condensates and oils) and water–sediment slurries. For a better understanding of mud volcano dynamics, the characterization of the fluid dynamics within mud volcano conduits; the presence, extent, and depth of the fluid reservoirs; and the connection among aquifers, conduits, and mud reservoirs play a key role. To this aim, we performed a geoelectrical survey in the Nirano Salse Regional Nature Reserve, located at the edge of the northern Apennines (Fiorano Modenese, Italy), an area characterized by several active mud fluid vents. This study, for the first time, images the resistivity structure of the subsoil along two perpendicular cross sections down to a depth of 250 m. The electrical models show a clear difference between the northern and southern sectors of the area, where the latter hosts the main discontinuities. Shallow reservoirs, where fluid muds accumulate, are spatially associated with the main fault/fracture controlling the migration routes associated with surface venting and converge at depth towards a common clayey horizon. There is no evidence of a shallow mud caldera below the Nirano area. These findings represent a step forward in the comprehension of the Nirano Salse plumbing system and in pinpointing local site hazards, which promotes safer tourist access to the area along restricted routes.

Historical Arch Bridges-Deterioration and Restoration Techniques

Historic buildings are the most valuable evidence of cultural heritage. They play an essential role in establishing a tangible link between the past and the present by understanding, interpreting, and tracing the epoch of civilization. Unfortunately, the high costs of restoration, vandalism, and arson take their toll. However, new technologies are having a positive impact on the restoration process and are becoming a suitable alternative to labor-intensive, expensive, and unsafe traditional inspections. Therefore, the role of non-destructive testing (NDT) as a new method is becoming more evident. Faro laser scanning, impact echo, impulse sound testing, and geoelectric tomography as non-destructive methods are leading to the inspection of historic structures to preserve their character. These new methods are representative of the development of non-contact techniques for the examination and documentation of structures. Non-destructive testing examines the internal and external structure of complex building components as well as defective areas, quantifies cracks, and detects near-surface moisture. The objective of this work is to identify new adventurous and traditional methods for the reconstruction of the Turkish arch bridges Dara-1 and Halilviran to determine the appropriate rehabilitation methods and their deterioration of construction materials, damage, and failure patterns. Bridge dimensions were measured using a Faro laser scanner, which allows inspectors to capture and evaluate data from bridges and structural components without permanently altering them. The laser captures bridge dimensions by scanning cross-sections of the structure in the horizontal and vertical planes. The data is exported in the form of point clouds that represent all visible aspects and actual dimensions of the bridge in 2D and 3D models. In comparison between traditional and laser scanning methods, the main advantages of the applied method are the time savings on-site and the creation of a three-dimensional model of the structure, which can be used to collect precise and accurate surface data of objects in a non-destructive manner. Doi: 10.28991/CEJ-2023-09-07-010 Full Text: PDF

Lithologic characterization of Iguosa erosion site using geoelectrical techniques

Considering the devastating menace of gully erosion for which lithology is one amongst several other agents that drives soil loss and gully erosion, Vertical Electrical Sounding (VES) and Electrical Resistivity (ERT) techniques were adopted to investigate subsurface lithology in Iguosa gully erosion site. PASI 16GL model resistivity meter was used in acquiring data for VES and ERT in the area under investigation. VES data acquired were processed both qualitatively and quantitatively, and geoelectric sections were generated using AUTOCAD software by combination of two or more interpreted VES results along a profile. ERT data were processed using Res2dinv software to an inverse model resistivity section. The geoelectric image generated were interpreted to obtain lithology of the subsurface. The analysis and interpretation of the subsurface image reveals presence of topsoil, sand, dry sand, clayey sand and coarse sand. The subsurface lithology within the study location is predominantly sandy. The result obtained from the resistivity of all profiles shows that erodibility increases with depth within this study area with corresponding high resistivity values. Due to the fact that sand within the study area is loose coarse and silty, which can give rise to high resistivity and causes erosion.

Application of 2D Geo-Electric Imaging and Geochemical Methods to Investigate Subsurface Contamination in Yenagoa Environs, Niger Delta, Nigeria

Application of 2D Geo-Electric Imaging and Geochemical Methods to Investigate Subsurface Contamination in Yenagoa Environs, Niger Delta, Nigeria

INVESTIGATION OF THE TECHNICAL CONDITION OF WATER DISCHARGE DEVICES OF HYDRAULIC STRUCTURES

Problem statement. Hydrotechnical structures undergo a process of inspection for their technical condition. This is necessary to maintain the durability of the structure. In the process of operation, structural defects occur, which are difficult to examine and investigate, due to the impossibility of access for visual inspection. Such defects include those formed in the body of gravity-type earth dams. This applies, first of all, to structures and devices that are located in the body of dams during their construction. They include, in particular, spillways and pipelines. Defects in these structures lead to leakage of water into the body of the dam, which eventually collapses from the inside. Timely detection of defects prevents the destruction of dams due to urgent repairs, and this extends the durability of the structure. The purpose of the article is to develop an analytical-instrumental method of finding, without destroying the body of the dam, erosional, loosened areas in leakage zones, and determining their volumes. Method. A modern method of geophysics, which is electrotomography, is used. As a theoretical justification, the method of the Earth's natural pulsed electromagnetic field (MENPEF) was taken as a basis. The result of the research is the development of a methodology using the methods of engineering geophysics: the method of the Earth's natural pulsed electromagnetic field (MENPEF) and geoelectric tomography. Scientific novelty lies in the fact that the method was developed for the first time for the examination of earth dambs spillways. Practical value. With the help of the developed method, in the future it will be possible to conduct surveys for earth dams of hydrotechnical structures for all organizations that are engaged in such work and have the necessary tools. Conclusions. An analytical-instrumental method of researching the sections of earth dams that cross the structures of ponds spillways and reservoirs has been developed. The location of the loosened soil halo around the spillway pipes inside the body of the earth dam was identified, and the volume of such soil was determined.

CHARACTERIZATION OF AQUIFER STRUCTURES IN THE NORTHEAST BASEMENT ROCK OF BURKINA FASO

This characterization study of the aquifer horizons is based on the geostatistical analysis of the drilling data in order to map the intrinsic parameters of the aquifers, namely the size of the alterations and the size of the fissured fringe. The STRM data were also used to map the topographic levels. Cross-analysis of all these parameters with borehole flow rates allowed us to define a context pattern that is favorable to groundwater deposits, by identifying the influence of the size of these parameters on productivity. The application of the geophysical method (electric drag and geoelectric tomography) has made it possible to obtain a 2D vertical section of the subsoil structure based on the distribution of electrical resistivity. The alteration profile includes the alterite reservoir, the fissure reservoir located above the solid rock sometimes affected by fractures (fault). The size of these different horizons varies from one point to another, thus defining contexts that are more or less favorable for the existence of groundwater deposits. The alteration thickness (AT) mapping defined two map units: alteration thicknesses of 15m or less and those greater than 15m. Erosion would have played a large role in this distribution as there is a clear link between alteration thickness and topography. The alteration thickness (AT) unit of less than or equal to 15 m has great surface water potential. It is the area where the topography is fairly low, and the fractured edges are generally of considerable thickness. They frequently coincide with the large shallow areas drained by the major waterways.

From Rockfall Observation to Operational Solutions: Nearly 20 years of Cryo-gravitational Hazard Studies in Mont-Blanc Massif

The enhanced rockfall frequency (V &gt; 100 m3) first noticed in the European Alps, has motivated investigations on high mountain rock walls and rock wall permafrost since the 2000s. Mont-Blanc massif (MBM) has become a pilot study area thanks to the wealth of data and knowledge on rockfall and permafrost dynamics acquired through successive research projects. Statistical analysis of rockfall distribution (&gt; 1300 events inventoried between 2007 and 2021) shows that they are related to permafrost distribution and increasing atmospheric temperature, opening promising perspective for developing forecasting tools to support mountain practitioners in their risk mitigation strategy. However, understanding how rock wall destabilizations develop is challenged by the variety of potentially involved thermo-hydro-mechanical processes. To face these challenges, research currently carried out in the MBM focuses on water infiltration and circulation processes in frozen rock walls by combining advanced numerical modelling approaches and ad hoc field surveys. The coupling of models simulating heat and water transport with geoelectrical imaging methods could allow assessment of ground water/ice distributions and contents that is highly relevant for geotechnical purposes. Concurrently, the combination of acquired data and knowledge in integrative approaches of landscape changes and hazards involving permafrost degradation, glacier retreat, possible lake formation and rock wall destabilization appears as an essential basis for land-planning concerns. Finally, thermal and hydrological interactions between rock wall permafrost and ice bodies nestled on rock faces (ice aprons and hanging glaciers) is another direction of research to be pursued with cross-disciplinary implications.