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1.
In the present study, the existence of cavities, voids, and fractures was verified at the site of the El-Elb Dam, which is located to the northwest of Riyadh City across Wadi Hanifa, using 2D electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) techniques. For this purpose, four ERT profiles were measured on the downstream side of the El-Elb Dam using the Syscal Pro Switch-72 resistivity meter. In addition, a GPR survey using a 400-MHz antenna and a SIR-3000 instrument was conducted along five profiles above the stilling basins on the downstream side of the dam and one radar profile was measured outside the stilling basins area across the course of the wadi. The resultant geophysical data were interpreted with the aid of information from a field-based structural and stratigraphic evaluation of the outcropped bedrock on the banks of the wadi course. The analysis of the inverted ERT and filtered radar sections revealed several resistivity and electromagnetic reflection anomalies that are identified laterally and vertically across the measured sections. These anomalies indicate the presence of fractures and karst features affected the limestone bedrock in the dam site. These near-surface karstified and fractured strata represent a critical hazard to the structural safety of the dam.  相似文献   

2.
Geoelectrical methods involving electrical resistivity tomography (ERT), self-potential (SP), frequency domain electromagnetic (FDEM), and very low frequency (VLF) methods have been used to provide valuable information in locating a known sulfide ore body in Soap Gulch, Montana. The study develops basis of comparison for the geophysical techniques employed. Ranges of resistivity along the area have been established using interpreted ERT which can help to understand the subsurface distribution of sulfides in the area. A sulfide body was delineated from the survey area corresponding to anomalously low resistivity values on the ERT section, negative SP, and high apparent current density zone in VLF. Depth to the localized ore zone ranges approximately from 10 to 20 m. FDEM data reflect the conductivity distribution of the shallow subsurface (less than 6 m deep); hence, the delineated sulfide zone had minimal contribution to FDEM measurements. The results of the study show that SP, VLF, and ERT methods provide significant information in localizing ore bodies. The survey revealed that the resistivity values obtained from ERT profile corroborate the FDEM, SP, and VLF from the area.  相似文献   

3.
Khuff Formation is of utmost importance in Saudi Arabia for oil and gas reservoir although it is composed mainly of limestone. This reason refers to the existence of intensive fractures which play a vital role in the increase in porosity and permeability of this formation. The fracture pattern in the study area was verified through 2D and 3D ground penetrating radar (GPR)-defined and electrical resistivity tomography (ERT)-defined surveys. In this respect, ten of 2D GPR surveys were collected along an intersected grid of profiles covering the study area while ERT data were collected along three profiles of the GPR grid. The results were interpreted in light of the field-based structural and stratigraphic assessment of the outcropping rocks. The analysis of the inverted ERT and filtered GPR sections revealed the presence of fractures. Several resistivity and electromagnetic reflection anomalies were laterally and vertically identified across the measured sections clarifying fractures that extend to a depth of 24 m in the limestone. Most fractures are oriented vertical to sub-vertical dipping both east-west and north-south.  相似文献   

4.
Self potential (SP) and electrical resistivity tomography (ERT) methods are used together with the results of groundwater samples hydrogeochemical analysis to assess the impact of the water leak from the landfill garbage site at NamSon located in Northern Hanoi on causing pollution to the surrounding environment and affecting geological structure. Selected survey area covers an area of 180 × 300 m lying in the low land of the NamSon site with a slope ranging about 8 m in direction NW–SE. There are three geophysical measurements lines denoted as T1, T2 and T3. Processing 180 SP data points has allowed to draw maps of equipotential epoch in the two periods in 2015 and 2016. The maps show four zones of SP positive anomalies with maximum amplitudes of about +20 mV where the groundwater flow direction is downward and five zones of SP negative anomalies with minimum values in a range from ?180 to ?260 mV where the groundwater flow direction is upward. Resistivity values of the subsurface layers of soils and rocks have been aquired from 2D inverse model for measuring ERT in March 2015 and March 2016. The results of the ERT allowed to define the low resistivity in the range 15–20 Ωm related to leachate plume from NamSon landfill site. Results of the physico-chemical analysis of groundwater samples from the existing six boreholes show increases in concentration of the measured pollutant parameters indicating contamination of the groundwater as a result of solid waste leachate accumulation. This result is affirmative evidence for the survey results by geophysical technique. The rapid decrease in quality of groundwater over the last year is probably due to the influence of the leachate from the NamSon landfill site.  相似文献   

5.
Sinkhole collapse is one of the main limitations in the development of karst areas, especially where bedrock is covered by unconsolidated material. Studies of sinkhole formation have shown that sinkholes are likely to develop in cutter (enlarged joint) zones as a result of subterranean erosion by flowing groundwater. Ground-penetrating radar (GPR) and electrical resistivity imaging or tomography (RESTOM) are well suited to mapping sinkholes because of the ability of these two techniques for detecting voids and discriminating subtle resistivity variations. Nine GPR profiles and two-dimensional electrical resistivity tomography have been applied, with relative success, to locate paleo-collapses and cavities, and to detect and characterize karst at two sinkhole sites near Cheria City where limestone is covered by about 10 m of clayey soils. The survey results suggest that GPR and RESTOM are ideal geophysical tools to aid in the detection and monitoring of sinkholes and other subsurface cavities.  相似文献   

6.
As part of a larger regional research program “KarstEAU”, the authors have applied electrical resistivity tomography (ERT) techniques to characterize heterogeneities in the Port-Miou coastal karst aquifer (Cassis, SE France). Field surveys were carried out on intensely fractured and karstified Urgonian carbonates. Extensive research has characterized macro- and micro-scale geology of the Port-Miou area and particularly underground water-filled conduits and fault/fracture and karst systems within a former quarry. The authors applied 2D ERT along two surface profiles of length 420 and 595 m to test capability for delineating subsurface conduits and possibly relationship between conduit and fault/fracture/karst orientation; and 3D ERT with a dense 120 electrode array at 1 m spacing (11 × 10 m) was applied over an area of the quarry that had been profiled using 3D georadar and which has had intensive nearby structural geological interpretation. The 2D profiling imaged several underground conduits at depths to >50 m below ground surface and below sea level, including possibly the main Port Miou submarine spring and smaller springs. The 2D profiling within the quarry provided a better understanding of the connectivity between major fractures and faults on the quarry walls and secondary springs along the coast supporting flow of the secondary springs along interpreted fracture orientations. In addition, 2D inversion-derived conductivity models indicate that high resistivity zones above sea-level are associated with non-saturated zones and low resistivity anomalies in the non-saturated zone are associated with residual clays in paleokarsts. A partitioned lower resistivity zone below sea-level can be associated with a higher porosity/permeability zone with fractures and karstic features. Inversion models of the dense 3D ERT data indicate a higher resistivity volume within the larger surveyed block. The survey characterized the non-saturated zone and the ERT resistivities are correlated with karst features interpreted by 3D georadar and visible in the inferior wall of the quarry.  相似文献   

7.
A series of geophysical parameters have been applied with geological perception to resolve the hydrogeological complexities over granitic terrain at Hyderabad, India. Frequent failure of borehole drillings and the thrust conditions of community have prompted a noninvasive suitable tool, applied at small scale for pinpointing potential well site. Geophysical scanning, viz. electrical resistivity tomography (ERT), spontaneous potential (SP), and electrical gradient profiling (GP) were employed within the restricted space of housing complex to obtain the true characteristics of the subsurface lithology, where anomalies by the underground utility structures have been nullified. Results showed, in ERT, the low order of resistivity range 123 to 200?Ωm showing a plume like weathered zone underlain by sudden slip of massive granite (>217?Ωm) was of great interest to proceed further in the process. Here, the switchover in SP value from +18 mV to ?17 mV and GP from mean value 10 to 90 mV/m was recorded. The anomalies in SP and GP were precisely coincided with the ERT where upcoming of subsurface massive granite next to the inferred fracture was noted. Drilling core logs satisfies the geophysical signatures ensuring the inferred saturated fracture with the total yield 1,302 gal/h.  相似文献   

8.
Electrical resistance tomography (ERT) was used to monitor a conductive plume dilution experiment that was conducted in fractured basalt in order to assess its applications in this type of fractured-rock environment. Tap water was injected into an injection well for 34 days to dilute a pre-existing potassium chloride (KCl) plume at a site in Idaho, USA. No further fluids were introduced artificially during a 62-day monitoring period. Both surface ERT and cross-borehole ERT were used to monitor dilution and displacement of the plume. A square grid of land-surface electrodes was used with the surface ERT. Three-dimensional images of surface ERT delineated areas of increased and decreased resistivities. Increasing resistivities are attributed to dilution/displacement of the KCl solution by tap-water invasion or the influx of seasonal recharge. Decreasing resistivities resulted from redistribution of residual KCl solution. Cross-borehole ERT was conducted between the injection well and each of seven surrounding monitoring wells. Polar plots of the injection-well resistivity data in the direction of each monitoring well delineate specific locations where tap water seeped from the injection well via preferential flow paths determined by time-dependent resistivity increases. Monitoring-well data indicate locations of clustered and isolated regions of resistivity changes.  相似文献   

9.
The present study is an attempt to assess the impact of a saline waste lagoon on the near subsurface through electrical resistivity tomography (ERT). Resistivity and IP imaging data have been collected on profiles close to the lagoon and at a far off location (control location). Water samples have been collected from the lagoon and a municipality drinking well close to it and analysed for the water chemistry. The geoelectrical sections indicate very low resistivity formations in the near subsurface in the vicinity of the lagoon as compared to the control profile. The water chemistry data from the monitoring well close to the profile also indicates very high total dissolved solids (8658 mg/L) and qualitatively supports the contamination of the near subsurface. The conductive formations in the vicinity of the lagoon can be attributed to the overflow from the lagoon or the seepage.  相似文献   

10.
The principal aim of this study is to assess the scope of monitoring diesel plume migration in a scaled aquifer model with a miniaturised electrical resistivity array. Respectively 1000 and 500 ml of diesel were injected in both the unsaturated and water-saturated zones of a sand body overlying a clay aquitard, and diesel migration was monitored with a miniature electrode array and an off-the-shelf resistivity meter. Inverted time-lapse electrical resistivity tomography (ERT) data reflect downward and lateral spreading of the diesel plume away from the injection point in the unsaturated zone. Diesel was also imaged to spread upwards and laterally away from the injection point in the saturated zone, as controlled by capillary rise. In both cases later-time ERT images reflected preferential pooling of diesel on the water table, as well as vertical smearing of pooled diesel in response to simulated water-table fluctuations. Repeat fluid electrical conductivity (EC) and dissolved oxygen (DO) measurements validate the observed changes in bulk resistivity caused by both diesel injections. Artefacts introduced by 2D inversion of 3D contaminant transport were abound. Time-lapse ERT imaging of diesel transport is therefore inferred to be feasible and well-suited to complementing conventional techniques of intrusive site investigation, although time-lapse 3D or 4D ERT imaging is strongly advocated.  相似文献   

11.
Low-permeability clayey and silty river terrace deposits are an important component in protecting underlying aquifers from contamination by agrochemicals and other contaminants. Such deposits also record deglaciation dynamics, meltwater drainage and local climatic variations. In this study, conducted over Mississippi River terraces near Savanna, Illinois, clayey slackwater terrace deposits and sandy terrace deposits are examined using resistivity soundings, ground-penetrating radar (GPR) profiles and direct-push conductivity logs. The clayey terrace deposits are characterized by low resistivity (10–35 ohm-m) and slow GPR wave velocity (0.07 m/ns), whereas non-clayey terrace deposits exhibit much higher resistivity (169–1,762 ohm-m) and faster GPR wave velocities (0.15 m/ns). Sandy and clayey terrace deposits may thus be differentiated and mapped on the basis of their geophysical response. Models based on resistivity soundings provide reasonably accurate estimates of the thickness of clayey slackwater deposits, but fail to reveal thin sands embedded in the clayey deposits. In some cases, the full thickness of the slackwater deposits was also not revealed. GPR profiles, however, imaged these embedded shallow sands and possibly imaged deeper sands below the base of the slackwater deposits, giving more accurate estimates of thickness. GPR also accurately resolved the thickness and character of sandy terrace deposits. Direct-push conductivity logs provide both accurate estimates of the thickness of clayey slackwater terrace deposits and a means of identifying thin embedded sands. In summary, resistivity soundings image these deposits at the lowest resolution with one-dimensional models, whereas GPR provides much higher resolution showing detailed layering within the upper several meters. Direct-push conductivity logs provide the highest resolution, but are invasive and only reveal stratigraphy at one location.  相似文献   

12.
复杂山区近地表调查技术是制约地震资料品质的主要因素。这里利用地质雷达和高密度电法相配合,在四川南江山区进行了近地表结构综合调查。地质雷达探测精度高,高密度电法探测深度大且能有效补充介质电性信息。通过微测井数据进行标定,建立了近地表结构的深度和速度模型,为地震静校正提供了依据。经研究结果表明,采用近地表调查数据进行静校正的地震品质得到了提高。  相似文献   

13.
Here, we describe an original geophysical multi-method approach applied to the Mount Marzano Fault System. This is one of the most hazardous seismogenic faults of the Apennines (Irpinia, southern Italy), and it was responsible for the 1980, Mw 6.9, earthquake, along with many others before. We carried out electrical resistivity tomography (ERT), ground penetrating radar (GPR) measurements, and horizontal-to-vertical spectral ratio (HVSR) microtremor analysis along several common transects designed across the potential and/or certain fault traces. The data obtained from these non-invasive, inexpensive, expeditious methods mutually integrate with and complement each other, providing a valuable subsurface image of the near surface fault architecture. ERT depicts the general shallow image of the fault zone and of the fault-controlled sedimentary basin, with the depth of the buried bedrock cross-correlated through ambient-noise HVSR results. GPR delineates the very shallow geometry of the fault and of the associated deformation. Coupled with previous paleoseismological studies, these data allow the evaluation of some fault parameters and the precise locating of the fault trace, to aid future paleoseismological investigations aimed at seismic risk reduction programs.  相似文献   

14.
The flood plain of the Nile River has been a safe dwelling throughout history. Recently with a growing population and vast growing urbanization, some buildings have started to experience structural damages, which are not related to their construction design, but rather to the ground conditions around the buildings' foundations. Variations in properties of the soil supporting the buildings' foundations such as soil-bearing capacity, moisture content, and scouring may eventually lead to the failure of these buildings. This study is attempting to characterize the variations in the soil properties around the City Star shopping mall, in eastern Cairo, where a large building has tilted over the past few years. This tilting may lead to the collapse of the whole building if it continues at the same rate. An integrated geophysical investigation including multi-channel analysis of surface wave (MASW), ground-penetrating radar (GPR), and 2-D electrical resistivity tomography (ERT) was used around the affected building to help detect possible causes of deterioration. The GPR data showed a soil-filled layer overlaying a thick bottom layer of higher moisture content. The MASW data revealed a middle layer of relatively low shear wave velocity sandwiched between two relatively high shear wave velocity layers. The ERT data showed an upper low resistivity layer overlying a high resistivity layer. Integrating the interpretations of the three geophysical methods provides a combined model that reflects lateral and vertical variation in the soil properties. This variation becomes dramatic near the tilted corner of the building.  相似文献   

15.
应用探地雷达和高密度电阻率法,在冀中平原中部某典型石油烃类污染场地进行探测,得到了浅源石油烃类污染物的异常特征。通过对探地雷达和高密度电法资料的分析,得出石油烃类污染物呈现低电阻率、低介电常数特性,根据这个特点圈定出了此污染场地内储油池区域的污染扩散晕。实践证明,这两种物探组合在此类污染场地探测中具有推广价值。  相似文献   

16.
Groundwater contamination is one of the most significant problems in arid countries. Al-Quwiy’yia region is an example of an area where the groundwater is contaminated as a result of infiltration of waste water in low-lying areas adjacent to inhabited zones. Such contamination poses significant environmental threats for the surrounding environment and groundwater. Surface observations and spatial distribution of contamination observed in the shallow aquifer indicate that the main contamination sources were from sewage as well as from waste water dumping. However, the main source of water supply for the whole area is groundwater abstracted from the relatively shallow aquifer. Therefore, the transient electromagnetic method (TEM) and 2D electrical resistivity tomography (2D ERT) have been applied close to the waste water dump site to characterize the response of pollution plumes. Both of these geoelectrical techniques are sensitive to electrical conductivity as well as to other physical properties, which are greatly influenced by the polluted groundwater. Therefore, it is possible to profile the contamination plumes, both vertically and horizontally, in the vicinity of the measured stations. The ERT profiles gave detailed information about the lateral distribution of the contaminated groundwater, whereas the TEM demonstrated the vertical extensions.  相似文献   

17.
The geology of the “Vence” landslide (0.8 million m3, south-eastern France) explains the complex hydrology of the site which plays a key role in the destabilization of the slope (water circulation within the sliding mass, fluid exchanges between superficial layers and deep karstic aquifer through faults). To understand fluid circulations within the unstable slope, a 9.5-year multi-parametric survey was set up. The survey combines electrical resistivity tomography (daily acquisition), rainfall records since 2006 and boreholes monitoring groundwater level since 2009. The objective of this work is to present an automated clustering analysis applied to the ERT data enabled to locate geological units displaying distinct hydrogeological behaviours. Clustering analysis, based on a hierarchical ascendant classification (HAC), helped to simplify the ERT section isolating three groups of apparent resistivity values. Comparing the variations of these clusters’ behaviours in time to the variations of the groundwater levels on site, we identified hydrogeological units. The role of the faults cutting the substratum is thereby highlighted. It is the simultaneous analysis of such a large real dataset that allowed obtaining robust results characteristic of the long-term behaviour of the natural hydrogeological system. This type of qualitative information on the variability of the slope hydrogeological behaviour both spatially and temporally is crucial to help improving the conversion of resistivity data into hydrologic quantities. Indeed, the definition of petrophysical models to convert ERT measurements into hydrological measurements should be site-specific and take into account the spatial and temporal variability of the medium. In this work, we show a method that can also help to focus on the areas in depth that have different levels of permeability and observe how the saturation degree evolves in time. This can be used to optimize the location of additional instrumentation (such as temperature probes and chemical sampling) and, thus, help in the prevention of the risk in such problematic areas.  相似文献   

18.
The objective of this study is to evaluate the effectiveness of DC resistivity surveys for imaging the wastewater percolation around the stabilization ponds in the Tenth of Ramadan City, the desert fringes of East Nile Delta, Egypt. Detailed resistivity surveys, including DC soundings and electrical resistivity tomography (ERT), were carried out along several profiles. Furthermore, synthetic modeling of ERT was designed to optimize the survey configurations and interpretation of the results. A 2D modeling of smoothness-constrained least-squares inversion scheme was applied to delineate the possible wastewater infiltration zones from oxidation ponds. Because the geoelectrical interpretation has a degree of non-uniqueness, the resistivity inversion was constrained using borehole lithological information and soil sample laboratory measurements. The DC inversion results indicate decreasing resistivity down to a depth of 15 m around waste disposal sites. The inferred soil zone close to the oxidation ponds was a mixture of sand, silt and clay. Moreover, the clay minerals were characterized by moderate swelling that could have reduced the vertical infiltration speed, causing wastewater seepage, especially around unlined disposal sites and open surface drains. Accordingly, the medium-to-low resistivity values can be attributed to wastewater leakage in clayey sand soil. Because the area slopes generally toward the northeast, the surface seepage was dominant in the shallow impermeable sandy clay subsoil. Therefore, measuring soil parameters is a complementary method to optimize resistivity interpretation, with potential for mitigating environmental hazards from wastewater leakage around disposal ponds.  相似文献   

19.
The contamination levels of soils and water resources in Calabar, Nigeria have been investigated using resistivity (vertical electrical sounding and electrical resistivity tomography), geochemical analyses of soil and water resources and textural analysis. Sixty randomly sited VES sites were investigated in two seasons while ERT investigations were performed along four profiles. The geochemical investigations were spread across seasons in order to track seasonal changes in physico-chemical parameters: hydrogen ion concentration (pH), electrical conductivity, total dissolved solids, chloride ion (Cl?), nitrate ion (\( {\text{NO}}_{ 3}^{ - } \)), bicarbonate (\( {\text{HCO}}_{ 3}^{ - } \)), sulphate ion (\( {\text{SO}}_{ 4}^{2 - } \)), calcium ion (Ca2+), sodium ion (Na+), potassium ion (K+) and magnesium ion (Mg2+). Additionally, concentrations of ammonium, aluminium and nitrite ions in soils were determined. Results show that ionic concentrations in the sand-dominated soils and water are within permissible limits and baseline standards. The resistivities follow known trends in the area. However, at the central waste disposal site, a localised thin (< 5 m), low resistivity (< 15 Ωm) anomaly suspected to be due to contamination by leachates was observed. Comparatively, the contaminated area is also characterised by marginal increase in ionic concentrations. Strong attenuation capacities of overlying and adjoining clay/lateritic sediments and optimal design of the waste dump site probably reduced the spread of contaminants. The contaminated zone need to be closely monitored so that it does not extend to the aquifers. Hence, all strategies presently being used in managing wastes in Calabar should be sustained.  相似文献   

20.
Three years after the oil spillage and pipeline explosion that claimed about 100 human lives at Ijegun Community of Lagos–Nigeria, a combination of carefully designed 2D Electrical Resistivity Profilling and Vertical Electrical Sounding methods was deployed to map and characterise the subsurface around the contaminated site. Data acquired were processed, forward modelled and tomographically inverted to obtain the multi-dimensional resistivity distribution of subsurface. The results of the study revealed high resistivity structures that indocate the presence of contaminant (oil plumes) of different sizes and shapes around the oil leakage site. These high resistivity structures are absent in the tomograms and resistivity-depth slices computed for Iyana—a linear settlement not affected by oil spillage. The five geo-electric layers and the resistivities delineated in the area are the top soil layer, 220–670 Ωm; clayey sand layer, 300–1072 Ωm; top sand layer, 120–328 Ωm; mudstone/shale layer, 25–116 Ωm and the bottom sand layer, 15–69 Ωm. The base of the first four geo-electric layers corresponds to 3.9, 8.4, 27.2 and 34.6 m respectively. The two groundwater aquifers delineated correspond to the third and fifth geo-electric layers. The top aquifer has been infiltrated by oil plumes. The depth penetrated by the oil plume decreases from 32 m to about 24 m across the survey profiles from the two ends. It was concluded that the contaminant plumes from the oil spillage are yet to be completely degraded as at the time of the study. It is recommended that the contaminated site be remediated to remove or reduce the contaminant oil in the subsurface.  相似文献   

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