scholarly journals VLF-EM and VES: an application to groundwater exploration in a Precambrian basement terrain SW Nigeria

2014 ◽  
Vol 57 (1) ◽  
Author(s):  
Adebowale Obasanmi Adelusi ◽  
Michael A. Ayuk ◽  
John Stephen Kayode
Keyword(s):  
Hard Rock ◽  
Surface Expression ◽  
Groundwater Exploration ◽  
Groundwater Development ◽  
Near Surface ◽  
Top Soil ◽  
Subsurface Layers ◽  
Soil Clay ◽  
Basement Structures ◽  
Basement Layer

<p>In a hard rock environment with surface or near surface expression of outcrops, the use of VES only becomes difficult due to its associated problems and limitations. However, the use of VLF-EM becomes imperative in mapping basement structures relevant to groundwater development. A total of 2100 VLF-EM data plus selected VES points were covered over 7 traverses with length varying from 3000 to 4500 m. The VLF-EM result mapped basement structures relevant in groundwater development. This is further studied using VES. Results of the investigation indicate that a HKH sounding curve is obtained with a maximum of five subsurface layers comprising: the top soil, clay/sandy clay unit, the fresh basement, fractured basement and the basement bedrock. The fractured basement layer constitutes the main aquifer unit with thickness of 20-25 m. The layer resistivity and thickness ranges are 60-100 ohm-m; 40-80 ohm-m, 1600-2100 ohm-m, 250-420 ohm-m, and 2200-7500 ohm-m; and 0.3-1.2 m, 1.9-2.5 m, 16.5-22.5 m and 22-30 m for the five layers respectively. The geoelectric results compared favorably well with drilling information to above 90%. The yield of the well is 2 L/s with good recharge capability.</p>

scholarly journals Vertical Electrical Soundings for Locating Groundwater Potential Zones in Osmania University Campus, Hyderabad, Telangana State, India

2015 ◽  
Vol 6 ◽  
Author(s):  
D. Vijay Kumar ◽  
G. Ramadass
Keyword(s):  
Hard Rock ◽  
Soil Layer ◽  
Groundwater Potential ◽  
University Campus ◽  
Groundwater Potential Zones ◽  
Vertical Electrical Soundings ◽  
Top Soil ◽  
Subsurface Layers ◽  
Electrical Soundings ◽  
Very High

<p>Based on the resistivity investigations Osmania University Campus, precisely depth and  resistivity of subsurface layers were computed, Various geoelectric sections along different profiels (I to VIII) was obtained and analyzed. The study area is showing four layered geoelectrical sections, the top soil layer of variable resisitivity  value between  11.2 to 599 Ωm, whose maximum thickness is 0.75 to 4.45 m.  The highly weathered second  layer resistivity value varing from1.72 to 1800 Ωm.  And thickness is 0.12 to 36.6m.  The third fractured layer indicated by resistivity value 16.3 to 46074 Ωm and thickness  is 4.9 to 87.4 m.  The basement that is associated with hard rock and very high resistivities ranging to infinity. The low restivity with thick overbuden and fractured bed rock constitute the aquifer units and the series of  basementt undulations identified from the geolelectrical sections  are potential points for groundwater  locations.</p>

Are There Better Disposal Methods?

2000 ◽  
Author(s):  
Hans Tammemagi
Keyword(s):  
Sustainable Development ◽  
Waste Disposal ◽  
Surface Expression ◽  
Abandoned Mines ◽  
Underground Mines ◽  
Open Pit ◽  
Near Surface ◽  
The Sustainable Development ◽  
Future Value ◽  
Deep Underground

Most of the solid waste generated by society ultimately winds up in near-surface landfills. Let us put our thinking caps firmly on, place our prejudices aside, and explore what other methods might be used to dispose of waste. We should seek, in particular, the approaches that best fulfill the three basic principles described in chapter 2. That is, we should strive to find disposal methods that are in accord with sustainable development. Existing and abandoned pits, quarries, and mines are attractive for waste disposal because a hole to contain the wastes has already been excavated. Such abandoned areas, when left unreclaimed, cannot be used for agriculture or other beneficial uses. Thus, they generally do not have significant market value and can often be obtained relatively cheaply. For these reasons, pits and quarries have been extensively used for landfills. Operating and abandoned mines, on which this section focuses, are somewhat similar to pits and quarries, though usually larger. Abandoned mines hold promise as disposal facilities because they are resource areas that have been depleted and thus have little future value. There are two basic types of mine: the open pit mine, which is effectively a large pit or hole in the ground; and the underground mine, where the mined-out openings are deep underground and there is no surface expression except for the shafts used to gain subsurface access. Because underground mines occupy minimal surface land, their use for waste disposal would be in accordance with the sustainable development principles that were advocated in chapter 2. Several European countries, with higher population densities and much smaller land mass than in North America, have long used abandoned underground mines to dispose of their rubbish. The major advantage of placing wastes deep in underground mines is that it is inherently safer than placing the wastes in a surface facility. The amount of groundwater and its flow rate decrease with depth; this fact, combined with the long transport paths back to the biosphere, minimizes the possibility that contaminants will be carried by groundwater to the surface, where they could damage the environment. The waste is contained deeper and more securely.

scholarly journals Effect of thermal relaxation on residual stress and microstructure in the near-surface layers of dual shot peened Inconel 625

2018 ◽  
Vol 10 (10) ◽  
pp. 168781401880053
Author(s):  
Lihong Wu ◽  
Chuanhai Jiang
Keyword(s):  
Residual Stress ◽  
Compressive Residual Stress ◽  
Elevated Temperatures ◽  
Thermal Relaxation ◽  
Diffraction Method ◽  
Relaxation Behavior ◽  
Inconel 625 ◽  
Surface Layers ◽  
Near Surface ◽  
Subsurface Layers

Thermal relaxation behavior of residual stress and microstructure in the near-surface layers of dual shot peened Inconel alloy 625 was investigated by X-ray diffraction method. Residual stress on the top surface layer was significantly relaxed in the first 15 min at the elevated temperatures of 500°C, 600°C, and 700°C. However, there was still high maximum compressive residual stress in subsurface layers. The relaxation behavior of residual stress has contributed to the thermally activated process. The activation enthalpy Δ H and m were calculated according to the Zener–Wert–Avrami method, the values of which were 1.59 eV and 0.4934, respectively. Microstructural evaluation revealed that it was slightly changed in the near-surface layers after various isothermal treatments. Accordingly, high level of compressive residual stress and dislocation density resulted in the retained mechanical properties of dual shot peened Inconel 625, which was discussed based on the relaxation of microstructure and microhardness.

scholarly journals Boat-towed radio-magnetotelluric and controlled source audio-magnetotelluric study to resolve fracture zones at Äspö Hard Rock Laboratory site, Sweden

2019 ◽  
Vol 218 (2) ◽  
pp. 1008-1031 ◽  
Author(s):  
Shunguo Wang ◽  
Mehrdad Bastani ◽  
Steven Constable ◽  
Thomas Kalscheuer ◽  
Alireza Malehmir
Keyword(s):  
Shallow Water ◽  
Penetration Depth ◽  
Large Scale ◽  
Hard Rock ◽  
High Water ◽  
Fracture Zones ◽  
Geological Structures ◽  
Near Surface ◽  
Controlled Source ◽  
Rock Laboratory

SUMMARY Boat-towed radio-magnetotelluric (RMT) measurements using signals between 14 and 250 kHz have attracted increasing attention in the near-surface applications for shallow water and archipelago areas. A few large-scale underground infrastructure projects, such as the Stockholm bypass in Sweden, are planned to pass underneath such water zones. However, in cases with high water salinity, RMT signals have a penetration depth of a few metres and do not reach the geological structures of interest in the underlying sediments and bedrock. To overcome this problem, controlled source signals at lower frequencies of 1.25 to 12.5 kHz can be utilized to improve the penetration depth and to enhance the resolution for modelling deeper underwater structures. Joint utilization of boat-towed RMT and controlled source audio-magnetotellurics (CSAMT) was tested for the first time at the Äspö Hard Rock Laboratory (HRL) site in south-eastern Sweden to demonstrate acquisition efficiency and improved resolution to model fracture zones along a 600-m long profile. Pronounced galvanic distortion effects observed in 1-D inversion models of the CSAMT data as well as the predominantly 2-D geological structures at this site motivated usage of 2-D inversion. Two standard academic inversion codes, EMILIA and MARE2DEM, were used to invert the RMT and CSAMT data. EMILIA, an object-oriented Gauss–Newton inversion code with modules for 2-D finite difference and 1-D semi-analytical solutions, was used to invert the RMT and CSAMT data separately and jointly under the plane-wave approximation for 2-D models. MARE2DEM, a Gauss–Newton inversion code for controlled source electromagnetic 2.5-D finite element solution, was modified to allow for inversions of RMT and CSAMT data accounting for source effects. Results of EMILIA and MARE2DEM reveal the previously known fracture zones in the models. The 2-D joint inversions of RMT and CSAMT data carried out with EMILIA and MARE2DEM show clear improvement compared with 2-D single inversions, especially in imaging uncertain fracture zones analysed in a previous study. Our results show that boat-towed RMT and CSAMT data acquisition systems can be utilized for detailed 2-D or 3-D surveys to characterize near-surface structures underneath shallow water areas. Potential future applications may include geo-engineering, geohazard investigations and mineral exploration.

Mineralogy of the near-surface expression of Au-As-Cu mineralization in an arid environment

1994 ◽  
Vol 58 (391) ◽  
pp. 315-323
Author(s):  
R. Bogoch ◽  
M. Shirav ◽  
A. Gilat ◽  
L. Halicz
Keyword(s):  
Iron Oxide ◽  
Surface Expression ◽  
Arid Environment ◽  
Solid Solution Phase ◽  
Near Surface ◽  
Amorphous Phases ◽  
Fine Grained ◽  
Precambrian Terrain ◽  
Spherical Droplets ◽  
Neutral Conditions

AbstractIn the arid, Late Precambrian terrain of southern Israel, a complex suite of minerals and amorphous species were deposited in host gneiss from fluids under near-neutral conditions within 1 m of the surface. The morphology of secondary gold appears to relate to its host mineral (skeletal-dendritic with quartz; multi-faceted crystals with arsenates; spherical droplets with iron oxide). The gold is very fine-grained, and was most likely complexed as a thiosulphate.Three amorphous phases are present (iron oxide, chrysocolla, Cu-Mn-(Fe-As) silicate). At least in part, gold and baryte appear to have crystallized out of a metal-Fe-oxide gel. Other minerals, including apatite, anglesite, and conichalcite, may have grown from appropriate crystallites present in the gel.The conichalcite occurs mainly as bladed to acicular radial spherulites. In the presence of lead, a solid solution phase between duftite and conichalcite (‘Pb-conichalcite’) was formed.

scholarly journals Combining Resistivity and Aeromagnetic Geophysical Surveys for Groundwater Exploration in the Maghnia Plain of Algeria

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Djamel Boubaya
Keyword(s):  
Groundwater Potential ◽  
Groundwater Exploration ◽  
Magnetic Data ◽  
Geoelectric Section ◽  
Resistive Layer ◽  
Near Surface ◽  
Groundwater Aquifer ◽  
Geophysical Surveys ◽  
Schlumberger Sounding ◽  
Topsoil Layer

The Maghnia plain in western Algeria is filled by Plio-Quaternary and Miocene sediments that rest unconformably on a basement of Jurassic rocks. Electrical sounding (VES), magnetic data, well information, and hydrogeological data have been used to explore for groundwater potential in the Maghnia plain. The interpretation of Schlumberger sounding data was first calibrated with the lithology of available nearby wells. Four geoelectrical layers were identified within the study area. They are a thin near surface topsoil layer with variable resistivities, a moderate resistive aquifer (15–30 ohm-m), a resistive aquifer (40–70 ohm-m), and a conductive clay layer (1–10 ohm-m). Near Sidi Mbarek, the geoelectric section is reduced to three layers: a topsoil layer, a conductive layer corresponding to the Miocene marls, and a deep resistive layer that correlates with the Oxfordian sandstones. The interpretation of VES data and the enhancement techniques of magnetic data enabled the identification of a number of unmapped faults that occur near recharge zones close to adjacent mountains. This study enabled us to study the extension of the known Plio-Quaternary aquifer of the Maghnia plain and to explore the possible existence of a second deep groundwater aquifer in Oxfordian sandstones.

scholarly journals Epistemic uncertainty and limitations of theκ0model for near-surface attenuation at hard rock sites

2015 ◽  
Vol 202 (3) ◽  
pp. 1627-1645 ◽  
Author(s):  
Benjamin Edwards ◽  
Olga-Joan Ktenidou ◽  
Fabrice Cotton ◽  
Norman Abrahamson ◽  
Chris Van Houtte ◽  
...  
Keyword(s):  
Hard Rock ◽  
Epistemic Uncertainty ◽  
Near Surface
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