Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

R. L. Dhar ¹, N. S. Krishnamurthy ¹, B. A. Prakash ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad-500007, IN

Abstract

Geohydrological investigations including deep resistivity Schlumberger soundings were carried out to locate suitable drilling sites for groundwater expIoitation near Ramgarh, Alwar district, Rajasthan. The area under study appears to be a synclinal valley and is covered by a thick piIe of sediments comprising sand, silt, clay, gravel, pebble, kankar and scree underlain by rocks of Ajabgarb Group, which are exposed north-west of the area. The subsurface layer parameters obtained from the sounding interpretation have been presented in the form of fence diagrams and a geoelectric section. Characteristic resistivities of various litho-units were obtained by correlating the lithology of an existing tube well with the geoelectrical sounding data. The correlation indicated that there is very little resistivity contrast between water-bearing sandy layers and the kankar and clay beds. However, the kankar and clay beds are mostly confined to the top 20 m or so. Although occurrence of clay has not been reported in rocks of Ajabgarh Group except for thin lenses, the present investigations reveal a surprisingly low resistivity for the formation underlying the bedrock, which may be an indication of its saline and clayey nature. The possibility of an altered horizon in the bedrock comprising metasediment through lateral inflow of water cannot be ruIed out.

Keywords

Hydrogeology, Groundwater, Resistivity Sounding.

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S. Chandra ¹, S. Atal ¹, N. S. Krishnamurthy ¹, k. Subrahmanyam ¹, R. Rangarajan ¹, D. V. Reddy ¹, P. Nagbhushanam ¹, J. V. S. Murthy ¹, S. Ahmed ¹, V. P. Dimri ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

No Abstract.

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Dewashish Kumar ¹, N. S. Krishnamurthy ¹, Shekeel Ahmed ¹, S. C. Jain ¹, R. L. Dhar ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

Mise-a-la-masse technique has been applied to map water filled fracture1 struck in bore wells in a small watershed near Hyderabad. The area consists of hard crystalline rock mainly granite where groundwater is mostly tapped from iractured rock. In the watershed, 25 wells have been drilled fairly distributed over the area on the basis of results of Vertical Electrical Soundings (VES) to study the groundwater conditions in the weatheredffractured aquifer system. Mise-a-la-masse and Spontaneous Polarization (SP) investigations were carried out at five out of these 25 sites, to delineate the lateral extension of fractures. The anomalies are clearly indicative at four locations and some indication is seen at the fifth location. Two bore wells drilled on the basis of these results have encountered fractures at the same depth as at the experimental site. It is concluded that mise-a-la-masse technique supplemented with S.P. investigations could be helpful in delineating the extension of fractures.

Keywords

Mise-a-la-Masse, SP, Electrical Mapping, Fractures in Hard Rock, Maheshwaram Watershed, Andhra Pradesh.

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N. S. Krishnamurthy ¹, V. Ananda Rao ¹, Dewashish Kumar ¹, K. K. K. Singh ², Shakeel Ahmed ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 606 (Council of Scientific and Industrial Research), IN
2 Central Institute of Mining and Fuel Research, Dhanbad - 826 001, IN

Abstract

Exploration and exploitation of coal seams is one of the major resources for the energy sector in any country but at the same time water filled voids/water logged areas in the old workings of these seams are very critical problems for the coal mining industry. In such situations, disasters like inundation, landslides, collapsing of the old seams may occur. In this regard, it is necessary to find out the water saturated/water filled voids and zones in the mining areas. Since no established technique is available to find such zones, an experimental study using Electrical Resistivity Imaging (ERI) has been carried out in one of the coal mining areas near Dhanbad, to find out the feasibility of finding the barrier thickness and the water logged area in underground coal mines. The area under study forms part of Jharia coalfield in Dhanbad district, Jharkhand state. The coal bearing rocks of Barakar Formation of Lower Permian age (Gondwana period) occur in the area under a thin cover (10 m to15 m) of soil and or alluvium. Coal bearing Barakar Formations consist mainly of sandstone of varying grain size, intercalation of shale and sandstone, grey and carbonaceous-shale and coal seams.

Since the water saturation reduces the resistivity of a formation to a large extent, water filled voids and old coal workings are expected to have significant resistivity contrast with the surrounding host rock. Hence, ERI technique was applied in such an environment as this technique uses high-density data acquisition both laterally and vertically by using multiple number of electrodes. Along with ERI, mise-a-la-masse (also called charged body) technique was also employed at one of the promising sites to find out the connectivity of water logged areas and also detection of these old workings from the surface measurements was analyzed. The interpreted 2D resistivity sections have clearly indicated the water bearing zone(s) along the profile which was well confirmed with the existing water level in the nearby borewells. On the other hand, this technique did not identify the size of the coal pillar and gallery (air filled voids), which might be due to the small size of the voids (i.e. about 2 m × 2 m) below a depth of 15m and more but have indicated altogether as a high resistive zone ranging from 600-1000 Ohm-m.

Keywords

Coal Seams, Water Filled Voids, Electrical Resistivity Imaging, Jharia Coalfield, Dhanbad, Jharkhand.

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