An engineering geological appraisal of the Lakhwar Dam, Garhwal Himalaya, India     

Sanjeev Sharma  Tarun Raghuvanshi  Atul Sahai 《Engineering Geology》1999,53(3-4):381-398

A 204 m high solid concrete gravity dam is proposed across the River Yamuna in Garhwal Himalaya, India. It will be located on dolerite rocks which have been intruded into the slates of Chandpur Formation. The present study includes the evaluation of the dam foundation by means of drifts, drill holes, water pressure tests and abutment slope stability studies. The water pressure test indicate the necessity of providing a grout curtain below the dam foundation. The analysis of the dam abutments for stability using the Limit equilibrium method indicates that the right abutment slope is kinematically unstable for plane failure mode. The plane failure analysis of the right abutment slope was carried out by modifying the Hoek and Bray (1981, Rock Slope Engineering, 3rd ed., Institute of Mining and Metallurgy, London) technique of plane failure analysis. The analysis reveals that right abutment slope may become unstable during the stripping operation. Based upon the analysis a safe cut slope design for the abutments have been suggested. Subsurface exploration by means of cross drift and drill holes has indicated a sheared contact of slate and dolerite in the foundation area. To avoid the settlement of the dam along this shear zone precautionary measures are suggested.  相似文献   

Deep exploration using long-offset transient electromagnetics: interpretation of field data in time and frequency domain     

Wiebke Mörbe  Pritam Yogeshwar  Bülent Tezkan  Tilman Hanstein 《Geophysical Prospecting》2020,68(6):1980-1998

In the framework of the Deep Electromagnetic Soundings for Mineral Exploration project, we conducted ground-based long-offset transient-electromagnetic measurements in a former mining area in eastern Thuringia, Germany. The large-scale survey resulted in an extensive dataset acquired with multiple high-power transmitters and a high number of electric and magnetic field receivers. The recorded data exhibit a high data quality over several decades of time and orders of magnitude. Although the obtained subsurface models indicate a strong multi-dimensional subsurface with variations in resistivity over three orders of magnitude, the electrical field step-on transients are well fitted using a conventional one-dimensional inversion. Due to superimposed induced polarization effects, the transient step-off data are not interpretable with conventional electromagnetic inversion. For further interpretation in one and two dimensions, a new approach to evaluate the long-offset transient-electromagnetic data in frequency domain is realized. We present a detailed workflow for data processing in both domains and give an overview of technical obstructions that can occur in one domain or the other. The derived one-dimensional inversion models of frequency-domain data show strong multi-dimensional effects and are well comparable with the conventional time domain inversion results. To adequately interpret the data, a 2.5D frequency-domain inversion using the open source algorithm MARE2DEM (Modeling with Adaptively Refined Elements for 2-D EM) is carried out. The inversion leads to a consistent subsurface model with shallow and deep conductive structures, which are confirmed by geology and additional geophysical surveys.  相似文献   

Climate Change: A Case Study Over India   总被引：1，自引：0，他引：1  

A. K. Sahai 《Theoretical and Applied Climatology》1998,61(1-2):9-18

Summary A brief account of various causes of climate change in recent decades and climate change trends in the Indian region is presented. It is of great importance to determine the influence of human activities on the likely climate change during recent decades. Local temperature is one of the major climatic elements to record the changes in the atmospheric environment caused by industrialization and urbanization. It is mentioned in the literature that there is either a cooling tendency or cessation of warming after the late 1950s at most of the Indian industrial cities. A case study of Nagpur, a centrally located city in India, is done to understand and the possible cause of cooling. Nagpur is the only city in India for which a long-term record of temperature, for urban (Mayo Hospital) and relatively suburban (Sonegaon Airport) area, is available. The study of the diurnal asymmetry in maximum and minimum temperatures indicates that the role of suspended particulate matter dominates over that of increasing greenhouse gases. Received April 15, 1998  相似文献   

Nightglow OH (8, 3) band intensities and rotational temperature at 23°S     

H. Takahashi  B.R. Clemesha  Y. Sahai 《Planetary and Space Science》1974,22(9):1323-1329

The OH (8, 3) band airglow emission has been observed over 1 year at a latitude of 23°S. The average band intensity observed was 385 Rayleighs with a nocturnal range typically less than 100 R. The nocturnal variation in rotational temperature was usually less than 10°K, and the mean temperature was 179°K. The nocturnal variation of intensity is usually uncorrelated with that of the rotational temperature. Time average values of these parameters do, however, show some correlation. On some occasions large post-twilight and pre-dawn intensity enhancements are observed.  相似文献   

Recent changes in the spatio-temporal characteristics of monsoon intraseasonal oscillations     

Joseph  Susmitha  Sahai  A. K.  Shabu  Hindhiya  Chattopadhyay  R.  Kaur  Manpreet 《Theoretical and Applied Climatology》2022,147(1-2):251-264

Theoretical and Applied Climatology - Monsoon intraseasonal oscillations (MISOs) define a significant proportion of intraseasonal variability of the Indian summer monsoon. In the backdrop of...  相似文献   

North Indian heavy rainfall event during June 2013: diagnostics and extended range prediction     

Susmitha Joseph  A. K. Sahai  S. Sharmila  S. Abhilash  N. Borah  R. Chattopadhyay  P. A. Pillai  M. Rajeevan  Arun Kumar 《Climate Dynamics》2015,44(7-8):2049-2065

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Engineering applications of remote sensing     

Baldev Sahai 《Journal of the Indian Society of Remote Sensing》1989,17(4):1-8

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On the recent strengthening of the relationship between ENSO and northeast monsoon rainfall over South Asia   总被引：1，自引：1，他引：1  

Pankaj Kumar  K. Rupa Kumar  M. Rajeevan  A. K. Sahai 《Climate Dynamics》2007,28(6):649-660

The southeastern parts of India and Sri Lanka receive substantial rainfall from the northeast monsoon (NEM) during October through December. The interannual variability in NEM rainfall is known to be significantly influenced by the El-Niño/Southern Oscillation (ENSO). Unlike the southwest monsoon (SWM), the NEM rainfall is enhanced during the warm ENSO events, and vice versa. In the context of the recent weakening of the inverse relationship between Southwest Monsoon (SWM) and ENSO, we examine the secular variations in the positive relationship between ENSO and NEM rainfall over South Asia, showing that their relationship has strengthened over the recent years. Based on the analysis of GISST, IMD/CRU precipitation and NCEP/NCAR reanalysis data, we suggest that this secular variation of the relationship is due to epochal changes in the tropospheric circulation associated with ENSO over the region.  相似文献   

Twin tropical cyclones in the Indian Ocean: the role of equatorial waves     

Sujata K. Mandke  A. K. Sahai 《Natural Hazards》2016,84(3):2211-2224

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On the production of traveling ionospheric disturbances by atmospheric gravity waves     

J. MacDougall  M.A. Abdu  I. Batista  P.R. Fagundes  Y. Sahai  P.T. Jayachandran 《Journal of Atmospheric and Solar》2009,71(17-18):2013-2016

This paper deals with how atmospheric gravity waves produce the traveling ionospheric disturbances (TIDs) that are observed by ionosondes. It is shown that, rather than directly producing variations of ionospheric height, a likely mechanism involves changes in ionization density by gradients in the horizontal atmospheric gravity wave air motion. These density changes can be observed as variations of the height of an ionospheric isodensity surface (the usual way of measuring TIDs). This mechanism involving enhancement/depletion of ionospheric density requires quite moderate atmospheric gravity wave air motion speeds, and works well at almost all latitudes.  相似文献