Sensitivity Analysis of Internal Dragline Dump stability: Finite Element Analysis     

Rajesh Rai  S. Kalita  T. Gupta  B. K Shrivastva 《Geotechnical and Geological Engineering》2012,30(6):1397-1404

The stability of mine waste dump is of paramount importance from economic and safety point of view. The present paper deals with the stability analysis of an internal dragline dump of an opencast coal mine by finite element method to classify input parameters in terms of sensitivity. Sensitivity analysis has been carried out for geometrical and geotechnical parameters of dump slope. It has been concluded from the results that ??friction angle?? is a more sensitive parameter as compared to the cohesion of dump material. The geometrical parameters of ??slope angle?? and ??height of dragline dump?? are classified as very high sensitive. The ??height of main dump?? could be classified as least sensitive, whereas, ??gradient of the seam?? and ??thickness of coal rib?? as medium sensitive parameters.  相似文献   

Studies of grand minima in sunspot cycles by using a flux transport solar dynamo model     

Bidya Binay  Karak Amab  Rai Choudhuri 《天文和天体物理学研究(英文版)》2013,(11):1339-1357

We propose that grand minima in solar activity are caused by simultane- ous fluctuations in the meridional circulation and the Babcock-Leighton mechanism for the poloidal field generation in the flux transport dynamo model. We present the following results： （a） fluctuations in the meridional circulation are more effective in producing grand minima; （b） both sudden and gradual initiations of grand minima are possible; （c） distributions of durations and waiting times between grand minima seem to be exponential; （d） the coherence time of the meridional circulation has an effect on the number and the average duration of grand minima, with a coherence time of about 30 yr being consistent with observational data. We also study the occurrence of grand maxima and find that the distributions of durations and waiting times between grand maxima are also exponential, like the grand minima. Finally we address the question of whether the Babcock-Leighton mechanism can be operative during grand minima when there are no sunspots. We show that an a-effect restricted to the upper portions of the convection zone can pull the dynamo out of the grand minima and can match various observational requirements if the amplitude of this a-effect is suitably fine-tuned.  相似文献   

On the Connection Between Mean Field Dynamo Theory and Flux Tubes     

Arnab Rai Choudhuri 《Solar physics》2003,215(1):31-55

Mean field dynamo theory deals with various mean quantities and does not directly throw any light on the question of existence of flux tubes. We can, however, draw important conclusions about flux tubes in the interior of the Sun by combining additional arguments with the insights gained from solar dynamo solutions. The polar magnetic field of the Sun is of order 10 G, whereas the toroidal magnetic field at the bottom of the convection zone has been estimated to be 100000 G. Simple order-of-magnitude estimates show that the shear in the tachocline is not sufficient to stretch a 10 G mean radial field into a 100000 G mean toroidal field. We argue that the polar field of the Sun must get concentrated into intermittent flux tubes before it is advected to the tachocline. We estimate the strengths and filling factors of these flux tubes. Stretching by shear in the tachocline is then expected to produce a highly intermittent magnetic configuration at the bottom of the convection zone. The meridional flow at the bottom of the convection zone should be able to carry this intermittent magnetic field equatorward, as suggested recently by Nandy and Choudhuri (2002). When a flux tube from the bottom of the convection zone rises to a region of pre-existing poloidal field at the surface, we point out that it picks up a twist in accordance with the observations of current helicities at the solar surface.  相似文献   

New record of Bathonian–Callovian calcareous nannofossils in the eastern Karakoram block: a possible clue to understanding the dextral offset along the Karakoram Fault     

Rajeev Upadhyay  Jyotsana Rai  Anshu K Sinha 《地学学报》2005,17(2):149-157

We report the first record of Bathonian–Callovian calcareous nannofossils from a marine sedimentary sequence of the eastern Karakoram block, in northern India. The calcareous mudstones and packstones, occasionally bearing red chert nodules, yielded calcareous nanofossils and Middle Jurassic Choffatia furcula ammonoids. Middle to Upper Jurassic nannofossil assemblage is dominated by representatives of the genus Watznaueria. The occurrence of Ansulasphaera helvetica whose range is Upper Bathonian–Upper Callovian, indicates a correlation with nannofossil zones NJ12–13. The occurrence of Cyclagelosphaera wiedmannii further infer an Upper Bathonian–Callovian age. These specimens show affinities with those found in a similar sedimentary formation exposed in north Karakoram. This suggests the existence of a narrow and elongated sedimentary basin, oriented in a NW–SE direction, at a latitude of c. 25°–30°N. At that time, the Karakoram block was situated near the already welded Qiangtang block of Asia. The northern and eastern Karakoram blocks were connected during Middle Jurassic. The activity and dextral offset of the Karakoram fault separated the Jurassic sedimentary formations of the northern and eastern Karakoram blocks by c. 150 km.  相似文献   

Seismically constrained two-dimensional crustal thermal structure of the cambay basin     

S. Thiagarajan  D. V. Ramana  S. N. Rai 《Journal of Earth System Science》2001,110(1):1-8

The temperature field within the crust is closely related to tectonic history as well as many other geological processes inside the earth. Therefore, knowledge of the crustal thermal structure of a region is of great importance for its tectonophysical studies. This work deals with the two-dimensional thermal modelling to delineate the crustal thermal structure along a 230 km long Deep Seismic Sounding (DSS) profile in the north Cambay basin. In this work P-wave velocities obtained from the DSS studies have been converted into heat generation values for the computation of temperature distribution. The model result reveals the Curie isotherm at a depth of ≈22 km and Moho temperature at around 900‡C.  相似文献   

Performance of elevated tanks in<Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">w</Emphasis></Subscript> 7.7 Bhuj earthquake of january 26th, 2001     

Durgesh C Rai 《Journal of Earth System Science》2003,112(3):421-429

The current designs of supporting structures of elevated water tanks are extremely vulnerable under lateral forces due to an earthquake and the Bhuj earthquake provided another illustration when a great many water tank stagings suffered damage and a few collapsed. The more popular shaft type stagings suffer from poor ductility of thin shell sections besides low redundancy and toughness whereas framed stagings consist of weak members and poor brace-column joints. A strength analysis of a few damaged shaft type stagings clearly shows that all of them either met or exceeded the strength requirements of IS:1893-1984, however, they were all found deficient when compared with requirements of the International Building Code. IS:1893-1984 is unjustifiably low for these systems which do not have the advantage of ductility and redundancy and are currently being underestimated at least by a factor of 3 and need an upward revision of forces immediately.  相似文献   

Modeling water-table fluctuations in a sloping aquifer with random hydraulic conductivity   总被引：1，自引：0，他引：1  

Kirti Srivastava  S. Rai  R. Singh 《Environmental Geology》2002,41(5):520-524

To prevent environmental problems like water logging and increase in soil salinity which are responsible for the degradation of the top productive soils, an optimum ditch drainage design is required. For this purpose a knowledge of the spatio-temporal variation of the water table is essential. In this study the spatio-temporal variation of the water table in a sloping ditch drainage system has been modeled from a stochastic point of view, incorporating randomness in hydraulic conductivity to get the expression for the mean and the standard deviation of the water-table height. The hydraulic conductivity has been considered to be a realization of a log-normal distribution. Application of these expressions in the prediction of mean water-table variation with the associated error bounds has been demonstrated with the help of a ditch drainage problem of a sloping aquifer. The sensitivity analysis has also been carried out to see the effect of variability in the hydraulic conductivity on the water-table fluctuations. The error bounds quantified on the water-table height will thus help in the decision-making process for proper drainage design.  相似文献   

Synergistic Application of Four Remedial Techniques at an Industrial Site     

Jean. M. Dasch  Abdul S. Abdul  Devi N. Rai  Thomas L. Gibson  Noel Grosvenor 《Ground Water Monitoring & Remediation》1997,17(3):194-209

The soil and ground water at a General Motors plant site were contaminated with petroleum products from leaking underground storage tanks. Based on the initial assessment, the site was complex from the standpoint of geology (clay layers), hydrology (a recharge zone with a perched water table), and contaminant (approximately 4800 gallons of mixed gasoline and oil). After a thorough study of remedial alternatives, a synergistic remedial approach was adopted including pump and treat, product removal, vapor extraction, and bioventing. The system was designed and implemented at the site through 22 dual-extraction wells. Over a 21-month period, 4400 gallons of gasoline and oil were removed from the system, including 59 percent by vapor extraction, 28 percent by bioventing, and 13 percent by pump and treat. Synergism between the various remedial methods was demonstrated clearly. Ground water pump and treat lowered the water table, allowing air to flow for vapor extraction. The vacuum applied for vapor extraction increased the ground water removal rate and the efficiency of pump and treat. The vapor extraction system also added oxygen to the soil to stimulate aerobic biodegradation.  相似文献   

Hydromorphogeological Mapping for Groundwater Prospecting Using Landsat-MSS Images — A Case Study of Part of Dhanbad District,Bihar     

A Tiwari  B Rai 《Journal of the Indian Society of Remote Sensing》1996,24(4):281-285

The Dhanbad district in Bihar, feces acate water scareity and is chronically drought prone. The groundwater resources in the area have not been fully exploited. The present study was undertaken to evaluate the groundwater prospective zones, Landsat-5 MSS data of band-2 and band-4 and false colour composite of band 2, 3, 4 were interpreted visually to differentiate different hydromarphogeological units and to delineate the major trends of lineaments. The different geomorphic features identified are linear ridges, residual hills, pediplain, buried pedtment and dissected pediplain, besides lineaments. The study shows that the pediplain and buried pediments are promising zones for groundwater prospecting.  相似文献   

辽西─冀北地区铀成矿遥感地质信息的研究     

于宝山  王殿柏  金时华  乔锐 《华东地质学院学报》1996,(4)

本文从辽西—冀北铀矿床成矿地质环境、时空分布及矿床特征出发，在以遥感信息为主，综合地质、物化探、水文等资料的全区性联幅应用开发、复合成图、综合分析以及重点地区的野外详细调查的基础上，运用切合全区地壳运动的演化理论，揭示了区内地壳演化及其结果的构造格局、区域地质背景、铀成矿条件和时空分布规律，建立了不同岩区环弧形构造解译标志，并阐述了其地质成因。解译了火山机构、小型封闭沉积盆地和铀矿密切相关的岩浆岩体，着重解译了控矿构造和矿化蚀变带的产状、类型，强调解译了卫片图像“热晕点”，并讨论了其地质意义和铀矿的关系，最后确定了遥感地质找矿模式和综合预测模型。  相似文献