Numerical modeling of combined effects of upward and downward propagation of shear bands on stability of slopes with sensitive clay          下载免费PDF全文

R. Dey  B. Hawlader  R. Phillips  K. Soga 《国际地质力学数值与分析法杂志》2016,40(15):2076-2099

Modeling of progressive development of zones of large inelastic shear deformation (shear band) that results from strain‐softening behavior of sensitive clays could explain the failure mechanisms of large landslides. Because of toe erosion, a shear band can be initiated and propagated upward (inward) from the river bank. On the other hand, upslope surcharge loading could generate shear bands that might propagate down towards the river bank. In the present study, upward and downward propagation of shear bands and failure of sensitive clay slopes are modeled using the Coupled Eulerian Lagrangian approach in Abaqus finite element (FE) software. It is shown that the formation and propagation of shear bands are significantly influenced by kinematic constraints that change with displacements of the soil masses, and therefore the propagation of an existing shear band might be stopped and new shear bands could be formed. The main advantages of the present FE modeling are: (i) extremely large strains in the shear bands can be successfully simulated without numerical issues, (ii) a priori definition of shearing zones is not required to tackle severe strains; instead, the FE program automatically identifies the critical locations for shear band formation and propagation. Toe erosion could significantly increase the slope failure potential because of upslope surcharge loading. FE analyses with a thick and thin sensitive clay layers show that the global failure could occur at lower surcharge loads in the former as compared to the latter cases. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Cost Optimization of Reinforced Earth Walls   总被引：1，自引：0，他引：1  

P. K. Basudhar  Amol Vashistha  Kousik Deb  Arindam Dey 《Geotechnical and Geological Engineering》2008,26(1):1-12

This paper deals with optimum cost (objective function) design of geosynthetic reinforced earth retaining walls subjected to static and dynamic loading. The design restrictions are imposed as design constraints in the analysis. Choice of the initial designed length and strength of the reinforcement, which are the elements of the design vectors are made in a way that it forms an initial feasible design vector. Thus the problem is one of mathematical programming. The constraints and the objective function being nonlinear in nature, the Sequential Unconstrained Minimization Technique (SUMT) has been used in conjunction with conjugate direction and quadratic fit methods for multidimensional and unidirectional minimization to arrive at the optimal (minimum) cost of the reinforced earth wall. Optimal cost tables are presented for different combinations of the loading and the developed procedure is validated by taking up an example problem. It has been found from the typical example problem that saving of the order of 7–8% can be made over the conventional design of mechanically stabilized earth (MSE) walls with the aid of design charts.  相似文献   

Direct radiative effects of anthropogenic aerosols on Indian summer monsoon circulation   总被引：1，自引：1，他引：0  

Sushant Das  Sagnik Dey  S. K. Dash 《Theoretical and Applied Climatology》2016,123(3-4):629-636

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Influence of Relative Pile-Soil Stiffness and Load Eccentricity on Single Pile Response in Sand Under Lateral Cyclic Loading     

Sudip Basack  Sandip Dey 《Geotechnical and Geological Engineering》2012,30(4):737-751

The environment prevalent in ocean necessitates the piles supporting offshore structures to be designed against lateral cyclic loading initiated by wave action, which induces deterioration in the strength and stiffness of the pile-soil system introducing progressive reduction in the bearing capacity associated with increased settlement of the pile foundation. A thorough and detailed review of literature indicates that significant works have already been carried out in the relevant field of investigation. It is a well established phenomenon that the variation of relative pile-soil stiffness (K _rs ) and load eccentricity (e/D) significantly affect the response of piles subjected to lateral static load. However, the influence of lateral cyclic load on axial response of single pile in sand, more specifically the effect of K _rs and e/D on the cyclic behavior, is yet to be investigated. The present work has aimed to bridge up this gap. To carry out numerical analysis (boundary element method), the conventional elastic approach has been used as a guideline with relevant modifications. The model developed has been validated by comparing with available experimental (laboratory model and field tests) results, which indicate the accuracy of the solutions formulated. Thereafter, the methodology is applied successfully to selected parametric studies for understanding the magnitude and pattern of degradation of axial pile capacity induced due to lateral cyclic loading, as well as the influence of K _rs and e/D on such degradation.  相似文献   

Super bursts and long bursts as surface phenomena of compact objects     

Monika Sinha  Mira Dey †  Subharthi Ray ‡§  Jishnu Dey ‡ 《Monthly notices of the Royal Astronomical Society》2002,337(4):1368-1372

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Strange pulsar hypothesis     

Raka Dona Ray Mandal  Monika Sinha †  Manjari Bagchi  Sushan Konar  Mira Dey ‡  Jishnu Dey 《Monthly notices of the Royal Astronomical Society》2006,365(4):1383-1386

It appears that there is a genuine shortage of radio pulsars with surface magnetic fields significantly smaller than ∼10⁸ G. We propose that the pulsars with very low magnetic fields are actually strange stars locked in a state of minimum free energy and therefore at a limiting value of the magnetic field which cannot be lowered by the system spontaneously.  相似文献   

Halo ejection in distant radio galaxies: jet feedback in massive galaxy formation     

Michael A. Dopita  Michiel Reuland  Wil van Breugel  Wim de Vries  S. A. Stanford  Huub Röttgering  George Miley  Bram Venemans  Hy Spinrad  Steve Dawson  Arjun Dey  Mark Lacy  Daniel Stern  Andrew Bunker 《Astrophysics and Space Science》2007,311(1-3):305-309

We present results from a Keck optical and near IR spectroscopic study of the giant emission line halos of the z>3 High Redshift Radio Galaxies (HiZRGs) 4C 41.17, 4C 60.07 and B2 0902+34. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km s⁻¹ and velocity shears consistent with rotation. The inner regions contain shocked, clumpy cocoons of gas closely associated with the radio lobes with disturbed kinematics and expansion velocities and/or velocity dispersions >1000 km s⁻¹. We also find evidence for the ejection of chemically enriched material in 4C 41.17 up to a distance of ∼60 kpc along the radio-axis. We infer that these HiZRGs are undergoing a final jet-induced phase of star formation with the ejection of most of their interstellar medium before evolving to become “red and dead” Elliptical galaxies.  相似文献   

Monitoring of River Center Line and Width—A Study on River Brahmaputra     

Aveedibya Dey  Rajib Kumar Bhattacharya 《Journal of the Indian Society of Remote Sensing》2014,42(2):475-482

Monitoring of river width and centerline is one of the most important activities in river engineering. Changes in the width and center line can be attributed to several reasons and monitoring these changes can be conveniently achieved with the aid of remote sensing images. In this study, digital image processing techniques have been implemented using the image processing tool-box available in MATLAB for studying temporal variations of width and centerline of the river Brahmaputra in its 300 Km reach in the state of Assam, India. The current study uses relatively high resolution imageries acquired from the LANDSAT series of satellites. Apart from the LANDSAT imageries, the low resolution imageries acquired by MODIS program is also used in order to see the variation in the obtained results. The evaluation of the results shows that the digital image processing technique is very handy and can be applied to obtain the centerline and width of a river. The evaluation also shows that the low resolution image can also be used for obtaining centerline of a river. However, it may give erroneous result when width of the river is narrow or very large.  相似文献   

A geospatial assessment of flood hazard in north-eastern depressed basin,Bangladesh     

Mohammad Abdul Quader  Hemal Dey  Md. Abdul Malak  Md. Zakiur Rahman 《Singapore journal of tropical geography》2023,44(2):277-299

Floods are a frequently occurring calamity in deltaic Bangladesh. This paper aims to assess the temporal expansion of waterbodies during flooding using geospatial techniques. Several water indices were applied to classify the satellite images at various temporal scales. Among them, the Normalized Difference Water Index (NDWI) showed the highest correlation (r = 0.831; where p = 0.01) with rainfall data. Specifically, the NDWI results showed that perennial waterbodies measured 37 km² and 60 km² in Sunamganj District in 2017 and 2019, respectively. The area of waterbodies notably increased 52-fold from March to April (37 km² to 1958 km²) during the pre-monsoon flash flood of 2017. During the July 2019 monsoon flood, waterbodies started to extend after May and flooded 2784 km² in area. NDVI analysis showed that in 2019, floodwater submerged 361.7 km² of vegetation cover. At the same time, the Surma River's flooding resulted in a 73.9 per cent inundation of the total area of the Sunamganj District. We hope that this study will provide better understanding of the varying nature of floods that occur in the low lying bowl shaped Haor region which will in turn assist the government with flood mitigation.  相似文献   

Imaging and visualizing the spectral signatures from Landsat TM and ‘τ’ value-based surface soil microzonation mapping at and around Agartala (India)     

Sudip Dey  Gunjan Mukherjee  Sushmita Paul 《国际地球制图》2013,28(2):144-158

This work aims to assess the soil microzonation of Agartala city and its surrounding areas based on spectral geophysical signatures. Different spectral resolutions of Landsat TM have been used for assessing the Normalized Difference Vegetative Index, spatial thermal emission representation and plant water moisture representation. Normalized Difference Vegetative Index (NDVI) was measured from band 4 (near-infrared (NIR)) and band 3 (photosynthetically active radiation (PAR)). The Digital Number (DN) values of thermal infrared band (TIR) were used for measuring spatial variation of thermal representation in the city area. A very simple model was developed for measuring thermal emission representative index from NDVI and automated classified TIR band. Overlaid NDVI and classified TIR shows the spatial distribution of thermal emission representative values. Classified mid-wave infrared band (MWIR) was used for measuring the surface geotherm units (τ) which are related with different types of soil. On the basis of spatial distribution of τ value which is clearly visible in a thermal emission representative map overlaid by classified MWIR, the soil microzonation map of the study area was prepared. This soil microzonation map shows that Agartala and its surrounding areas are characterized by four types of soil which are related to different geomorphic and geological units. The soil of this area is classified as dry sandy soil and sandy clay soil of the highland areas and wet sandy alluvium and clayey alluvium of the flood plain area.  相似文献