Stability assessment of jointed rock slope with different crack infillings under various thermomechanical loadings     

Pushpendra Sharma  Amit Kumar Verma  Anil Negi  Manish Kumar Jha  Pradeep Gautam 《Arabian Journal of Geosciences》2018,11(15):431

Thermoelastic deformation of rock significantly affects the stability of rock slope because thermoelastic strains may cause fracture propagation under favorable condition of failure. Rock slope stability depends on the balance between shear stress and shear resistance along the plane of weakness. Due to warming of rock slopes by heat transfer phenomena, viz. conduction and convection, considerable change in induced stresses (normal and shear) and resistance takes place which further causes instability in rock slope. In this paper, a two-dimensional finite element model has been used to simulate the stability of jointed rock slope containing crack in its upper surface. Four different cases have been simulated on the basis of infilling material (air, water, ice, water and ice) in the crack. Stability of rock slope is examined in terms of shear displacement and factor of safety for different thermal conditions of slope surface. A comparative study has been done for the four cases of infilling material in the crack. The various affecting parameters, viz. shear displacement, factor of safety, shear strength along the joint, and different surface temperature conditions, are illustrated by means of graphs. It has been found that the values of horizontal and vertical displacements are in the range of millimeters. The maximum values of horizontal and vertical displacements are 2.17 mm. Moreover, the maximum values of vertical compressive and tensile stresses are 15.4 MPa and 4.45 MPa respectively for the said four cases. According to the infilling material in the crack, the stability of the rock slope for the given geometry of slope is found in the following order: crack filled with ice < crack filled with ice and water < crack filled with water < empty crack. Validations of numerical results have been done from previous studies, and it has been found that the trends of normal stress, shear strength, and shear displacement along the joint are well matched.  相似文献   

The vorticity axis flip and its control on mineralization     

Manish A. Mamtani 《Journal of the Geological Society of India》2013,81(1):27-30

This paper discusses the possible role of vorticity axis flip in controlling fluid flow and consequent development of hydrothermal deposits. Structural, kinematic and vorticity data from the vicinity of the Singhbhum Shear Zone (SSZ) are used to propose a two stage model to explain hydrothermal mineralization. It is suggested that in the initial stage, fractures, weak planes, foliations and/or shear zones develop. Fracture permeability is weak at this stage, as a consequence of which fluid pressure builds up. Variation in stress orientation during a later stage of deformation results in enhancement of fracture network, fracture permeability and its anisotropy. If a significant vorticity axis flip accompanies this variation in stress orientation, then it pumps the fluids into the fracture network, thus yielding hydrothermal mineral deposits. In the case of SSZ, the vorticity axis flip is envisaged to have taken place from steeply plunging (anticlockwise) during the early stage, to sub-horizontal during the late stage. The SSZ became a northerly dipping thrust at this late stage and the rotation around the sub-horizontal vorticity axis was such that the rocks comprising the northern block were thrust over southern block (Singhbhum granitoid). According to the author, this vorticity axis flip must have been critical in pumping up the fluids along the SSZ to form quartz veins that host mineral deposits.  相似文献   

Climatic control on extreme sediment transfer from Dokriani Glacier during monsoon,Garhwal Himalaya (India)   总被引：2，自引：0，他引：2  

Amit Kumar  Akshaya Verma  Dwarika Prasad Dobhal  Manish Mehta  Kapil Kesarwani 《Journal of Earth System Science》2014,123(1):109-120

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Explosive erosion during the Phoenix landing exposes subsurface water on Mars     

Manish Mehta  Nilton O. Renno  John Marshall  Anita Sengupta  Jasper F. Kok  Raymond E. Arvidson  Mark T. Lemmon 《Icarus》2011,211(1):172-194

While steady thruster jets caused only modest surface erosion during previous spacecraft landings on the Moon and Mars, the pulsed jets from the Phoenix spacecraft led to extensive alteration of its landing site on the martian arctic, exposed a large fraction of the subsurface water ice under the lander, and led to the discovery of evidence for liquid saline water on Mars. Here we report the discovery of the ‘explosive erosion’ process that led to this extensive erosion. We show that the impingement of supersonic pulsed jets fluidizes porous soils and forms cyclic shock waves which propagate through the soil and produce erosion rates more than an order of magnitude larger than that of other jet-induced processes. The understanding of ‘explosive erosion’ allows the calculation of bulk physical properties of the soils altered by it, provides insight into a new behavior of granular flow at extreme conditions and explains the rapid alteration of the Phoenix landing site’s ground morphology at the northern arctic plains of Mars.  相似文献   

Rocks,fabrics and magnetic anisotropy: an introduction to the issue in honour of František Hrouda     

Manish A. Mamtani  Martin Chadima  Helga de Wall  Reinhard O. Greiling 《International Journal of Earth Sciences》2012,101(3):605-607

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Does AMS data from micaceous quartzite provide information about shape of the strain ellipsoid?     

Manish A. Mamtani  C. S. Vishnu 《International Journal of Earth Sciences》2012,101(3):693-703

Anisotropy of magnetic susceptibility (AMS) in micaceous quartzites with mean susceptibility (K _m) >50 × 10⁻⁶ SI units is known to be on account of the orientation distribution of the para/ferromagnetic minerals (e.g. micas, magnetite), which comprise the minor phase in the rocks. However, the strain in such deformed micaceous quartzites is dominantly accommodated by the quartz grains, which are the major phase in them. The objective of this paper is to explore the extent to which AMS data from micaceous quartzites provide information about the shape of the strain ellipsoid. AMS analysis of 3 quartzite blocks is performed, and the shape of the AMS ellipsoid is recorded to be oblate. From AMS data, the three principal planes of the AMS ellipsoid are identified in each block and thin sections are prepared along them. Quartz grain shape (aspect ratio, R _q), intensity of quartz and mica shape preferred orientation (κ_q and κ_mi, respectively) and 2D strain (E) recorded by quartz are measured in each section. R _q, κ_q, κ_mi and E are all noted to be minimum in the section parallel to the magnetic foliation plane as compared to the other two sections. This indicates that the quartz grains have oblate shapes in 3D and accommodated flattening strain, which is similar to the shape of the AMS ellipsoid. The role of mica in causing Zener drag and pinning of quartz grain boundaries is discussed. It is concluded that during progressive deformation, migration of pinned grain boundaries is inhibited. This causes enhanced recrystallization at the grain boundaries adjacent to the pinned ones, thus guiding the shape modification of quartz grains. A strong correlation is demonstrated between κ_q and κ_mi as well as κ_mi and E. It is inferred that fabric evolution of quartz was controlled by mica. Hence, the shape of the AMS ellipsoid, which is on account of mica, provides information about shape of the strain ellipsoid.  相似文献   

Post-seismic deformation associated with the 2001 Bhuj earthquake     

Pallabee Choudhury  J. K. Catherine  V. K. Gahalaut  Sumer Chopra  Rakesh Dumka  Ketan Singha Roy 《Natural Hazards》2013,65(2):1109-1118

We report the results of GPS measurements of post-seismic deformation due to the 2001 Bhuj earthquake in the Kachchh region, western India. The estimated horizontal velocity vectors in ITRF05 are in the range of 48?C49?mm/year in N46?C50°E. The observed velocity at the Gandhinagar permanent site, a far off site from the earthquake source region and probably unaffected by the post-seismic deformation, is 49?±?1?mm/year in N47°E, which is consistent with the predicted motion of Indian plate at Gandhinagar. At other sites in the source region, transient post-seismic deformation is found to be low; it attenuated rapidly within 3?C4?years of the earthquake and is much low now. Our results support the idea that mantle rheology is weak in the region.  相似文献   

Estimation of Source Parameters of M w 6.9 Sikkim Earthquake and Modeling of Ground Motions to Determine Causative Fault     

Sumer Chopra  Jyoti Sharma  Anup Sutar  B. K. Bansal 《Pure and Applied Geophysics》2014,171(7):1311-1328

In this study, source parameters of the September 18, 2011 M _w 6.9, Sikkim earthquake were determined using acceleration records. These parameters were then used to generate strong motion at a number of sites using the stochastic finite fault modeling technique to constrain the causative fault plane for this earthquake. The average values of corner frequency, seismic moment, stress drop and source radius were 0.12 Hz, 3.07 × 10²⁶ dyne-cm, 115 bars and 9.68 km, respectively. The fault plane solution showed strike-slip movement with two nodal planes oriented along two prominent lineaments in the region, the NE-oriented Kanchendzonga and NW-oriented Tista lineaments. The ground motions were estimated considering both the nodal planes as causative faults and the results in terms of the peak ground accelerations (PGA) and Fourier spectra were then compared with the actual recordings. We found that the NW–SE striking nodal plane along the Tista lineament may have been the causative fault for the Sikkim earthquake, as PGA estimates are comparable with the observed recordings. We also observed that the Fourier spectrum is not a good parameter in deciding the causative fault plane.  相似文献   

Evaluation of machine learning tools as a statistical downscaling tool: temperatures projections for multi-stations for Thames River Basin, Canada     

Manish Kumar Goyal  Donald H. Burn  C. S. P. Ojha 《Theoretical and Applied Climatology》2012,108(3-4):519-534

Many impact studies require climate change information at a finer resolution than that provided by global climate models (GCMs). This paper investigates the performances of existing state-of-the-art rule induction and tree algorithms, namely single conjunctive rule learner, decision table, M5 model tree, and REPTree, and explores the impact of climate change on maximum and minimum temperatures (i.e., predictands) of 14 meteorological stations in the Upper Thames River Basin, Ontario, Canada. The data used for evaluation were large-scale predictor variables, extracted from National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis dataset and the simulations from third generation Canadian coupled global climate model. Data for four grid points covering the study region were used for developing the downscaling model. M5 model tree algorithm was found to yield better performance among all other learning techniques explored in the present study. Hence, this technique was applied to project predictands generated from GCM using three scenarios (A1B, A2, and B1) for the periods (2046–2065 and 2081–2100). A simple multiplicative shift was used for correcting predictand values. The potential of the downscaling models in simulating predictands was evaluated, and downscaling results reveal that the proposed downscaling model can reproduce local daily predictands from large-scale weather variables. Trend of projected maximum and minimum temperatures was studied for historical as well as downscaled values using GCM and scenario uncertainty. There is likely an increasing trend for T _max and T _min for A1B, A2, and B1 scenarios while decreasing trend has been observed for B1 scenarios during 2081–2100.  相似文献   

Microtremor study for evaluating the site response characteristics in the Surat City of western India     

A. P. Singh  Abhijitsinh Parmar  Sumer Chopra 《Natural Hazards》2017,89(3):1145-1166

The Surat City, which is the second most populated city in the state of Gujarat in western India, warrants site-specific seismic hazard assessment due to its rapid urbanization and proximity to major seismogenic zones. This study reports results of microtremor investigations at 72 single stations and 4 arrays in an area of 325 km² spanning the city. The resonant frequencies, associated peak amplification values and liquefaction vulnerability indices were deduced from the horizontal to vertical spectral ratios. Ground amplification (A_HVSR) in the range of 3.0–5.0 was observed in the 2.0–4.0-Hz frequency band at most of the sites. A secondary A_HVSR between 2.0 and 3.0 is also observed in the 6.0–7.0-Hz frequency band at a few sites. Locales that are most susceptible to liquefaction are identified based on their vulnerability index (K _g) exceeding the value of 10. The shear wave velocities (V _s) ≥ 500 m/s inferred from array measurements occur at 38 m depth in the western part and ~16 m depth in the eastern part of city. The response spectra estimated from strong motion data recorded at an accelerograph site in Surat from three earthquakes of M _w ≥ 3.2 that occurred in Kachchh, Saurashtra and Narmada regions are in accordance with our inferences of characteristic site frequencies and amplification. Our results, in agreement with the damage scenario during the 2001 Bhuj earthquake, provide valuable inputs for site-specific seismic hazard evaluation of the Surat City.  相似文献