Behaviour of Cellular Reinforced Sand Under Triaxial Loading Conditions

Cellular reinforcement is a three dimensional reinforcement used for reinforced soil structures. Behaviour of such reinforcement is important for its use in actual practice. Present paper focuses on the behavior of cellular reinforcement in sand under the triaxial loading conditions. Series of triaxial tests are performed on unreinforced and reinforced sand with single layer as well as double layers of cellular reinforcements with 75 mm sample diameter. Six different reinforcement heights of cellular reinforcements (varying from 3 to 50 mm) are used along with one sheet reinforcement of thickness 1 mm. From the experimental failure patterns of the triaxial samples, multiple zones of failure are observed as an effect of cellular reinforcement. Deviator stress–strain curves are studied for single and double layers of cellular reinforcement under three different confining pressures. Peak deviator stress is found increasing with increasing height of cellular reinforcement, which shows the confining effect of cellular reinforcement. Shear strength parameters are evaluated and are found increasing with increase in height of cellular reinforcement, also cellular reinforcement with heights 10 mm and more have showed increased shear strength parameters, as compared to 1 mm thick sheet reinforcement. This assures better behavior performance of cellular reinforcement over the planar one. Failure patterns are also visualized by finite element analysis and found in accord with experimental observations Horizontal displacement for reinforced samples visualized multi-zoned failure pattern. Finite element results for deviator stress–strain relationship are found in reasonably good accord with experimental results.     

The micro-glitch in PSR B1821−24: a case for a strange pulsar?

The single glitch observed in PSR B1821−24, a millisecond pulsar in M28, is unusual on two counts. First, the magnitude of this glitch is at least an order of magnitude smaller  (Δν/ν∼ 10⁻¹¹)  than the smallest glitch observed to date. Secondly, all other glitching pulsars have strong magnetic fields with   B ≳ 10¹¹ G  and are young, whereas PSR B1821−24 is an old recycled pulsar with a field strength of  2.25 × 10⁹ G  . We have earlier suggested that some of the recycled pulsars could actually be strange quark stars. In this work, we argue that the crustal properties of such a strange pulsar are just right to give rise to a glitch of this magnitude, explaining the scarcity of larger glitches in millisecond pulsars.     

Occurrence of népouite in the serpentinite of the Manipur ophiolite belt,Northeastern India: Implication for melt-rock interaction in a supra-subduction zone

Serpentinization is pervasive in the ultramafic rocks of Manipur ophiolite belt (MOB), Northeastern India. Electron microprobe data of a serpentinite from the Ukhrul-Nungbi sector of MOB shows Ni-rich serpentine mineral (NiO = 33.4-33.9 wt %, SiO₂= 37.55-38.96 wt %, MgO= 14.83-16.89 wt %). The composition and X-ray diffraction pattern characterize this Ni-rich serpentine mineral as népouite which is suggested to be a hydrothermal alteration product of NiO-rich olivine in a fore-arc peridotite. The genesis of this NiO-rich olivine is attributed to the melt-rock interaction in a supra-subduction zone setting.     

Geospatial modelling of flood susceptibility pattern in a subtropical area of West Bengal,India

Flood hazards are the most destructive among all natural disasters and are a constant threat to human’s life and property. Effective disaster risk reduction strategies can be improved by geospatial approach in the way of producing information and knowledge that are useful to plan truly effective actions for the protection from floods. This research aims to develop a quantified predictive model of flood susceptibility in the Ghatal and Tamluk subdivision of Medinipur district of West Bengal, India, by means of empirically selected and weighted spatial predictors of flood. The weighted prediction model is used to quantify the spatial associations between individual geospatial factors within the flood inundated study area. Yule’s coefficient and distance distribution analysis are used to assign weights to individual geo-factors, and finally weighted spatial predictors are integrated to a multi-class index overlay analysis to derive the spatially explicit predictive model of flood susceptibility. The resultant susceptibility model reveals that approximately 32.35 and 52.99% of the total study areas (3261.45 km²) are under the category of high-to-moderate flood susceptible zone. Quantitative results of this study could be integrated into the policy process in the formulation of local and national government plans for the future flood mitigation management and also to develop appropriate infrastructure in order to protect the lives and properties of the common people of the Medinipur district.     

Study on water-soluble ionic composition of PM10 and related trace gases over Bay of Bengal during W_ICARB campaign

Aerosol (PM₁₀) samples were collected and its precursor gases, i.e., NH₃, NO, NO₂, and SO₂ measured over Bay of Bengal (BoB) during winter months of December 2008 to January 2009 to understand the relationship between particular matter (PM) and precursor gases. The observations were done under the winter phase of Integrated Campaign on Aerosols, gases and Radiation Budget (W_ICARB). The distribution of water-soluble inorganic ionic composition (WSIC) and its interaction with precursor gases over BoB are reported in present case. Average atmospheric concentration of NH₃, NO, NO_2, and SO₂ were recorded as 4.78?±?1.68, 1.89?±?1.26, 0.31?±?0.14, and 0.80?±?0.30?μg?m^?3, whereas WSIC component of PM₁₀, i.e., NH₄ ⁺, SO₄ ^2?, NO₃ ^?, and Cl^? were recorded as 1.96?±?1.66, 8.68?±?3.75, 1.92?±?1.75, and 2.48?±?0.78?μg?m^?3, respectively. In the present case, abundance of nss-SO₄ ^2? in the particulate matter is recorded as 18?%. It suggests the possibility of long-range transport as well as marine biogenic origin. Higher SO₄ ^2?/(SO₂?+?SO₄ ^2?) equivalent molar ratio during the campaign indicates the gas-to-particle conversion with great efficiency over the study region.     

Ammonia emission from subtropical crop land area in India

Ammonia (NH₃) emission from wheat (November to April) and rice (July to October) crops was measured using the chemiluminescence method at a subtropical agricultural area of India during 2009?C2010. Samples were collected from the canopy height during different growth stages of wheat crop to study the variations of NH₃ emission during different growth stages of the crop. Background atmospheric concentration of NH₃ was measured at 5 m height at the study site. Background NH₃ concentration was subtracted from the NH₃ concentration at crop canopy height to estimate the emission of NH₃ from crop canopy. The NH₃ emission from the wheat crop were recorded as 33.3 to 57.0; 15.3 to 29.2; 10.3 to 28.0; 8.7 to 23.9 and 13.9 to 28.9 ??g m^?2 d^?1 during sowing, crown root initiation (CRI), panicle initiation, grain filling and maturity stages of the crop respectively. The NH₃ emission followed a diurnal pattern with significant correlation with ambient temperature at different crop growth stages. Cumulative seasonal NH₃ emission to the atmosphere was accounted for the loss of ??10% of applied N-fertilizer during the wheat crop growing period. Immediate increase in NH₃ emission was recorded from rice crop, grown under temperature gradient tunnel (TGT). However, the NH₃ emission inside the TGT decreases within 3?C4 h after the N-fertilizer application. Continuous estimation of NH₃ concentration at the crop canopy inside the TGT, suggests that the NH₃ emission to the atmosphere reaches its peak within ??20 h of N-fertilizer application and continues up to 5 d following a diurnal pattern.     

Hydrochemical and isotopic evidence of recharge,apparent age,and flow direction of groundwater in Mayo Tsanaga River Basin,Cameroon: bearings on contamination

Unplanned exploitation of groundwater constitutes emerging water-related threats to MayoTsanaga River Basin. Shallow groundwater from crystalline and detrital sediment aquifers, together with rain, dams, springs, and rivers were chemically and isotopically investigated to appraise its evolution, recharge source and mechanisms, flow direction, and age which were used to evaluate the groundwater susceptibility to contamination and the basin’s stage of salinization. The groundwater which is Ca–Na–HCO₃ type is a chemically evolved equivalent of surface waters and rain water with Ca–Mg–Cl–SO₄ chemistry. The monsoon rain recharged the groundwater preferentially at an average rate of 74 mm/year, while surface waters recharge upon evaporation. Altitude effect of rain and springs show a similar variation of −0.4‰ for δ¹⁸O/100 m, but the springs which were recharged at 452, 679, and 773 m asl show enrichment of δ¹⁸O through evaporation by 0.8‰ corresponding to 3% of water loss during recharge. The groundwater which shows both local and regional flow regimes gets older towards the basins` margin with coeval enrichment in F⁻ and depletion in NO₃ ⁻. Incidentally, younger groundwaters are susceptible to anthropogenic contamination and older groundwaters are sinks of lithologenic fluoride. The basins salinization is still at an early stage.     

Low CodaQcin the Epicentral Region of the 2001 Bhuj Earthquake ofMw7.7

On 26 January, 2001 (03:46:55,UT) a devastating intraplate earthquake of M_w 7.7 occurred in a region about 5 km NW of Bhachau, Gujarat (23.42°N, 70.23°E). The epicentral distribution of aftershocks defines a marked concentration along an E-W trending and southerly dipping (45°) zone covering an area of (60 × 40) km². The presence of high seismicity including two earthquakes of magnitudes exceeding 7.7 in the 200 years is presumed to have caused a higher level of shallow crustal heterogeneity in the Kutch area; a site lying in the seismic zone V (zone of the highest seismicity for potentially M8 earthquakes) on the seismic zoning map of India. Attenuation property of the medium around the epicentral area of the Bhuj earthquake covering a circular area of 61,500 km² with a radius of 140 km is studied by estimating the coda-Q_c from 200 local earthquakes of magnitudes varying from 3.0–4.6. The estimated Q₀ values at locations in the aftershock zone (high seismicity) are found to be low in comparison to areas at a distance from it. This can be attributed to the fact that seismic waves are highly scattered for paths through the seismically active and fractured zone but they are well behaved outside the aftershock zone. Distribution of Q₀ values suggests that the local variation in Q₀ values is probably controlled by local geology. The estimated Q₀ values at different stations suggest a low value of Q=(102 ± 0.80)^*f^{(0.98 ± 0.02)} indicating an attenuative crust beneath the entire region. The frequency-dependent relation indicates a relatively low Q_c at lower frequencies (1–3 Hz) that can be attributed to the loss of energy due to scattering attenuation associated with heterogeneities and/or intrinsic attenuation due to fluid movement in the fault zone and fluid-filled cracks. The large Q_c at higher frequencies may be related to the propagation of backscattered body waves through deeper parts of the lithosphere where less heterogeneity is expected. Based on the attenuation curve estimated for Q₀=102, the ground acceleration at 240 km distance is 13% of 1 g i.e., 0.13 g agreeing well with the ground acceleration recorded by an accelerograph at Ahmedabad (0.11 g). Hence, it is inferred that the Q₀ value obtained from this study seems to be apt for prediction of ground motion for the region.     

Radioelemental study of Kolaghat,thermal power plant,West Bengal,India: possible environmental hazards.

Coal combustion in power plants in India produces large quantities of coal-related wastes, e.g. fly ash and bottom ash. Indian coals used in power stations are of high ash content, thus resulting in the generation of large amounts of fly ash (~100 million tons/year). Combustion of coal results in enhanced concentration of most radionuclides found in waste materials. In the present work, an attempt has been made to assess the radiological impact of the Kolaghat thermal power plant in West Bengal, India. The fly ashes and coal from the power plant were analysed for ²³⁸U, ²³²Th and ⁴⁰K by a NaI (Tl)-based gamma-ray spectrometer. The results show that ²²⁶Ra and ²³²Th range from 81.9-126 and 132-169 Bq/kg in fly ash and 25-50 and 39-55 Bq/kg in coal. These results are high compared to those of other thermal power plants of India. Hence, the Kolaghat fly ash has a significant amount of radioactivity which, if not properly disposed, will be a serious threat to the ambient environment.     

Relocation of Early and Late Aftershocks of the 2001 Bhuj Earthquake Using Joint Hypocentral Determination (JHD) Technique: Implication toward the Continued Aftershock Activity for more than Four Years

We employed layered model joint hypocentral determination (JHD) with station corrections to improve location identification for the 26 January, 2001 M_w 7.7 Bhuj early and late aftershock sequence. We relocated 999 early aftershocks using the data from a close combined network (National Geophysical Research Institute, India and Center for Earthquake Research Institute, USA) of 8–18 digital seismographs during 12–28 February, 2001. Additionally, 350 late aftershocks were also relocated using the data from 4–10 digital seismographs/accelerographs during August 2002 to December 2004. These precisely relocated aftershocks (error in the epicentral location<30 meter, error in the focal depth estimation < 50 meter) delineate an east-west trending blind thrust (North Wagad Fault, NWF) dipping (~ 45°) southward, about 25 km north of Kachchh main land fault (KMF), as the causative fault for the 2001 Bhuj earthquake. The aftershock zone is confined to a 60-km long and 40-km wide region lying between the KMF to the south and NWF to the north, extending from 2 to 45 km depth. Estimated focal depths suggest that the aftershock zone became deeper with the passage of time. The P- and S-wave station corrections determined from the JHD technique indicate that the larger values (both +ve and -ve) characterize the central aftershock zone, which is surrounded by the zones of smaller values. The station corrections vary from −0.9 to +1.1 sec for the P waves and from −0.7 to +1.4 sec for the S waves. The b-value and p-value of the whole aftershock (2001–2004) sequences of M_w ≥ 3 are estimated to be 0.77 ± 0.02 and 0.99 ± 0.02, respectively. The p-value indicates a smaller value than the global median of 1.1, suggesting a relatively slow decay of aftershocks, whereas, the relatively lower b-value (less than the average b-value of 1.0 for stable continental region earthquakes of India) suggests a relatively higher probability for larger earthquakes in Kachchh in comparison to other stable continental regions of the Indian Peninsula. Further, based on the b-value, mainshock magnitude and maximum aftershock magnitude, the Bhuj aftershock sequence is categorized as the Mogi's type II sequence, indicating the region to be of intermediate level of stresses and heterogeneous rocks. It is inferred that the decrease in p-value and increase in aftershock zone, both spatially as well as depth over the passage of time, suggests that the decay of aftershocks perhaps could be controlled by visco-elastic creep in the lower crust.