A comparative study of soil erosion modelling by MMF,USLE and RUSLE

The quantitative assessment of spatial soil erosion is valuable information to control the erosion. The study area in a part of Narmada river in central India is selected. The main objective is to assess and compare the results obtained from three soil erosion models using GIS platform. Variation in the rate of erosion of the three models is compared considering varying slope, soil and land use of the area. Three models selected are Morgan–Morgan–Finney (MMF), Universal Soil Loss Equation (USLE) and Revised Universal Soil Loss Equation (RUSLE). The best fit or the most reliable model for the study area is selected after validation with the observed sedimentation data. The results give –39.45%, –9.60% and 4.80% difference in the values of sedimentation by MMF, USLE and RUSLE, respectively, from the observed data. Finally, RUSLE model has been found to be most reliable for the study area.     

Study of seasonal variation of PM2.5 concentration associated with meteorological parameters at residential sites in Delhi,India

The seasonal variation of particulate matter and its relationship with meteorological parameters were measured at five different residential sites in Delhi. Sampling was carried out for one year including all three seasons (summer, monsoon, and winter). The yearly average concentration of particulate matter (PM_2.5) was 135.16 ± 41.34 µg/m³. The highest average values were observed in winter (208.44 ± 43.67 µg/m³) and the lowest during monsoon season (80.29 ± 39.47 µg/m³). The annual average concentration of PM_2.5 was found to be the highest at the Mukherjee Nagar site (242.16 µg/m³ ) during the winter and lowest at (Jawaharlal Nehru University) JNU (35.65 µg/m³) during the monsoon season. The strongest correlation between PM mass and a meteorological parameter was a strong negative correlation with temperature (R2=0.55). All other parameters were weakly correlated (R2<0.2) with PM mass.

     

Using spatial statistics to identify the uranium hotspot in groundwater in the mid-eastern Gangetic plain,India

The occurrence of uranium in groundwater is of particular interest due to its toxicological and radiological properties. It has been considered as a relevant contaminant for drinking water even at a low concentration. Uranium is a ubiquitously occurring radionuclide in the environment. Four hundred and fifty-six (456) groundwater samples from different locations of five districts of South Bihar (SB) were collected and concentrations of uranium (U) were analyzed using a light-emitting diode (LED) fluorimetric technique. Uranium concentrations in groundwater samples varied from 0.1 µg l^?1 to 238.2 µg l^?1 with an average value of 12.3 µg l^?1 in five districts of Bihar in the mid-eastern Gangetic plain. This study used hot spot spatial statistics to identify the distribution of elevated uranium concentration in groundwater. The hypothesis whether spatial distribution of high value and low value of U is more likely spatially clustered due to random process near a uranium hotspot in groundwater was tested based on z score and Getis-Ord Gi* statistics. The method implemented in this study, can be utilized in the field of risk assessment and decision making to locate potential areas of contamination.     

Mechanical Study of Shear Failure of Vertical Goaf Drainage Hole

Geotechnical and Geological Engineering - Most of the published research on goaf-hole failures are performed using 2D numerical analyses. However, 2D analyses of the goaf-hole failure mechanism,...     

Characterization of suspended sediment in Meltwater from Glaciers of Garhwal Himalaya

Glacierised basins are significant sources of sediments generated by glacial retreat. Estimation of suspended sediment transfer from glacierised basins is very important in reservoir planning for hydropower projects in Himalaya. The present study indicates that storage and release of sediment in proglacial streams may categorise the pattern of suspended sediment transfer from these basins. Assessment of suspended sediment concentration (SSC), suspended sediment load (SSL) and yield has been undertaken for Dunagiri Glacier basin located in Garhwal Himalaya (30^o33'20”N, 79^o53'36”E), and its results are compared with the Gangotri and Dokriani glaciers sharing close proximity. Out of the total drainage basin area, about 14.3 % of the area is glacierised. Data were collected for five ablation seasons (1984–1989, barring 1986). The mean daily SSCs for July, August and September were 333.9, 286.0 and 147.15 mg/l, respectively, indicating highest concentration of mean daily suspended sediment in July followed by August. SSL trends were estimated to be 93.0, 57.0 and 21.3 tonnes. About 59% of the total SSL of the melt period was transported during the months of August and September. Sediment yield for the study basin was computed to be 296.3 t km^?2 yr ^?1. It is observed that the cumulative proportion of SSC precedes the discharge throughout the melt season except in the year 1987. Release of SSL in terms of total load is less in the early part of melt season than in the later stage as compared to that of discharge. Diurnal variations in SSC reach their maximum at 2400 h, and therefore, SSC was found to be high during night (2000–0400 h). There was a good relationship between SSC and SSL with discharge for the ablation seasons (1988 and 1989). Mean monthly SSC and mean monthly SSL provide a good exponentional relationship with mean monthly temperature. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of physico-chemical components on the consolidation behavior of soft kaolinites

Pore solution salinity has important bearing on engineering behavior of marine sediments as they influence electrochemical stress (A–R) and differential osmotic stress (?π) of the salt-enriched clays. The electrochemical stress (A–R) is contributed by van der Waals (A) attraction and diffuse ion layer repulsion (R), while the differential osmotic stress (?π) is governed by the differences in dissolved salt concentrations in solutions separated by osmotic membrane. The paper examines the relative influence of differential osmotic stress (Δπ) and electrochemical stress (A–R) on the consolidation behavior of slurry consolidated kaolinite specimens, which are known to be encountered in recent alluvial marine sediments. Methods are described to evaluate the magnitudes of these physico-chemical components and their incorporation in true effective stress. Results of the study demonstrate that differential osmotic stress finitely contributes to true effective stress. The contribution from differential osmotic stress enables kaolinite specimens to sustain larger void ratio during consolidation.     

Performance of base‐isolated reinforced concrete buildings under bidirectional seismic excitation considering pounding with retaining walls including friction effects

Seismic pounding of base‐isolated buildings has been mostly studied in the past assuming unidirectional excitation. Therefore, in this study, the effects of seismic pounding on the response of base‐isolated reinforced concrete buildings under bidirectional excitation are investigated. For this purpose, a three‐dimensional finite element model of a code‐compliant four‐story building is considered, where a newly developed contact element that accounts for friction and is capable of simulating pounding with retaining walls at the base, is used. Nonlinear behavior of the superstructure as well as the isolation system is considered. The performance of the building is evaluated separately for far‐fault non‐pulse‐like ground motions and near‐fault pulse‐like ground motions, which are weighted scaled to represent two levels of shaking viz. the design earthquake (DE) level and the risk‐targeted maximum considered earthquake (MCE_R) level. Nonlinear time‐history analyses are carried out considering lower bound as well as upper bound properties of isolators. The influence of separation distance between the building and the retaining walls at the base is also investigated. It is found that if pounding is avoided, the performance of the building is satisfactory in terms of limiting structural and nonstructural damage, under DE‐level motions and MCE_R‐level far‐fault motions, whereas unacceptably large demands are imposed by MCE_R‐level near‐fault motions. In the case of seismic pounding, MCE_R‐level near‐fault motions are found to be detrimental, where the effect of pounding is mostly concentrated at the first story. In addition, it is determined that considering unidirectional excitation instead of bidirectional excitation for MCE_R‐level near‐fault motions provides highly unconservative estimates of superstructure demands. Copyright © 2014 John Wiley & Sons, Ltd.     

New Method to Compute Seismic Active Earth Pressure on Retaining Wall Considering Seismic Waves

In earthquake prone areas, calculation of seismic active earth pressure on retaining wall is very important. Analytical methods till date for computation of seismic active earth pressure do not consider the effect of Rayleigh wave though it constitutes about 67 % of the total seismic energy. In this paper a new dynamic approach is proposed by considering all possible seismic waves viz. primary, shear and Rayleigh waves for estimation of seismic active earth pressure on rigid retaining wall by satisfying all the boundary conditions. Limit equilibrium method is used for estimation of optimised seismic active earth pressure for a rigid retaining wall supporting cohesionless backfill with critical combinations of seismic accelerations. The seismic influence zone obtained in this study is about 22 and 17 % larger when compared with available pseudo-static and pseudo-dynamic methods respectively, which indicates the significant effect of Rayleigh wave. Also, there is an increase of about 14 and 6 % in seismic active earth pressure coefficient when the present results are typically compared with pseudo-static and pseudo-dynamic methods respectively. Moreover present results compare well with the available experimental results. Present results are more critical for the design estimation of seismic active earth pressure by considering all major seismic waves as proposed in the new dynamic approach.     

Filtration and Clogging Behavior of Geotextiles with Roorkee Soils

Geotextile filters are rapidly replacing graded granular filters as the standard of practice in geotechnical design. The objective of the present study is to predict the behavior of the geotextile filter for the locally (Roorkee—India) available soils using three different geotextiles (two nonwoven and one woven). Nonwoven geotextiles are commonly used in filtration applications. This paper evaluates the long-term performance of two needle-punched nonwoven geotextiles and one woven geotextile. Filtration tests on soil–geotextile filter systems were conducted in the laboratory in order to evaluate the filtration and clogging behavior. Laboratory test program, include evaluation of performance of two different nonwoven and one woven geotextile filters in combination with locally available Solani River Sand and Clayey Soil. The paper describes the concept and details of the Fine Fraction Filtration (F³) test and presents data on three different geotextiles, which were evaluated using three different soil types. It is deduced that in all filtration applications, the non-woven geotextile would perform better than the woven geotextile.     

Uncertainty analysis of soil erosion modelling using different resolution of open-source DEMs

The Digital Elevation Model (DEM) is one of the important parameters of soil erosion assessment and notable uncertainties are found in using different resolutions of the DEM. Revised Universal Soil Loss Equation model has been applied to analyze the effect of open-source DEMs with different resolution and accuracy on the uncertainties of soil erosion modelling in a part of the Narmada river basin in Madhya Pradesh in central India. Selected open-source DEMs are GTOPO30 (1 km), SRTM (30 and 90 m), CARTOSAT (30 m) and ASTER (30 m), used for estimating erosion rate. Results with better accuracy are achieved with the high-resolution DEMs (30 m) with higher vertical accuracy than the coarse resolution DEMs with lower accuracy. This study has presented potential uncertainties introduced by the open-source DEMs in soil erosion modelling for better understanding of appropriate selection and acceptable errors for researchers.