Static and dynamic active earth pressure

Summary The dynamic active earth pressure on retaining structures due to seismic loading is commonly obtained by using the modified Coulomb's approach which is known as the Mononobe-Okabe method. This method has generally been used for cohesionless soils only. A general solution for the determination of total (i.e. static and dynamic) active earth force for a c- soil as backfill was developed by Prakash and Saran in 1966 based on the simplifying assumption that adhesion between the wall-soil interface is equal to the cohesion of the soil, that the surface of the backfill is horizontal, and that the effect of the vertical acceleration can be neglected. This note presents an improved method for calculating the static and dynamic active force behind a rigid retaining wall based on its geometry, inclination of the backfill, surcharge, strength parameters of the backfill, and the adhesion between the wall face and the soil. The effects of adhesion, inclination of backfill, and vertical components of seismic loading for a typical retaining wall are discussed.     

Study on effect of surface roughness on overland flow from different geometric surfaces through numerical simulation

Effect of variability in surface roughness on overland flow from different geometric surfaces is investigated using numerical solution of diffusion wave equation. Three geometric surfaces rectangular plane, converging and diverging plane at slopes 1 to 3% are used. Overland flow is generated by applying rainfall at constant intensity of 10 mm/h for period 30 min and 100 min. Three scenarios of spatial roughness conditions viz. roughness increasing in downstream direction, roughness decreasing in downstream direction and roughness distributed at random are considered. Effect of variability of roughness on overland flow in terms of depth, velocity of flow and discharge along the distance from upstream to downstream for different geometric surfaces are discussed in detail. Results from the study indicate that roughness distribution has significant effect on peak, time to peak and overall shape of the overland flow hydrograph. The peak occurs earlier for the scenario when roughness increases in downstream direction as compared to scenario when roughness is decreasing in downstream for all three geometric surfaces due to very low friction factor and more velocity at the top of the domain. The converging plane attains equilibrium state early as compared to rectangular and diverging plane. Different set of random values result in different time to peak and shape of hydrograph for rectangular and diverging plane. However, in case of converging plane, the shape of computed hydrographs remains almost similar for different sets of random roughness values indicating stronger influence of converging geometry than effect due to variation of roughness sequence on computed runoff hydrograph. Hierarchically, the influence of geometry on overland flow is stronger than the influence of slope and the influence of slope is stronger than the influence of roughness. Copyright © 2013 John Wiley & Sons, Ltd.     

Risk and the South Asian monsoon

South Asia’s dependence on the monsoon has always been a source of economic uncertainty. This paper examines the history of ways of thinking about the monsoon and risk, focusing on India. The science of meteorology, and a growing interest in ways to mitigate monsoon risk, developed in response to major famines. Piecemeal interventions, including a series of canals and small dams, began India’s hydraulic transformation. By the middle of the twentieth century, massive hydraulic engineering emerged as the dominant solution to controlling the monsoon’s risks. Large dams account for the largest share of government expenditure in independent India, but since the 1960s, intensive and mostly unregulated groundwater exploitation has played a greater role in meeting irrigation needs. The expansion in India’s irrigated area and an expansion in food production. But this has come at a cost: millions have been displaced by dam construction; groundwater exploitation has reached unsustainable levels, and has had an effect on regional climate.     

Enhanced velocity mixed finite element methods for modeling coupled flow and transport on non-matching multiblock grids

The enhanced velocity mixed finite element method, due to Wheeler et al. (Comput Geosci 6(3–4):315–332, 2002), is analyzed and extended to the problem of modeling slightly compressible flow coupled to the transport of chemical species through porous media, on non-matching multiblock grids. Applications include modeling bio-remediation of heavy oil spills and many other subsurface hazardous wastes, angiogenesis in transition of tumors from dormant to malignant states, transport of contaminants in ground water flow, and acid injection from well bores to increase permeability of surrounding rock. The analysis and numerical examples presented here demonstrate convergence and computational efficiency of this method.     

Interference effect of two closely-spaced shallow strip foundations on geogrid-reinforced sand

Summary Geotextiles and geogrids are now being used extensively in many civil engineering construction works. This study presents some laboratory model test results for the ultimate bearing capacity of an isolated, and two closely-spaced, strip foundations resting on unreinforced sand, and sand reinforced with layers of geogrid. Based on the model test results, the variation of the group efficiency with the centre-to-centre spacing of the foundation has been determined.     

Study of electron energy and angular distributions and calculations of X-ray,EUV line flux and rise times

Evolution of energy and angular distributions of electrons has been studied by combining small-angle analytical treatment with large-angle Monte Carlo calculations as a function of column density for initially monoenergetic and monodirectional electrons. The incident electron energies considered are 20, 30 and 60 keV at 0°, 30° and 60° angles of incidence. Using these distributions, time evolution of extreme ultraviolet (EUV) spectrum has been studied. The slopes of the curves calculated compare well with the experimentally observed curve.     

Thermosolutal instability of a partially-ionized Hall plasma in porous medium

The thermosolutal instability of a partially-ionized plasma in porous medium is considered in the presence of a uniform vertical magnetic field to include the effects of collisions and Hall currents. For the case of stationary convection, Hall currents and medium permeability have destabilizing effects whereas the stable solute gradient has stabilizing effect on the system. The collisional effects disappear for stationary convection. The sufficient conditions for the existence of overstability are obtained.     

Numerical analysis as applied to the environmental interpretation of carbonate microfacies of some sub-Himalayan carbonates (lower upper precambrian) in northwestern India

Forty-three samples of (1) Sirban Limestone of Riasi, Jammu and Kashmir State, India, based on six mineralogic and petrographic presence-absence variables, and (2) 36 samples of Bilaspur Limestone based on 11 presence-absence mineralogic and petrographic variables, were numerically classified by Q-mode cluster analysis using Sokal and Michner's Simple Matching Coefficient. Sirban Limestone of Riasi yielded 10 clusters or groups indicating four depositional environments: (1) intertidal, (2) intertidal to subtidal, (3) subtidal, and (4) deep-water basinal. Similarly, Bilaspur Limestone yielded nine clusters indicative of the same four environments. A Q-mode ordination of the Riasi samples and of Bilaspur Limestone shows a generalized shelf-to-basin carbonate deposition profile. Results of this study substantiate earlier conclusions of Rao (1979) based on field, mineralogic, and petrographic study of the above-mentioned carbonates.