Department of Civil & Infrastructure Engineering

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IIT Jodhpur

The knowledge of fluid flow through rock fractures is directly related to hydrocarbon migration, waste disposal, and carbon dioxide sequestration. The hydraulic nature and response of the fractures are directly controlled by the roughness of the fracture surfaces. However, this parameter is hard to understand because it can behave differently under different ambient conditions. The prevalent controlling parameters are the fracture inflow pressure, aperture of the fracture, and shearing displacement during flow. To understand the influence of these parameters, a systematic study was carried out numerically on different fracture geometries. In this paper, two-dimensional fractures with different surface roughness were simulated in a finite-element modeling (FEM) program, and the fluid-flow parameters were evaluated. The Navier-Stokes (NS) equation was used to model the fluid flow through the roughness profiles generated using Barton's joint roughness coefficient. By simulating the laminar fluid flow through the NS equation and predicting the particle transport using a streamline particle-tracking method, the flow-velocity profiles, outlet-pressure distribution, Reynolds number, shear rates, and particle transmissivity were measured. The parameters at different locations along the length of the fractures were compared to identify changes in the fluid flow. The models show that local undulations have considerable effect on the fluid flow. The velocity and shear-rate evolution, pore-pressure distribution, and Reynolds number of the flow indicate the presence of a strong wall effect on the fluid flow. The aperture and shearing displacements of the fracture walls also have significant control over the wall effect. © 2015 American Society of Civil Engineers.

World University root node

International Journal of Geomechanics

Fluid flow through rough rock fractures: Parametric study

The effect of heat treatment and the layer orientation on the tensile properties of granitic gneiss were studied under the unconfined stress condition. The tensile strength of the samples was studied using a Brazilian configuration, and the geochemical and microstructural properties were studied using the X-ray diffraction technique as well as scanning electron microscopy (SEM), respectively. The fracture pattern and the geometrical analyses were performed using the digital photographs. The results show that both the heat treatment and layer orientation have strong control on the tensile strength, force-parallel and layer-parallel strains, and on the tensile fracture geometry. A general decrease in the tensile strength of the rock was documented with the increasing heat treatment. Although, in the heat-treated samples, X-ray diffraction study do not reveal any major change in the mineral composition, but the SEM shows the development of several micro-cracks in the grains. In the samples with different layer orientation, along with the changes in the tensile strength and layer-parallel to force-parallel strain ratio, the layer activation under shear stress is also noticed. Here, the ratio between the tensile to shear stress, acting along the layers is thought to be the major controlling factor of the tensile properties of rocks, which has many applications in mining, civil constructions, and waste disposal work. © 2015, Springer-Verlag Wien.

Rock Mechanics and Rock Engineering

Effect of Heat Treatment and Layer Orientation on the Tensile Strength of a Crystalline Rock Under Brazilian Test Condition

This paper presents the evaluation of the optimum mixing ratio of sand-tire chips (STC) mixtures based on void ratio and shearstrength properties. Locally available sand and tire chips of 20×10 mm size are adopted. Different STC mixtures, in the range 10-70% by weight of tire chips (TC), are considered, along with pure sand (0% TC) and pure tire chips (100% TC). Specific gravity, density, and large direct shear tests were conducted for various samples. The volume of voids and weight-volume relations were determined from the dry unit weight and specific gravity values obtained for various mixtures. The results showed that the addition of tire chips up to 40% by weight showed significant decrease of void ratio by 43%. Shear-strength properties, like angle of internal friction values, are increased with TC contents up to 30%. Based on experimental results, the optimum percentage of tire chips of the selected size is in the range of 30-40% by weight, which is the equivalent of 50-60% by volume. Further, the STC mixture at the optimum ratio results in lightweight material with 20% less unit weight with better strength parameters and compressibility behavior, which can effectively be used for geoengineering applications. © 2015 American Society of Civil Engineers.

Journal of Materials in Civil Engineering

Evaluation of the optimum mixing ratio of a sand-tire chips mixture for geoengineering applications

This paper attempts to probabilistically estimate the surface soil moisture content (SMC) by using the synthetic aperture radar data provided by radar imaging satellite1. The novelty of this paper lies in: 1) developing a combined index to understand the role of all the backscattering coefficients with different polarization and soil texture information in influencing the SMC; 2) using normalized incidence angles, which enables the model to be applicable for different incidence angles; and 3) determination of uncertainty range of the estimated SMC. The dimensionality problem, which is frequently observed in the multivariate analysis, is reduced in the development of the combined index by the use of supervised principal component analysis (SPCA). The SPCA also ensures the maximum attainable association between the developed combined index and surface SMC above wilting point (WP). The association between the combined index and the surface SMC above WP is modeled through joint probability distribution by using the Frank copula. The model is developed and validated with the field soil moisture values over 334 monitoring points within the study area. The outcomes obtained by applying the proposed model indicate an encouraging potential of the model to be applied for bareland and vegetated land (<30 cm height). © 1980-2012 IEEE.

IEEE Transactions on Geoscience and Remote Sensing

Satellite-based probabilistic assessment of soil moisture using C-band quad-polarized RISAT1 data

The diffusion equation of suspended sediment concentration in a wide sediment- laden stream flow is dependent on the vertical gradient of streamwise velocity and the sediment diffusivity. This study aims at investigating the influence of the streamwise velocity laws on the suspended sediment concentration distributions, resulting from the solution of the diffusion equation. Firstly, the sediment concentration distributions are obtained numerically from the solution of the diffusion equation using different velocity laws and compared with the experimental data. It is found that the power-law approximation produces good computational results for the concentration distributions. The accuracy of using a power-law velocity model is comparable with the results obtained from other classical velocity laws, namely log-law, log wake-law and stratified log-law. Secondly, a novel analytical solution is proposed for the determination of sediment concentration distribution, where a power-law, wall-concentration profile is coupled with a concentration wake function. The power-law model (for velocity and concentration) is calibrated using the experimental data, and then a generalized wake function is obtained by choosing a suitable law. The developed powerlaw model involving the wake function adjusted by an exponent predicts the sediment concentration distributions quite satisfactorily. Finally, a new explicit formula for the suspended-load transport rate is derived from the proposed theory, where numerical computation of integrals, as needed in the Einstein theory, is avoided. © 2016 The Authors. Sedimentology and 2016 International Association of Sedimentologists.

Sedimentology

Distribution of suspended sediment concentration in wide sediment-laden streams: A novel power-law theory

The development of secondary boundary layer for a steady entry of fluid flow in a horizontal curved pipe is analysed using the turbulent boundary layer approach. Outside the boundary layer (within the central core), the inviscid fluid motion is treated by using the Euler and the continuity equations, whereas inside the boundary layer, the Pohlhausen method is applied, assuming a one-seventh power law of velocity for solving the integrals of the Navier-Stokes equations. The growth of the secondary boundary layer is slow with an increase in azimuthal angle, while it is gradual along the outer pipe-wall with an increase in radial angle and becomes abruptly faster near the separation point. The wall shear stress decreases with azimuthal angle, whereas it increases with radial angle attaining a peak and then decreases to zero at the separation point along the outer pipe-wall. © 2015 International Association for Hydro-Environment Engineering and Research.

Journal of Hydraulic Research

Entry flow in curved pipes: Turbulent boundary layer approach

This experimental and analytical study investigates the double-averaged (DA) turbulent flow characteristics within an array of large gravel obstacles found atop a porous gravel bed. Analysis of the experimental data reveals that the DA streamwise velocity preserves the logarithmic law above the form-induced sublayer, while a linear law and a third-degree polynomial function apply within the form-induced and interfacial sublayers, respectively. The form-induced shear stress is 70% of the DA Reynolds shear stress (RSS) occurring at the virtual bed level. The DA turbulent kinetic energy (TKE) components, streamwise and vertical, attain their peak values at the obstacle crest level, while they diminish sharply below the virtual bed level. The fluxes of the TKE streamwise and vertical components, however, change their signs slightly below the crest level, indicating a changeover of the dominance of the bursting events. For the TKE budget, the TKE production, diffusion, and pressure energy diffusion rate terms attain their peak values at the crest level, while the TKE dissipation rate has its peak value at the virtual bed level. Third-order moments of velocity fluctuations follow the linear relationship, and their signs change slightly below the crest level. The quadrant analysis suggests that the sweep events are the governing mechanism at the near-bed flow region, while the ejection events become predominant with an increase in vertical distance. The quadrant plots of the form-induced velocity components display a pseudo-elliptical scatter within the interfacial sublayer and a small circular cluster above the form-induced sublayer. © 2016 American Society of Civil Engineers.

Journal of Hydraulic Engineering

Turbulence in a gravel-bed stream with an array of large gravel obstacles

A new mathematical framework of the steady unseparated turbulent flow over a wavy (sinusoidal) boundary is derived by treating the Reynolds averaged Navier-Stokes (RANS) equations. Theoretical formulations for the flow profile, boundary shear stress and Reynolds shear stress distributions are obtained assuming a power law of streamwise velocity and accounting for the effects of curvilinear streamlines induced by the wavy boundary. The flow profiles, and distributions of boundary shear stress and Reynolds shear stress are computed for different flow parameters and presented in graphical forms. In subcritical flow, the flow profile is out of phase with the wavy boundary; while the boundary shear stress distribution is almost in phase with the wavy boundary. Instead, the flow profile and the boundary shear stress distribution in supercritical flow are opposite to those in subcritical flow. Upstream of the crest of wavy boundary the vertical distribution of the Reynolds shear stress is characterized by a concave shape because of an accelerated flow; while downstream of the crest it is a convex shape because of a decelerated flow. The theoretical results show a satisfactory agreement with the experimental data. The analysis is then extended to the mobile boundary flow to determine the phase lag distance between the locations of the maximum sediment flux and the maximum boundary shear stress. The influence of the flow Froude number on the phase lag is more pronounced than the resistance parameter. © ASCE.

Theory of turbulent flow over a wavy boundary

The theory of hydrodynamic phenomenon of the axisymmetric circular far-wake flow behind a sphere is revisited in this study by the generalized similarity solution of the governing momentum equations to obtain the solutions to the second order in respect of the inverse distance from the sphere center. In case of a laminar wake, the nonlinear equation is derived from the Navier-Stokes equations; while in case of a turbulent wake, it is obtained from the Reynolds averaged Navier-Stokes (RANS) equations and the eddy viscosity concept. The first-order Oseen-type linearization yields solutions well known in the literature, but the second-order solutions obtained in this study are novel. © 2015 American Society of Civil Engineers.

Journal of Engineering Mechanics

Circular far-wake flow behind a sphere: Solutions to the second order

Non-refractory submicron (NR-PM1) aerosols were measured during the late winter period (February-March) via an Aerodyne High Resolution Time of Flight Aerosols Mass Spectrometer (HR-ToF-AMS) along with Black Carbon (BC) and trace gasses in an industrial city, Kanpur, situated in the Gangetic Plain (GP) of India. The composition of NR-PM1 aerosols was dominated by organics (54%), followed by inorganics (36%), and BC (10%). Source apportionment via Positive Matrix Factorization (PMF) of AMS measured organic aerosols (OAs) revealed 6 factors. Factors are identified as 2 types of oxidized organic aerosols (OOAs), 2 types of biomass burning organic aerosols (BBOAs), freshly emitted hydrocarbon-like organic aerosols (HOAs) and oxygenated primary organic aerosols (OPOAs). A substantial increase in relative OOA contributions (200%) and O/C ratio (26%) has been observed from the high loading events (HLE) to the low loading events (LLE). Back trajectory analysis indicated that the study location received contributions from regional and long-range transported aerosols. OA composition and evolution during this study period were also very different from those observed during a fog influenced peak winter period of December-January. This is the first study to present detailed aerosol composition during the late winter period in India highlighting the changes in OA composition and chemistry within the same winter season. © 2016 The Royal Society of Chemistry.