Lakshmi N. Reddi

COMPARISON OF INTERNAL AND SURFACE EROSION USING FLOW PUMP TESTS ON A SAND-KAOLINITE MIXTURE

The purpose of this paper is to assess the difference between surface and internal erosion processes using results from flow pump tests. Samples of 70% Ottawa sand + 30% kaolinite mixture were used with distilled water and NaCl solutions as permeants. Two kinds of tests were conducted, a surface erosion test where the permeant was pumped through a cylindrical hole of 7-mm diameter and an internal erosion test where the permeant was pumped through intact compacted samples in compaction permeameters. A simple capillary tube model was used to estimate the critical shear stresses needed to cause erosion in surface erosion experiments. It was found that although surface erosion critical shear stresses were exceeded in the intact soil samples, particle clogging in the pores and redeposition of eroded particles prevented mobilization of particles into the effluent stream. Erosion rates estimated using surface erosion parameters were significantly greater than those observed in internal erosion experiments. The results suggest that the fate of eroded particles, including particle redeposition and pore clogging, may govern the internal erosion process far more than the surface erodibility of the soil.

Geoenvironmental Engineering : Principles and Applications

Principles and processes soil formation and composition soil structure flow of water in solids mass transport and transfer in solids non-aqueous phase liquids (NAPLs) in solids fundamentals of contaminated site treatment introduction technical basis for treatment technique selection principles of site treatment techniques fundamentals of waste containment introduction containment system configurations elements of containment system design barrier composition and performance.

A physically based model for mobilization of kaolinite particles under hydraulic gradients

A physically based model was developed for analyzing the movement of colloidal clay particles in laboratory soil columns. The physical mechanisms of detachment of particles from the soil matrix, their subsequent transportation in the pore water, and possible entrapment or clogging were included in the model. The performance of the model was evaluated by comparisons with laboratory experimental results. A sensitivity analysis was performed to reveal the relative importance of the parameters in prediction of colloidal particle concentrations and fluxes. Soils with greater initial porosity led to smaller effluent concentrations, but contributed to greater overall particle removal. An increase in soil detachability, a parameter which expresses the ease with which colloids are removed from parent soil matrix, caused greater removal to a point. Beyond a threshold value, the suspended load of colloids in pore suspension exceeds the carrying capacity of the flow causing deposition and concentration reduction.

A Comprehensive Review on Water Quality Parameters Estimation Using Remote Sensing Techniques

Remotely sensed data can reinforce the abilities of water resources researchers and decision makers to monitor waterbodies more effectively. Remote sensing techniques have been widely used to measure the qualitative parameters of waterbodies (i.e., suspended sediments, colored dissolved organic matter (CDOM), chlorophyll-a, and pollutants). A large number of different sensors on board various satellites and other platforms, such as airplanes, are currently used to measure the amount of radiation at different wavelengths reflected from the water’s surface. In this review paper, various properties (spectral, spatial and temporal, etc.) of the more commonly employed spaceborne and airborne sensors are tabulated to be used as a sensor selection guide. Furthermore, this paper investigates the commonly used approaches and sensors employed in evaluating and quantifying the eleven water quality parameters. The parameters include: chlorophyll-a (chl-a), colored dissolved organic matters (CDOM), Secchi disk depth (SDD), turbidity, total suspended sediments (TSS), water temperature (WT), total phosphorus (TP), sea surface salinity (SSS), dissolved oxygen (DO), biochemical oxygen demand (BOD) and chemical oxygen demand (COD).

Stabilization of phenolics in foundry waste using cementitious materials

Abstract A series of experiments were conducted to stabilize the phenolics in foundry sands from Kansas using four different types of binders — Portland cement, fly ash, kaolinite, and bentonite. Strength and leachability of stabilized mixes of foundry sand were analyzed to assess their feasibility in construction and geotechnical applications. The results suggest that compressive strength was acquired relatively faster in fly ash than in cement and, in general, it varied inversely with the proportion of foundry sand in the stabilized mix. Lesser amounts of phenolic compounds leached from fly ash-stabilized mixes than from cement-stabilized mixes. The leachate analyses for both total phenolics and 2,4,6-trichlorophenol indicate that increasing percent replacement of foundry sands enhances stabilization. These results are supported by scanning electron micrographs which showed increased porosity in the case of cement-stabilized mixes. The swelling potential and instability of bentonite-stabilized mixes rendered the leachate quality unpredictable. The general conclusion that fly ash stabilizes phenolics better than Portland cement may lead to development of a cost-effective solution for stabilizing phenolics in foundry sands and may have important implications in the construction industry.

Water quality assessment and apportionment of pollution sources using APCS-MLR and PMF receptor modeling techniques in three major rivers of South Florida.

In this study, principal component analysis (PCA), factor analysis (FA), and the absolute principal component score-multiple linear regression (APCS-MLR) receptor modeling technique were used to assess the water quality and identify and quantify the potential pollution sources affecting the water quality of three major rivers of South Florida. For this purpose, 15years (2000-2014) dataset of 12 water quality variables covering 16 monitoring stations, and approximately 35,000 observations was used. The PCA/FA method identified five and four potential pollution sources in wet and dry seasons, respectively, and the effective mechanisms, rules and causes were explained. The APCS-MLR apportioned their contributions to each water quality variable. Results showed that the point source pollution discharges from anthropogenic factors due to the discharge of agriculture waste and domestic and industrial wastewater were the major sources of river water contamination. Also, the studied variables were categorized into three groups of nutrients (total kjeldahl nitrogen, total phosphorus, total phosphate, and ammonia-N), water murkiness conducive parameters (total suspended solids, turbidity, and chlorophyll-a), and salt ions (magnesium, chloride, and sodium), and average contributions of different potential pollution sources to these categories were considered separately. The data matrix was also subjected to PMF receptor model using the EPA PMF-5.0 program and the two-way model described was performed for the PMF analyses. Comparison of the obtained results of PMF and APCS-MLR models showed that there were some significant differences in estimated contribution for each potential pollution source, especially in the wet season. Eventually, it was concluded that the APCS-MLR receptor modeling approach appears to be more physically plausible for the current study. It is believed that the results of apportionment could be very useful to the local authorities for the control and management of pollution and better protection of important riverine water quality.

Finite-Depth Seepage below Flat Aprons with Equal End Cutoffs

Closed-form theoretical solutions for steady seepage below a horizontal impervious apron with equal end cutoffs are obtained using Schwarz-Christoffel transformation. The resulting implicit equations involving elliptic integrals are used to obtain various seepage characteristics in nondimensional floor-profile ratios. These ratios are further expressed in the form of design charts and as algebraic equations. The results have been validated by comparing the solutions with the available exact solutions for infinite-depth cases.

Flow and distribution of fluid phases through porous plant growth media in microgravity: Progress to date

Results from plant growth experiments utilizing particulate growth media during space flight revealed difficulties associated with providing reliable reproducible gaseous and water supply to plant roots. These limitations were attributed to insufficient understanding of liquid configuration and growth media transport processes in reduced gravity. The objective of this NASA-funded research program is to develop a framework for modeling and quantitative characterization of physical processes associated with flow of wetting and non-wetting phases in particulate plant growth media in microgravity. This paper provides an overview of research plans and current status of research activities. Characterization and modeling of substrate water retention and transport properties in microgravity is key to management and control of gas and liquid fluxes within plant root zones. Modeling efforts will focus on both 1) a pore network model for describing discontinuous fluid phase transport (ganglia/blobs) and 2) a statistical distribution model describing water retention and hydraulic conductivity as functions of various pore configurations. Minimizing hydrostatic forces within porous media by using thin samples on earth may provide an approximation to microgravity conditions. In our preliminary study we have used Magnetic Resonance Imaging (MRI) to detect and track the evolution of liquid configuration and dynamics within thin slices of opaque porous media (Aquafoam with mean pore size of 50 μm). Both twoand three dimensional temporal MRI imaging has been performed in thin Aquafoam slices positioned vertically and horizontally (to simulate the effect of gravity). The wetting front exhibited percolation-type patterns and fingering. Preliminary results show that gravity dominates liquid flow even for low Bond numbers. Although the capillary forces are very strong the small hydrostatic pressure built in the initial liquid volume determines the subsequent evolution of the wetting front.

Feasibility of in situ implementation of vibrations to mobilize NAPL ganglia

Abstract A growing number of incidents of nonaqueous phase liquid (NAPL) spills in the recent past have warranted development of innovative and cost‐effective remediation technologies. Of particular concern is the entrapment of LNAPL (NAPL lighter than water) in the form of ganglia or blobs near the water table by virtue of strong capillary forces. The residual ganglia are the leftover component after pumping of free product and typically occupy 20 to 60% of the pore space. Mobilization of these ganglia would require unrealistically high hydraulic gradients and is often beyond the scope of pump‐and‐treat processes. This paper deals with the feasibility of in situ implementation of localized vibrations for controlled mobilization and collection of LNAPL ganglia. Specifically, the paper covers three components. First, the principles involved in soil‐water‐NAPL interactions under the influence of vibrations are discussed. The effects of vibrations on a soil‐NAPL‐water medium are postulated in terms of pore s...

Nonparametric Monitoring for Geotechnical Structures Subject to Long-Term Environmental Change

A nonparametric, data-driven methodology of monitoring for geotechnical structures subject to long-term environmental change is discussed. Avoiding physical assumptions or excessive simplification of the monitored structures, the nonparametric monitoring methodology presented in this paper provides reliable performance-related information particularly when the collection of sensor data is limited. For the validation of the nonparametric methodology, a field case study was performed using a full-scale retaining wall, which had been monitored for three years using three tilt gauges. Using the very limited sensor data, it is demonstrated that important performance-related information, such as drainage performance and sensor damage, could be disentangled from significant daily, seasonal and multiyear environmental variations. Extensive literature review on recent developments of parametric and nonparametric data processing techniques for geotechnical applications is also presented.