One-dimensional Soil Column Research Articles

Aqueous solubility enhancement and desorption of hexachlorobenzene from soil using a plant-based surfactant

A plant-based surfactant extracted from fruit pericarps of Sapindus mukorossi (Ritha) is proposed for remediation of contaminated soil from a local hazardous waste site. Natural surfactants can be prepared using a very simple water extraction of fruit pericarp powder. Natural surfactant solutions are employed to enhance the aqueous solubility of a hydrophobic organic compound, hexachlorobenzene (HCB), and to desorb HCB from soils in batch and one-dimensional flow-through soil column experiments. The solubility of HCB in natural surfactant solutions increased linearly with surfactant concentration beyond the critical micelle concentration. The mass of dry Ritha powder required to solubilize 1 mg of HCB in 1 liter of water was comparable to sodium dodecylsulfate solution and other commercial surfactants. HCB concentration in the aqueous solutions approached 90% of the HCB solubility in the respective natural surfactant solutions when soils contaminated to high levels were used for desorption. HCB recovery was up to 90% of the total HCB for soils contaminated with lower levels. Desorption behavior observed for natural surfactant solutions was similar to SDS solutions. Natural surfactant solutions performed more efficiently than a simple water flood in recovering HCB from one-dimensional soil columns. The HCB concentration in the effluent was found to be as high as 80% of the surfactant-enhanced HCB solubility in respective solutions. The results of this study provide a strong case for pursuing natural surfactant solutions in further research.

Soil Washing Potential of a Natural Surfactant

Biodegradable natural surfactants obtained from plants can be an attractive alternative to synthetic surfactants in the remediation of contaminated soils. In this research, a plant-based surfactant obtained from the fruit pericarp of Sapindus mukurossi, a tree generally grown in tropical regions of Asia, is tested. A simple and economical method for the preparation of the surfactant is developed. An empirical formula for the surfactant was determined to be (C26H31O10)n. The aqueous solubilities of hexachlorobenzene (HCB) and naphthalene in the natural surfactant solutions were found to vary linearly with the concentration of the surfactant showing trends comparable to that of typical com mercial surfactants. Natural surfactant solutions were also employed for flushing HCB from one-dimensional soil columns. HCB recoveries after 12 pore volumes of flushing with 0.5 and 1% natural surfactant solutions were 20 and 100 times more than that recovered by water flooding. These promising results warrant further re...

Parametric studies on vertical boundary location in dynamic finite element analyses

Two parametric studies are performed to achieve convergent solutions to dynamic finite element analyses of structures on semi-infinite foundations. The first study considers a linear elastic foundation, whereas the latter is about a structure on a saturated clay foundation. Plane strain conditions are assumed. Uniform horizontal earthquake accelerations are applied at the base of the structure-foundation systems. One-dimensional soil column responses are prescribed at the vertical boundaries of the two-dimensional finite element models. The sizes of the finite element analysis domains are gradually increased by changing the location of the vertical boundary and the effect of the vertical boundary location to the solution at the origin is discussed.

媒介変数1次近似法による不確定な線形地盤の地震応答量の評価 : 媒介変数1次近似法(その1)

The first-order intervening variable method for the stochastic estimation of the seismic response of the indeterminate ground is presented. This method is based on the Taylor expansion as to the intervening variables which are the functions of the stochastic variables. This method enables to deal with the problem where the nonlinearity of variation of response as to the variation of stochastic variables is remarkable without the loss of the simplicity. The power-function, quadratic-function, and spline-function are employed as the intervening functions. The Monte Carlo Simulation of one-dimensional soil column are carried out to demonstrate the effectiveness of the presenting method.

Multiphase Approach to Thaw Subsidence of Unsaturated Frozen Soils: Equation Development

Construction and maintenance of engineering structures in arctic regions demands an understanding of and the ability to cope with environmental problems produced by permafrost. Where thawing of the permafrost cannot be prevented, the range, amount, and extent of degradation are factors that must be taken into account in the design of engineering structures. Predictions of these factors are facilitated by the use of a mathematical model designed to predict the physical system under consideration. This study addresses the problem by developing a predictive model to describe permafrost thaw subsidence based upon a complete formulation of the problem. This problem is one of multiphase (air, ice, water, and solid) transport and deformation in a porous medium. The conservation of mass equations for liquid water, ice with phase change, and deforming soil solids are developed. Darcy's law is extended to include moisture movement due to thermal gradients. The quasi-static equilibrium equations and stress-strain relations that assume a perfectly elastic solid matrix are also employed. Simultaneous variations of moisture retention and phase-composition curves with temperature and pore pressure are also incorporated in the model. The energy-conservation equation, which includes terms due to viscous dissipation and compression effects, along with the other equations expressed, is found to satisfactorily represent the physical processes occurring in thawing permafrost soils. Approximations to simulate the thawing of a one-dimensional soil column are then developed from the general model.

Effects of nonlinear sorption on the diffusion of benzene and dichloromethane from two air-dry soils

In order to teat for the effects of nonlinear sorption on the diffusive transport of volatile organic compounds (VOCs) through air-dry soils, diffusion and sorption experiments were conducted with two air-dry soils using benzene and dichloromethane (DCM). Sorption isotherms in the presence of relative humidity were measured in both soils using a static sorption chamber and were in excellent agreement with the BET model. Diffusive emission rates from isothermal and uniformly contaminated air-dry soils were measured in a one-dimensional soil column under transient conditions. Matching the linear equilibrium sorption diffusion model to the emission rate data resulted in apparent diffusivities that were found to increase with increasing initial VOC concentration in the soil

Discrete ice lens theory for frost heave beneath pipelines

The discrete ice lens theory of frost heave in one-dimensional soil columns was developed to provide a better physical basis for engineering predictions of frost heave in soils. The theory has now been extended to the two-dimensional heat- and mass-flow situation beneath a buried chilled pipeline. Although the frozen and unfrozen soil regions beneath a buried cold pipeline are two dimensional, and the temperature and water-flow fields are potentially complex, considerable simplifications can be made by invoking the so-called quasi-static approach for estimating temperature fields around the buried pipeline. It is proposed that the curved, quasi-static temperature profiles available from published relationships are appropriate for frost-heave predictions in the two-dimensional region beneath a pipeline. Using these curved temperature profiles in the same program and solution procedure developed previously for one-dimensional soil columns allows frost-heave predictions for a buried pipeline to be carried out with a minimum of computational effort. Therefore, the lengthy and tedious numerical procedures that have been a feature of previous attempts to model heat and mass flow and the resulting frost heave in two dimensions can be avoided. The procedure has been used to predict the frost depth and heave beneath two well-documented pipeline test sections at Calgary, Alta., and Caen, France, with very good agreement between prediction and observation. Some predictions for a practical field situation indicate the initial ground temperature plays an important role in frost heave, frost penetration, and the time at which the final ice lens forms in the freezing soil. Key words : frost heave, discrete ice lens, pipeline, segregation potential, hydraulic conductivity of frozen soil.

A Study on Lateral Dashpots for Soil-Structure Interaction and its Application to a Simplified Technique

The dynamic characteristics of embedded rigid foundations are studied using the boundary element method. Lateral dashpots are introduced to the soil in plane strain in order to represent the wave propagation toward the third direction from a slice of the soil and their effects are examined. The impedance functions and foundation input motions are presented for the case of a rigid foundation embedded in a half-space or a stratum and for the case of two rigid foundations also embedded in a half-space. The effect of the lateral dashpots on the soil-structure interaction is studied where the embedment, the bedrock and the adjacent foundation are considered. The numerical examples are provided by comparing the results obtained by two-dimensional, approximate three-dimensional and exact three-dimensional analyses. The efficiency of the dashpots is confirmed, in particular, for a foundation embedded in a half-space. Based on this result, the lateral dashpots are introduced to onedimensional soil columns which represent a half-space around an embedded foundation. From this assumption, the impedance functions are easily obtained in an explicit form and the foundation input motions are evaluated using the substructure technique. The validity of this simplified technique is confirmed by comparing its results with those obtained by a three-dimensional boundary element analysis.

埋込み剛基礎の動特性に基づく動的擬似3次元効果の考察 : 境界要素法による動的擬似3次元効果に関する研究(その2)

In this paper the effect of viscous dashpots introduced in two-dimensional representations on the response of structures due to seismic waves is examined by the boundary element method. To clarify the mechanism of approximate three-dimensional effect two embedded foundation system is analyzed. First the boundary element formulation of the soil-structure interaction problem for the case of rigid foundations embedded in an elastic soil is developed in conjunction with a substructure approach. It is worthy of note that an appropriate approach has to be taken for the approximate three-dimensional analysis to obtain foundation input motions and driving forces. Using the method two-dimensional and approximate three-dimensional analyses of rigid foundations embedded in a soil are made and results are compared with three-dimensional ones obtained by the boundary element method(Yoshida et al., 1986). Rigid foundations embedded in a finite soil layer underlain by a rigid rock are also analyzed to investigate the effect of soil layering. Results show that addig dashpots gives a good estimation of three-dimensional effect as long as a single foundation is embedded in a half space and that it gives excessive radiation damping for multiple foundation system and foundations embedded in a layered soil. In the latter part of this paper above mentioned approximate three-dimensional effect is investigated by considering a one-dimensional soil column supported by dashpots and also by analyzing the distribution of radiated energy. It is clarified from one-dimensional analysis that adding dashpots tends to increase real parts of impedance functions while imaginary parts remain almost unchanged. Comparing distribution patterns of radiated energy clearly shows that the radiated energy is too rapidly absorbed by additional dashpots and that the existence of an adjacent foundation or a soil layer may be underestimated.