Multivariate Study on Phenanthrene Sorption in Soils

Batch tests and different statistical tools of data analysis were used to re-evaluate the overall effect of soil characteristics and liquid phase composition on the extent of phenanthrene adsorption in complex soil-water systems. The linear isotherm models was capable of adequately describing the equilibrium data under extremely varying conditions of soil type, environmental conditions (pH, temperature, ionic strength) and amendments (surfactant, oil, dispersing agent, glucose). Consistent with existing mechanistic models, the multivariate approach also identified the organic carbon content (foc) of soil as the key parameter controlling the phenanthrene adsorption constant (Kd) in nonamended systems (Koc was 17,700 mL/g). From studying the effect of the amendments, two interactions (surfactant-pH and surfactant-oil) and two main effects (surfactant and oil) have been detected. An empirical linear model of Kd as a function of foc, pH, oil content of soil, and surfactant dose was developed for the range of conditions studied. The proposed model and modeling approach can be adapted to other types of contaminants or variables for specific natural and engineered systems.     

Coupled Continuum-Discrete Model for Saturated Granular Soils

A coupled hydromechanical model was used to analyze the mesoscale pore fluid flow and microscale solid phase deformation of saturated granular soils. The fluid motion was idealized using averaged Navier–Stokes equations, and the discrete element method was employed to model the assemblage of solid particles. The fluid–particle interactions were quantified using established semiempirical relationships. Simulations were conducted to investigate the three-dimensional response of sandy deposits when subjected to critical and overcritical upward pore fluid flow. These simulations revealed complex response patterns after the onset of quicksand conditions and provided valuable insight into the associated mechanisms. The employed model provides an effective tool to assess the microscale mechanisms and characteristics of the partially drained response of saturated granular media.     

Hydraulic Damping of Saturated Poroelastic Soils During Steady-State Vibration

A theoretical study of the steady-state response of a saturated poroelastic soil column during compressional and rotational harmonic vibrations is presented. Hydraulic damping due to Biot flow is evaluated for top-drained and double-drained boundary conditions and for compressional and rotational motions using the theory of a damped single-degree-of-freedom system. For compressional motions, the dynamic response of gravels and sands is highly influenced by the compressibility of the pore fluid. More hydraulic damping occurs as soil hydraulic conductivity increases and as the column boundary conditions change from top drained to double drained. On the other hand, hydraulic damping for rotational motions is significantly less than that for compressional motions and is dependent on a dimensionless hydraulic conductivity parameter Ks. For Ks within the range of 10?3–100, hydraulic damping may have an important contribution to total soil damping, especially at small strain levels.     

Assessment of Dynamic Stability of Foundations on Saturated Sandy Soils

This paper deals with the dynamic analysis of foundations in saturated soils. In the first part, a mathematical formulation is briefly outlined in which soil is considered as a two-phase medium comprising the soil skeleton and voids filled with a viscous fluid. Such formulation is suitable for describing a solid-fluid transition associated with the liquefaction phenomenon. Subsequently, the notion of dynamic stability is reviewed and a simple criterion is introduced, leading to the definition of a stability factor. The mathematical framework is illustrated by a numerical example involving a foundation subjected to seismic excitation. The effect of viscosity of liquefied material on the stability of the system is examined.     

Effect of Penetration Rate on Cone Penetration Resistance in Saturated Clayey Soils

In this paper, the effects of penetration rate on cone resistance in saturated clayey soils are investigated. Shear strength rate effects in clayey soils are related to two physical processes: the increase of shear strength with increasing rate of loading and the increase of shear strength as the process transitions from undrained to drained. Special focus is placed on this second effect. Cone penetration tests were performed at various penetration rates both in the field and in a calibration chamber, and the resulting data were analyzed. The field cone penetration tests were performed at two test sites with fairly homogeneous clayey silt and silty clay layers located below the groundwater table. Additionally, tests with both cone and flat-tip penetrometers in sand-clay mixtures were performed in a calibration chamber to investigate the change in drainage conditions from undrained to partially drained and from partially drained to fully drained. A series of flexible-wall permeameter tests were conducted in the laboratory for various clayey sand mixtures prepared at various mixing ratios in order to obtain values of the coefficient of consolidation, which is required to estimate the penetration rates below which penetration is drained and above which penetration is undrained. A correlation between cone resistance and drainage conditions was established based on the results of the calibration chamber and field penetration tests.     

Microstructural Interpretation on Reliquefaction of Saturated Granular Soils under Cyclic Loading

It is well known that the resistance to liquefaction of a saturated sand decreases sharply when it has been presheared, either cyclically or quasi statically, beyond a threshold value. The possible mechanism is discussed in light of recent findings on the microstructural anisotropy developed in preshearing (induced anisotropy). A columnlike structure, through which applied stress is mainly transmitted, grows parallel to the major principal stress direction in the strain hardening process. Voids, randomly distributed at first, are also connected in series between the columnlike structures. The anisotropic structure can carry the increasing stress as long as the major stress is applied parallel to the elongation direction of the structure. However, it becomes extremely unstable when the major stress is rotated. The excess pore-water pressure increases markedly under undrained cyclic loading, particularly when the connected voids are stressed perpendicular to their elongation direction. This is the reason why once liquefied sand sharply loses liquefaction resistance in a subsequent reliquefaction test.     

Sorption of Statin Pharmaceuticals to Wastewater-Treatment Biosolids, Terrestrial Soils, and Freshwater Sediment

The sorption kinetics and equilibrium endpoints of two widely prescribed anionic lipid-regulating pharmaceuticals—atorvastatin and simvastatin acid—were evaluated for wastewater-treatment plant primary clarifier biosolids, a peat soil, a sandy soil, and a stream sediment. All equilibrium isotherms were linear over an aqueous concentration range of 0.01?μg/L to greater than 100?μg/L. Log?Koc values for statin sorption to biosolids were 2.91 and 2.96 for atorvastatin and simvastatin acids, respectively. Comparative isotherm experiments with the peat soil, sandy soil, and stream sediment found log?Koc values for atorvastatin of 2.96, 2.70, and 3.20, respectively, and values of 2.89, 2.81, and 3.33 for simvastatin acid, respectively. Sorption was noncompetitive between the two statin drugs. Temperature changes did not affect sorption of either statin over the range of 5–32°C, indicating that heats of sorption were near zero. Taken together, these observations suggest that despite its anionic structure, statin sorption occurs via partition (solubilization) of the hydrophobic part of the molecule into the sorbent organic matter. Results from kinetic experiments show that statin sorption to biosolids reaches equilibrium much more rapidly compared to the soils and sediment, as the mass-transfer-rate coefficient, α, for the two-site equilibrium/kinetic model is approximately one-order-of magnitude higher for the biosolids. Presentation of these sorption data provides a requisite first step for future studies of statin fate and transport in wastewater-treatment plants and the environment.     

Improved Approach to Construct Constitutive Surfaces for Stable-Structured Soils Covering Both Saturated and Unsaturated Conditions

Constitutive surfaces are indispensable for investigation of the behavior of soils. Saturated and unsaturated soils coexist in most engineering problems and it is meaningful to develop constitutive surfaces covering both saturated and unsaturated conditions which help to investigate the behavior for both saturated and unsaturated soils in a unified way. At present, the methodologies used for saturated and unsaturated soils are different and few researchers consider the constitutive surfaces for saturated soils. For unsaturated soils, the suction-controlled triaxial tests are usually laborious, time consuming, costly, and may not justify routine engineering projects. This paper discusses the role of constitutive surfaces in soil mechanics and presents an improved approach over existing interpolation methods to construct the constitutive surfaces for saturated and unsaturated conditions for a stable-structured soil using simple laboratory tests.     

Experimental Study on the Shearing Behavior of Saturated Silty Soils Based on Ring-Shear Tests

The shearing behavior of saturated silty soils has been examined extensively by performing undrained and partially drained (the upper drainage valve of the shear box was open during shearing) ring-shear tests on mixtures of a sandy silt with different loess contents. By performing tests at different initial void ratios, the shear behavior of these silty soils at different initial void ratios is presented and discussed. Undrained-shear-test results showed that the liquefaction phenomena in ring-shear tests were limited within the shear zone; for a given void ratio or interfine void ratio, both the peak and steady-state shear strengths decreased with increase of loess content. The partially drained shear tests revealed that a great reduction in the shear strength could result after the shear failure, due to the buildup of excess pore-water pressure within the shear zone; the magnitude of reduction in shear strength after failure was affected by the initial void ratio, the shear speed after failure, as well as the loess content in the sample. For a given void ratio or interfine void ratio, with increase of loess content, the drained peak shear strength became smaller, while the brittleness index became greater. It was also found that due to localized shearing, the permeability of the soil within the shear box after drained shearing could be three orders of magnitude smaller than before shearing.     

Application of an Intraparticle Diffusion Model to Describe the Release of Polyaromatic Hydrocarbons from Field Soils

The fate and transport of chemicals of concern released from field soils must be known to protect human and ecological receptors. A mechanistic approach to modeling chemical release from soil is advantageous to implement effective remediation strategies at an impacted site. The focus of this research was to gain an understanding of the processes causing slow release of polyaromatic hydrocarbons (PAHs) from field soils collected at sites with historical releases. A mechanistically based intraparticle diffusion model was applied to experimentally measured hydrocarbon release data and particle size distributions obtained from three field soils. For these field soils, the intraparticle diffusion model was able to describe the measured chemical release data. Fitted effective diffusion coefficients (Deff) of the intraparticle diffusion model correlated to expected results. Trends were found to exist between the Deff and both the molecular weight (MW) and the octanol–water partition coefficient (Kow) of the PAH analyzed for the field soils with low organic carbon content. For these soils, the relationships suggest that intraparticle diffusion processes may be responsible for slow desorption and it may be possible to estimate Deff values for a soil or contaminated media with similar intraparticle properties using a readily measured chemical characteristic such as MW and Kow.     

Quaternized Poly(4-Vinylpyridine) Coated Activated Carbon: Diffusion Controlled Sorption of Chromium(VI)

Quaternized poly(4-vinylpyridine) coated activated carbon has been proven to be successful in removal and recovery of Cr(VI) from aqueous solution. However, the key component of the mass transfer operations and the diffusion coefficient has not been determined. In this study, adsorption of Cr(VI) was investigated at different initial concentrations. A finite bath diffusion control model with changing bulk concentrations was derived analytically, and a constant related to radius of the absorbent particle and the fractional attainment of adsorption was first introduced into this model. Results indicated that the adsorbent provided fast adsorption kinetics and the modified diffusion-control model fitted the experimental data well. The observed sorption kinetics was consistent with the finite bath diffusion, with an average value of 4.10×10?6?cm2/s for the product of the distribution coefficient and the effective diffusivity in the adsorption of Cr(VI) on the quaternized poly(4-vinylpyridine) coated activated carbon.     

Removal of Hexachlorobenzene and Phenanthrene from Clayey Soil by Surfactant- and Ultrasound-Assisted Electrokinetics

Removal of nonpolar contaminants such as most organic compounds are transported primarily by electroosmosis in electrokinetic remediation, thus the process is effective only if the contaminants are soluble in pore fluid. Hydrophobic organic compounds such as hexachlorobenzene (HCB) and phenanthrene (PHE) can adsorb strongly to clayey soil. Therefore, in this study, enhancements were done by adding 2-hydroxylpropyl-β-cyclodextrin surfactant and ultrasonication comparably to assist the electrokinetic treatment in improving the mobility of these hydrophobic compounds. The results show that HCB and PHE were mobilized and removed in both cases. But HCB is more difficult to remove than PHE, because of its highly stable nature and low water-solubility property. Ultrasound-assisted test performed better PHE reduction than surfactant-assisted test, because ultrasound can degrade the contaminant through oxidation by free radicals.     

Study of Expansive Soils and Residential Foundations on Expansive Soils in Arizona

Construction on expansive soils is challenging and thus prone to some problems and litigation. The engineering community makes extensive use of local experience and empirical procedures to address these problems. Although there has been extensive study of expansive soils and foundations on expansive soils, data related to performance of residential structures are limited in general and limited in the Phoenix area, in particular. In this study, an overview of the Phoenix Valley, Arizona, geotechnical practice and foundation performance related to residential structures on expansive clays, was developed through surveys and interviews with geotechnical engineers, structural engineers, and homebuilders. Using data obtained from files of Phoenix area geotechnical firms and government agencies, the existing Natural Resource Conservation Service map showing expansive soil locations throughout the Phoenix region was updated through the use of correlation developed in this study relating expansion index to common soil index properties such as Atterberg limits and percent passing the No. 200 sieve. Files of forensic investigations linked to expansive soil regions were made available for this study by several geotechnical engineering firms, and Phoenix Valley areas where forensic investigations have been identified, were mapped for comparison to regions identified in the updated map as having expansive soils. Comparison of the forensic investigation map to the updated map of expansive clay locations revealed that most of the forensic investigations were in regions identified with clays labeled as high to moderately high expansion potential, with a few forensic investigations in regions of medium expansion potential. Finally, unsaturated flow analyses were conducted for an Arizona expansive clay profile for two very different landscaped conditions of well-irrigated turf and desert landscape. The results of the numerical analyses were consistent with the reported observations and modes of failure identified through the surveys and interviews conducted with engineering and homebuilder professionals, including the finding that site drainage was found to be extremely important to good foundation performance, regardless of the type of landscape selected.     

六氯苯在TiO2催化下的光降解研究

[目的]对六氯苯污染的废水进行处理研究.[方法]采用使六氯苯预先吸附到催化剂表面,在TiO2催化作用下的光降解.[结果]研究表明,HCB/TiO2的量、Fe3+浓度、H2O2用量对六氯苯的光催化影响较大;TiO2表面覆盖度、体系pH值对六氯苯的光催化影响相对较小.[结论]在UV/TiO2/H2O2条件下,TiO2可有效地催化降解HCB,当表面覆盖度为4×10-5 mol/g,HCB/TiO2用量为50 mg,H2O2用量16 mmol/L时,室温条件下90 min六氯苯脱氯率可达94.8%.     

Modeling of Settlement in Saturated and Unsaturated Municipal Landfills

Municipal solid waste (MSW) landfills are not only used to dispose the refuse in most economical way but also utilized as a viable land in today’s waste management strategy. Settlement prediction is an important issue in order to guarantee the integrity of any postclosure structure on landfills. In this study, landfill settlement in saturated and unsaturated landfills is investigated by developing a one-dimensional mathematical model and performing numerical experiments. Under the saturated conditions, the landfill is considered to be completely liquid saturated by preventing gas generation at all times. On the other hand, for the unsaturated case, we assume that a gas mixture comprised of methane and carbon dioxide is generated as a result of microbial decomposition of MSW deposited. The gas generation is assumed to follow a first-order kinetic approach. The liquid phase and gas mixture are considered compressible as well as the solid matrix (landfill body). After the governing equations were discretized using the Galerkin finite-element method, the Gaussian elimination technique is employed for a solution. In saturated landfills, the settlement is mainly caused by the overburden weight of the waste deposited. Further, the mass loss due to waste decomposition contributes for an additional settlement in unsaturated landfills. The predicted settlements are within the range reported in the literature. The model developed can simulate porosity, pressures, saturations, and stress profiles in settling landfills as well as to predict the transient and ultimate settlements in saturated and unsaturated landfills.     

大孔膦酸树脂吸附钬的研究

大孔膦酸树脂(MPAR)对Ho(Ⅲ)的吸附在pH=4.59时最佳,静态饱和吸附容量244.8mg/g(树脂),测得298K时表观吸附速率常数k298=5.45×10-5s-1,吸附热力学参数△H=18.6kJ·mol-1,△S=190.6J·mol·K-1,△G=-38.2kJ·     

Damage Modeling of Saturated Rocks in Drained and Undrained Conditions

A new anisotropic damage model is proposed to describe the mechanical and poromechanical behavior of brittle rocks in drained and undrained conditions. Although phenomenological, the model is based on physical grounds of micromechanical analysis. Induced damage is represented by a second rank tensor, which is related to the density and orientation of microcracks. Damage evolution is related to propagation of the microcracks. The effective elastic compliance of the damaged material is obtained from a specific form of the Gibbs free enthalpy function. Irreversible damage-related strain due to residual opening of microcracks after unloading is also captured. The originality of our approach is that a poromechanical model of a saturated medium is constructed by extension of the mechanical model for dry material using micromechanical relationships. All the model parameters are determined from triaxial compression tests performed on dry material. The proposed model is applied to coupled poromechanical tests performed on typical brittle rock in saturated conditions. Comparison between test data and numerical simulations shows overall good agreement. The model proposed is able to describe the main features of poromechanical behavior related to microcracks induced in brittle geomaterials.     

Modeling Acoustic Waves in Saturated Poroelastic Media

In this paper we present a comparison of the linear wave analysis for four models of poroelastic materials. A nonlinear thermodynamical construction of a two-component model of such materials requires a dependence on the porosity gradient. In the linear version this dependence may or may not be present. Consequently, we may work with the model without a dependence on this gradient which is identical to Biot’s model or we can use the so-called full model. In both cases we can construct simplified models without a coupling between partial stresses introduced by Biot. These simplified models have the advantage that their application to, for instance, surface wave analysis yields much simpler mathematical problems. In the present work we show that such a simplification for granular materials leads to a good qualitative agreement of all four models in ranges of porosity and Poisson’s ratio commonly appearing in geotechnical applications. Quantitative differences depend on the mode of propagation and vary between 10 and 20%. We illustrate the analysis with a numerical example corresponding to data for sands. Simultaneously we demonstrate severe limitations of the applicability of Gassmann relations which yield an instability of models in a wide range of practically important values of parameters.     

饱和蒸汽发电在天铁的应用

天铁炼钢厂转炉汽化冷却系统回收的饱和蒸汽因其品位低而难以充分利用。通过对炼钢转炉汽化冷却系统回收蒸汽用于发电的可行性进行探讨和论证,对转炉汽化冷却系统蒸汽系统进行工艺优化和改进,应用回收蒸汽发电关键技术,成功地实现了饱和蒸汽的完全回收并转化为高品质电能,避免了蒸汽放散,节约了电能。