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Soil cracking is a common natural phenomenon. The existence of soil cracks has significant effects on the engineering properties of clayey soil, and can cause significant problems in geotechnical, geological, and environmental aspects. Understanding of the potential mechanisms of soil cracking is essential in assessments of potential damages to earthen infrastructures. We review the past research efforts devoted to the experimental investigations and applications of fracture mechanics in soil cracking, attempting to provide a better understanding of the formation mechanism of desiccation cracking with a perspective of fracture mechanics. This review analyzes the influence of soil cracking on soil engineering properties and the significance of soil cracking phenomena. Past and current formulations of soil fracture criteria and their experimental investigation are discussed. This review reveals the factors that affect the mechanisms of soil fracture can be divided into two groups, namely soil intrinsic properties and test-related factors. The applications of fracture mechanics in soil cracking are also discussed with particular focus on soil fracture models that are separately based on linear elastic fracture mechanics (LEFM), elastic plastic fracture mechanics (EPFM), and numerical simulations of soil cracking based on fracture mechanics. Some challenges and prospects of the applications of fracture mechanics in soil cracking are presented. Fracture mechanics is a significant method to explain soil crack initiation and propagation. It is expected that researchers can gain better understanding of the range of fracture mechanics applications in soil cracking, and seek improvements and extensions of existing models through this review.

In order to improve the mechanical properties of dredged sludge, short polypropylene fibers were used as physical reinforcement, while cement and fly ash were used as chemical stabilizers. Different mass percentages of fiber (i.e., 0%, 0.05%, 0.1%, 0.2%, 0.4%, and 0.8%), cement (i.e., 15%, 20%, and 25%), and fly ash (i.e., 15% and 30%) were added to dredged sludge at two initial high water contents (i.e., 92% and 120%) and evaluated using physical experiments. The unconfined compression test was performed on samples after curing them for 28 days. The results show that inclusion of cement and fly ash can significantly increase the dry density and reduce the water content of dredged sludge after curing, consequently enhancing the unconfined compressive strength (UCS). It is found that chemical stabilization can increase the stiffness and brittleness of dredged sludge. However, excessively high fly ash fraction in the mix inhibits strength development in cement-stabilized dredged sludge. The inclusion of fiber decreases the initial stiffness and enhances the UCS, strain at failure, and residual strength of dredged sludge. The UCS increases with fiber content and then decreases slightly, with the optimal fiber content being 0.1%. Fiber reinforcement generates a distinct transition zone in the stress–strain curve, which enlarges with increasing fiber content. The contribution of fiber reinforcement to the strength of dredged sludge is more pronounced at relatively lower water content. The inclusion of fiber can temper the brittleness of chemical-stabilized dredged sludge with more ductile behavior by inducing a ‘bridging’ effect. This effect helps in reducing loading-induced cracking of the stabilized sludge.

Under the influence of climate warming, sea level rise and human activities, seawater intrusion has become a significant problem. Seawater intrusion salinates groundwater and impacts on ecological environment and society. It needs to be monitored to scale to environment in order to develop and implement preventive or remedial measures. In-situ large-scale monitoring of groundwater salinity is a key step in the prevention of seawater intrusion. However, current monitoring technologies are either too labor-intensive or excessively expensive when used in large-scale in-situ monitoring. Optical fiber techniques that are presently used in measurements of salinity are mostly limited to laboratory experiments. Herein, a fiber Bragg grating (FBG) salinity sensor for in-situ monitoring of groundwater salinity is proposed. The sensor is composed of a FBG coated with polyimide (PI) and an uncoated FBG for salinity sensing and temperature compensation. On the basis of feasibility test and analyses using water diffusion model, a mathematical matrix for calculating salinity and temperature is proposed and applied to salinity measurement in gravel aquifers. The results indicate that the sensitivity coefficients of FBG coated with lamellar polyimide, to water salinity and temperature, are −0.0358 nm/%, 0.0321 nm/°C, respectively. The uncoated FBG is only sensitive to temperature, and the sensitivity coefficient is 0.0095 nm/%. The results of gravel aquifer measurements show that the FBG salinity sensor has good repeatability and consistency with measurements obtained with an electronic salinity meter. The absolute and RMS errors of the salinity measurements are −0.16 to 0.21%, 0.1048%, respectively, and the absolute and RMS errors of temperature are −0.31 to 0.33 °C, 0.1917 °C, respectively. The FBG salinity sensor provides a new means for in-situ monitoring of seawater intrusion.

Reservoir landslide, as one of the most serious geohazards, is worldwide distributed. To investigate its triggering factors and mechanisms that underlie its propagations, a real-time monitoring system based on Fiber Bragg Grating (FBG) technology was designed for the Majiagou landslide in the Three Gorges Reservoir (TGR) region. Through analyses of inclinometer data, it is found that there are two sliding surfaces existed in the Majiagou landslide and that the deeper sliding surface is the critical one. It accounts for nearly 80% of the deformation of the landslide. This information necessitated the recording of the displacement at the deeper sliding surface, together with the rainfall, water level, pore water pressure, temperature of the landslide using a real-time monitoring system. After analyzing the multi-parameter data in detail, it is found that observed deformation is mainly governed by reservoir water levels, while precipitation has some minor effects. The reservoir water level is the determining factor of landslide deformation when it exceeds 160 m or lower than 150 m. Whereas the reservoir water level varies from 150 m to 160 m, the fluctuation velocity plays a dominant role. The relationship between the variation of seepage field and kinematic evolution of Majiagou landslide is recognized. The average displacement rate of Majiagou landslide is within 0.1 mm/day, signifying that the landslide is still creeping presently. The results are significant with respect to stability evaluation and formulation of early warning plans for the reservoir landslide.

Although many methods of soil moisture measurement exist, there remains a lack of soil moisture sensor with small volume, high precision, excellent real-time performance and distributed monitoring capability. In this paper, a fiber Bragg grating (FBG)-based carbon fiber heated sensor (CFHS) that can overcome the deficiencies in soil moisture movement is proposed. The CFHS consists of a carbon fiber rod with a diameter of 5 mm, quasi-distributed FBG sensors on an optical fiber, a coating, two binding posts, and two electric cables. Laboratory calibration tests have been conducted to establish an empirical piece-wise relationship between the temperature characteristic value and soil moisture for sand, silt and clay. A laboratory validation test under normal gravity and a centrifuge test under overweight conditions, have been performed to verify the feasibility of this technique for soil moisture monitoring. The test results show that the CFHS can (i) accurately record soil moisture under normal gravitational and overweight conditions and (ii) track the evolution of capillary zones, and the generation and migration of moisture transition zones under centrifuge acceleration. During a response period of 5 min, the accuracy is 0.033 m3/m3 under 1 g condition, and 0.047 m3/m3 under overweight condition. With the advantages of small sensor size, low disturbance of soil mass and wide adaptability in physical model tests, the proposed method can achieve distributed soil moisture measurement at different scales and with high efficiency.

Evaporation of water from soils is a three-stage process that has great significance in stress development in exposed geotechnical structures, generation of dusts that can cause environmental pollution and respiratory ailments, and dereliction of land by generating drought conditions. In this study, the factors that influence water evaporation from soil have been divided into two categories: external, referring to atmospheric conditions and interior, covering surficial soil characteristics and water content conditions. Particularly, five different sets of laboratory based evaporation tests were performed using cylindrical (150 mm diameter and 7–28 mm height) samples of clayey soil mixed with quartzite sands (three grainsize ranges: 0.2–0.5 mm, 0.5–1.0 mm, and 2.0–3.0 mm) in weight proportions ranging from 0% to 50% to evaluate the effects of soil texture, mineralogy and initial compactive state on its free water evaporation process at room temperature (20–22 °C) and relative humidity (50 ± 2%) conditions. The evaporation tests were performed using mass loss measurements on soil samples to an accuracy of 0.01 g. Findings show that in the first stage of soil drying, water content decreases continuously with time while the ratio of actual to potential evaporation, Ea/Ep stays mostly stable. During the falling rate stage, both water content and Ea/Ep decrease significantly. However, the water content varies but not significantly due to the low value of residual evaporation rate in the residual evaporation stage. Soil with lower sand content starts the falling rate stage at higher water content: 32.52% at added sand proportions of 0% versus 21.87%, 20.65%, 20.45%, 20.26% and 18.34% at added sand proportions of 10%, 20%, 30%, 40%, and 50% respectively. Larger soil sample thicknesses accelerate water evaporation rate and extend the constant evaporation rate stage. Soil particle size was not found to have significant impact on evaporation rate on per unit weight of added soil basis. The evaporation rate increases in direct proportionality to increase in initial water content and dry density.

Chemical dust suppressants generally require more than one application to exposed ground surfaces to maintain the soil wetness level required to reduce dust emissions under the combined action of wind, high ambient temperature, low relative humidity, and vehicular traffic. A quantitative methodology is herein formulated for estimation of the cost-effectiveness of dust suppression with chemical agents within a specified construction duration. This is applied to the 3 polymers: sodium carboxymethyl cellulose (CMC A), polyacrylamide (PAM B) and polyethylene oxide (PEO A) used on 2 base soils (sodium montmorillonite (Na-montmorillonite) and kaolinite (K)). Polymer aqueous concentrations ranging from 0.5 g/L to 10 g/L, with distilled water as control, were used to perform desiccation tests at 25 °C and 30% relative humidity. The results show that liquid loss kinetics alone which indicated CMC A at 8 g/L and 4 g/L aqueous concentrations for Na-montmorillonite during 891 h and kaolinite during 696 h, respectively, may not provide complete information on the potential cost-effectiveness of dust suppressants over multiple applications in the field. It identifies water and PAM B at

The effects of wetting-drying (W-D) cycles on the desiccation-induced cracking of a fat clay (CH) as well as the role of soil suction in the evolution of soil strength, were investigated. Cylindrical block soil samples (50 mm in diameter and 100 mm in height) compacted to a dry density of 1.3 Mg/m3, were subjected to 3 stages of drying at a temperature of 22 ± 2 °C, the first of which had an initial water content of 25%. Three parallel samples were retrieved and tested for unconfined compressive strength (UCS) and surface fracture characteristics at moisture content levels ranging from 13% to 25%. Analyses of images of crack patterns obtained using stereological software, indicate that the pattern of increases in UCS with decreasing moisture content induced by drying, is strongly affected by the intensity of cracks on the samples. Desiccation cracking only occurred in the 2nd and 3rd stages of soil drying. During the first stage of drying, the stress-strain curve of the soil exhibited increase in slope with decreasing water content. This implies the domination of suction at the initial stages. The number of crack segments observed on samples, increases with W-D cycles, thus decreasing soil brittleness. However, increase in W-D cycles does not significantly affect the soil water retention characteristics. These findings illustrate the significant role played by soil suction in strengthening soils against the degradation effects of cracks during the early stages of drying. As drying proceeds, the proliferation of cracks eventually reduces soil strength as soil suction is overcome. Therefore, in developing structures on clayey soils that will be subjected to seasonal changes in moisture content, assessments of the balance of the effects of suction and soil desiccation cracking should be made.

Dredged sludge has poor mechanical properties and its safe disposal is highly risky. Fiber has been considered as an effective additive for soil reinforcement because of its cost effectiveness, easy adaptability, and reproducibility. The main objective of this research is to investigate the effects of polypropylene fiber on hydro-mechanical behavior of dredged sludge. A series of compression and direct shear tests were performed on dredged sludge samples with different percentage contents of polypropylene fiber 0%, 0.05%, 0.1%, 0.2%, 0.4%, and 0.8% by weight of dredged sludge and the direct shear tests were performed at vertical stresses of 50, 100, 200 and 400 kPa. The test results indicate that inclusion of fiber improves shear strength of sludge with increasing compression, void ratio, consolidation coefficient and hydraulic conductivity. The optimum fiber content for these improvements was found to be 0.1%. Presumably the post-consolidation moisture content of sludge after consolidation is minimal at this fiber content, although the shear strength continues to increase with fiber content even after consolidation. The shear strength of samples with the fiber contents of 0.8% is 1.48, 1.58, 1.42, 1.27 times that of the non-reinforced samples under respective consolidation pressures of 50, 100, 200 and 400 kPa, and the reinforcement efficiency is most significant under a pressure of 100 kPa. The strain hardening tendency is more pronounced with the increase of fiber content in the late shear failure process. The results of this study indicate that the mechanism of fiber reinforcement for the consolidation test is “bridging” as different from the shear strength test, which is “friction”. This realization should impact upon the failure patterns of fiber reinforced materials.

On the basis of textural and hydro-mechanical characteristics, bentonite has been proven to be an effective buffer/backfill material for long-term containment of high-level radioactive waste (HLW) in deep geological repositories. Herein, the results of experiments performed to investigate the swelling equilibrium limit (SEL) of bentonite under various boundary conditions are presented. A special apparatus was employed to simulate various stress–strain boundary conditions, including constant volume (CV), constant vertical stress (CVS), and constant stiffness (CS). Bentonite samples were prepared with various initial dry densities ranging from 1.5 to 1.7 g/cm3 and vertically stressed to different levels. During wetting, they were subjected to different boundary conditions before the swelling strain or swelling pressure reached equilibrium. Test results indicate that stress–strain boundary conditions have significant effects on the measured swelling strain and swelling pressure of the tested bentonite. More specifically, the relationship between the sequence of swelling pressure under different boundary conditions is CV > CS > CVS, while the relationship between the sequence of swelling strain is CVS > CS > CV. In addition, the characteristics of SEL curves are governed by the initial dry density and vertical stress with the effect of dry density being more significant. Based on these results, several SEL curves were developed to index the effects of boundary conditions on swelling potential of bentonite. They can be used to evaluate the final stress and volume states of bentonite during fluid infiltration under the range of boundary conditions possible in HLW repositories.

Contaminant sorption reactions in soils are generally heterogeneous, multi-steps solid–liquid reactions that compliment transport processes. For contaminant barrier materials, reaction heterogeneity is promoted by variability in the mineralogy and grain size distribution of materials required in mix proportions to satisfy various design functions. The adsorption/desorption of contaminants in barrier systems is necessary for performance assessments. In this paper, the sorption/desorption rates of Pb 2+ and Cd 2+ on Na-montmorillonite ((OH) 4 Si 8 Al 4 O 20 nH 2 ONa) and kaolinite ((OH) 8 Si 4 Al 4 O 10 ) were investigated by varying nature of aqueous contaminants and clay. Heavy metals including Pb 2+ and Cd 2+ were adsorbed/desorbed on the clays at pH levels of 2, 3, 4, and 7 for 48 h. Sorption/desorption of these heavy metals was found to be influenced by point of zero charge, cation exchange capacity, particle size, pH of the system, complexation of metals, and hydrated ionic radius of metals. As a result, Elovich equation was found to adequately explain the kinetics of Pb 2+ and Cd 2+ on two clay minerals with the squared correlation coefficients ( R 2 ) that range from 0.70 to 0.99. At pH 2, removal rate were 36.3% for Pb 2+ and 64.5% for Cd 2+ from Na-montmorillonite while 67.1% for Pb 2+ and 75.0% Cd 2+ from kaolinite, respectively. The results obtained from the Elovich equation could be useful for assessing the sorption equilibrium for the metals potentially attained in soil barrier systems.

A series of desiccation tests were performed to investigate the effects of both interfacial friction and layer thickness on desiccation cracking behavior of soil. Nine groups of slurry specimens with different interfacial roughness and layer thicknesses were prepared and dried under a constant temperature of 30 °C. During drying, the change in water content was recorded and the dynamic process of soil cracking was monitored with a digital camera at different time intervals. Using digital image processing technique, the propagation characteristics of desiccation cracks on soil sample surfaces were quantitatively described with a series of geometric parameters. The results show that the initiation and propagation of cracks occur at relatively high water content ranging from 10% to 40% during drying. For the same soil layer thickness, the larger the interfacial roughness, the faster the propagation velocity of soil cracks. However, the influence of interfacial friction on soil cracking decreases with increase in soil layer thickness. Besides, there is a negative linear relationship between soil layer thickness and peak propagation velocity of soil cracks. During drying, the critical water content (wf, refers to the water content when the propagation of soil cracks tends to stabilize) decreases with increase in interfacial roughness under the same soil layer thickness. The final morphology of the desiccation crack network on each soil sample is significantly influenced by both the interfacial friction and soil layer thickness. The intensity of soil cracking increases with increase in interfacial roughness or decrease in soil layer thickness. These results also confirm that the effects of interfacial friction and layer thickness on soil desiccation cracking are coupled. Generally, the interface friction effect is more pronounced for thinner soil layers.

Water infiltration in soil is a complex process that still requires appreciation of interactions among three phases (soil particles, water and air) to enable accurate estimation of water transport rates. To simulate this process, the Green&ndash, Ampt (GA) model and the Modified Green-Ampt (MGA) model introduced in the paper &ldquo, A new method to estimate soil water infiltration based on a modified Green&ndash, Ampt model&rdquo, have been widely used. The GA model is based on the hypothesis that the advance of the wetting front in soil under matric suction can be treated as a rectangular piston flow that is instantaneously transformed after passage of the infiltration front, and the MGA model does not contain the influence of pore size change. This cannot accurately reflect the soil moisture change process from unsaturation to saturation. Due to soil stratification and other inhomogeneity, predictions produced with these models often differ widely from observations. To quickly obtain the soil moisture distribution after passage of the wetting front for horizontal infiltration, an improved modified Green&ndash, Ampt (IMGA) model is presented, which estimates the soil moisture profile along a horizontal column in a piecewise manner with three functions. A logarithmic function is used to describe the gradual soil saturation process in the transmission zone, and two linear functions are used to represent the wetting zone. The algorithm of the IMGA model for estimating the water infiltration rate and cumulative infiltration is configured. To verify the effectiveness of IMGA model, a lab model test was performed, and a numerical model was built to solve the horizontal one-dimensional Richards equation using the finite&ndash, element method. The results show that the IMGA model is more accurate than the GA and MGA models. The horizontal soil moisture profiles obtained by the IMGA model are closer to the measured data than the numerical simulation results. The relative errors of the MGA and IMGA models decrease with an increase in infiltration time, whereas that of the GA model first decreases and then increases with infiltration time. The primary novelty of this study is nonlinear description of soil moisture content distribution, and derivation of unit transfer coefficient.

The purpose of this research paper was to review the different molecular biology techniques that are used in landfill investigations. The methods discussed include polymerase chain reaction (PCR), fluorescent in situ hybridization (FISH) and phospholipid fatty acid analysis (PLFA). Operation of landfills as bioreactors is now becoming a common practice, which involves the identification of different microbiological activities that facilitate the eventual breakdown of landfill wastes into useful and innocuous materials. In this review, the two important microbial activities that are discussed include methanotrophic process, carried out by methanotrophic bacteria, and methanogenic processes, carried out by methanogenic bacteria. Other bacteria encountered in landfills such as Nitrosospira and Nitrosomonas are also briefly discussed. As the name of these processes imply, methane oxidation and methane production by these microbial activities in landfills constitute another main focus of this paper. The application of these molecular biological techniques in real-time has also been demonstrated in studies involving the investigation of methanogenic diversity and activity in municipal solid waste landfill leachates and this is also discussed further. The results and conclusions of different research studies that focused on these techniques are hereby identified, discussed and summarized. Key words: Bioreactors, polymerase chain reaction (PCR), fluorescent in situ hybridization (FISH), phospholipid fatty acid analysis (PLFA), methanogens, methanotrophs, landfilling.

High content of expansive clay minerals coupled with exposure to moisture content fluctuations, is known to cause alternate swelling and shrinkage of soils. Typically, this phenomenon causes deformation and failure of structures that are constructed on such soils. The design and implementation of countermeasures against slope failures and associated failures of structural foundations in field scenarios in which expansive soils are exposed require an integrated analysis of the soil mineralogical structural characteristics and stratification, site topography and the orientation of structures relative to the unstable soil beds. In this combined field and laboratory study, it has been found that mantling of ridge tops by expansive clay soils in Yun County, China, makes buildings sited therein, more susceptible to settlement and structural damage than on the slopes and valley floor where sandstone and gravelly rock pose limited volume change risks. This investigation shows that topography of the ridge-and-gully and engineering properties of expansive soils are two significant determinants of the severity of slope failure, and the engineering measures taken in the past 25 years have been validated to be cost-effective for controlling slope failures in Yun County, China.

Three types of polyurethane were synthesized from mixtures of toluene diisocyanate, polyethylene glycol and polypropylene glycol for use in soil stabilization to improve the erosion resistance. The three polyurethanes were tested at different aqueous concentrations and sand:clay mixtures at weight ratios of 1:1, 1:3 and 1:5. The results of the rainfall simulation, unconfined compression and direct shear tests showed that the polyurethanes improve both strength and erosion resistance significantly. The observed improvement in soil erosion resistance is attributable to the physico-chemical interaction of the long-chain macro-molecules of polyurethane with the clay fraction of the soil.

In seismically active areas, waste-containment systems (WCS) can be damaged by earthquakes that generate significant ground acceleration. In such circumstances, contaminants can be released into the environment. Current state-of-the-art earthquake damage risk-assessment methodologies, Hazards U.S. Multi-Hazard (HAZUS-MH), need to incorporate contaminant-release models to enable more complete environmental impact assessments for existing and planned waste-containment systems. Contaminant-release and transport probabilities that determine the prospect of functional failure of waste-containment systems depend on a wider range of structural, geologic, hydrologic, and human factors than are covered by the structural failure probabilities of conventional structures such as buildings, roads, and bridges. The release of contaminants from WCS, and the cost of remediation depend on conditional probabilities that span the intensity and frequency of the initiating event, the structural damage of the WCS, and the fate and transport of the released contaminants in the subsurface. In this paper, the necessity and approach to linking HAZUS-MH to contaminant-release models are discussed along with relevant factors. The quantitative link that is advocated in this paper would expand the utility of HAZUS-MH in facilities design and environmental impact assessments.

The stabilization potential of negatively charged sodium carboxymethyl cellulose (CMC) solution was assessed through investigation of its retention on clays under environmental conditions that promote soil desiccation. Sodium montmorillonite and kaolinite, commonly used in clayey soils, were mixed with aqueous CMC solutions in concentrations ranging from 0 to 10 g/L. These samples were dried in a specially-designed desiccation chamber which was operated at a temperature of 25°C and relative humidity of 30%. The results show an inverse proportionality between liquid loss and CMC concentration. Liquid loss from clayey soil follows the first-order reaction with a rate constant in the range of 4.6–6.7 mg/h. CMC half-lives on sodium montmorillonite during desiccation ranged from 103 to 181 h for an aqueous concentration range of 0.5–10 g/L compared to 108 h for distilled water. For kaolinite, more liquid was retained at 10 g/L CMC concentration than at other concentrations, but liquid retention was generally insignificant. These conclusions are valid for a desiccation duration of 890 h, a time that is reasonably simulative of the duration of exposures of bare ground surfaces to weather elements. The experimental results are explained in terms of the role of CMC molecular interactions with clay minerals in controlling fluid flow to desiccating clay surfaces.

The capacity of white rot fungus, Pleurotus ostreatus, to biodegrade naphthalene present in sandy-clay-loam soil samples at concentrations of 50, 100, 200, and 500 mg/L was investigated experimentally. Using high-pressure liquid chromatography (HPLC), triplicate samples of liquid extracts from both fungus-inoculated and control (noninoculated) soil samples were taken at time periods of 0, 30, 60, and 90 days for determination of residual naphthalene concentrations. Relevant factors (naphthalene concentration, treatment duration, and residual naphthalene concentration) and their interaction were compared for both inoculated and control samples, using pair plots and level of significance. Overall, samples inoculated with P. ostreatus had reduced naphthalene concentrations to 1–40% of initial concentrations for the 90-day sampling period, compared with 63–82% for control treatments. In the control soil samples, extractable naphthalene increased by approximately 2–5% of initial content between 60 and 90 days...

Catalytic incineration of toluene over γ-Al2O3-supported copper–manganese oxide catalysts in the temperature range of 433 K–553 K was investigated using a fixed-bed flow reactor. Catalysts were characterized using Brunauer-Emmett-Teller surface area analysis, scanning electron microscopy, temperature-programmed reduction, temperature-programmed oxidation, X-ray photoelectron spectroscopy, and X-ray diffraction. Incineration of toluene was achieved at temperatures up to 553 K and it was found that the weight ratio of reactants (Cu:Mn) was optimized to be 15:10. Brunauer-Emmett-Teller surface area results had no correlation with the activity of the catalysts. Results of temperature-programmed reduction/temperature-programmed oxidation and X-ray photoelectron spectroscopy showed that the redox peak of the 15Cu-10Mn catalyst shifted at lower temperatures and the binding energy shifted toward higher oxidation levels. These results show that high binding energy and high redox capacity are the causes of...

Desiccation cracking in drying soil is a common natural phenomenon, and it significantly impacts the soil’s mechanical and hydraulic behavior. In this study, experimental desiccation tests were conducted on an initially saturated soil layer. Several aspects of the behavior of the soil—water evaporation, volume shrinkage, crack initiation, and propagation—were investigated. By applying image processing techniques, the geometric or morphological characteristics of the crack patterns were quantitatively described. The results show that cracking occurred during the constant evaporation rate stage, when the soil was still fully saturated at a water content of 41%. A growing crack obeys certain objective laws, and it finally splits the soil surface into relatively regular patterns: The first crack generally occurs on surface defects at the bottom of “potholes” and at the fringe of aggregates. Cracks intersect with one another at right angles, and the final crack pattern is dominated by square shapes. Most crack...

This study investigated the effect of inoculation of white rot fungus, Pleurotus ostreatus, incubation time, and levels of contamination on anthracene degradation in contaminated soil over a 90-day period. Control samples were set up to compare rates of degradation at different levels of anthracene contamination in soil. Using HPLC, extracts from soil were analyzed on intervals of 30 days to determine the level of anthracene remaining in soil. After 90 days of incubation, it was observed that time, level of contamination, and fungal treatment affected the rate of degradation of all levels of anthracene contamination, inoculated soil showed more degradation of anthracene (76–89%) compared to control soil (33–51%). It was also observed that concentration of the anthracene increased at different sampling dates in some of the soil samples. In this study, such increase in anthracene concentration was attributed to errors of extraction, sorption of the anthracene to soil particles, and possible repolymerization of anthracene in soil organic matter. The release of ligninolytic enzymes such as lignin peroxidase, laccase, and manganese peroxidase by Pleurotus ostreatus was associated with the anthracene degradation observed. A general observation indicates that an interaction between time, level of contamination, and soil treatment is vital in the degradation of high levels of anthracene contamination by the white rot fungus.

Laboratory-scale NMR studies of transformer oils reveal the presence of highly branched aliphatic and aromatic hydrocarbons with evidence of proportional balance in both aged and new oils. The primary to secondary proton ratios of aged oils were determined to be approximately 1, whereas the ratio ranged from 1.120 to 1.194 in new oils. Analyses indicate that several transitions in the chemistry of oil components contributed to the observed composite peaks and did not allow the identification of specific compounds beyond their functional groups. Resonances of non-hydrocarbons are observed for concentrations between 2 and 4 ppm, while the aromatic families occur at concentrations between 9 and 6 ppm. No consistent trend is observed between oil aging and the evolution of oil chemical composition. However, the color numbers, 0.50–1.82, increase with the oil age and the direction of color change matches that of increasing turbidity from new (T34 and T44) to old oils (T14 and T24). This implies that turbidity may be a dependable method of indexing the aging of transformer oils.

Textural changes can manifest in emplaced barrier materials for contaminants in response to their stabilization with aqueous polymers against desiccation stresses that can induce cracking. In this Part II of the two-part article, experimental studies of clay and sand/clay barrier materials were performed to determine their shrinkage, drying rate (DR), and cracking patterns when admixed with aqueous polymers such as polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose, and chitosan. Aqueous concentrations used were in the range of 0–5 g/L, and DR tests were performed at 25°C and 30% relative humidity. Shrinkage tests were performed at 75°C. As evident in the shrinkage results for chitosan and polyethylene oxide with 90:10 mixture of sand:montmorillonite, high aqueous polymer content may not necessarily translate to greater resistance to barrier material shrinkage. Results show that almost all polymer-amended barrier samples exhibit better shrinkage characteristics (low shrinkage ratio an...

The environmental challenges from coal mining include coal mine accidents, land subsidence, damage to the water environment, mining waste disposal and air pollution. These are either environmental pollution or landscape change. A conceptual framework for solving mine environmental issues is proposed. Clean processes, or remediation measures, are designed to address environmental pollution. Restoration measures are proposed to handle landscape change. The total methane drainage from 56 Chinese high methane concentration coal mines is about 101.94 million cubic meters. Of this methane, 19.32 million, 35.58 million and 6.97 million cubic meters are utilized for electricity generation, civil fuel supplies and other industrial purposes, respectively. About 39% of the methane is emitted into the atmosphere. The production of coal mining wastes can be decreased 10% by reuse of mining wastes as underground fills, or by using the waste as fuel for power plants or for raw material to make bricks or other infrastructure materials. The proper use of mined land must be decided in terms of local physical and socio-economical conditions. In European countries more than 50% of previously mined lands are reclaimed as forest or grass lands. However, in China more than 70% of the mined lands are reclaimed for agricultural purposes because the large population and a shortage of farmlands make this necessary. Reconstruction of rural communities or native residential improvement is one environmental problem arising from mining. We suggest two ways to reconstruct a farmer's house in China.

Use of aqueous-phase polymers as stabilizers for contaminant barrier materials against cracking in the field requires optimization of polymer solution concentration, barrier material mix composition, and mixing conditions. Physicochemical characteristics of the polymer solution such as viscosity, conformation of dissolved polymer molecules, and polydispersity affect the response of polymer-amended barrier materials to desiccation stresses imposed by a combination of low relative humidity and high temperature. In this Part I of the two-part article, the viscosity–concentration characteristics of aqueous polyvinyl alcohol (PVA), polyethylene oxide (PEO), carboxymethyl cellulose (CMC), and chitosan (CHT) were experimentally analyzed. Results indicate that the intrinsic viscosities of polymer solutions can be affected by polydispersity of the polymers. Also, the use of NaCl solution as a solvent for the negatively charged CMC promotes cationic–dipole interactions that maintain linearity of the viscos...

Herein, the Georadiological Barrier Gamma Attenuation Model that is developed in Part 1 of this paper, is utilized to estimate the attenuation of gamma (γ) rays by earthen barriers of various thicknesses and material composition. Activities of radioactive isotopes are calculated and coupled with an exponential absorption equation, to estimate γ exit intensities from these georad barriers. The results indicate that γ attenuation by georad barriers is more significantly affected by barrier thickness than by barrier density. A 33% increase in thickness from 15 to 20 cm produces a 50% reduction in emitted γ intensity, while a 33% increase in density from 1.5 to 2.0 g∕ cm3 produces a 19% reduction for a barrier comprising 45% sand, 25% clay, and 30% water (by weight). This model can be used to optimize barrier material mix composition, density, and thickness to increase γ attenuation in emergency response at existing radiologically contaminated sites and during response scenarios.

The distribution of large aggregate particles in concrete is a significant determinant of concrete strength, durability and wave/fluid transmission characteristics. These characteristics are important with respect to the performance of concrete containment systems for interim storage of radioactive waste. Even distribution of aggregate particles within concrete matrix promotes spatial uniformity of concrete characteristics and minimizes the weakness that can develop in aggregate-deficient portions. The internal heterogeneity of concrete can be assessed destructively through standard load testing or indirectly through imaging and stereological analysis of obtained images. In this paper, an indexing methodology is developed and applied to the analysis of the areal and volumetric distribution of aggregates in samples extracted from hardened concrete grout for waste storage. Analyses of 301 mm mini-slices that were reconstructed into 4 full slices on the basis of a fixed aggregate diameter of 16.93 mm indicat...

Clayey soil is an essential component of waste containment systems. The orientation of soil particles relative to gradients of heat, hydraulic pressure and stress is a significant factor as regards the stability and hydraulic conductivity of waste containment barriers. In this paper, an analytical method called Standard Deviational Ellipse Method, which is often used for point set distribution analysis in Geographical Information System (GIS), is used to analyze particle orientation quantitatively. Through the conversion and processing of soil microstructural images, the orientation angles of soil particles are herein determined and correlated spatially across planar cross-sections. This methodology is demonstrated for a selected SEM image of a clayey soil of 0.558 porosity. The results show that the predominant orientation angle of soil particle averages is 13.445° with an anisotropic ratio of 11.49°. These results indicate that the soil sample is mostly isotropic.

Mixture rules that enable the estimation of the characteristics of composite mixtures using data on the characteristics of their components are useful in reducing the frequency and cost of material testing for construction quality assurance prediction of barriers in waste containment systems. Different components of a mixture have characteristics that may not always be represented in direct proportion to their contents in the composite mixture. In this paper, the interaction effects of such mixtures are scaled in terms of an aggregation index. This index is formulated on the basis of metal sorption capacity measurements and used to investigate four mix designs, covering different weight proportions of four materials (Ottawa sand, fly ash, diatomaceous earth and Ca-montmorillonite). Computations using test data obtained through cadmium sorption tests indicate an increase in aggregation by up to 50% for mixtures with high clay content (10%). Also, values of aggregation index were found to be less than 1 for...

Mining affects the environment in different ways depending on the physical context in which the mining occurs. In mining areas with an arid environment, mining affects plants’ growth by changing the amount of available water. This paper discusses the effects of mining on two important determinants of plant growth—soil moisture and groundwater table (GWT)—which were investigated using an integrated approach involving a field sampling investigation with remote sensing (RS) and ground-penetrating radar (GPR). To calculate and map the distribution of soil moisture for a target area, we initially analyzed four models for regression analysis between soil moisture and apparent thermal inertia and finally selected a linear model for modeling the soil moisture at a depth 10 cm; the relative error of the modeled soil moisture was about 6.3% and correlation coefficient 0.7794. A comparison of mined and unmined areas based on the results of limited field sampling tests or RS monitoring of Landsat 5-thermatic mapping (TM) data indicated that soil moisture did not undergo remarkable changes following mining. This result indicates that mining does not have an effect on soil moisture in the Shendong coal mining area. The coverage of vegetation in 2005 was compared with that in 1995 by means of the normalized difference vegetation index (NDVI) deduced from TM data, and the results showed that the coverage of vegetation in Shendong coal mining area has improved greatly since 1995 because of policy input RMB¥0.4 per ton coal production by Shendong Coal Mining Company. The factor most affected by coal mining was GWT, which dropped from a depth of 35.41 m before mining to a depth of 43.38 m after mining at the Bulianta Coal Mine based on water well measurements. Ground-penetrating radar at frequencies of 25 and 50 MHz revealed that the deepest GWT was at about 43.4 m. There was a weak water linkage between the unsaturated zone and groundwater, and the decline of water table primarily resulted from the well pumping for mining safety rather than the movement of cracking strata. This result is in agreement with the measurements of the water wells. The roots of nine typical plants in the study area were investigated. Populus was found to have the deepest root system with a depth of about 26 m. Based on an assessment of plant growth demands and the effect of mining on environmental factors, we concluded that mining will have less of an effect on plant growth at those sites where the primary GWT depth before mining was deep enough to be unavailable to plants. If the primary GWT was available for plant growth before mining, especially to those plants with deeper roots, mining will have a significant effect on the growth of plants and the mechanism of this effect will include the loss of water to roots and damage to the root system.

The hydraulic shovel excavator has found significant applications in surface mining, construction, and geotechnical operations due to its flexibility and mobility. The key to high availability and utilization of this shovel is adequate understanding of machine dynamics and machine-formation interactions among other technical, operating, safety, and economic factors. These shovels are capital intensive, complex in design and operation within severely constrained environments. Detailed dynamic modeling and analysis are required to understand their effective utilization for achieving efficient operating performance and economic useful lives. Previous attempts at solving these problems are limited because they do not provide knowledge on the resistive forces and moments for efficient excavation. In this paper, the Newton-Euler techniques are used to develop hydraulic shovel dynamic models with numerical examples. Detailed analysis of the results shows that: (1) the kinematics of the stick-bucket joint (joint ...

The textural characteristics of engineered clay barriers of deeply buried radioactive waste repositories are likely to change in response to hydro-thermo-mechanical stresses during the 10 000-year service and risk analysis period. Expected textural changes stem from a combination of processes, the most significant of which is smectite illitization. To pose significant risks of radionuclide release from buried waste canisters, illitization must, as a minimum, produce barrier textural changes that are significant within the timeframe in which radioactive activity is still significant. Besides, the canister must be damaged, principally through corrosion by substance-laden infiltrating moisture. In the current paper, simulations of three scenarios of illitization of a clay barrier that is initially 100% smectite under a temperature regime that does not exceed 150°C indicate that the accumulation of potassium ions ( ) borne by infiltrating water close to the waste canister is likely to be insignificant within ...

Petroleum-based transformer oil performs the dual roles of insulator and electrolyte depending on charges in the oil. The availability of charges for conduction influences the level of voltage breakdown in the mineral oil and depends on the intensity of physicochemical processes such as redox action, hydrolysis, photodegradation, sludge/particle development, and gas formation arising from thermal, mechanical, chemical, and electrical stresses in the oil. Previous investigators have focused mostly on single oil aging indicators to build models for estimation of the aging rates of transformer oils, within a time frame that is too short relative to the operational service life of transformers. In this research, the interdependence of oil voltage breakdown and changes in oil physicochemical characteristics was investigated experimentally using T24 and T14 oils. Tests were performed with a DTS-100D oil tester for voltage breakdown and a HKV 4000 series high kinematic viscosity bath. The calculated activation e...

The effects of charge reversal about the measured point of zero charge (pH(0) approximately 5.2) of untreated and treated Sete Lagoas lateritic soil of Brazil on aqueous polymer sorption was investigated. The polymers are anionic sodium carboxymethyl cellulose (CMCA), nonionic polyethylene oxide (PEO), and cationic polyacrylamide (PAM). They were prepared at aqueous concentrations and pH ranges of 0.1-2.0 g l(-1) and 2-9, respectively. Soil treatment involved the removal of iron oxides by treatment with dithionate-bicarbonate-citrate. Batch sorption test results show that the presence of iron oxides in lateritic soil tends to suppress sorption of CMCA (especially at pH=pH(0)) and PEO (for the whole pH range) but has uncertain effects on cationic PAM sorption. CMCA sorption on the untreated soil improves on either side of pH(0), in direct proportionality to solution concentration, except at pH4.0, where disassociation of the polymer molecules may decrease sorption energy. Increase in the sorption of non-cationic polymers (CMCA and PEO) at pHpH(0) is attributable to dispersion of clay, cation bridging and polymer molecular reconfiguration. For cationic PAM, electrostatic bonding to negatively charged soil particle surfaces accounts for the sorption increase. For treated soil samples, polymer sorption pattern is similar to those expected for the montmorillonitic clayey soils of temperate zones. These results indicate that the pH(0) of lateritic soils, within the regime that exists in the field, should be considered in assessing the potential effectiveness of polymer dust suppressants for tropical lateritic soils.

Physicochemical interactions between polymer molecules and clay particles affect the swelling rate and magnitude of expansive clay soils. The effectiveness of aqueous solutions of three polymers: Sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), polyethylene oxide (PEO) ranging in concentration from 0.5 to 10 g∕L , as soil stabilization agents against Na-montmorillonite swelling was analyzed. Rates of volumetric swelling of Na-montmorillonite upon hydration were recorded over durations ranging from 120 to 200 h , and data were used to compute the volumetric swelling ratio (VSR), an expression of the clay volume at any time relative to the initial volume of clay in the immersion tube. The results show that PAM, the cationic polymer reduces the VSR by as much as 40% relative to distilled water. PAM molecular weight and concentration have minimal effects on VSR although sorption of PAM of higher molecular weight (PAM B) is favored at aqueous concentration below 2 g∕L . Data from x-ray diffraction a...

Preliminary data from controlled experiments indicate that in plasma electrolysis, metallic electrodes do not have to be immersed in water to produce hydrogen and oxygen as in the case of traditional electrolysis. Instead, the electrodes can interact with water through atmospheric pressure plasmas located between the electrode tips and the water surface. Experiments and spectral analysis of the light emitted by the plasmas as well as mass spectroscopic testing of gases from a region near the negative electrode, clearly indicate that the plasma associated with the negative electrode evolves hydrogen from the water. When a single plasma electrode was used in conjunction with a conventional immersed metal electrode, vigorous bubbling was observed at the immersed electrode. In very broad but fundamental terms, the advantage of this method is that high velocity transport of hydrogen through gas phase plasma-bounding regions (i.e., plasma sheaths) might replace low-speed diffusion through liquid phase that is currently used in conventional electrolysis. This process is likely to increase the rate of generation and collection of hydrogen over those of current electrolysis methods with high potential for integration into fuel cell systems and modular units for augmentation of small-scale power systems for distributed electricity generation.

The enormous amount of wastes produced during wood processing operations in many countries provides challenging opportunities for the use of wood waste as a construction material. In this research, wood waste (sawdust and wood shaving) ash (WWA) of pretreated timber of 0, 5, 10, 15, 20, 25, and 30% by weight of cement was added as a supplement to a concrete of mix proportion 1:2:4:0.56 (cement:sand:coarse aggregate:water cement ratio), and the strengths and the water absorption of the matrix were evaluated. Also, the metal leachability of WWA was analyzed. The compressive and the flexural strengths of WWA concrete for the ages investigated ranged from 12.83 to 28.66 N∕ mm2 , and 3.65 to 5.57 N∕ mm2 , respectively, with the lowest values obtained at 30% additive level of ash. When compared with the strength of plain concrete (control), the compressive and flexural strengths of WWA concrete were between 62 and 91% and 65 and 98%, respectively, of the former. The trend of the water absorption of WWA concrete...

Halogenated aliphatic compounds (HACs) can be reduced by iron sulfides in aqueous systems. Generally, the thermodynamics and kinetics of dehalogenation reactions are controlled by the mineralogical and particle surface characteristics of the iron sulfide, the composition of the HAC and reaction conditions such as component concentrations, pH and Eh. In this theoretical and experimental investigation of CCl4 and C2Cl6 reduction by FeS and FeS2, the roles of hydrophobic and hydrophilic sites on the iron sulfides were analyzed. Experimental data obtained through zeta potential measurements, were used along with the Gouy-Chapman model and the simple two-layer surface complexation model to relate iron sulfide surface hydroxyl densities to the degree of HAC dehalogenation. The surface hydroxyl site densities of FeS and FeS2 were found to be 0.11 sites/nm2 and 0.21 sites/nm2, respectively. During the dehalogenation reaction process, CCl4 was found to decrease to its first intermediate product CHCl3 within the first 20 hours followed by a slower process of conversion to CH2Cl2. The results also show that FeS is less hydrated (more hydrophobic) than FeS2. For CCl4 and C2Cl6, FeS is a better dehalogenator than FeS2. These results imply that particle surface hydrophobicity is a critical factor in surface-mediated dehalogenation of chlorinated compounds.

Contaminant migration from polluted sites that are excessively permeable to fluids can be minimized by ground stabilization through grouting with cementitious materials. Analyses of the long term drying process of 2.75 mm diameter samples of cement–bentonite grouted soils from Dover, Del. in an environmental chamber maintained at a temperature of 25°C and relative humidity of 30% indicate that for most samples, the water-filled porosity (0.02–0.033) varied in a quasi-sinusoidal pattern with respect to drying time. Measurements of ultrasonic wave transit time with a James V-Meter correlated in time, with moisture loss determinations by weight loss measurements, show that in the initial 0–65 day drying period, the escape of moisture and consequent increase in air-filled porosity is responsible for the decrease in ultrasonic pulse velocity. Thereafter, increases in pulse velocity values ranging from 50 to 260 m∕s observed for the reaction products at sustained drying at 25°C, provide enough activation energy...

In order to understand the mechanism by which aqueous polymers improve the resistance of clayey barrier soils to stresses, it is important to precisely determine the quantity of polymer that is sorbed onto barrier soil from aqueous solution. Batch sorption test results performed to analyze polyacrylamide (PAM) sorption from aqueous solutions by Na-montmorillonite (Nammt) indicate that viscosity measurement provides higher sorption amounts of PAM (0.1539 g/g of Nammt) than thermogravimetric analyzer (TGA) measurement (0.0533 g/g of Nammt). Statistical analyses of sorption data for both methods performed at various concentrations ranging from 0.1 to 4.0 g/L show that in general, the thermogravimetry is more consistent than viscometry. The demerit of viscometry is that the amount of polymer sorbed on solids is estimated indirectly through measurements of polymer solution concentration. Some free polymer molecules may still exist within interparticle pores of the separated solid fraction and can impose higher levels of sorption than actual levels. In the case of TGA, freezing drying of samples, which is a part of the test protocol, extracts pore liquid containing polymer molecules by sublimation. This leaves behind polymer molecules that are actually sorbed on soil particles, thereby producing lesser and more realistic sorption data than viscometry can provide.

In this paper, class F fly ash, bottom ash, polypropylene fibers, and nylon fibers were evaluated as potential stabilizers in enhancing volume change properties of sulfate rich expansive soils. As a part of the research evaluation, a comprehensive laboratory experimental program was designed and conducted on two different subgrade soils from two locations in Texas. Four dosage levels of each stabilizer, two compaction moisture content levels, and 14 days curing period were investigated. Volume change behavioral tests including volumetric free swell, volumetric shrinkage strain, and vertical swell pressure tests were conducted on both isolated stabilizer treated and combined ash-fiber stabilized soils. Ash stabilizers showed improvements in reducing swelling, shrinkage, and plasticity characteristics by 20–80% whereas fibers treatments resulted in varied improvements. In combined treatments, class F fly ash mixed with nylon fibers was the most effective treatment on both Dallas and Arlington soils, where the soil property enhancements were considered average-to-moderate. Possible mechanisms that resulted in the soil property improvements are discussed along with the recommended stabilizers and their dosages for expansive soil treatments.

A quality control methodology was implemented for aggregate distribution in concrete that can be used in waste containment using the analytical method developed in Part I of this paper. This involves the comparison of three concrete placement methods: rodding, vibration, and placement with neither rodding nor vibration. The concrete mix consists of coarse (#4 stone and #67 stone) aggregate and fine aggregate, the latter of which is sand (making up 29.4% by weight). The experimental results have been used herein to develop quality control charts based on the deviation index, the range of the deviation index within each cylinder, and nonconformity of the aggregate to even distribution, respectively. The nonconformity quality control chart is found to be the most appropriate scheme for evaluating aggregate distribution deviation. The results obtained from the nonconformity quality control chart show that the upper control limit, when specified at three times the square root of the mean deviation index, has a value of 23.4. This is a relatively large value and the deviation indices per slice all fall below it, indicating that the quality of the concrete mix is satisfactory.

Even distribution of aggregate particles in matrices is the target of random mixing processes that are used in the preparation of construction materials to enhance the postplacement uniformity of characteristics. This is particularly important for waste containment barrier concrete where strength, durability, and minimal permeability are desirable. An index, herein referred to as the deviation index (DI) was developed and applied to the cross-sectional areas and volume elements of concrete containing large aggregate to describe distribution deviations of large aggregate particles from perfectly even volumetric distribution. The Poisson distribution and the goodness of fit test were used to describe deviations. Experimental results were obtained from concrete batching tests, designed and performed to compare two mixing methods (rodding and vibration) and a control. The results show no significant uneven distribution as the χ2 values are less than 19.6 at 5% significance level. Within the bounds of these lo...

The excitation of structural components and liquid contents of surface impoundments by seismic waves can generate turbulence that is large enough to overtop the bounding berms. In cases in which the liquids are wastes from industrial/municipal operations, their release from impoundments can pose significant risks to the environment. In this analysis, the freeboard magnitudes that can accommodate liquid head levels in impoundments are determined through linkage of configuration of waves in the liquid surface to incident seismic wave characteristics, liquid characteristics and impoundment design. For an impoundment site in a region of ground acceleration levels ranging from 0.2 to 1.0 g and impacted by seismic shear wave velocity of 180 m/s, freeboard requirements are in the range of 0.004–2.0 m on soft soil; 0.008–0.7 m on medium-dense soil; and 0.002–0.1 m for dense soil. For the same impoundment design, ground acceleration and incident wave characteristics, freeboard requirements are directly proportional to the depth of the soil mantle over bedrock. The impoundment slope, which is a key parameter with regards to liquid holding volumetric capacity of the impoundment, is a less significant parameter than depth to bedrock with regard to the size of the required freeboard. This implies that siting of an impoundment should be considered to be critical to impoundment performance in seismic zones.