Добірка наукової літератури з теми "Clay soils Drying"

This note provides practical guidelines for the use of microwave drying in the determination of soil water contents. The results are based on over 250 individual tests performed on sand, sandy clay, estuarine clay, marl, lateritic clay, kaolin, and bentonite (sodium). All soils tested fell into one of three distinct categories and drying times for each are presented as a function of initial sample mass. The recommended drying times give results within 0.5 wt% of those obtained by standard oven drying. No limitations were observed in the performance of a 600-W domestic microwave oven. Key words: water contents, microwave, drying, sand, silt, clay, procedures.

Gelatin, a biopolymer derived from animal proteins, has been selected to stabilize three fine-grained soils by determining select index and engineering properties. Specimens for California Bearing Ratio (CBR) were tested using three different curing methods, i.e., thermally cured at 60 °C, unsoaked, and 7 days air-cured submerged specimens. The amount of gelatin added to the soil ranged from 0.5% to 2% by soil weight. The sequence of the interaction between gelatin and the clays is as follows: (A) The biopolymer solution is adsorbed and agglomerated onto the surface of the clay. (B) The presence of Al3+, Si4+, and K+ ions on the clay promotes the blending of connective linkages with negatively charged gelatin. (C) The connection reinforcements harden with the curing period and subsequent drying of the stabilized soils. (D) Drying of the gelatin–clay complex also establishes alternative bonding modes such as van der Waals interactions and ligand exchange. The biopolymer formed dry, rigid films after 72 h which were responsible for coating and reinforcing the soil particles. Thermal curing by 1% addition of gelatin yielded the maximum CBR of 91.42%, 141.1%, and 122.3% for high compressible clay, low compressible clay, and low compressible silt, respectively, and a maximum Unconfined Compressive Strength (UCS) of 3968 kN/m2 for the low compressible clay. The UCS results revealed that brittle failure was predominant for the gelatin-amended soils after 28 days of curing while shear failure was observed for the treated soils tested 2 h after sample preparation. Tests on pH revealed that the gelatin-stabilized soils displayed marginal variations after 28 days. Spectroscopic analysis revealed the various types of bonds between gelatin and the clays. A reduction in mass of 9% was observed for the alternate wetting and drying of the high compressible clay after a period of 12 cycles. The adsorption of the clay–gelatin complex was indicated by variation in average particle diameter and specific surface. Savings in 450 m3 and 93.75 m3 of coarse aggregates and dense bituminous macadam, respectively, were observed for a 1 km pavement for the stabilized low compressible clay.

Cracking in soils that are undergoing drying is controlled by soil suctions and by soil properties such as compression modulus, Poisson's ratio, shear strength, tensile strength, and specific surface energy. The paper reviews the occurrence and morphology of cracks in dry-climate regions of Australia and Canada. After reviewing the behaviour of unsaturated soils and the mechanics of cracking, solutions are developed based on (i) elasticity theory, (ii) the transition between tensile and shear failure, and (iii) linear elastic fracture mechanics. The solutions are compared and related to crack depths observed in the field. Key words : clay, cracks, crust, shear strength, soil suction, tensile strength, unsaturated soil, weathering.

Clay materials have many environmental applications, especially in situations where a hydraulic barrier is desired. However, as the plasticity of clay increases, cracks tend to develop during cycles of long dry spells. This is particularly a concern in the construction of covers or installation of landfill liners prior to waste filling. In the present study, specimens prepared from three natural clayey soils from Iran used for clay barrier construction, and one artificial clayey soil, were subjected to cycles of wetting and drying. Surface cracks of different dimensions formed as a result of drying. Specimens with the largest volumetric shrinkage strains typically contained the highest number of cracks. Specimens that developed cracks were subjected to hydraulic conductivity testing. The results showed that the dimension of cracks increased with increasing plasticity index and clay content and, so, the initial hydraulic conductivity increased with increasing plasticity index and cycles of drying and wetting. Cracking increased the hydraulic conductivity by 12–34 times, depending on the plasticity of the soil. After a long saturation time, the hydraulic conductivity of the soils decreased with an increase in saturation time, which could be associated with a self-healing process that affects the soils by different degrees.Key words: desiccation, cracking, plasticity, hydraulic conductivity, clay barriers, self-healing, volumetric shrinkage.

By using of shrinkage curve, the empirical relationship between the degree of saturation and the void ratio on drying path was established for four types of soils including sand, silt, clay and soft clay. It was indicated that during the process of drying, the soil samples continuously shrunk with the decrease of saturation degree. For test samples of sand and silt, the curve of saturation degree and void ratio is flat; For test samples of clay and silt clay, however, the shrinkage of the soil samples was almost fulfilled when the degree of the saturation of soil samples decreased to 90% and the void ratio of the soil samples almost kept unchanged while the degree saturation of soil was reduced to 70%.

Drying of three mineral soil samples (clay content 4—58 %, organic carbon content 1—5 %) equilibrated at 75.5 % relative humidity was studied. The soils were dried in an oven at +50°C, +70°C and + 105°C for 4 and 8 hours and in a desiccator over pure concentrated H2SO4 and P2O5. Drying over desiccants for 8 hours removed less water than drying at + 50°C. Drying over desiccants for 3—7 days was as efficient as drying at +70°C, for 14—24 days as efficient as 4 hours of drying at + 105°C. Eight hours of drying at + 105°C seemed to be too drastic, because it caused a greater weight loss in the clay sample of 5 % organic carbon content than did prolonged desiccant-drying. Drying at + 70°Cremoved as much water from fine sand which contained 4 % clay as prolonged desiccant-drying.

In the field of soil drying methods, rapid microwave heating is progressively replacing conventional techniques. Due to the specific heat transport caused by microwaves, the drying process can significantly modify soil structure, which, in turn, can influence mechanical and filtration characteristics. In this study, we compared structural changes of exemplary non-cohesive (medium quartz sand (MSa)) and cohesive soil (silty clay mainly composed of kaolinite (siCl)). The sample materials were subjected to three different drying methods: air-drying, conventional oven (CO) drying, and microwave oven (MO) drying (MO). Soil structure was studied using X-ray microtomography (XµCT) and described in detail by image analysis methods. The study showed that the analyzed types of heating had a negligible effect on the structure of the sands, but a significant impact in the case of silty clay. Such a phenomenon is discussed and explained in this paper. The study advances the testing of soils microwave drying in a geotechnical laboratory.

Shrinkage characteristics and COLE and PLE values of undisturbed natural aggregates of clay soils from the Netherlands were measured. The course of the shrinkage process upon drying varied strongly between soils, and very often the measured characteristics diverged from the theoretical curve. Some Dutch clay soils are amongst the strongest swelling and shrinking soils in the world, with volume decreases of aggregates up to 49% between saturation and oven-dryness, and 42% between saturation and a pressure head of -16 000 cm. Potential subsidence of a Dutch field soil due to shrinkage is up to 15 cm. In some Netherlands clay soil, as a result of normal shrinkage, the aggregates remain saturated throughout the whole year; only inter-aggregate pores such as shrinkage cracks, contain air. (Abstract retrieved from CAB Abstracts by CABI’s permission)

The present work investigates the desiccation effects on a lime-treated clayey silt. Original experimental techniques have been developed to control suction conditions (with osmotic technique) and to track volume variations and cracks occurrence upon drying. Free and constrained dryings are performed to evaluate the shrinkage potential (for free drying) and the conditions of desiccation crack triggering (upon constrained drying). Also, indirect tensile tests and uniaxial compression tests are carried out to evaluate the strength at various suctions. Those investigations have been performed on natural and lime-treated clayey silt in order to emphasis the role of the lime treatment in the triggering and/or mitigation of the cracking process. At the end, generalized effective stress framework with an effective stress parameter χ calibrated according to a power law is used to provide a constitutive interpretation of the occurrence of desiccation cracks in relation with the water retention properties, the soil stiffness, the tensile strength and the geometrical constraints of the soil samples. For the used compacted materials, it is demonstrated that the lime treatment postpones the occurrence of desiccation cracks and so, plays a favourable role in the stabilization of soft soils subject to drying.

Smectite is generally a high-swelling clay. However, the smectite found in marine quick clays in the Ariake Bay area of Japan is a low-swelling clay like illite and kaolinite. The low swelling properties of an Ariake marine clay are investigated here in terms of consolidation, swelling, and shrinkage characteristics. The void ratios in compression curves of soils containing sodium are lower at 0.01 N than at 1.0 N NaCl concentration, and the slopes of swelling curves are independent of salt concentration in the pore water and cation valency. These tendencies are contrary to those observed for montmorillonite and a paddy soil containing high-swelling smectite. Measurements of swelling pressure suggest that the smectite in the Ariake marine clay exhibits little intracrystalline swelling even after saturation with Na. The volume shrinkage of the Ariake marine clay by air-drying is smaller than that of the paddy soil. Key words: compressibility, marine clays, smectite, swelling.

L'argile est largement répandue à la surface de la Terre, et comme elle est facilement disponible, elle a été largement utilisée comme matériau de construction depuis très longtemps. L'argile peut être utilisée non seulement comme barrière naturelle dans les noyaux des barrages, mais aussi comme matrice pour le stockage pour les déchets radioactifs en raison de ses propriétés de rétention. Le comportement mécanique des matériaux argileux est complexe, une des difficultés réside dans le fait qu’il soit sensible l’eau. Durant le processus de dessiccation, les sols argileux subissent un phénomène de retrait qui peut provoquer des fissurations. L’objectif de cette thèse vise, dans un premier temps, à développer une approche numérique capable de reproduire le phénomène du retrait, ainsi que la distribution de la teneur en eau et de la succion. Dans un deuxième temps, en se basant sur la décomposition du tenseur de déformation en une partie élastique (loi de Hooke) et une partie hydrique (représentant le retrait), une méthode de calcul par éléments finis est proposée pour décrire et aider à comprendre le comportement observé durant la dessiccation. Enfin, dans le but de reproduire la distribution des fissures, la méthode basée sur des éléments finis étendus (X-FEM) est utilisée. Les simulations numériques sont basées sur l'analyse des résultats d’essais de dessiccation d’argiles de laboratoire. L'application de la technique de corrélation d'images numériques (CIN) dans les essais de dessiccation rend l'étude du processus de séchage plus précise. Les résultats expérimentaux réalisés dans des travaux antérieurs et en cours montrent que les argiles, sur le chemin de séchage, vont générer une déformation de retrait causée par la perte d'eau. En simulation cette déformation est liée à la variation de la teneur en eau des argiles grâce à la fonction de Fredlund. Sur les essais utilisés le retrait de séchage suit une loi globale anisotrope liée à la géométrie de l’échantillon d’argile testé. Le coefficient de taux de retrait, appelée aussi le coefficient d’anisotropie, est utilisé pour décrire en simulation ce phénomène. Pour construire la loi constitutive permettant d’aborder le séchage des argiles molles initialement saturées, serait d'utiliser deux tenseurs de contrainte indépendants, liés à la décomposition du tenseur de déformation totale en tenseur de déformation dû au retrait au séchage (partie induite en raison de la variation de succion) et un tenseur appelé déformation « mécanique » qui sera dû au développement de contraintes liées au blocage du processus de retrait. Le tenseur de déformation mécanique peut être lié à la contrainte totale en utilisant une la loi élastique linéaire. La résistance de sol argileux initialement saturé augmente au cours de la dessiccation. Le résultat de fissuration, dans le sol sous succion contrôlée, est le résultat de compétitions entre l’augmentation de résistance de sols et l’endommagement causé par le retrait au cours de dessiccation. Le critère d’amorçage de fissure hydrique de sol est basé sur l’endommagement et la résistance de sol. Le critère de propagation de fissure, quant à lui, est basé sur la théorie de conservation d’énergie. Pour reproduire une répartition de fissure, basé sur la méthode d’éléments finis étendu (X-FEM). La loi de Weibull est utilisée pour prendre en compte la répartition hétérogène du sol. Après la validation de modèle numérique, des applications dans le domaine géotechnique peuvent être envisagées
Clay soil is widely distributed on the Earth’s surface, and because it is cheap and readily available, clay soil has been widely used as a building material for a very long history. Furthermore, clay can be used as not only a natural barrier in the dam cores, but also a matrix for the storage of radioactive wastes because of its retention properties. The mechanical behavior of clay materials is complex, one of the difficulties is that it is sensitive to water. During the desiccation process, clay soils undergo shrinkage, which can cause cracking. The aim of this thesis is, initially, to develop a numerical approach capable of reproducing the phenomenon of shrinkage, the distribution of water content as well as that of suction. In a second step, based on Coussy's theory for unsaturated porous media, and the mechanics of unsaturated soils, a constitutive law will be proposed to describe the behavior observed during desiccation. Finally, to reproduce the cracks distribution, based on the extended finite element method (X-FEM). The realization of numerical simulation is based on the analysis of the desiccation experiments of clay soils in laboratory. The application of the digital image correlation (DIC) technology in the desiccation experiments makes the study on the desiccation process in clay soils more accurate. The experimental results show that the clay soils will generate the theoretical shrinkage deformation caused by its own water loss in the drying path. This deformation in simulation can be related to the water content of clays through the Fredlund function. The desiccation shrinkage of clay soils has an anisotropic phenomenon. The coefficient of shrinkage ratio is used to describe this phenomenon in simulation. One of the ways to construct the constitutive of the initially saturated soft clays during drying could be in using two independent stress tensors which will enable the decomposition of total strain tensor into strain tensor due to drying shrinkage (induced part due to suction variation) and a “mechanical” strain tensor due to the total stress variation. Mechanical strain tensor can be related to total stress by using stiffness matrix. In fact, the initially saturated clay soil resistance increases during desiccation. The result of cracking in the soil under controlled suction is the result of competitions between increased soil resistance and damage caused by shrinkage during desiccation. The soil moisture crack initiation criterion will be based on soil damage and resistance. The criterion of crack propagation, meanwhile, will be based on the theory of conservation of energy. To reproduce the cracks distribution, based on X-FEM. Weibull's law will be used to consider the heterogeneous distribution of the soil. After digital model validation, applications in the geotechnical field are then considered

Soft soil stabilization frequently uses cement, lime, fly ash, etc., but very limited studies were conducted on the long-term durability of stabilized soil. The present research work deals with the long-term durability of commercially available soil (i.e., EPK clay) stabilized with ordinary Portland cement and polypropylene fiber using a realistic approach, where the effect can be noticed in each weathering cycle. In the present study, two different tests (i.e., wetting-drying and freezing-thawing) were conducted to analyze the long-term durability of stabilized soil. Cycles of higher temperature followed by rainfall, which generally occurs in southern states of the US, were analyzed by the wetting-drying test; and on the other hand, cycles of freezing temperature followed by normal temperature, which generally occurs in northern states of the US and Canada, were analyzed by the freezing-thawing test. For the mid-continental region where freezing, normal, and higher temperature followed by rainfall are expected to occur, hence both the test method i.e., wetting-drying and freezing-thawing, were suggested. Laboratory experimental investigations were conducted to find the percentage loss of stabilized soil during wetting-drying and freezing-thawing tests, which were used as a durability indicator for cement and cement-fiber stabilized soil. Stabilized samples were subjected to harsh environmental conditions in a laboratory set up, and their deterioration was observed and studied after each wetting-drying and freezing-thawing cycle. In the real world, stabilized soil encounters seasonal cycles of monsoon and summer in long run of its service life which was simulated in rapid weathering cycles in laboratory setup. EPK clay samples were stabilized with different percentages of cement, and a mix of cement-fiber combination and were subjected to 12 cycles of wetting-drying and freezing-thawing cycles separately to determine the percentage loss of soil in accordance with the ASTM standards. Finally, based on percentage loss of soil of those stabilized samples which survived up to 12 cycles of weathering action, the optimum content of stabilizing agent was determined for wetting-drying and freezing-thawing tests. Results of wetting-drying tests indicate that EPK clay stabilized with ordinary Portland cement and fiber combination survived up to 12 cycles, but only 10% cement + 0.5% fiber was durable against wetting-drying based on percentage loss. For all the samples stabilized with 10% cement + 0.5% fiber combination, the percentage loss of soil when subjected to durability test was less than 7%, which satisfy the Portland Cement Association’s (PCAs) durability specification. The results of freezing-thawing tests indicate that the EPK clay stabilized with 10% cement, 5% cement + 0.5% fiber, and 10% cement + 0.5% fiber survived up to 12 cycles and were durable against freezing-thawing based on percentage loss of soil i.e., less than 7% which satisfy the Portland Cement Association’s durability specification.

Expansive soils are a worldwide problem especially in the regions where climate is arid or semi arid. These soils swell when they are exposed to water and shrink when they dry. Cyclic swelling and shrinkage of clays and associated movements of foundations may result in cracking of structures. Several methods are used to decrease or prevent the swelling potential of such soils like prewetting, surcharge loading, chemical stabilization etc. Among these, one of the most widely used method is using chemical admixtures (chemical stabilization). Cyclic wetting and drying affects the swell &ndash
shrink behaviour of expansive soils. In this research, the effect of cyclic swell &ndash
shrink on swell percentage of a chemically stabilized expansive soil is investigated. Class C Fly Ash is used as an additive for stabilization of an expansive soil that is prepared in the laboratory environment by mixing kaolinite and bentonite. Fly ash was added to expansive soil with a predetermined percentage changing between 0 to 20 percent. Hydrated lime with percentages changing between 0 to 5 percent and sand with 5 percent were also used instead of fly ash for comparison. Firstly, consistency limits, grain size distributions and swell percentages of mixtures were determined. Then to see the effect of cyclic swell &ndash
shrink on the swelling behavior of the mixtures, swell &ndash
shrink cycles applied to samples and swell percentages were determined. Swell percentage decreased as the proportion of the fly ash increased. Cyclic swell-shrink affected the swell percentage of fly ash stabilized samples positively.

Organic matter decomposition in terrestrial system is of vital importance for nutrient cycling and ecosystem function. Soil microorganisms are the key drivers of decomposition which regulates the availability of inorganic nutrients through immobilisation and mineralisation. The size of the soil organic C pool is twice that of C in the atmosphere and more than twice of that in vegetation. Thus, organic matter decomposition in soil greatly influences the C flux between soil and the atmosphere. Therefore understanding factors influencing organic matter decomposition is important for climate change mitigation and soil fertility. In this thesis, the effects of residue mixing, removal of water-extractable organic C, clay subsoil addition to sandy soil and drying and rewetting on decomposition were investigated. Organic matter decomposition is influenced by both internal and environmental factors. Plant residues are an important source of soil organic C and decomposition of plant residues has been studied extensively. However, residues from different species or above- and below-ground residues are often mixed and less is known about factors influencing decomposition of residue mixtures. Shoot and root residues of three Australian native perennial grass species [Wallaby grass (Danthonia sp); Stipa sp and Kangaroo grass (Themeda triandra)] and barley (Hordeum vulgare L.) were mixed to create nine different residue mixtures (1:1 mixture). Soil respiration was measured over 18 days. Cumulative respiration in residue mixtures differed from the expected value (average of cumulative respiration of individual residues) in most cases with synergistic interactions occurring in 56 % of the mixtures (expected < measured value), antagonism in 22 % (expected > measured value). Synergism occurred when residues with relative similar decomposition rate were mixed, while antagonism occurred when the decomposition rate of individual residues differed strongly. Furthermore, a negative correlation was found between the change in microbial biomass C (MBC) and available N concentration between the start of the experiment and day 18 and cumulative respiration on day 18. The interaction with respect to cumulative respiration was not reflected in MBC and available N concentrations. Cumulative respiration and MBC concentration were greater in soil amended with residues with higher water-extractable organic C (WEOC) concentration, compared to those with lower WEOC concentration, either individually or as in mixtures. Between 2 and 30 % of organic C in residues is water-extractable and its importance in stimulating decomposition has been shown previously. Water-extractable organic C can be leached by heavy rainfall or irrigation, but little is known about the effect of addition of residues from which the WEOC was removed by extraction or leaching on microbial activity and biomass. Shoot residues of barley (Hordeum vulgare L.) were extracted five times for maximal removal of WEOC or were leached up to eight times to partially remove WEOC. Maximum WEOC removal decreased both soil respiration and MBC concentration in the first week, but MBC concentration at the end of the experiment was greater with extracted residues compared to the original residues. With leached residues, partial removal also reduced respiration rate in the first 10 days. However, MBC concentration was greatest with residue leached eight times, suggesting great substrates utilisation efficiency. In South Australia a large area of land is covered by sandy soils (3.2 million ha), with a heavy textured soil underneath, so called ‘duplex soil’. Due to the lack of binding sites for organic matter and nutrients and large pore size, sandy soils are often characterised by low organic matter content, low nutrient and water retention capacity and rapid organic matter decomposition. Addition of clay-rich subsoil to sandy soil has been shown to increase crop yield and water retention in sandy soils. Additionally, clay particles could bind organic matter. However, little is known about the effect of clay subsoil addition to sandy soil on soil respiration after addition of residue mixtures. Clay subsoil was added to a sandy top soil at 10 and 30 % (w/w). Residues of barley (Hordeum vulgare L.) and two native perennial grass species (Danthonia sp and Themeda triandra) were added individually or as 1:1 mixture. Increasing clay addition decreased cumulative respiration and extractable C concentration in soil with individual residues and mixtures. No interaction was observed in terms of cumulative respiration in sandy soil alone, but at addition of 10 % clay subsoil, antagonism occurred in two residue mixtures, and at 30 % clay addition synergism occurred in one of the mixtures. It can be concluded that clay soil addition to sandy soil does not only alter decomposition rate but also interactions in residue mixtures. In Mediterranean climate such as in South Australia long periods of dry and hot weather are interrupted by occasional rainfall or irrigation. Although the effect of drying and rewetting (DRW) has been studied extensively, the factors determining the respiration flush upon rewetting and total cumulative respiration are not fully understood. A sandy soil amended with different proportion of clay subsoil (0, 5, 10, 20, 30, and 40 %) was exposed to a single DRW event. Expressed per g soil, cumulative respiration in the constantly moist control (CM) decreased with increasing clay soil addition rate, but cumulative respiration in the DRW treatment did not vary among clay soil treatments. However, when expressed per g total organic C (TOC), cumulative respiration in the DRW treatment increased with increasing clay subsoil addition rate. Addition of clay subsoil increased water retention capacity during drying, thus microbial activity. The respiration flush one day after rewetting was greater than the respiration rate in CM only in treatments with 20-40 % clay addition rate. The response of respiration to DRW may be influenced by land management due to its effect on the soil organic C pool and differ between soil size fractions. An incubation experiment was conducted with soils collected from two plots with a long history of different management (wheat-fallow rotation and permanent pasture). The soils were sieved to 4-10 mm and <2 mm to obtain two size factions. There were five moisture treatments with the same length (48 days). The CM treatment was maintained at 50 % of maximum water-holding capacity (WHC) throughout. In the DRW treatments, the number of dry and moist days was equal but the number of DRW events ranged from one to four (1 to 4DRW). Cumulative respiration per g TOC at the end of the experiment was greater in the <2 mm than in the 4-10 mm fraction in both soils and was highest in CM and 1DRW. In wheat soil, cumulative respiration decreased from 1DRW to 3DRW, whereas it decreased only between 2 to 3DRW in pasture soil. Cumulative respiration in the second moist period was greater in 3DRW than in 2DRW (8 and 12 prior moist days) whereas cumulative respiration in the third moist period was greater in 4DRW than in 3DRW (12 and 16 prior moist days). It can be concluded that the response of respiration to drying and rewetting is more strongly influenced by management than size fraction. Cumulative respiration upon rewetting is influenced not only by the number of DRW cycles but also the number of moist days prior to rewetting. Three incubation experiments were carried out to assess the relationship between cumulative respiration per g TOC and the number of moist or dry days with the two soils used in the previous experiment. In the first experiment, the CM and DRW treatments had the same total length (10 days) with different proportions of moist and dry days in the DRW treatments. The second and third experiment had DRW cycles of dry and moist period of equal length with one cycle in Experiment 2 and two cycles in Experiment 3. Soil in the CM was maintained at 50 % of WHC throughout for all experiments. Total cumulative respiration per g TOC was greater in wheat than in pasture soil which can be explained by the greater proportion of particulate organic matter in the former. In the first experiment, cumulative respiration in the dry period was not influenced by the number of dry days, but cumulative respiration in moist period increased with number of moist days. Total cumulative respiration in the DRW cycle was negatively correlated with the number of dry days and positively correlated with the number of moist days. Cumulative respiration in DRW treatments was lower than in CM when the proportion of moist days was less than 50 % of the total length with the difference becoming greater with decreasing proportion of moist days. In both the second and the third experiment, total cumulative respiration increased with increasing number of days with a greater increase in CM than in DRW treatments. When subjected to two DRW cycles in the third experiment, total cumulative respiration in each DRW cycle was also positively correlated with the number of moist days with the slope greater in first than in the second DRW cycle. In conclusion, cumulative respiration in DRW cycles is mainly a function of the number or proportion of moist days and little influenced by soil management. An incubation experiment was conducted with the soil from the wheat-fallow rotation to determine the influence of number of dry and moist days and their distribution in two DRW cycles on respiration rate and cumulative respiration in each DRW cycle. The number of moist and dry days ranged in either the first or second DRW cycle between 10 and 35. The constantly moist treatments were maintained at 70 % of WHC throughout. Cumulative respiration in CM was greater than that in DRW treatments with the difference greater in treatments with varying number of dry days than those with varying number of moist days. Cumulative respiration in the dry period differed little among DRW treatments. The flush of respiration upon rewetting increased with number of prior dry days. Respiration rates in the moist period of the first cycle were higher than in the second cycle only up to 17 days, indicating that the effect of prior substrate utilisation in 5 moist days in the first cycle is limited to first 17 days in the moist period of second cycle. Cumulative respiration in the moist period increased with the number of prior dry or moist days with the increase greater in treatments varying in number of moist days than those varying in number of dry days. Cumulative respiration was greater when the number of moist or dry days varied in the first than in the second cycle. It is concluded that the number of dry days influences the size of the respiration flush after rewetting, while the number and distribution of moist days affect cumulative respiration. To summarise, the studies described in this thesis showed: • Cumulative respiration in residue mixtures relative to that of the individual residues depends on residue type and soil clay content. • Removal of WEOC from residues reduces initial respiration rates but not always cumulative respiration. • Addition of clay to sandy soil not only reduces cumulative respiration but also alters respiration in dry and moist periods of DRW cycles. • Cumulative respiration in DRW treatments is mainly influenced by the length of the moist period: (i) total length of the moist period determines total cumulative respiration at the end of the DRW treatments, and (ii) number of prior moist days influences respiration in the subsequent cycles.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2015

Chapter 3 gives examples of how grapevines, being woody perennials, have the potential to develop extensive, deep root systems when soil conditions are favorable. One of the most important factors governing root growth is a soil’s structure, the essential attributes of which are • Spaces (collectively called the pore space or porosity) through which roots grow, gases diffuse, and water flows • Storage of water and natural drainage following rain or irrigation • Stable aggregation • Strength that not only enables moist soil to bear the weight of machinery and resist compaction but also influences the ease with which roots can push through the soil The key attributes of porosity, aeration and drainage, water storage, aggregation, and soil strength are discussed in turn. Various forces exerted by growing roots, burrowing animals and insects, the movement of water and its change of state (e.g., from liquid to ice) together organize the primary soil particles—clay, silt, and sand—into larger units called aggregates. Between and within these aggregates exists a network of spaces called pores. Total soil porosity is defined by the ratio . . . Porosity = Volume of pores/Volume of soil . . . A soil’s A horizon, containing organic matter, typically has a porosity between 0.5 and 0.6 cubic meter per cubic meter (m3/m3)—also expressed as 50% to 60%. In subsoils, where there is little organic matter and usually more clay, the porosity is typically 40% to 50%. Box 4.1 describes a simple way of estimating a soil’s porosity. Total porosity is important because it determines how much of the soil volume water, air, and roots can occupy. Equally important are the shape and size of the pores. The pores created by burrowing earthworms, plant roots, and fungal hyphae are roughly cylindrical, whereas those created by alternate wetting and drying appear as cracks. Overall, however, we express pore size in terms of diameter (equivalent to a width for cracks). Table 4.1 gives a classification of pore size based on pore function.

The effect of wetting-drying cycles on deformation characteristics of an unsaturated clay model slope is investigated in this study. The model slope was compacted using kaolin clay mixed with thirty percent of fine sand. The deformations of slope were measured using particle image velocimetry (PIV) technique. The test results revealed that the model slope deforms mainly within a depth of 300 mm and the displacements of soil mass are nearly perpendicular to slope surface in the first two cycles. Such displacements, however, vanish gradually in the subsequent cycles. On the other hand, the magnitude of displacement along slope surface increases with the number of wetting-drying cycles. The depth affected by wetting-drying cycles increases gradually with the number of wetting-drying cycles and becomes stable finally.

Prior to the introduction of plastic pipe many gas utilities used cast iron to build their gas distribution network. Currently, there is approximately forty thousand kilometres of cast iron pipe in service in North America and a further two hundred thousand kilometres in Europe. Mostly found in dense urban locations, the cost of replacing these systems can be significantly high, such that extending the life of these systems is now a common strategy. The main problem has been leakage from bell and spigot joints caused by road vibration, freeze/thaw cycles of the ground, and the swelling and drying of clay soils. Repair technologies have evolved from mechanical joint clamps, to elastomeric seals, to shrink sleeves, to encapsulants and finally to anaerobics. The most advanced of these technologies involve the use of anaerobic sealants which are injected into the jute packing by drilling into the pipe bells. These sealants have been studied at Cornell University for longevity, and are predicted to withstand many years of service. The use of anaerobics has been adapted to work with robotics that allows the injection to take place from the inside of the pipeline while the gas main is in operation. This technology allows 24 joints to be sealed from a single excavation. The robot is a tethered electro-mechanical device that allows visual location of the joint, internal drilling into the jute packing, and injection of the sealant. A semi-rigid umbilical cable contains the electrical, hydraulic, and communication lines, and a unique drive mechanism that allows for remote operation and positioning. The development of this prototype technology was conducted by Engineering Services Inc. (ESI) of Toronto at the request of Enbridge Consumers Gas and was co-funded by Consolidated Edison of New York. Over 2000 joints have been successfully sealed in the last two years and the system is expected to be commercially available within the next year. Internal robotic repair of live mains is an industry first and has the potential to significantly reduce both costs and disruption of road excavations in urban areas.

The overall objectives of the project were: (a) To measure and study in situ the effect of irrigation with reclaimed sewage effluents on redox processes and related chemical dynamics in soil profiles of agricultural fields. (b) To study under controlled conditions the kinetics and equilibrium states of selected processes that affect redox conditions in field soils or that are effected by them. Specifically, these include the effects on heavy metals sorption and desorption, and the effect on pesticide degradation. On the basis of the initial results from the field study, increased effort was devoted to clarifying and quantifying the effects of plants and water regime on the soil's redox potential while the study of heavy metals sorption was limited. The use of reclaimed sewage effluents as agricultural irrigation water is increasing at a significant rate. The relatively high levels of suspended and, especially, dissolved organic matter and nitrogen in effluents may affect the redox regime in field soils irrigated with them. In turn, the changes in redox regime may affect, among other parameters, the organic matter and nitrogen dynamics of the root zone and trace organic decomposition processes. Detailed data of the redox potential regime in field plots is lacking, and the detailed mechanisms of its control are obscure and not quantified. The study established the feasibility of long-term, non-disturbing monitoring of redox potential regime in field soils. This may enable to manage soil redox under conditions of continued inputs of wastewater. The importance of controlling the degree of wastewater treatment, particularly of adding ultrafiltration steps and/or tertiary treatment, may be assessed based on these and similar results. Low redox potential was measured in a field site (Site A, KibutzGivat Brenner), that has been irrigated with effluents for 30 years and was used for 15 years for continuous commercial sod production. A permanently reduced horizon (Time weighted averaged pe= 0.33±3.0) was found in this site at the 15 cm depth throughout the measurement period of 10 months. A drastic cultivation intervention, involving prolonged drying and deep plowing operations may be required to reclaim such soils. Site B, characterized by a loamy texture, irrigated with tap water for about 20 years was oxidized (Time weighted average pe=8.1±1.0) throughout the measurement period. Iron in the solid phases of the Givat Brenner soils is chemically-reduced by irrigation. Reduced Fe in these soils causes a change in reactivity toward the pesticide oxamyl, which has been determined to be both cytotoxic and genotoxic to mammalian cells. Reaction of oxamyl with reduced-Fe clay minerals dramatically decreases its cytotoxicity and genotoxicity to mammalian cells. Some other pesticides are affected in the same manner, whereas others are affected in the opposite direction (become more cyto- and genotoxic). Iron-reducing bacteria (FeRB) are abundant in the Givat Brenner soils. FeRB are capable of coupling the oxidation of small molecular weight carbon compounds (fermentation products) to the respiration of iron under anoxic conditions, such as those that occur under flooded soil conditions. FeRB from these soils utilize a variety of Fe forms, including Fe-containing clay minerals, as the sole electron acceptor. Daily cycles of the soil redox potential were discovered and documented in controlled-conditions lysimeter experiments. In the oxic range (pe=12-8) soil redox potential cycling is attributed to the effect of the daily temperature cycle on the equilibrium constant of the oxygenation reaction of H⁺ to form H₂O, and is observed under both effluent and freshwater irrigation. The presence of plants affects considerably the redox potential regime of soils. Redox potential cycling coupled to the irrigation cycles is observed when the soil becomes anoxic and the redox potential is controlled by the Fe(III)/Fe(II) redox couple. This is particularly seen when plants are grown. Re-oxidation of the soil after soil drying at the end of an irrigation cycle is affected to some degree by the water quality. Surprisingly, the results suggest that under certain conditions recovery is less pronounced in the freshwater irrigated soils.

Tillage modifies soil structure, altering conditions for plant growth and transport processes through the soil. However, the resulting loose structure is unstable and susceptible to collapse due to aggregate fragmentation during wetting and drying cycles, and coalescense of moist aggregates by internal capillary forces and external compactive stresses. Presently, limited understanding of these complex processes often leads to consideration of the soil plow layer as a static porous medium. With the purpose of filling some of this knowledge gap, the objectives of this Project were to: 1) Identify and quantify the major factors causing breakdown of primary soil fragments produced by tillage into smaller secondary fragments; 2) Identify and quantify the. physical processes involved in the coalescence of primary and secondary fragments and surfaces of weakness; 3) Measure temporal changes in pore-size distributions and hydraulic properties of reconstructed aggregate beds as a function of specified initial conditions and wetting/drying events; and 4) Construct a process-based model of post-tillage changes in soil structural and hydraulic properties of the plow layer and validate it against field experiments. A dynamic theory of capillary-driven plastic deformation of adjoining aggregates was developed, where instantaneous rate of change in geometry of aggregates and inter-aggregate pores was related to current geometry of the solid-gas-liquid system and measured soil rheological functions. The theory and supporting data showed that consolidation of aggregate beds is largely an event-driven process, restricted to a fairly narrow range of soil water contents where capillary suction is great enough to generate coalescence but where soil mechanical strength is still low enough to allow plastic deforn1ation of aggregates. The theory was also used to explain effects of transient external loading on compaction of aggregate beds. A stochastic forInalism was developed for modeling soil pore space evolution, based on the Fokker Planck equation (FPE). Analytical solutions for the FPE were developed, with parameters which can be measured empirically or related to the mechanistic aggregate deformation model. Pre-existing results from field experiments were used to illustrate how the FPE formalism can be applied to field data. Fragmentation of soil clods after tillage was observed to be an event-driven (as opposed to continuous) process that occurred only during wetting, and only as clods approached the saturation point. The major mechanism of fragmentation of large aggregates seemed to be differential soil swelling behind the wetting front. Aggregate "explosion" due to air entrapment seemed limited to small aggregates wetted simultaneously over their entire surface. Breakdown of large aggregates from 11 clay soils during successive wetting and drying cycles produced fragment size distributions which differed primarily by a scale factor l (essentially equivalent to the Van Bavel mean weight diameter), so that evolution of fragment size distributions could be modeled in terms of changes in l. For a given number of wetting and drying cycles, l decreased systematically with increasing plasticity index. When air-dry soil clods were slightly weakened by a single wetting event, and then allowed to "age" for six weeks at constant high water content, drop-shatter resistance in aged relative to non-aged clods was found to increase in proportion to plasticity index. This seemed consistent with the rheological model, which predicts faster plastic coalescence around small voids and sharp cracks (with resulting soil strengthening) in soils with low resistance to plastic yield and flow. A new theory of crack growth in "idealized" elastoplastic materials was formulated, with potential application to soil fracture phenomena. The theory was preliminarily (and successfully) tested using carbon steel, a ductile material which closely approximates ideal elastoplastic behavior, and for which the necessary fracture data existed in the literature.