Dissertationen zum Thema „Soils“

Pipelines that are used for the transport of energy and services are very important lifelines to modem society. Though pipelines are generally buried in unsaturated soils, the design guidelines are based on the assumption that the soil is either dry or fully saturated. For certain geotechnical problems, this assumption may not be acceptable because the water meniscus formed between soil particles creates an additional normal force between them by suction, which in turn forms temporary bonds. A recent series of large-scale physical model experiments at the Pipeline Engineering Research Laboratory (PERL) of Tokyo Gas, Japan show a higher peak load under unsaturated conditions compared to dry conditions. In contrast, recent experiments performed at Cornell University (CU) show that the soil-load due to lateral pipeline movement in dry and unsaturated sands are virtually the same. Thus, the effect of partial saturation on soil loading to pipeline may be different depending on soil type, moisture content and density. The current study investigates this problem through triaxial testing and constitutive modelling of the unsaturated soils used for the experiments and finite element simulations of the experiments. The mechanical behaviour of the sands used in the physical model experiments has been investigated by conducting a series of laboratory experiments. When compacted to the same energy level, Tokyo Gas sand exhibits larger strength in unsaturated conditions than in dry conditions at low confining stress levels mainly due to the suction-induced apparent cohesion generated by the fine particles present in the sand. In contrast, for coarser Cornell sand, the suction effect is found to be small even at low confining stress level, and hence the strength in unsaturated conditions is similar to that in dry ( or fully saturated) conditions. To capture the observed behaviour of dry as well as unsaturated soils, advanced constitutive soil models were developed. For dry (or fully saturated) soils, the modified Mohr-Coulomb and Original Nor-Sand (Cheong, 2006) models were able to simulate the general behaviour including the strain softening effect. To cater for the behaviour of unsaturated soils, the saturated versions of the NorSand and the modified Mohr-Coulomb models were modified in conjunction with the generalised effective stress framework. By simulating the triaxial experimental data, it is demonstrated that the developed models can predict the realistic soil behaviour of unsaturated soils. Using the developed models, the large scale physical model experiments of pipelines subjected to lateral soil movements at PERL and CU were simulated by the explicit finite element method. Good agreement was found between the numerical models and the experiments. Further FE analyses were conducted to investigate the pipeline behaviour under lateral soil movement at conditions of different HID's, moisture contents, and relative densities. The results were synthesized to produce new normalised pipe load charts. Three dimensional finite element analysis was performed to simulate the soil-pipeline interaction under strike-slip fault movements. The finite element model was first validated by comparing the computed results to the data produced from a full scale experiment carried out at CU. The analysis was then further extended by varying the initial conditions of the sand (sand type, density, moisture content, etc.), pipe material, pipe burial depth, and pipeline-fault rupture inclination. It was found in all cases that the peak lateral loads on the pipelines subjected to strike-slip fault movements are less than or equal to the peak loads computed by the 2-D lateral movement simulations.

The present work is a contribution to description and understanding of the distribution and movement of water in swelling soils. In order to investigate the moisture distribution in swelling soils a detailed knowledge of volume change properties, flow characteristics and total potential of water in the soil is essential. Therefore, a possible volume change mechanism is first described by dividing the swelling soils into four categories and volume change of a swelling soil is measured under different overburden pressures. The measured and calculated (from volume change data) overburden potential components are used to check the validity of the derivation of a load factor, ∝. Moisture diffusivity in swelling soil under different overburden pressures is measured using Gardner's (1956) outflow method. Behaviour of equilibrium moisture profiles in swelling soils is theoretically explained, solving the differential equation by considering the physical variation of individual soil properties with moisture content and overburden pressure. Using the measured volume change data and moisture potentials under various overburden pressures, the behaviour of possible moisture profiles are described at equilibrium and under steady vertical flows in swelling soils. It is shown that high overburden pressures lead to soil water behaviour quite different from any previously reported.

Copies of author's previously published articles in pocket inside back cover. Bibliography: leaves 147-160. This thesis outlines the factors affecting soil strength and structural stability and their interrelationship in salt-affected soils. The objectives of this study are to investigate the influence of clay particles on soil densification and mellowing, the mellowing of compacted soils and soil aggregates as influenced by solution composition, the disaggregation of soils subjected to different sodicities and salinities and its relationship to soil strength and dispersible clay and the effect of organic matter and clay type on aggregation of salt-affected soils.

Bibliography: leaves 147-170. Aims to determine the influence of sodicity on the nature and decomposition of organic matter; and the influence of organic matter and its components on the structural stability of sodic soils.

An experiment was set up to investigate the effects of soil loosening on the drainage efficiency of a structurally unstable silty clay loam in Devon. Such soils are common to the Palaeozoic slates of South West England, and in many parts of Wales and Scotland. The dominance of the fine earth fraction these soils by silt sized particles and the associated low clay fractions ( 10-35%) gives rise to weak structures that are unsuitable f or mole drainage. Six drains were laid with permeable fill at a 20 m spacing on a gently sloping site at Seale-Hayne College Farm. A year after installation half the site was loosened to a depth of 0.4 m. The whole site was then cultivated and winter wheat sown. The study concentrated on the modification of the soil physical environment and water transmission routes following loosening operations for autumn re-wetting, the winter period and spring drying. Data collection involved the analysis of drainflow hydrographs and the measurement of soil water physical parameters. Results from an intensive twelve month monitoring period indicate that the modification of subsoil to improve drainage does not necessarily give the results expected . In this study it has been shown that loosening of an unstable silty clay loam did not enhance drainage, in fact the reverse was true which can have dire consequences in terms of trafficability and plant root growth. Loosening lead to an increased porosity which resulted in a greater, albeit temporary, retention of water within the disturbed zone. This means that loosened soils were wetter prior to a rainstorm and remained so for a longer period after rainfall. This response, in turn lead to significant reductions in soil shear strength, which has important implications for successful crop husbandry in the autumn and spring periods when field operations are necessary. Further work is required to assess the temporal persistence of soil loosening on soil physical conditions and crop responses.

Thesis (M.S. in civil engineering)--Washington State University, August 2009.
Title from PDF title page (viewed on Aug. 10, 2009). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 45-46).

Copies of author's previously published articles inserted. Bibliography: leaves 195-230. In this study the soil aqueous phase chemistry of Zn and Cu in alkaline sodic soils are investigated. The chemistry of trace metal ions at indigenous concentrations in alkaline sodic soils are reported. Metal ions at low concentrations are measured by the graphite furnace atomic absorption spectrometry (GFAAS) technique.

Thesis (Ph.D.)--University of Delaware, 2006.
Principal faculty advisors: Karl E. Wommack, Dept. of Plant & Soil Sciences, University of Delaware; Mark Radosevich, Dept. of Biosystems Engineering and Soil Science, University of Tennessee. Includes bibliographical references.

Persistent soil compaction by heavy-axle-load vehicles is a growing concern for the long-term productivity of clay soils. For optimum soil management, however, we must be able to evaluate adequately soil structural damages. This study compares different methods of assessing soil structure as affected by compaction and subsoiling treatments in a clay soil under corn production.
The tests used were: total porosity as calculated from densimeter readings and from soil cores; structural porosity; water desorption characteristics; and soil profile examination. These tests were performed in three layers of 20 cm and evaluation was based on their practicality and their ability to differentiate between treatments and to correlate with corn yield.
The results confirm that total porosity is a poor indicator of compaction in the subsoil. In soil profile assessments, ped descriptions were preferable to examination of pores. Water content and saturation deficit at $-$4.0 and $-$100 kPa were the best indicators of treatments and plant response.

Thesis (Ph. D.)--West Virginia University, 2001.
Title from document title page. Document formatted into pages; contains xii, 170 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2002.
Title from document title page. Document formatted into pages; contains x, 282 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

Rapid anthropogenic climate change is one of the greatest challenges that human civilisation will face in the 21st century. A 25-180 % increase in atmospheric carbon dioxide content since the early 1800’s and a predicted increase of 2-3% each year will lead to a 2-6°C rise in tropospheric temperatures. The consequences of increased atmospheric temperatures are profound and would put unsustainable strain on human infrastructure, which was conservatively estimated in the Stern Review (2006) to cost approximately 20% of GDP. Given the political, technical, economic and social barriers preventing the transition to a low carbon economy, there is an unequivocal need to research ‘geoengineering’ technologies that can bridge the gap between carbon emission reduction targets and actual emissions. Soil mineral carbonation is one such technology. The atmosphere is one of the smallest carbon pools at the Earth’s Surface (depending on how each pool is demarcated). Soils turn over the quantity of carbon in the atmosphere in under a decade and collectively form one of the largest carbon pools (3-4 times the quantity of carbon in the atmosphere). Land use change since the agricultural revolution has released 256 GtC (40 % of anthropogenic emissions). Research investigating the potential for carbon accumulation in soils is primarily focused on restoring organic carbon concentration to pre-agricultural values through modification of farming practices. The research presented in this thesis is the first that explores the potential of increasing the inorganic carbon pool as an emissions mitigation technology. Inorganic carbon accumulation is promoted by introducing divalent cation rich (predominantly calcium and magnesium) silicate and hydroxide minerals into the soil, which weather and supersaturate the soil solution with respect to carbonate minerals (predominantly calcite, aragonite, magnesite and dolomite). The carbon in the resultant precipitate is derived from the atmosphere. This is analogous to mineral carbonation technologies which induce carbonate precipitation from silicate weathering in industrial scale reactors at elevated temperatures and pressures. However, carbonation in soil exploits natural weathering processes to the same effect with minimal energy and infrastructure input. The research presented in this thesis broadly investigates soil mineral carbonation by contributing work towards the fundamental issues associated with application of soil mineral carbonation technology. Research activity described herein covers a range of laboratory batch weathering experiments, field work, geochemical modelling, plant growth trials, soil microcosm experiments and literature reviews. While eclectic, all work packages contribute to the same goal of describing the efficacy, effectiveness and potential impacts of soil mineral carbonation. The efficacy of mineral carbonation technology is primarily limited by the availability of appropriate silicate bearing material. A literature search suggests that approximately 15-16 Gt a- 1 of silicate rich ‘waste’ materials are produced as a consequence of human activity. This has a carbon capture potential between 190 and 332 MtC a-1, which is equivalent to other emissions mitigation strategies. Quarrying silicate specifically for carbonation is a suggested strategy that may be able to store on the order of 102 GtC a-1 (based on two sites in the US). Therefore, mineral carbonation may form part of global mitigation strategies collectively equivalent to 14 GtC a-1 to stabilise the CO2 concentration of the atmosphere at 500 parts per million by volume. Considering that the potential capacity of soil mineral carbonation is sufficient to act as a substantial emissions mitigation strategy it was appropriate to investigate issues associated with the application of such a technology. In the first instance, sites known to contain silicates were investigated. These include soils developed on natural silicates (on the Whin Sill in Northumberland), construction and demolition waste (at a brownfield site and waste transfer stations) and slag (at a former steelworks). Interpretation of fieldwork results suggests that inorganic carbon accumulation is rapid (up to 38 gC kg-1(soil) a-1), and is orders of magnitude xxv greater than organic carbon accumulation in natural soils. The average concentration of inorganic carbon (20-30 Kg m-3) is equivalent to organic carbon in natural soils. The unusually light carbon and oxygen isotope ratios of the carbonate (-3.1 ‰ and -27.5 ‰ for δ13C and -3.9 ‰ and -20.9 ‰ for δ18O) were used to determine that up to 55% of the carbon was derived from the atmosphere. The rate of carbon capture, which is the same as the precipitation rate of carbonate, is a function of solution chemistry. The more supersaturated a solution is with respect to a carbonate mineral, the more rapid the precipitation rate. Saturation of a solution is a function of divalent cation and carbonate anion concentration. Therefore, the supply of each of these components was investigated in laboratory experiments. Batch weathering experiments were used to investigate the supply of calcium from artificial silicates (hydrated cement gel). Up to 70-80 % of the calcium contained in the mineral was removed, which is consistent with efficiencies reported for conventional mineral carbonation. The log rate of weathering was between -10.66 and -6.86 mol Ca cm-2 sec-1, which is several orders of magnitude greater than that usually reported for natural silicates. Microcosm experiments were conducted to investigate the rate of supply of carbonate from the organic carbon mineralisation in high pH solutions. The research clearly demonstrates that high pH solutions inhibit the breakdown of organic carbon as a function of nutrient supply. Where organic carbon was successfully mineralised the log rates (-3.4 mmol g-1(field moist soil) sec-1) were equivalent to that found in previous studies. While the influx of dissolved carbonate mineral components into the soil solution is the primary controlling step in the rate of carbon accumulation, there is a complex relationship between soil physical properties and geochemistry. This was highlighted in a numerical model that was constructed for this thesis, which suggests that soil pore volume and particle size distribution are important variables. An additional numerical model was constructed to investigate the transportation of silicate material to the application site. This model suggests that an economics of soil mineral carbonation is a function of transport costs, the value of the silicate material and the price of carbon. Field observations, growth trials, microcosm experiments and previous research suggest a complex interaction between biology, weathering and carbonate precipitation. Additional work is required to investigate carbonate precipitation mediated by plant and microorganism activity and the degree to which soil mixed with silicates impact on ecosystem functioning. This research has demonstrated that mineral carbonation in soils could form a substantial emissions mitigation strategy, but additional work is required in a number of areas to which this thesis provides a suitable foundation.

Existing nitrogen (N) fertilizer recommendations for Irish grassland do not account for the potential variability in soil N supply through N mineralization. Research carried out within this thesis aims to identify a suitable N test that can estimate the potential range of N supplied in temperate soils and to increase the knowledge of soil metabolites linked with soil N mineralization. To fulfill these aims a series of interlinking studies were conducted. Initially laboratory studies investigating various soil N pools and N tests were undertaken, then a more in depth analysis of the carbon (C) and N metabolites in these soils was conducted using proton nuclear magnetic resonance spectroscopy (1H NMR). Following this a microcosm study was conducted to validate the laboratory findings and finally, field studies to investigate the temporal variability of soil N pools and their relationship with grass production. The laboratory studies found that there was large differences in mineralizable N (MN) capacity between Irish grassland soil types and that the Illinois soil N test (ISNT-N) was the best rapid predictor of MN across these soil types. The 1 H NMR analysis of these soils identified 7 metabolites, most as labile sources of C linked as regulators of N mineralization. The microcosm experiment, showed that a model combining ISNT-N, total oxidized N (TON), C:N and the interaction of ISNT-N X C:N best predicted grass OM production and N uptake. In the field study, soil mineral N was found to be highly transient, over the 15 month sampling period, while MN was less variable. Daily grass OM production was mainly explained by climatic variables and further evaluation across multiple seasons is therefore warranted. Overall this study highlights the real opportunity to improve N use efficiency with soil N testing, hence reducing costs to the farmer and losses to the environment.

Field experiments were conducted in Arizona in 2001 at three locations (Maricopa, Marana, and Safford). The Maricopa and Safford experiments have been conducted for14 consecutive seasons and the Marana site was initiated in 1994. The original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (Gossypium hirsutum L.) and American Pima (G. barbadense L.) cotton. The experiments have each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive, N application regimes did not benefit yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating the residual N effects associated with each treatment regime was initiated and no fertilizer N was applied. Therefore, all N taken-up by the crop was derived from residual soil N. In 2001 there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. The lint yields were very uniform at each location and averaged 1500, 1100, and 850 lbs. lint/acre for Maricopa, Marana, and Safford, respectively.

Field experiments investigating N fertilizer management in irrigated cotton production have been conducted for the past 15 seasons at three Arizona locations on University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2002, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 and the Marana site was initiated in 1994. The original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (Gossypium hirsutum L.) and American Pima (G. barbadense L.) cotton. The experiments have each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive N application regimes did not consistently benefit yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating the residual N effects associated with each treatment regime was initiated and no fertilizer N was applied. Therefore, all N taken-up by the crop was derived from residual soil N. In 2001, there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. The lint yields were very uniform at each location and averaged 1500, 1100, and 850 lbs. lint/acre for MAC, MAR, and SAC, respectively. In 2002, results were very similar at the MAC and MAR locations. Trends associated with residual fertilizer N effects are not evident at either location just two seasons following N fertilizer applications.

Field experiments aimed at investigating N fertilizer management in irrigated cotton production have been conducted for the past 16 seasons at three University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2003, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 and the Marana site was initiated in 1994. Original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (Gossypium hirsutum L.) and American Pima (G. barbadense L.) cotton. Each experiment has utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between fruit retention levels and N needs of the crop. This pattern was further reflected in the final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive N application regimes did not consistently benefit yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating residual N effects associated with each treatment regime was initiated with no N fertilizer applied. Therefore, all N taken-up by the crop was derived from residual soil N. In 2001, 2002, and even 2003 there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. Lint yields were very uniform at each location in 1991 and averaged 1500, 1100, and 850 lbs. lint/acre for MAC, MAR, and SAC, respectively. In 2002, results were very similar and yields averaged 1473 and 1060 lbs. lint/acre for MAC and MAR locations respectively. The results for 2003 were similar to the results of the prior two years with yields at 1322 and 1237 lbs. lint/acre for MAC and MAR, respectively. Trends associated with residual fertilizer N effects are not evident at either location following three consecutive seasons of N fertilizer treatments.

Field experiments aimed at investigating N fertilizer management in irrigated cotton production have been conducted for the past 16 seasons at three Arizona locations on University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2004, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 and the Marana site was initiated in 1994. The original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (Gossypium hirsutum L.) and American Pima (G. barbadense L.) cotton. The experiments have each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location reveal a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive N application regimes did not consistently increase yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating the residual N effects associated with each treatment regime was initiated and no fertilizer N was applied. Therefore, all N taken-up by the crop was derived from residual soil N. In 2001, 2002, 2003 and even 2004 there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. The lint yields were very uniform at each location in 1991 and averaged 1500, 1100, and 850 lbs. lint/acre for MAC, MAR, and SAC, respectively. In 2002, results were very similar and yields averaged at 1473 and 1060 lbs. lint/acre for MAC and MAR locations respectively. The 2003 results were not different from the prior two years of results and yields averaged at 1322 and 1237 lbs. lint/acre for MAC and MAR respectively. In 2004, yields averaged 828 and 1075 lbs. lint/acre. Trends associated with residual fertilizer N effects are not evident at either location four seasons following N fertilizer applications.

Field experiments aimed at investigating N fertilizer management in irrigated cotton production have been conducted for the past 16 seasons at three Arizona locations on University of Arizona Agricultural Centers (Maricopa, MAC; Marana, MAR; and Safford, SAC). In 2001-2005, residual N studies were conducted at two of these locations (MAC and MAR). The MAC and SAC experiments have been conducted each season since 1989 and the Marana site was initiated in 1994. The original purposes of the experiments were to test nitrogen (N) fertilization strategies and to validate and refine N fertilization recommendations for Upland (G. hirsutum L.) and American Pima (G. barbadense L.) cotton. The experiments have each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. At each location, treatments varied from a conservative to a more aggressive approach of N management. Results at each location revealed a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The higher, more aggressive N application regimes did not consistently benefit yields at any location. Generally, the more conservative, feedback approach to N management provided optimum yields at all locations. In 2001, a transition project evaluating the residual N effects associated with each treatment regime was initiated and no N fertilizer was applied. Therefore, all N taken-up by the crop was assumed to be derived from residual soil N. However irrigation water analysis showed that NO₃⁻-N concentration levels added to the crop ranged from about 5-9 ppm. In 2001-2005 there were no significant differences among the original fertilizer N regimes in terms of residual soil NO₃⁻-N concentrations, crop growth, development, lint yield, or fiber properties. The lint yields were very uniform at each location and season. Trends associated with residual fertilizer N effects are not evident at either location for five seasons following N fertilizer applications.

This thesis covers two major themes: the first relates to the development of a constitutive soil model, and the second is the development of a model to predict the behaviour of fibre-reinforced soils. The hardening soil (HS) model is an advanced constitutive plasticity model which is applicable to the analysis of many soil types including sands and clays (Schanz et al., 1999; Benz, 2007). This model is explored in depth, and several improvements to the model are proposed. The first improvement is the formulation of a new hardening shear yield surface to replace the previous hardening shear surface and failure surface. The second is the implementation of the model in a robust return mapping scheme. The scheme used is the closest point projection method of Simo and Hughes (2006), which is tailored specifically to this implementation of the model. This constitutive soil model and return mapping scheme is hereinafter referred to as the HS-LC model. The HS-LC model is then used in finite element analyses and compared to published experimental and predicted data obtained from the prior versions of the HS model. It was found that the new HS-LC model was able to reproduce results from both the experimental data and the previous models. The numerical stability of the proposed model was also tested with a step size study, a mesh density study, and investigation of convergence rates for simulations. The second main theme of this thesis is fibre-reinforced soils. The motivation for reinforcing soils is first explored, then a literature review is conducted on different reinforcement types; focussing on fibre-reinforcement. Experimental results from the literature are then discussed, along with several models which predict the behaviour of fibre-reinforced soil. Results from an experimental study (Chatzopoulos, 2015; Wang, 2015) of fibre-reinforced sand are presented and discussed. A series of triaxial compression tests were conducted; in which fibre content, fibre length, and fibre type were varied. It was found that some fibre types added a significant amount of strength to the soil, where other types added little strength. All fibres studied here were manufactured from polypropylene, it was therefore concluded that the geometry had a significant impact on the strength contribution for the composite. This study also found that when the fibre diameter was too large or too fine relative to the sand particle size, then the particles would not bind to the fibre. An additional unique study was also carried out in relation to fibre composites. This was a series of fibre pullout tests, where a fibre was pulled through a prescribed length of compressed, dry soil. In this test it was found that the peak bond strength was linked to the compressive stress acting on the fibre. A novel fibre-soil composite model was also formulated which is based on micro-mechanical relationships between soil and fibre, from findings of the literature review and the experimental study. The proposed model is based on the well known shear lag model (Cox, 1952) and is modified to also include the effects of fibre debonding. The model takes the form of a representative volume element (RVE), which is homogenised using a statistical approach (Bazant and Oh, 1986). The proposed fibre model is then combined with the new HS-LC model using the rule of mixtures. The composite model is then used to predict the behaviour of the tests in the experimental study. Predictions of the triaxial tests closely matched the experimental results in the shear stress response, however, were less accurate for the prediction of volumetric strains. It was concluded that further work is required in the development of this model before it can be considered in routine design.

Collapse phenomenon is exhibited by two types of residual soils. The first category of collapsing residual soils is believed to be transported soils that have undergone post-depositional pedogenesis. The second category of collapsing residual soils is highly weathered and leached soils formed by in-situ weathering of parent rock. Residual red soils occur in Bangalore District of Karnataka State. Physical and chemical weathering of the gneissic parent rock formed the residual soils of Bangalore District. The red soils of Bangalore District are generally moderate to very highly porous (porosity range 35-50%). These soils are also unsaturated owing to presence of alternate wet and dry seasons and low ground water table. Moderately to highly porous, unsaturated red soils occur in Pernambuco State of Brazil. These residual soils formed by weathering of gneissic rock significantly collapse on wetting under external pressures. Kaolinite is predominant clay mineral in the red soils of Bangalore and Pernambuco Districts. Similarities exist in the mode of soil formation, clay mineralogy, porosity and degree of saturation (Sr) values of the red soils from Pernambuco State, Brazil, and Bangalore District. Given the collapsible nature of red soils from Pernambuco State, Brazil, the red soils from Bangalore District also deserve to be examined for their potential to collapse in the compacted and undisturbed conditions. The roles of initial dry density, compaction water content, clay content and flooding pressure (the external stress at which a laboratory specimen is inundated is termed as flooding pressure in this thesis) in determining the collapse behaviour of compacted soils are well recognized. However, the influences of above parameters on the collapse behaviour of compacted red soil specimens from Bangalore District are lacking. Such studies are essential as they help to identify the critical compaction parameters (dry density and water content), soil composition, and applied stress level that needs to be controlled by the fill designer in order to minimize wetting-induced collapse. The importance of matric suction in the collapse behaviour of unsaturated soils is well recognized. Yet, the influence of matric suction in the collapse behaviour of compacted soils has only been indirectly examined by varying the compaction water content/degree of saturation of the soil specimens. The climate of Bangalore District is characterized by alternate wet and dry seasons which affects the soil microstructure and the matric suction. Both these parameters have a significant influence on collapse behaviour of unsaturated soils. Cyclic wetting and drying is expected to have a significant bearing on the collapse behaviour of residual soils and is therefore examined. The red soil deposits of Bangalore District are important from foundation engineering view point as they are subjected to structural loading. Owing to the presence of alternate wet and dry seasons and low ground water table, red soil deposits of Bangalore District are more often than not unsaturated. These foundation soils would however be susceptible to increase in moisture content from causes such as infiltration of rainwater, leakage of pipes or watering of lawns and plants. Given the porous and unsaturated nature of undisturbed red soils from Bangalore district, their collapsible nature deserves to be examined for reliable estimation of foundation settlements. To achieve the above objectives, experiments are performed that study: 1.The influence of variations in compaction dry density, initial water content and matric suction, clay content and flooding pressure on the collapse behaviour of a representative red soil sample from Bangalore District. 2.The influence of repeated wetting and drying on the collapse behaviour of compacted red soil specimens. 3.The collapsible nature of undisturbed red soil samples from different locations in Bangalore District. The organization of this thesis is as follows: After the first introductory chapter, a detailed review of literature highlighting the need to study the collapse behaviour of unsaturated red soils of Bangalore District, Karnataka in the compacted and undisturbed states comprises Chapter 2. Chapter 3 presents a detailed experimental programme of the study. Details of representative and undisturbed red soil samples from Bangalore District, Karnataka State, India were used in the study are provided. Determination of collapse potential of compacted and undisturbed soil specimens using conventional oedometer is discussed. Determination of matric suction of compacted and undisturbed specimens by ASTM Filter paper method and pore size distributions by mercury intrusion porosimetry is detailed. Methods to perform cyclic wetting and drying of compacted red soil specimens in modified oedometer assemblies is detailed. These experiments are performed to examine the influence of cyclic wetting and drying on the collapse behaviour of compacted red soil specimens. Chapter 4 examines the collapse behaviour of a compacted red soil from Bangalore District. The influence of variations in compaction dry density, initial water content and matric suction, flooding pressure and clay content on the collapse behaviour of the representative red soil from Bangalore District are examined. Besides measuring the initial matric suction of the compacted red soil specimens, mercury intrusion porosimetry was performed on selected compacted red soil specimens. Experimental results showed that compacted red soils from Bangalore District exhibited tendency to swell and collapse at the experimental range of densities and water contents. Red soil specimens compacted to relative compactions > 90 % at water contents below OMC swelled at flooding pressures lower than 200 kPa. Red soil specimens compacted to relative compactions < 90 % at water contents below OMC significantly collapsed at flooding pressures larger than 200 kPa. Hence maintenance of the design water content during construction of compacted red soil fills is essential to minimize wetting induced volume changes. Experiments showed that the relative abundance of coarse pores (60 to 6 μm, pore radius) were mainly affected on increasing the relative compaction of the specimens from 84 % (dry density = 1.49 Mg/m3) to 100 % (dry density = 1.77 Mg/m3). The relative abundance of the coarse and fine (0.01 to 0.002 μm) pores were both affected on increasing the compaction water content from 10.6 to 26.4 %. These variations in pore size distributions provided better insight into the variations of collapse potential with variations in compaction parameters. ASTM filter paper method showed that for the selected compaction conditions the initial matric suction of the compacted red soil specimens varied between 60 and 10,000 kPa. Further, variations in degree of saturation at a constant relative compaction or variations in relative compaction at a constant degree of soil saturation notably affected the matric suction of the compacted soil specimens. It was also inferred that a clay soil with a higher liquid limit is characterized by a higher matric suction at a given water content. Variations in clay content affected the collapse potentials of soil specimens compacted to dry densities of 1.49 and 1.66 Mg/m3. These specimens exhibited maximum collapse at about 26 % clay content. It is suggested that greater destabilization of inter-particle contacts caused by loss of matric suction on flooding was primarily responsible for the soil specimen containing the critical clay content of 26 % to exhibit maximum collapse potential. Increase in initial dry density, initial water content, clay content of the soil specimen and flooding pressure increased the time-duration of collapse of the compacted soil specimens. The time-duration of collapse was observed to range between 3 and 100 minutes for the tested specimens. Chapter 5 examines the influence of alternate wetting and drying on the collapse behaviour of compacted red soil specimens of Bangalore District. The compacted specimens were subjected to alternate wetting and drying cycles at surcharge pressures of 6.25 and 50 kPa in modified oedometer assemblies. Studies were also performed to examine whether the initial placement conditions have any bearing on the collapse behaviour of red soil specimens subjected to four cycles of wetting and drying. Mercury intrusion porosimetry was performed on a few desiccated red soil specimens. Experimental results showed that cyclic wetting and drying caused the desiccated specimens to exhibit similar or lower swell and collapse potentials than the compacted specimens. Such a behaviour resulted despite the desiccated specimens (specimens subjected to four cycles of wetting and drying are termed as desiccated specimens) possessing similar void ratios but much lower water contents than the compacted specimens. The restraining influence of the desiccation bonds and alteration of soil structure is considered responsible for the reduced swell and collapse tendencies of the desiccated specimens. The desiccation bonds imparted higher apparent preconsolidation pressures to the desiccated specimens. The initial compaction conditions also have a strong bearing on the collapse potentials of the desiccated specimens. Compacted red soil specimens subjected to cyclic wetting and drying under a higher surcharge pressure of 50 kPa exhibited larger swell potentials and lower collapse potentials than specimens desiccated at 6.25 kPa. Besides their lower void ratios, the presence of stronger desiccation bonds also contributed to their lower collapse potentials. The presence of stronger desiccation bonds in specimens desiccated under higher surcharge pressure was indicated by their higher apparent preconsolidation pressures. Chapter 6 examines the collapse behaviour of undisturbed red soil specimens from three locations in Bangalore District at a range of flooding pressures. Studies on the variations in initial water content and effect of remoulding on the collapse behaviour of the undisturbed specimens is supplemented by measuring the initial matric suction and performing mercury intrusion porosimetry experiments. Experimental results showed that based on their collapse potential at 200 kPa, the undisturbed red soils of Bangalore District classified as troublesome to moderately troublesome foundation soils. The bonded structure of the undisturbed red soil specimens imparted them higher apparent preconsolidation pressures and lower swell/collapse potentials than their remoulded counterparts. Variations in in-situ dry density, degree of saturation and relative distribution of pore sizes affected the matric suction and collapse potentials of the undisturbed specimens Chapter 7 summarizes the conclusions of this thesis.

Collapse phenomenon is exhibited by two types of residual soils. The first category of collapsing residual soils is believed to be transported soils that have undergone post-depositional pedogenesis. The second category of collapsing residual soils is highly weathered and leached soils formed by in-situ weathering of parent rock. Residual red soils occur in Bangalore District of Karnataka State. Physical and chemical weathering of the gneissic parent rock formed the residual soils of Bangalore District. The red soils of Bangalore District are generally moderate to very highly porous (porosity range 35-50%). These soils are also unsaturated owing to presence of alternate wet and dry seasons and low ground water table. Moderately to highly porous, unsaturated red soils occur in Pernambuco State of Brazil. These residual soils formed by weathering of gneissic rock significantly collapse on wetting under external pressures. Kaolinite is predominant clay mineral in the red soils of Bangalore and Pernambuco Districts. Similarities exist in the mode of soil formation, clay mineralogy, porosity and degree of saturation (Sr) values of the red soils from Pernambuco State, Brazil, and Bangalore District. Given the collapsible nature of red soils from Pernambuco State, Brazil, the red soils from Bangalore District also deserve to be examined for their potential to collapse in the compacted and undisturbed conditions. The roles of initial dry density, compaction water content, clay content and flooding pressure (the external stress at which a laboratory specimen is inundated is termed as flooding pressure in this thesis) in determining the collapse behaviour of compacted soils are well recognized. However, the influences of above parameters on the collapse behaviour of compacted red soil specimens from Bangalore District are lacking. Such studies are essential as they help to identify the critical compaction parameters (dry density and water content), soil composition, and applied stress level that needs to be controlled by the fill designer in order to minimize wetting-induced collapse. The importance of matric suction in the collapse behaviour of unsaturated soils is well recognized. Yet, the influence of matric suction in the collapse behaviour of compacted soils has only been indirectly examined by varying the compaction water content/degree of saturation of the soil specimens. The climate of Bangalore District is characterized by alternate wet and dry seasons which affects the soil microstructure and the matric suction. Both these parameters have a significant influence on collapse behaviour of unsaturated soils. Cyclic wetting and drying is expected to have a significant bearing on the collapse behaviour of residual soils and is therefore examined. The red soil deposits of Bangalore District are important from foundation engineering view point as they are subjected to structural loading. Owing to the presence of alternate wet and dry seasons and low ground water table, red soil deposits of Bangalore District are more often than not unsaturated. These foundation soils would however be susceptible to increase in moisture content from causes such as infiltration of rainwater, leakage of pipes or watering of lawns and plants. Given the porous and unsaturated nature of undisturbed red soils from Bangalore district, their collapsible nature deserves to be examined for reliable estimation of foundation settlements. To achieve the above objectives, experiments are performed that study: 1.The influence of variations in compaction dry density, initial water content and matric suction, clay content and flooding pressure on the collapse behaviour of a representative red soil sample from Bangalore District. 2.The influence of repeated wetting and drying on the collapse behaviour of compacted red soil specimens. 3.The collapsible nature of undisturbed red soil samples from different locations in Bangalore District. The organization of this thesis is as follows: After the first introductory chapter, a detailed review of literature highlighting the need to study the collapse behaviour of unsaturated red soils of Bangalore District, Karnataka in the compacted and undisturbed states comprises Chapter 2. Chapter 3 presents a detailed experimental programme of the study. Details of representative and undisturbed red soil samples from Bangalore District, Karnataka State, India were used in the study are provided. Determination of collapse potential of compacted and undisturbed soil specimens using conventional oedometer is discussed. Determination of matric suction of compacted and undisturbed specimens by ASTM Filter paper method and pore size distributions by mercury intrusion porosimetry is detailed. Methods to perform cyclic wetting and drying of compacted red soil specimens in modified oedometer assemblies is detailed. These experiments are performed to examine the influence of cyclic wetting and drying on the collapse behaviour of compacted red soil specimens. Chapter 4 examines the collapse behaviour of a compacted red soil from Bangalore District. The influence of variations in compaction dry density, initial water content and matric suction, flooding pressure and clay content on the collapse behaviour of the representative red soil from Bangalore District are examined. Besides measuring the initial matric suction of the compacted red soil specimens, mercury intrusion porosimetry was performed on selected compacted red soil specimens. Experimental results showed that compacted red soils from Bangalore District exhibited tendency to swell and collapse at the experimental range of densities and water contents. Red soil specimens compacted to relative compactions > 90 % at water contents below OMC swelled at flooding pressures lower than 200 kPa. Red soil specimens compacted to relative compactions < 90 % at water contents below OMC significantly collapsed at flooding pressures larger than 200 kPa. Hence maintenance of the design water content during construction of compacted red soil fills is essential to minimize wetting induced volume changes. Experiments showed that the relative abundance of coarse pores (60 to 6 μm, pore radius) were mainly affected on increasing the relative compaction of the specimens from 84 % (dry density = 1.49 Mg/m3) to 100 % (dry density = 1.77 Mg/m3). The relative abundance of the coarse and fine (0.01 to 0.002 μm) pores were both affected on increasing the compaction water content from 10.6 to 26.4 %. These variations in pore size distributions provided better insight into the variations of collapse potential with variations in compaction parameters. ASTM filter paper method showed that for the selected compaction conditions the initial matric suction of the compacted red soil specimens varied between 60 and 10,000 kPa. Further, variations in degree of saturation at a constant relative compaction or variations in relative compaction at a constant degree of soil saturation notably affected the matric suction of the compacted soil specimens. It was also inferred that a clay soil with a higher liquid limit is characterized by a higher matric suction at a given water content. Variations in clay content affected the collapse potentials of soil specimens compacted to dry densities of 1.49 and 1.66 Mg/m3. These specimens exhibited maximum collapse at about 26 % clay content. It is suggested that greater destabilization of inter-particle contacts caused by loss of matric suction on flooding was primarily responsible for the soil specimen containing the critical clay content of 26 % to exhibit maximum collapse potential. Increase in initial dry density, initial water content, clay content of the soil specimen and flooding pressure increased the time-duration of collapse of the compacted soil specimens. The time-duration of collapse was observed to range between 3 and 100 minutes for the tested specimens. Chapter 5 examines the influence of alternate wetting and drying on the collapse behaviour of compacted red soil specimens of Bangalore District. The compacted specimens were subjected to alternate wetting and drying cycles at surcharge pressures of 6.25 and 50 kPa in modified oedometer assemblies. Studies were also performed to examine whether the initial placement conditions have any bearing on the collapse behaviour of red soil specimens subjected to four cycles of wetting and drying. Mercury intrusion porosimetry was performed on a few desiccated red soil specimens. Experimental results showed that cyclic wetting and drying caused the desiccated specimens to exhibit similar or lower swell and collapse potentials than the compacted specimens. Such a behaviour resulted despite the desiccated specimens (specimens subjected to four cycles of wetting and drying are termed as desiccated specimens) possessing similar void ratios but much lower water contents than the compacted specimens. The restraining influence of the desiccation bonds and alteration of soil structure is considered responsible for the reduced swell and collapse tendencies of the desiccated specimens. The desiccation bonds imparted higher apparent preconsolidation pressures to the desiccated specimens. The initial compaction conditions also have a strong bearing on the collapse potentials of the desiccated specimens. Compacted red soil specimens subjected to cyclic wetting and drying under a higher surcharge pressure of 50 kPa exhibited larger swell potentials and lower collapse potentials than specimens desiccated at 6.25 kPa. Besides their lower void ratios, the presence of stronger desiccation bonds also contributed to their lower collapse potentials. The presence of stronger desiccation bonds in specimens desiccated under higher surcharge pressure was indicated by their higher apparent preconsolidation pressures. Chapter 6 examines the collapse behaviour of undisturbed red soil specimens from three locations in Bangalore District at a range of flooding pressures. Studies on the variations in initial water content and effect of remoulding on the collapse behaviour of the undisturbed specimens is supplemented by measuring the initial matric suction and performing mercury intrusion porosimetry experiments. Experimental results showed that based on their collapse potential at 200 kPa, the undisturbed red soils of Bangalore District classified as troublesome to moderately troublesome foundation soils. The bonded structure of the undisturbed red soil specimens imparted them higher apparent preconsolidation pressures and lower swell/collapse potentials than their remoulded counterparts. Variations in in-situ dry density, degree of saturation and relative distribution of pore sizes affected the matric suction and collapse potentials of the undisturbed specimens Chapter 7 summarizes the conclusions of this thesis.

Thesis (Ph.D.) -- La Trobe University, 2006.
Research. "A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy, [to the] Centre for Applied Alpine Ecology, Department of Agricultural Sciences, School of Life Sciences, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora". Includes bibliographical references (leaves 172-186). Also available via the World Wide Web.

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
A presente dissertação tem por objeto a análise teórica - comparativa, implementação computacional e avaliação da capacidade de simulação dos modelos constitutivos para solos, com ênfase nos solos não saturados. Primeiramente, são analisados os modelos básicos, clássicos e avançados formulados para solos saturados ou secos, assim como os modelos desenvolvidos para solos não saturados, incluindo também alguns modelos para solos estruturados. A seguir, e para testar a sua capacidade de modelagem, são implementadas as matrizes constitutivas de alguns dos modelos analisados para a retroanálise e previsão de comportamento de três solos residuais na condição saturada e não saturada. Como complemento da pesquisa, um dos modelos é utilizado na simulação de provas de carga com placa em solo residual pelo MEF, para os casos de saturação e umidade natural. Finalmente, são apresentadas organizadamente as conclusões gerais e particulares obtidas, assim como sugestões para futuras pesquisas no tema do presente trabalho.
The objective of this thesis is to present a critical review of the main constitutive soil models published in the literature, discussing and evaluating their abilities to simulate the mechanical behavior of geological materials under the theoretical and numerical points of view, with emphasis on unsaturated soils. Firstly, some basic, classical and advanced soil models are presented and discussed, as well as a few other recent constitutive relationships specially developed for unsaturated and structured materials. In the sequence, in order to assess the efficiency and overall performance of some selected models, the respective constitutive matrices were numerically implemented for prediction and back-analysis of the response of three residual soils, in saturated and unsaturated conditions. As a complement of this research, one of the soil models is used to simulate the results of some plate load tests on a residual soil deposit through the finite element method. Finally, the general conclusions of this work are presented and some suggestions are made to aid future research in the area of soil modeling.