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1
Parathiras, Vasilis. "Stress-density relationships for an agricultural soil". Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/40978.
Testo completoAbstract (sommario):
Triaxial tests under high loading rates and different confining pressures simulate the multi-pass effect of a tractor wheel loading on the soil. A volume measuring technique was developed to be used in triaxial tests conducted under high loading rates.
A sandy clay agricultural soil was tested under predetermined conditions using an INSTRON loading frame, a differential pressure transducer and an APPLE Il + microcomputer. A preliminary analysis indicated that the measuring technique that was developed, was capable of recording volume changes under high loading rates. Stress-density plots were created using the obtained data and a mathematical model was developed relating stress to density. Stress-strain data was used to evaluate the soil parameters under the Mohr-Coulomb failure criteria. Furthermore, the influence of the initial soil density on the soil behavior was evaluated and subsequently compared to the results of a similar study conducted under a different initial density.
Master of Science
2
Bones, Emma Jean. "Predicting critical shear stress and soil erodibility classes using soil properties". Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52198.
Testo completoAbstract (sommario):
As scouring around foundations is the most common cause of bridge failures, one of the most pressing questions of this research is to determine whether or not it is possible to predict the critical shear stress of different soil types using only soil property information. This report shows that it is possible to predict critical shear stress and determines the soil properties that are required to predict the critical shear stress based on soils from Georgia. Multiple methods to predict soil erodibility categories are developed based on the amount of soil information available to the researcher. The report shows how the methods to predict soil erodibility can be integrated with HYRISK, a scour risk assessment tool. In particular, the probabilities of bridge failures and expected economic losses are calculated for approximately 40 bridges in Georgia; soil erodibility characteristics for these bridges are calculated using the methods developed in this thesis. The goal of this thesis is to provide a faster and more cost-effective approach to calculate critical shear stress ranges likely to be encountered at a bridge foundation. Implementation of theses methodologies will help balance funding for new and existing bridges while simultaneously ensuring safe bridge foundation and minimizing economic consequences associated with overbuilding a bridge and/or having to retrofit or replace a bridge that has scour damage due to underbuilding it to withstand a major storm event.
3
Du, Plessis Keith R. (Keith Roland). "Biological indicators of copper-induced stress in soil". Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52719.
Testo completoAbstract (sommario):
Thesis (MSc)--University of Stellenbosch, 2002.ENGLISH ABSTRACT: The concentrations of copper (Cu) in vineyard soils of the Western Cape range from 0.1 to 20 ppm. However, more than 160 tons of the fungicide copper oxychloride are annually being sprayed on these vineyards. This has raised concerns that Cu may accumulate in these soils, resulting in a negative impact on the soil biological processes, especially since the soils in the Western Cape are slightly acidic, making Cu more mobile and available for soil organisms than would have been the case in alkaline soils. The goal of the initial part of this study was therefore to identify those soil microbial communities indigenous to the Western Cape, which are most susceptible to Cu-induced stress as a result of the addition of copper oxychloride. These potential bioindicators of Cu-induced stress were first searched for in uncultivated agricultural soil from Nietvoorbij experimental farm. Consequently, a series of soil microcosms was prepared by adding various concentrations of Cu as a component of copper oxychloride, to each of eight aliquots of soil: 0 (control), 10, 20, 30, 40, 50, 100, 500 and 1000 ppm. The resulting concentrations of exchangeable Cu in these microcosms were found to be 2 (control), 12,23,34,42,59, 126,516 and 1112 ppm. Selected microbial communities in each microcosm were subsequently monitored over a period of 245 days. It was found that the culturable microbial numbers did not provide a reliable indication of the effect of Cu on community integrity. However, analyses of terminal-restriction fragment length polymorphism (T-RFLP) community fingerprints and especially analyses of the whole community metabolic profiles, revealed that shifts in the soil microbial communities took place as the Cu concentration increased. Direct counts of soil protozoa also revealed that the addition of Cu to the soil impacted negatively on the numbers of these eukaryotes. To confirm these findings in other soil ecosystems, the impact of copper oxychloride on whole community metabolic profiles and protozoan numbers were investigated in soils from Koopmanskloof commercial farm and Nietvoorbij experimental farm. These potential bioindicators were subsequently monitored in a series of soil microcosms prepared for each soil type by adding the estimated amounts of 0 (control), 30, 100 and 1000 ppm Cu as a component of copper oxychloride to the soil. The results confirmed the fmdings that elevated levels of copper impact negatively on the metabolic potential and protozoan numbers of soil. Consequently, it was decided to investigate a combination of protozoan counts and metabolic profiling as a potential bioindicator for Cu-induced stress in soil. Data collected from all the microcosms containing exchangeable Cu concentrations ranging from 1 ppm to 1112 ppm was used to construct a dendrogram using carbon source utilization profiles in combination with protozoan counts. It was found that the microcosms grouped into clusters, which correlated with the concentration of exchangeable Cu in the soil. Under the experimental conditions used in this study, the combination of protozoan counts and metabolic profiling seemed to be a reliable indicator of Cu-induced stress. However, this bioindicator must be further investigated in other soil types using other types of stress inducing pollutants. In addition to the above fmdings it was also found that the numbers of soil protozoa was particularly susceptible to Cu-induced stress in soils with a low soil pH. This is in agreement with the fmdings of others on the bio-availability of heavy metals in low pH soils. In these soils, nutrient cycling as a result of protozoan activity, may therefore be particularly susceptible to the negative impact of copper to the soil.
AFRIKAANSE OPSOMMING: Die konsentrasies van koper (Cu) in wingerdgronde van die Wes-Kaap wissel tussen 0.1 en 20 dpm. Meer as 160 ton van die fungisied koper-oksichloried word egter jaarliks op dié wingerde gespuit, wat kommer laat ontstaan het oor die moontlike akkumulasie van Cu in dié grond en die gevaar van 'n negatiewe impak op die biologiese prosesse in die grond. Die gevaar word vererger deur die feit dat die Wes-Kaapse grond effens suur is, wat Cu meer mobiel en beskikbaar maak vir grondorganismes as wat die geval sou wees in alkaliese grond. Die eerste doelstelling van hierdie studie was dus om die mikrobiese gemeenskappe in die grond, wat inheems is aan die Wes-Kaap, te identifiseer wat die meeste vatbaar is vir Cu-geïnduseerde stres as gevolg van die toevoeging van koper-oksichloried. Hierdie potensiële bioindikatore van Cu-geïnduseerde stres is eerstens gesoek in onbewerkte landbougrond van die Nietvoorbij-proefplaas. 'n Reeks grondmikrokosmosse is gevolglik berei deur verskillende konsentrasies Cu, as 'n komponent van koperoksichloried, by elk van agt hoeveelhede grond te voeg naamlik 0 (kontrole), 10,20, 30, 40, 50, 100, 500 en 1000 dpm. Die gevolglike konsentrasies van uitruilbare Cu in hierdie mikrokosmosse was 2 (kontrole), 12, 23, 34, 42, 59, 126, 516 en 1112 dpm. Geselekteerde mikrobiese gemeenskappe in elke mikrokosmos is vervolgens oor 'n tydperk van 245 dae bestudeer. Daar is gevind dat die kweekbare mikrobiese tellings nie 'n betroubare aanduiding kon gee van die uitwerking van Cu op gemeenskapsintegriteit nie. Die ontledings van terminale-restriksie fragment lengte polymorfisme (T-RFLP) gemeenskapsvingerafdrukke en veral van die metaboliese profiele van die totale gemeenskap, het getoon dat verskuiwings in die grondmikrobiese gemeenskappe plaasgevind het met 'n toename in Cu-konsentrasies. Direkte tellings van grondprotosoë het ook aangedui dat die toevoeging van Cu tot die grond 'n negatiewe uitwerking op die getalle van hierdie eukariote gehad het. Om dié resultate te bevestig, is die impak van koper-oksichloried op die metaboliese profiele van totale gemeenskappe en protosoë-getalle in ander grond-ekosisteme vervolgens bestudeer deur grond van die kommersiële plaas Koopmanskloof en die Nietvoorbij-proefplaas te gebruik. Dié potensiële bioindikatore is vervolgens bestudeer in 'n reeks grondmikrokosmosse, wat vir elke grondtipe voorberei is deur die toevoeging van beraamde hoeveelhede van 0 (kontrole), 30, 100 en 1000 dpm Cu as 'n komponent van koper-oksichloried. Die resultate het die bevindings bevestig dat verhoogde vlakke van Cu 'n negatiewe uitwerking het op die metaboliese potensiaal en op die protosoëgetalle in die grond. Daar is gevolglik besluit om 'n kombinasie van protosoë-tellings en metaboliese profiele te ondersoek as 'n potensiële bioindikator van Cu-geïnduseerde stres in grond. Data van al die mikrokosmosse wat uitruilbare Cu bevat, wisselend van 1 dpm tot 1112 dpm, is gebruik om 'n dendrogram te konstrueer wat koolstofbronbenuttingsprofiele in kombinasie met protosoë tellings gebruik. Daar is gevind dat die mikrokosmosse groepe vorm wat korrelleer met die konsentrasie uitruilbare Cu in die grond. Onder die eksperimentele kondisies wat in dié studie gebruik is, wil dit voorkom of die kombinasie van protosoë-tellings en metaboliese profiele 'n betroubare indikator van Cugeïnduseerde stres is. Hierdie bioindikator moet egter verder in ander grondtipes en met ander tipes stres-induserende besoedeling ondersoek word. By bogenoemde bevindings is daar ook gevind dat die getalle grondprotosoë besonder gevoelig is vir Cu-geïnduseerde stres in grond met In lae pH. Dit is in ooreenstemming met die bevindings van andere met betrekking tot die bio-beskikbaarheid van swaar metale in grond met 'n lae pH. In dié tipe grond mag nutriëntsiklering as gevolg van protosoë aktiwiteit besonder gevoelig wees vir die negatiewe uitwerking van koper in die grond.
4
Keller, Thomas. "Soil compaction and soil tillage - studies in agricultural soil mechanics /". Uppsala : Dept. of Soil Sciences, Swedish Univ. of Agricultural Sciences, 2004. http://epsilon.slu.se/a489.pdf.
Testo completo
5
Ching, Peter. "Creep in sands a study of time dependent deformation of reclamation sand fill under constant effective stress /". Click to view the E-thesis via HKUTO, 2001. http://sunzi.lib.hku.hk/hkuto/record/B43894598.
Testo completo
6
Gavel-Solberg, Vegard. "Development and Implementation of Effective Stress Soil Models". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bygg, anlegg og transport, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-26552.
Testo completoAbstract (sommario):
Soil exhibit complex behavior that require advanced models to recreate stiffness and strength during loading. The complex behavior may be due to preconsolidation, dilation and contraction, softening, anisotropy, stress dependency or other effects.Today, an effective stress based soil model for soft Scandinavian clays is being developed at NTNU, as part of the ongoing research project GeoFuture. The goal of this thesis is to implement and develop an effective stress based soil model, applying the concept of modular programming used in the GeoFuture project.The soil model was implemented using Fortran and MATLAB code for application in PLAXIS. Modular programming was used to separate the implemented code into two material independent codes and one material dependent code. For development of the model, only the material dependent code needs to be modified.A simple linear elastic-perfect plastic Drucker--Prager model was implemented at first. Simulations in PLAXIS were performed, using the implemented model and the Mohr--Coulomb model in PLAXIS to compare the behavior. For simulation of triaxial compression and extension tests, the models gave the same behavior. In plane strain conditions, the implemented model gave a softer response close to failure. The same strength is obtained for the two models, yet greater deformations arise before failure in the Drucker--Prager model.Applying the advantage of modular programming, the model was further developed to include strain hardening and stress dependent dilatancy. Two formulations of stress dependent dilatancy were used to reproduce behavior of sand in undrained conditions. Simulations of undrained triaxial tests using the model were performed, showing that only one formulation gave the intended behavior.The stress dependent dilatancy was finally related to a critical void ratio for a critical state. Using both constant and mean stress dependent elastic stiffnesses, undrained triaxial compression tests on Toyoura sand were simulated. Simulations gave a good fit between the test results and the simulations. The mean stress dependent stiffness gave superior simulations compared to the constant stiffness.During the development of the model, continuous testing has been executed. The concept of modular programming has shown to perform well. After establishing the first framework with material dependent and independent routines, including new features, or even changing constitutive model, is a manageable and convenient task. The concept yields a good tool for implementing and developing constitutive models of soils.As the strength of the implemented model must be correlated manually to the relevant stress state, further development of the model should include a Lode angle dependency of the strength. Mobilization dependent dilatancy is not included and would improve the performance. A more complete evaluation of material properties from laboratory tests with subsequent simulations would be of great interest to indicate the predictive capacity of the model.
7
Fernandez, Americo Leon. "Tomographic imaging the state of stress". Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/20698.
Testo completo
8
Ho, Mei Yung. "Governing parameters for stress-dependent soil-water characteristics, conjunctive flow and slope stability /". View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202007%20HO.
Testo completo
9
Hoyos, Laureano R. Jr. "Experimental and computational modeling of unsaturated soil behavior under true triaxial stress states". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/32773.
Testo completo
10
Mun, Byoung-Jae. "Unsaturated soil behavior under monotonic and cyclic stress states". Texas A&M University, 2004. http://hdl.handle.net/1969.1/1361.
Testo completoAbstract (sommario):
The objectives of this dissertation are to measure and calculate surface free energies of soil particles, to understand the mechanical behavior of unsaturated silty sand through first studying the stress-strain relationship, the effects of matric suction and pore water chemistry and second to interpret the behavior by the critical state frame work, to develop a method to predict cone tip resistance in unsaturated soils, and to present the concept of pseudo strain and dissipated pseudo strain energy.
Universal Sorption Device (USD) is developed to measure surface free energies of soil particles. The test results on a soil sample shows that specific surface area increased with decreasing particle size. The components of surface free energies and the work of adhesion increased with decreasing particle size.
A servo controlled triaxial testing device is developed to test 15.24 cm in height and 7.62 cm in diameter, recompacted specimens of unsaturated soil under varying matric suction and different pore chemistry. During the test, the matric suction is maintained constant. Results from the triaxial drained tests are used for validation of the constitutive models proposed by Alonso et al. (1990). Predictions from the model are in good agreement with experimental results.
The critical state model for unsaturated soil is used to calculate cone tip resistance in unsaturated silty sand. The calculated cone tip resistance is used to evaluate the liquefaction potential of unsaturated soils. The results from the stress based liquefaction potential analysis reveal that even in an unsaturated condition soil is susceptible to liquefaction.
By applying the pseudo strain concept, it is possible to account for the viscous resistance of water during cyclic loading. The results of undrained cyclic triaxial tests are used to calculate pseudo-strain and dissipated pseudo strain energy. The results of calculated dissipated pseudo strain energy suggest that the effect of initial matric suction is evident. On the other hand, the effect of surface tension increase or decrease due to existence of chemical on the pore water is negligible.
11
Copeland, Stephen Mark 1955. "Soil water potential as related to the Crop Water Stress Index of irrigated cotton". Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/276940.
Testo completoAbstract (sommario):
The application of the crop water stress index (CWSI) method to irrigation scheduling is enhanced by knowledge of the relationship between CWSI and soil water potential (SWP) and how this relationship is affected by soil texture. A study using the same cultivar of cotton on three different soils was conducted in southern Arizona over a single growing season. Detailed data were collected of CWSI and soil moisture content for several treatments that scheduled irrigations at threshold CWSI values. CWSI was correlated with soil water potential values calculated from pressure plate determined moisture release curves. Spatial variability of soil characteristics necessitated use of average rather than plot specific moisture release curves. Analysis showed a linear CWSI-SWP relationship that varied greatly with soil depth and study site. The study concluded that soil profile average SWP alone does not normalize the CWSI between sites with different soil textures.
12
Bloomer, S. T. "Stress-strain behaviour of soils containing electrolytes". Thesis, University of Sunderland, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381589.
Testo completo
13
Cunningham, Mark Robert. "The mechanical behaviour of a reconstituted, unsaturated soil". Thesis, Imperial College London, 2000. http://hdl.handle.net/10044/1/8699.
Testo completo
14
Sze, Hon-yue, e 施漢裕. "Initial shear and confining stress effects on cyclic behaviour and liquefaction resistance of sands". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45700837.
Testo completo
15
Lai, Chun Hon. "Experimental study of stress-dependent soil-water characteristics and their applications on numerical analysis of slope stability /". View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202004%20LAIC.
Testo completo
16
Al-Tabbaa, A. "Permeability and stress-strain response of speswhite kaolin". Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382516.
Testo completo
17
Maswoswe, Justice. "Stress paths for compacted soil during collapse due to wetting". Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/8265.
Testo completo
18
Mohammad, Vali Samani Abbas. "Travel-time tomography for stress reconstruction in granular soil media". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq22221.pdf.
Testo completo
19
Elder, Donald McGillivray. "Stress strain and strength behaviour of very soft soil sediment". Thesis, University of Oxford, 1985. http://ora.ox.ac.uk/objects/uuid:48050e2f-832d-47f4-9e3b-b922176f451b.
Testo completoAbstract (sommario):
Introduction: When fine grained natural sediments or artificially produced waste materials are transported and deposited through water, several different phases of behaviour are observed. These have been described variously as suspension, free settling, compression settling, intermediate and consolidating soil phases. Transitions between each are not always distinct in terms of material properties or behaviour and time spent in the early phases before a conventional soil state is attained can be a significant proportion of the total period of engineering interest. The eventual state attained following procession through these stages may be very different to that if the soil had been remoulded at the same final density. Standard engineering models exist which can describe soil behaviour well in separate phases under particular conditions, but these are of limited validity when extended to more general conditions and wider volumetric ranges than those for which they were formulated. The number of factors required to describe the entire range of behaviour is consequently larger than that for any one phase, and many of these factors are more familiar in fields of chemistry, geology or sedimentology than in classical soil mechanics. This thesis discusses, in engineering terms, the engineering behaviour observed in a particular soil during the general sedimentation and self weight consolidation process. In the second chapter existing knowledge about behaviour at zero or low stresses is reviewed and evaluated with respect to common assumptions made, often implicitly, in formulating predictive models. It is shown that while these models have been extensively developed to a stage where they can approximate many aspects of soil behaviour, the lack of fundamental investigations carried out in parallel with their development has often led to inadequate appreciation of the causes of discrepancies between modelled and real behaviour. This has occurred particularly where standard geotechnical testing equipment and methods devised for stiff soils have been used to obtain global average relationships between engineering parameters. Even where modified tests have been developed, instrumentation has sometimes been inadequate and measurements too infrequent, so that data available have necessarily been analysed only in terms of constitutive forms assumed already. In chapter three experimental techniques are proposed which, where possible will allow soil behaviour to be examined under the least restrictive conditions of one dimensional compression so that basic engineering concepts may be analysed. Chapter four describes the testing programme and presents direct results of experiments. Chapter five analyses compression behaviour and establishes some trends which can be observed for particular parameters and relationships, and which exist between experiments under different initial and boundary conditions. Similar analysis of strength behaviour is undertaken in chapter six, where results obtained using different testing methods are compared. In the final chapter the general relevance of these results and their implications for engineering problems are discussed. Some suggestions are made for future work. Areas of application Improved knowledge about cohesive waterborne sediments can result in considerable savings for related industries. In the United Kingdom the annual cost of maintenance dredging is £25m (I.C.E. Costal Engineering Research Panel, 1985). In East Coast ports alone reduction of the distances travelled by each dredger would lead to a saving of £270,000 per annum, per kilometre reduction. Studies at Rotterdam Europort (Kirby, Parker, van Oostrum, 1979) show that although a channel dredged recently may quickly refill with sediment to a depth which echo-sounding techniques might indicate to be unnavigable, the strength may be so low as to allow passage of vessels virtually unimpeded. A density of 1.2 Mg/m3 is now used by the Rijkswaterstaat to define the "Nautical Depth" of a channel, stated to be "a density within the suspension above whose altitude vessels can safely sail." Dredging control using information from gamma ray densimeters has enabled production increases of up to 50% to be obtained in the Europort area. In the United States $30m was spent in a 5 year period on a dredging research programme aimed at improving disposal methods (Haliburton, 1977). Considerable volumes of waste material are also produced by the mining industry. The phosphate industry in Florida produces 40 million tons by dry mass per annum at an initial 3% solids by mass which even after two years retains void ratios around 10, due to the high content of attapulgite, a clay mineral consisting of long fibrous particles with large specific surface. Disposal areas for these clays occupy over 50,000 acres and are surrounded by 300 miles of dams, posing significant environmental and safety problems (Bromwell, Oxford, 1977). Failures of underwater slopes have been well documented. In muds deposited recently in the Mississippi Delta area very low shear strengths combine with apparently high excess pore pressures and presence of gas bubbles to cause instability for slope angles less than 1°. Recent research carried out a Oxford suggests that presence of gas may cause high excess pressures to be deduced where none exist. Duncan and Buchignani (1973) analysed a slope failure in San Francisco Bay which occurred during cutting of a slope from a normally consolidated clayey silt. The importance of accurate determination of an in situ parameters for analysis was shown by the estimated saving of $200,000 through using a slope of 7:8 rather than 1:1, decreasing the supposed safety factor from 1.26 to 1.17. Analysis of error sources showed that an error of only 4% in the soil density could reduce this safety factor by 10%. Similar problems due to changes in loading or boundary conditions occur where natural changes, such as increase in water current, cause erosion of a sediment layer which might, for example, be supporting an underwater cable or pipeline. In all these areas in situ property determination in solid of low density provides major problems. Density is often the only quantity that can be measured both accurately and continuously and then only when a stable platform can be maintained. Recovery of high quality samples from these layers is virtually impossible, so that there is a strong need for correlations between density and other properties such as strength and compressibility.
20
Manuel, Theodore Llewellyn. "Effect of soil nutrient status on stress tolerance in Proteaceae". Bachelor's thesis, University of Cape Town, 1988. http://hdl.handle.net/11427/25615.
Testo completoAbstract (sommario):
Protea lepidocarpodendron grown on low, medium and high nutrient treatments exhibited the lowest, and similar evapotanspiration rates respectively over a 9 day water stress cycle (experimental period). In stressed and unstressed treatments, stomatal conductance and transpiration rates of plants grown on the low nutrient treatment was generally lower than that of plants grown on the medium and high nutrient treatments where stomatal conductance and transpiration rates were similar. Stressed plants grown on the low, medium and high nutrient treatments exhibited the lowest, intermediate and highest photosynthetic rates respectively. Stessed plants grown on the medium and high nutrient treatments exhibited a dramatic decrease in transpiration rates ands stomatal conductance from day 5 to 7, and a dramatic decrease in photosynthetic rates from day 3 to 7. Stressed plants grown on the low nutrient treatment showed a far less dramatic decrease in transpiration rate, stomatal conductance and photosynthetic rate over the 9 day period. For stressed plants, photosynthetic rates varied between 0.08-5.39 uMOLm⁻²s⁻¹, 1.17-7.48uMOlm⁻²s⁻¹ and 1.15-8.65uMOLm⁻²s⁻¹ for plants grown on low, medium and high nutient treatments respectively. Unstressed plants grown on low. medium and high nutrient treatments exhibited the lowest, highest and intermediate photosynthetic rates respectively. In all stressed treatments, photosynthetic rates showed a steady decline from day 1 to day 7, whereafter a dramatic increase occurred in the medium and high nutrient treatments, and a less dramatic increase in plants grown on the low nutrient treatment. These decreases and increases in photosynthetic rates was not parallelled in the stomatal conductance and transpiration rates of the unstressed plants. For unstressed plants, photosynthetic rates varied between 1.4s-4.4 uMOLm⁻²-s⁻¹, 1.65-6.7 uMOLm⁻²s⁻¹ and 3.42-8.76 uMoLm⁻²s⁻¹ for plants grown on low, medium and high nutrient treatments respectively. Plants grown on low nutrient treatments exhibited the highest LSW (182.3 gm⁻²), highest whole plant mass (WPM) (1.07g), followed by high (LSW=1.76 gm⁻²,WPM=0.83g) and medium (LSW=167.28 gm⁻² ,WPM=0.79g) nutrient treatments. Total plant nitrogen content was inversely related to LSW and WPM on low (3.84 mgNplant⁻¹), high (4.18 mgNplant⁻¹) and medium (5.28 mgNplant⁻¹) treatments. Root : ratio between treatments were similar.
21
Nguyen, Gia Huynh Truong. "Evaluating soil erodibility parameters with mini-JET under various soil moisture conditions". Kansas State University, 2016. http://hdl.handle.net/2097/34526.
Testo completoAbstract (sommario):
Master of ScienceDepartment of Biological & Agricultural Engineering
Aleksey Y. Sheshukov
Soil erosion is one of the main reasons for agricultural land degradation in the world. Losses of land because of high soil erosion rates and rapidly expanding population result in significant reduction of cultivated land area per capita, and shortage of food on the global scale. Soil erosion can be a major source of sediment in the aquatic systems leading to reduction of organism population and poor water quality. Many factors affect soil erodibility, such as, soil properties, rainfall, topographic features, land use, and management practices, among others. The impacts of soil moisture content, however, are not well understood and. therefore, the primary goal of this study was to quantify two soil erodibility parameters, the erodibility coefficient and critical shear stress, under different soil moisture conditions using the jet erosion test (JET). The JET test uses the apparatus (called mini-JET) that creates an impinging jet of water into the soil and records the resulting scour depth over time. The scour depth time series are then fitted into a non-linear soil erosion equation, yielding the sought values of erodibility parameters. For this study, more than 40 soil samples were collected from several sites in Kansas, processed, and prepared to conduct JET tests in the lab setting. The effects of tillage and soil moisture content were of interest to this study. The results showed varied effects of soil type and sample soil moisture condition on the scour depth development and parameters sensitivity. The critical shear stress decreased and the erodibility coefficient increased with the increase of initial moisture content for clay loam soil, while critical shear stress did not change for sandy loam soil. The study also revealed higher erosive properties of soil collected from the tilled field compared to the no-till field.
22
Shibuya, Satoru. "Undrained behaviour of granular materials under principal stress rotation". Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/7979.
Testo completo
23
Griffiths, Robert Iwan. "Soil bacteria and carbon flux : the correlation with diversity and perturbation". Thesis, University of Newcastle Upon Tyne, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289179.
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Unutmaz, Berna. "Assessment Of Soil". Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12610285/index.pdf.
Testo completoAbstract (sommario):
Although there exist some consensus regarding seismic soil liquefaction assessment
of free field soil sites, estimating the liquefaction triggering potential beneath
building foundations still stays as a controversial and difficult issue. Assessing
liquefaction triggering potential under building foundations requires the estimation of
cyclic and static stress state of the soil medium. For the purpose of assessing the
effects of the presence of a structure three-dimensional, finite difference-based total
stress analyses were performed for generic soil, structure and earthquake
combinations. A simplified procedure was proposed which would produce unbiased
estimates of the representative and maximum soil-structure-earthquake-induced
iv
cyclic stress ratio (CSRSSEI) values, eliminating the need to perform 3-D dynamic
response assessment of soil and structure systems for conventional projects.
Consistent with the available literature, the descriptive (input) parameters of the
proposed model were selected as soil-to-structure stiffness ratio, spectral
acceleration ratio (SA/PGA) and aspect ratio of the building. The model coefficients
were estimated through maximum likelihood methodology which was used to
produce an unbiased match with the predictions of 3-D analyses and proposed
simplified procedure. Although a satisfactory fit was achieved among the CSR
estimations by numerical seismic response analysis results and the proposed
simplified procedure, validation of the proposed simplified procedure further with
available laboratory shaking table and centrifuge tests and well-documented field
case histories was preferred. The proposed simplified procedure was shown to
capture almost all of the behavioral trends and most of the amplitudes.
As the concluding remark, contrary to general conclusions of Rollins and Seed
(1990), and partially consistent with the observations of Finn and Yodengrakumar
(1987), Liu and Dobry (1997) and Mylonakis and Gazetas, (2000), it is proven that
soil-structure interaction does not always beneficially affect the liquefaction
triggering potential of foundation soils and the proposed simplified model
conveniently captures when it is critical.
25
Jetchick, Elizabeth. "Stress, deformation and micromorphological aspects of soil freezing under laboratory conditions". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0001/NQ32336.pdf.
Testo completo
26
Clinton, D. B. "The determination of soil parameters for design from stress path tests". Thesis, City University London, 1987. http://openaccess.city.ac.uk/8330/.
Testo completoAbstract (sommario):
The thesis concerns investigation and measurement of the elastic deformation properties of an anisotropic soil within the context of critical state soil mechanics. The soil tested is a heavily overconsolidated Gault Clay. Laboratory triaxial testing on 38 mm samples is used to measure and soil 100 mm diameter stiffness. A microcomputer-based control system has been developed for use with hydraulically-operated triaxial cells to enable stress path testing, and this is described. The axial and radial stresses and the back pressure can be varied independently to produce any desired stress path. A method of measurement of anisotropic of loading stiffness is developed using various pairs and unloading cycles, or stress path probes. tried, with isotropic, undrained cycles proving to be of most Several alternatives are uniaxial and constant pi use. For the soil tested, measured modulus values are found to be about 25% in error if anisotropy is neglected. Factors affecting stiffness measurements are assessed, including sample disturbance, soil structure, threshold and stress history effects, design of the apparatus and test procedure. Elasticity theory for cross-anisotropic soils is reviewed, particularly as it relates to the triaxial apparatus. The way in which elasticity theory is incorporated in the critical state model is discussed. Isotropic compression a~ swelling test the compression law usually used in the results question critical state model. Theoretical difficulties have been found with this law when formulating an elastic soil model within critical state theory. A series of stress probe tests is used to investigate the variation of elastic stiffness parameters with soil state. The results are compared with patterns of soil behaviour found from strain path tests.
27
Ma, Qifu. "Soil salinity and water stress modify crop sensitivity to SO2 exposure". Thesis, Ma, Qifu (1993) Soil salinity and water stress modify crop sensitivity to SO2 exposure. PhD thesis, Murdoch University, 1993. https://researchrepository.murdoch.edu.au/id/eprint/42300/.
Testo completoAbstract (sommario):
Sulphur dioxide (SO2) is a pnmary gaseous pollutant which has toxic effects on the growth, yield and quality of both agricultural and natural plant species. Although plant responses to SO2 exposure have been extensively studied, much less is understood concerning the influences of other environmental stresses on the expression of effects of gaseous air pollutants. Evaluation of such interactions should be of an economic importance in agriculture and horticulture since plants growing in the field usually encounter air pollution and other stresses simultaneously. Soil water stress and salinity are the common environmental stresses and they have some physiological similarities. This thesis aims to investigate to what extent water stress and salinity modify or amplify the detrimental effects of SO2 on foliar injury, plant growth and yield, and some physiological and biochemical changes in potato (Solanum tuberosum L. cv. Russet Burbank) and soybean (Glycine max L. cv. Buchanan) crops under field conditions.
SO2 exposure induced growth reductions in well-watered potato plants but usually not in the water-stressed plants, indicating a protective function of soil moisture stress in the response of plants to SO2. This could be caused by a reduced SO2 uptake m water-stressed plants, as well-watered plants had much higher leaf sulphur concentrations than did the water-stressed plants at the same SO2 fumigation levels. SO2 also increased leaf sulphur concentrations in soybean, but simultaneous exposure to SO2 and salinity significantly decreased leaf sulphur concentrations when compared with exposure to SO2 alone. As a consequence, SO2-induced foliar injury was more severe in the well-watered or nonsaline plants than in the water-stressed or saline plants.
Exposure conditions can also be important in determining the response of a plant to stress interactions. Contrasts of sequential and simultaneous exposures to SO2 and salinity were made in this project so as to examine stress compensatory mechanisms and predisposition characteristics. It was found that low salinity pretreatment (27 mM NaCl) ameliorated the detrimental effects of SO2 on soybean growth probably by inducing stomatal closure. However, high salinity (48 mM NaCl) treated plants, which also showed high stomatal resistance, were severely injured by subsequent SO2 exposure especially at high SO2 concentrations (300 nl 1-1). It was likely that high salinity pretreatment decreased or even destroyed plant homeostasis due to direct injury of high ion concentrations. By comparison, plants pretreated with SO2 became vulnerable to salt injury and those pretreated with high SO2 were killed after 12 days of high salt stress. This was probably because SO2 altered the patterns of assimilate allocation favouring shoot growth at the expense of root growth and induced other metabolic changes. As a consequence, the resistance of polluted plants to salinity stress was reduced.
SO2 pollutant increased the shoot to root ratios by either reducing root growth or stimulating shoot growth, whereas soil moisture stress had the opposite effect. Exposure to 300 nl 1-1 SO2 under well-watered conditions induced an increase in the shoot to root (including tuber) ratios of potato plants early in the growing season. In contrast, water stress decreased the ratios in the control and 110 nl 1-1 SO2 treatments, but not at 300 nl I-1 SO2 indicating that high SO2 had disrupted this acclimatory response to soil moisture stress. SO2-induced increase in the shoot to root ratios was also observed in the soybean experiments. However, it appeared that soil salinity did not significantly affect the ratios.
High SO2 decreased the number and weight of root nodules, and suppressed nodule nitrogenase activity. Consequently, both shoot and root nitrogen concentrations were reduced. In combination with low salinity, however, the adverse effects of high SO2 on nodule number, specific nodule activity and plant nitrogen concentrations were ameliorated. Biomass was usually not very sensitive to the interactive effects of SO2 and salinity, probably because it is slower to respond to the stresses following physiological and biochemical processes. In the field, stress interactions may become even more complicated due to interactions with other environmental stresses.
In conclusion, moderate soil salinity and moisture stress can modify crop sensitivity to SO2 exposure mainly through stomatal mechanisms. Such interactions, together with the knowledge of interactions of gaseous au pollutants and other environmental stresses (e.g. light, humidity and temperature), are important when we attempt to establish dose or concentration-response relationships for the development of predictive models for the effects of air pollutants on crops or native plants. Environmental factors may readjust the dose thresholds of au pollutants, above which detrimental effect are likely and below which insignificant effects or growth stimulations occur. Therefore, air quality standards designed to protect vegetation may need to· consider variations in regional environmental conditions.
28
Aria, Shadi. "Load-settlement and stress-strain behaviour of geotextile-reinforced sandy soil". Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2018. https://ro.ecu.edu.au/theses/2167.
Testo completoAbstract (sommario):
During the past few decades, many studies have been conducted to investigate the load-settlement behaviour of geosynthetic-reinforced foundations, and researchers proposed different methods to improve the performance of geosynthetic-reinforced foundation soils as well as to develop empirical equations to estimate their bearing capacity. In the recent past, using geotextile reinforcement with wraparound ends has been recommended to strengthen the foundation soil aimed at improving the effectiveness of using geosynthetic reinforcements. However, there are still areas that received far too little attention in the past, e.g. the optimum geometric parameters in geosynthetic-reinforced sandy soils with or without using wraparound reinforcement technique. An optimal design and the effectiveness of employing geosynthetic material for strengthening the foundation soil require an extensive knowledge of the load-settlement behaviour and failure mechanism of reinforced soils.
This thesis presents extensive laboratory measurements and numerical analysis conducted to (i) investigate the effect of angle of internal friction of soil on the optimum burial depth of the reinforcement and the bearing capacity of the geosynthetic-reinforced sandy soil based on numerical modelling, (ii) study the effects of reinforcement geometrical parameters, namely land width occupied by the reinforcement, and the lap length of the wrapped ends, based on numerical modelling, (iii) present experimental evaluations of the effectiveness of the wraparound reinforcement technique for improving the bearing capacity and load-settlement characteristics of sandy soils, and (Das & Sivakugan) study the strain distribution and the mobilisation of tensile modulus in geotextile reinforcement buried within the sandy soil. In the experimental phase, laboratory model strip footing tests were performed to investigate the influence of wraparound lap length and occupied land width on the load-settlement behaviour of sandy soil. In addition, an instrumentation program with pressure cells and strain gauges was designed to investigate stress and strain distribution within the sand bed. The test results show that the existence of wraparound ends of the geotextile reinforcement improves the bearing capacity of sand bed by about 70% comparing with reinforced foundation soil without wraparound ends. The strain distribution observations reveal that the theoretical solution may overestimate the tensile strength of the geotextile in the range of 30-60 % that can be due to the in-isolation methods being used by standards to measure the tensile modulus of geosynthetics.
In the numerical phase, first, a numerical model was built to investigate the effect of the angle of internal friction of sand on the optimum burial depth of geosynthetic reinforcement. Numerical outputs reveal that the optimum burial depth depends significantly on the angle of internal friction of sand, and has a linear relationship with the height of the active wedge beneath the footing. In the second stage, a parametric study of the wraparound reinforcement technique was carried out to investigate the effects of geometrical parameters of wraparound reinforcement on the bearing capacity of the sandy soil. The model was used to critically analyse the reinforcing mechanisms for improved bearing capacity caused by wraparound ends. The results reveal that the efficiency of reinforced models with wraparound ends in terms of occupied land area is about 100% higher than that of without wraparound ends. The research carried out as presented in this thesis demonstrates that the wraparound geosynthetic reinforcement technique can be highly beneficial in a location of limited land width for foundation construction.
29
Naesgaard, Ernest. "A hybrid effective stress – total stress procedure for analyzing soil embankments subjected to potential liquefaction and flow". Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/34004.
Testo completoAbstract (sommario):
Seismic design of major civil structures (bridges, dams and embankments) is moving increasingly towards using performance design methodologies which require determination of earthquake induced movements. Development of these numerical design tools and procedures for use in engineering practice for estimating the earthquake induced ground deformations of potentially liquefiable soil is the topic of this dissertation.
Fully coupled effective stress numerical analyses procedures developed at the University of British Columbia (UBC) were used to simulate field and centrifuge test case histories. These analyses can offer considerable insight, but due to the complexity of the problem and variability of the parameters involved, there is considerable uncertainty. The author, therefore, recommends that the relatively new state-of-the-art effective stress analyses should be augmented by carrying out an additional analysis compatible with conventional design processes. This latter analysis uses published post-liquefaction “residual” soil strengths derived from back-analysis of field case histories by others. The developed design methodology uses the effective stress (UBCSAND) soil constitutive model for dynamic analyses, and empirical “residual” post-liquefaction soil strengths for a post-shaking total stress static analysis. In the proposed approach, the effective stress dynamic analysis is used to determine zones of liquefaction, to quantify earthquake induced deformations, and to provide overall insight. The post-shaking total stress static analysis, with “residual” strength parameters used in elements which liquefied, is carried out to capture the effects of complex stratigraphy and localization that may be missed by the effective stress model.
Calibration and validation of the UBCSAND model was undertaken by comparing the model with field case histories and laboratory simple shear, shake table, and centrifuge tests. The measured response of some centrifuge tests being used for validation was indicative of the centrifuge model not being fully saturated. This was problematic as P-wave measurements within the centrifuge model suggested full saturation. A series of triaxial tests with P-wave measurements was carried out. These tests, and the numerical modeling of them, showed that high P-wave velocities were not always indicative of full saturation and they provided a logical explanation for the observed centrifuge response.
30
Chen, Rui. "Experimental study and constitutive modelling of stress-dependent coupled hydraulic hysteresis and mechanical behaviour of an unsaturated soil /". View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202007%20CHEN.
Testo completo
31
Wu, Dan Hua. "The effect of water potential on soil microbial biomass". Thesis, University of Aberdeen, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290290.
Testo completoAbstract (sommario):
This study investigated the effect of water potential on soil microbial C and N pools. Two soil types were treated with additions of salt solution to establish osmotic water potentials, and by ceramic plate - pressure chamber apparatus to establish matric water potentials. Soils were then subjected to short-term incubations. Soil microbial C and N contents (BC and BN) were measured mainly by the fumigation-extraction and fumigation-incubation methods. Results showed that both Microbial C and N pools were markedly affected by soil water potential. The soil microbial C content always showed an increase with increasing water stress and then a decrease beyond a threshold value of water stress, compared to the microbial C content at a control water potential of -0.03 MPa (-0.3 Bar). This response pattern to water stress was true, not only for osmotic stress, but also for matric stress, and regardless of the osmotic agent employed. The response pattern of the microbial N pool to water stress generally contrasted with that of the C pool, and depended on the osmotic strength of the extraction solution (K2SO4) used in the determination. Non-isotonic extraction after fumigation resulted in a decrease in microbial N content with increasing water stress, while isotonic extraction resulted in an increase with increasing water stress, beyond a threshold value of water stress. Soil microbial C/N ratio always increased with increasing water stress. Matric water stress had a more marked effect on BC and BN than osmotic stress. The possible reasons for the response patterns of BC, BN and microbial C/N ratio have been discussed in this thesis. Some suggestions on the methodology of microbial biomass measurement for water stressed soil samples have been made, and mainly relate to the biomass fumigation techniques and possible changes in the Kc, Kce and Kn values under water stress, and to the substrate induced respiration (SIR) method and suppressed respiration under water stress.
32
Zeywar, Nadim Shukry 1959. "Effect of sensor placement on the relationships of crop water stress index, soil moisture tension and soil moisture content". Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/191981.
Testo completoAbstract (sommario):
A field experiment was conducted to investigate the feasibility of making one measurement of soil moisture tension/content or crop water stress index (CWSI), and from it determine when and how much to irrigate. Cotton (Gossvpium hirsutum C.V. DPL-90) was planted in a sandy loam soil prepared with an underground drip irrigation system. Measurements of soil moisture tension, soil moisture content, plant temperature, and wet- and dry-bulb temperatures were made. The results indicate that soil moisture tension above 0.30 m and soil moisture content above 0.50 m in the root zone can be used as good indicators for CWSI or vice versa. Further work is required using different irrigation systems and different crops in larger land areas.
33
Ibarra, Sandra. "A model of stress distribution and cracking in cohesive soils produced by simple tillage implements /". Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38205.
Testo completoAbstract (sommario):
The objective of this research was to further understand the behavior of the soil under the action of a tillage tool, with the purpose of finding a relation between the tool geometry and the resultant soil seed bed. Thus the problem consisted of understanding the mechanics of producing soil break up and to find a logical method of analyzing it.The problem was solved using fundamental principles of soil mechanics and force equilibrium analyzis. As a result, a mathematical model was developed which describes three failure zones within the cut soil volume. The model can be programmed into a computer to generate maps of normal and shear stresses to visualize the three failure zones.
The failure zones are the shear failure zone, the tensile fracturing zone and the no failure zone. The tensile fracturing zone is delimited by the tensile stress reaching the tensile strength of the soil at the given soil moisture content and soil density. The tensile strength of the soil was measured using an apparatus and method designed in this research.
The mathematical model gives an explanation of the mechanics of crumbling and the shape of the failed volume, but it does not give information concerning soil aggregate quality and arrangement within the soil furrow. Then, a method of analyzing the formed aggregates was developed which considers some soil physical properties of aggregates.
The study concluded that the smaller tool width and the smaller tool rake angle, among the ones used in this research, produced the most efficient geometry in producing the largest amount of soil break up, the most uniform aggregate formation and the most stable aggregate arrangement. The same tool geometry requires less energy per unit volume of soil disturbed. The best performance is produced at the lowest soil water content among those tested.
34
Tse, Man Kit. "Influence of stress states on soil-water characteristics, conjunctive surface-subsurface flow modelling and stability analysis /". View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202007%20TSE.
Testo completo
35
Liao, Chung-Lon. "Applications of cone, vane and vane-cone to predict stress-strain behaviour of unsaturated cohesive soil". Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72788.
Testo completo
36
Mellander, Per-Erik. "Spring water stress in Scots pine : interaction of snow and soil temperature /". Uppsala : Dept. of Environmental Assessment, Swedish Univ. of Agricultural Sciences, 2003. http://epsilon.slu.se/s287.pdf.
Testo completo
37
Fidelibus, Matthew, Chris Martin e Jean Stutz. "Contributions of Beneficial Soil Fungi to Drought Stress Tolerance of Young Citrus". College of Agriculture, University of Arizona (Tucson, AZ), 1997. http://hdl.handle.net/10150/220566.
Testo completoAbstract (sommario):
Four arbuscular mycorrhizal (AM) fungal isolates (Glomus sp.) from disparate edaphic conditions were screened for effects on whole -plant transpiration of juvenile 'Volkamer' lemon (Citrus volkameriana Ten. and Pasq.) plants of similar shoot mass and canopy leaf area. Mycorrhizal and non -mycorrhizal plants were grown in 8 -liter containers for 2.5 months under well- watered conditions before subjection to three consecutive soil drying episodes of increased severity (soil moisture tensions of -0.02 [still moist], -0.06 [moderately dry], and -0.08[dry] MPa respectively). Whole plant transpiration measurements were made on the last day of each soil drying episode and measurements were repeated on the first and second days after re- watering, when soil profiles were moist. The percent root length colonized by AM fungi differed among isolates. Three AM fungal isolates, Glomus sp. 25A, Glomus mosseae (Nicol. & Gerde.) Gerde. & Trappe 114C, and Glomus intraradices Schenck & Smith FL 208-3 increased root length and subsequently increased lemon plant water use. Conversely, plants inoculated with Glomus mosseae 51C did not enhance lemon plant root length nor improve plant water use compared with nonmycorrhizal control plants. Inoculating citrus with AM fungi that promote root extension may reduce plant water deficit stress under field conditions.
38
Emam, Taraneh Megan. "The Role of Soil Biota, Abiotic Stress, and Provenance in Plant Interactions and Restoration". Thesis, University of California, Davis, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3706585.
Testo completoAbstract (sommario):
In this dissertation, I asked how soil biota, abiotic stress, and plant provenance influence plant communities and interactions between plants. Soil biota can have positive or negative effects on individual plants, and also influence the diversity and productivity of plant communities through their net effects on individuals and by mediating plant-plant interactions. However, the level of abiotic stress experienced by plants is likely to drive plant responses to soil mutualists and antagonists. Additionally, plant provenance (e.g. population origin) can influence responses to abiotic soil conditions as well as to soil organisms. Understanding how these three interacting components shape plant interactions may improve success of restoration and invasive plant management. During restoration, the goal is typically to create conditions conducive to native plant reestablishment. However, amelioration of disturbed areas by reducing abiotic stress or by adding beneficial soil organisms may unintentionally increase colonization and growth of non-native plants. Using the applied context of mine restoration, I examined how soil biota, abiotic stress, and plant provenance affected plant communities and interactions in four studies.
In Chapter 1, I found that both a native grass (Bouteloua gracilis ) and an invasive grass (Bromus tectorum) responded positively to soil biota when grown alone in the greenhouse. However, when grown together, the presence of soil biota increased the competitive ability of Bromus, while the removal of soil biota increased competition by Bouteloua. Results supported the hypothesis that invasive species such as Bromus often have positive responses to soil biota in the invaded range, but I also found that Bromus response to soil biota removal varied considerably by site.
In Chapters 2 and 3, I examined how methods used during restoration (application of stockpiled soil and inoculation with soil biota) affected native and non-native plant growth in field plots. I found that native plant biomass and non-native plant biomass both tended to increase when soil abiotic stress was ameliorated through the addition of deeper stockpiled soil. In addition, both native and non-native grasses responded positively to the use of local soil an as inoculant, while non-native forbs responded negatively to local soil inoculum. However, native plants only received significant benefits from inoculation when targeted application to native seedling transplants was used. Commercial mycorrhizal fungal inoculum did not affect plant growth. In studies of both stockpiled soil addition and soil inoculation, year was an important factor in determining plant responses. Variation in effects by year may reflect differences in precipitation timing or amount, or changes associated with plant and soil biota growth over time.
In Chapter 4, I used a greenhouse experiment to examine how one type of soil biota, arbuscular mycorrhizal fungi (AMF), influenced plant-plant interactions. I also manipulated abiotic stress (soil phosphorus availability) and plant provenance (stress-tolerant ecotype versus competitive ecotype) to assess whether these factors influenced AMF-mediated interactions among plants. I found that allowing or denying AMF hyphal access between neighboring pots altered plant reproduction. Inflorescence production was substantially decreased when hyphal access was allowed between two stress-tolerant plants. In addition, when hyphal access was permitted from a stress-tolerant plant to a competitive plant, the competitive plant flowered slightly sooner, whereas allowing hyphal access between two stress-tolerant plants led to slightly slower flowering. These results did not appear to be driven by abiotic stress or plant nutrition. It is possible that AMF transmission of infochemicals may play a role in regulating plant phenology and reproduction; however, further research in this area is needed.
39
Salman, Talib H. "Triaxial behaviour of partially saturated granular soils at low stress levels". Thesis, University of Sheffield, 1995. http://etheses.whiterose.ac.uk/10232/.
Testo completoAbstract (sommario):
Granular soil is used as a backfilling material in trenches that are prepared for the installation, repair and replacement of service pipes. The soil is likely to be partially saturated and subjected to low stress levels (<100 kPa), as it exists at shallow depths (about 5m below the ground). A new double-wall triaxial cell has been designed for testing partially saturated granular specimens with height/diameter equal to 375mm/150mm, at low stress levels. The cell is able to make separate measurements and control of the pore air and pore water pressures. It was designed to make specimen stress and strain measurements internally. A conventional triaxial cell was modified to carry out tests on saturated granular specimens of the same dimensions at low stress levels. Two gradings of Limestone, fine and coarse, with maximum particle sizes of 5mm and 20mm respectively are used in the triaxial tests. The experimental results showed that the suction in the range 25 kPa to 75 kPa can have an effect on the volume, stiffness and shear strength of partially saturated granular soils at low stress levels. The results also showed that there is a linear relationship between q and (p-u_a) for the unsaturated soils or (p-u_w) for the saturated soils. And Fredlund's equation cannot be used to predict the shear strength of partially saturated granular soils at low stress levels, if the value of φ'is taken from tests carried out on saturated specimens. The results also showed that there was a relationship between q,(p-u_a), suction, specific volume and water content, all at failure.
40
Henderson, Marc Bryson. "Changes in Streambank Erodibility and Critical Shear Stress Due to Surface Subaerial Processes". Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/33114.
Testo completoAbstract (sommario):
Previous studies have shown that soil erodibility and critical shear stress are highly influenced by weathering processes such as freeze-thaw cycling and wet-dry cycling. Despite over forty years of research attributing changes in soil properties over time to climate-dependent variables, little quantitative information is available on the relationships between streambank erodibility and critical shear stress and environmental conditions and processes that enhance streambank erosion potential. The goal of this study was to investigate temporal changes in streambank erodibility and critical shear stress due to surface weathering.
Soil erodibility and critical shear stress were measured monthly in situ using a multi-angle submerged jet test device. Environmental and soil data were also collected directly at the streambank surface to determine freeze-thaw cycles, soil moisture, soil temperature, bulk density, soil erodibility, critical shear stress, and other atmospheric conditions that could impact bank erosion potential. Statistical tests, including a nonparametric alternative to ANOVA and multiple comparison tests, were used to determine if temporal changes in soil erosion potential were greater than spatial differences. Regression analyses were also utilized to identify the factors contributing to possible changes in soil erodibility, critical shear stress, and bulk density.
The nonparametric alternative to ANOVA in combination with Dunnâ s nonparametric multiple comparison test showed soil erodibility was significantly higher (p=0.024) during the winter (November - March) and the spring/fall (April - May, September - October). Regression analyses showed 70 percent of soil erodibility variance was attributed to freeze-thaw cycling alone. Study results also indicated that bulk density is highly influenced by climate changes since gravimetric water content and freeze-thaw cycles combined explain as much as 86 percent of the variance in bulk density measurements.
Results of this study show significant amounts of variation in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes, specifically changes in soil moisture and temperature. These results have potential implications for streambank modeling and restoration projects that assume constant values for soil erodibility. Watershed models and restoration designs should consider the implications of changing soil erodibility during the year in model development and stream restoration designs.Master of Science
41
Khan, Muhammad Umer Arif. "Experimental and mathematical investigations of soil-conduit interaction within a loaded soil slope". Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2021. https://ro.ecu.edu.au/theses/2458.
Testo completoAbstract (sommario):
Buried conduits are an essential feature of modern underground infrastructure. They are the primary source of utility conveyance around the world because of their economic and safety benefits. The understanding of soil-conduit interaction is vital to ensure the stability of a soilconduit system. Starting in the early 1900s, numerous studies have been conducted to investigate various aspects of the soil-conduit interaction. The researchers have suggested that soil-conduit interaction generally depends on soil type, conduit material, diameter and burial depth of the conduit, applied loading, and soil movement around the buried conduit. However, a vast majority of these studies have analysed the soil-conduit interaction under a level ground surface. However, in reality, conduits not only travel across plain areas but also pass through hilly terrains to reach the end consumers. Keeping this practical fact in view, limited research studies have been carried out in the past, especially investigating the effect of changing landscape on the soil-conduit interaction. However, significant research gaps still remain, which require further detailed study to enhance the understanding of the soil-conduit interaction in sloping terrains.
This research aims to analyse the soil-conduit interaction in a loaded soil slope through experimental and numerical methods. For this purpose, extensive laboratory experimentation, finite element modelling, analytical formulation, and intelligent modelling have been conducted. The experimental study investigated the following aspects: (a) the load-settlement response and bearing capacity of a footing located over a conduit buried within a soil slope, and (b) the stress distribution around a conduit buried within a soil slope. A finite element model was developed to study the structural response of a conduit buried within a soil slope to the applied surface pressure. An attempt was also made to analytically formulate an expression to calculate the vertical load on a conduit buried under a sloping terrain. Finally, this research also focused on building executable finite element modelling-artificial intelligence-based models and converting them into simple mathematical equations for estimating the following: (a) width of Marston’s soil prism for the reinforced concrete and corrugated steel conduits, and (b) settlement of a footing located over a conduit buried within a soil slope.
In the experimental phase, laboratory model tests have been conducted on a strip footing located on top of conduits buried within a soil slope, under static loading condition. The design of the model test cell and the conduit installation technique helped in reducing the scale influence. Using this test setup, two aspects of soil-conduit interaction have been studied, including the effect of the buried conduit on load-settlement response and bearing capacity of the overlying footing, and the stress distribution around the buried conduit due to the applied surface pressure. The experimental results have shown that the conduit buried within a soil slope can have both negative and positive effects on the load-settlement response and bearing capacity of the overlying footing. The negative impact generally happens when the buried conduit intersects with the shear failure planes of the loaded footing and may result in a 252% higher footing settlement and a 40% reduction in its bearing capacity. To avoid any adverse effect on the load-bearing ability of the surface footing, the conduit should be buried at a depth of least three times the footing width. Further, the stress distribution around a conduit buried within a soil slope is highly dependent on the distance of the buried conduit from the yielding soil mass and the resulting soil-conduit interaction. The vertical stress on the crown of a conduit buried within a soil slope can be 84% higher than that of the conduit buried under the level ground.
In the numerical phase, a commercial finite element modelling software has been employed to investigate the structural response of a conduit buried within a sandy soil slope to the applied surface pressure. The developed numerical model has been validated by using results from the aforementioned experimental phase. The comprehensive study included the effect of the proximity of the free slope surface on the conduit deflections, shape deformations, and developed bending moments. The movements of soil particles in relation to the buried conduits have also been discussed in detail. The results show that due to the proximity to the free slope surface, the conduit undergoes unrestricted deformation on the slope side of the conduit, which causes a conduit deflection that is 360% higher than the conduit buried under the level ground. Further, the slope side shoulder of the conduit also experiences high bending moment, which can be 590% higher than the conduit buried under the level ground. To avoid the effect of the slope surface on the conduit, it needs to be buried at a crest distance of more than five times its diameter or at a burial depth that exceeds three times its diameter.
An expression has been developed in the analytical phase for calculating the vertical load on a conduit buried under a sloping ground surface. Using the arching phenomenon, the soil over the buried conduit (inner soil prism) was assumed to yield relative to the adjacent stationary soil mass. Thereafter, the concept of stress transformation has been used to calculate the stresses on a soil element located under a sloping surface, which have been defined along inclined principal planes. The results obtained from the developed analytical expression show that a 10-degree increment in slope angle increases the vertical load on a conduit by about 19.87%. The results of the derived analytical expression have also been compared with numerically obtained results for illustrating the accuracy of the developed expression.
For data analytic methods, extensive finite element modelling (FEM) has been conducted to generate a large-scale dataset. The FEM allows incorporating a wide range of input parameters used to define different types of soils and buried conduits, and their intricate relationships, on the model outputs. The generated FEM-based dataset has been used to build various artificial intelligent (AI) models. The predictive strength of the models has been checked through crossvalidation approach, rigorous statistical testing, and multi-criteria approach. This approach has been utilized for estimating the width of Marston’s soil prism for the reinforced concrete and corrugated steel conduits, and the settlement of a footing located over a conduit buried within a soil slope. For the estimation of the Marston’s soil prism, Artificial Neural Network (ANN) model appeared to be the most accurate for reinforced concrete ( R2 = 0.983, MSE = 0.1268, RMSE = 0.356, and MAE = 0.247), and corrugated steel ( R2 = 0.959, MSE = 0.0166, RMSE = 0.128, and MAE = 0.045) conduits. Whereas, for estimation of the settlement of a footing located over a conduit buried within a soil slope, Multi-layer perceptron (MLP) has been the most accurate with r, RMSE, NSE, SI, and RPD values of 0.974, 0.323, 0.928, 0.44, and 3.75, respectively, and highest ranking (total score = 48). The aforementioned accurate models have been employed to develop simple mathematical equations for the convenient use of practicing engineers.
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Hermle, Sandra. "Reactions of a young forest ecosystem to heavy metal stress in the soil /". Zürich, 2004. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=15723.
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Dyer, M. R. "Observation of the stress distribution in crushed glass with applications to soil reinforcement". Thesis, University of Oxford, 1985. http://ora.ox.ac.uk/objects/uuid:98dee0c7-5e27-45b7-aef8-01bd56240671.
Testo completoAbstract (sommario):
The research described in this dissertation follows on from the study made by Jewell (1980)into the effects of tensile reinforcement on the mechanical behaviour of sand. For this study Jewell used the direct shear test with reinforcement placed about the central plane as shown in fig. 1.1. The direct shear test was chosen for the following reasons. (1) The reinforcement variables could be better controlled and examined in a unit cell test than in modular field studies of soil reinforcement systems. (2) The pattern of deformation is similar to that experienced by soil in which a rupture band develops, with the principal axes of stress, strain and strain increment free to rotate as is the case in model and field structures. (3) The overall shear strength of the sample is measured directly at the boundaries of the apparatus. The direct shear tests were monitored by boundary measurements and internal measurements using a radiographic technique. The findings are outlined below with reference made to relevant observations by other researchers. 1) The optimum orientation for a relatively flexible steel grid was found to be approximately along the direction of principal tensile strains in the unreinforced sand, see fig.1.2. This indicated that the reinforcement functioned by limiting tensile strains in the sand. McGown et al. (1978) obtained a similar result for plane strain cell tests on sand containing a single layer of flexible reinforcement. However in both studies the reinforcement was observed to waken the sand. Jewell recognized weakening to occur when the steel grid was placed along the direction of principal compressive strains in the unreinforced sand. This was attributed to a reduction in vertical effective stress. McGown et al. observed weakening of the sand when the reinforcement orientation approached the rupture band which developed in the sand alone. This was recognized to be the direction of zero-extension in the unreinforced sand. The weakening was linked to a lower bond between soil and reinforcement than soil alone. 2) Internal strains determined by Jewell showed the tensile reinforcement modified strains in the sand over a well defined zone, see fig.1.3. This resulted in a significant rotation of principal axes of strain increment, with the bond of major strains which developed across the centre of the box in the unreinforced sand being prohibited from forming. This agreed with boundary measurements, indicating the reinforcement functioned by limiting tensile strains in the sand. Consequently a less favourable mode of failure took place. The limit of rotation of principal axes of strain increment was understood to be the alignment of a direction of zero-extension in the sand with the reinforcement. These findings agree with the ideas expressed by Basset and Last (1978) on the mode of action of tensile reinforcement, which in particular was related to the effect of tensile reinforcement on the strain field in a reinforced earth wall as shown in fig.1.4. 3) For efficient use of tensile reinforcement it was demonstrated that the bond with sand should be as high as possible. This could be achieved by roughening the surface. Alternatively, the bond was improved by introducing openings or apertures in the reinforcement, changing the shape to a grid. It appeared that the bond for a suitably proportioned grid could be as high as for a fully roughened surface. 4) The longitudinal stiffness of tensile reinforcement was observed to affect the magnitude and rate of increase in strength in the direct shear tests. The rupture strain of tensile reinforcement relative to maximum tensile strains of the soil, under the same operational stress conditions, have also been observed to influence the reinforcing effect in terms of its limiting behaviour, i.e. whether brittle or ductile (McGown, et al. 1978). With regards to the performance of reinforced earth walls, Al-Hussanini and Perry (1976) observed that steel reinforced strips produced a stiffer and stronger structure than a more extensible fabric reinforcement, even though surface roughness was less. The importance of reinforcement tensile stiffness is recognized in limit equilibrium designs for tensile reinforced soil structures by limiting the available reinforcement force to the tensile strains that can develop in the soil (e.g. Jewell 1985). For highly structured non-woven and composite geotextiles, McGown et al. (1982) demonstrated that the stress-strain behaviour can be significantly affected by soil confinement. Testing wider strips in isolation was not found to replicate the effects of soil confinement. Another factor which needs to be considered when assessing the tensile property of a polymer reinforcement is creep. McGown et al. (1984) illustrated an appropriate method of interpreting creep data using isochronous curves, which enable long term laboratory test data to be extrapolated to the design life of the soil structure. 5) The strain and hence stress fields in the reinforced direct shear tests have been shown to be complex and non-uniform. However Jewell successfully modelled the variation of reinforcing effect for tensile reinforcement at different orientations by using a simple limit equilibrium analysis, see fig.1.5. The effect of the tensile reinforcement force was represented as: - an increase in the normal effective stress acting on the central plane of the box due to the normal component of the force and - a reduction in the applied shear stress due to the parallel component of the force to the central plane. Subsequently this analysis has been applied to limit equilibrium design methods for reinforcing soil retaining walls and embankments, Jewell et al. 1984, and Jewell 1982 respectively. 6) A reduction in the reinforcing effect for individual reinforcement due to the presence of other reinforcement was observed in the shear box. This loss of efficiency of individual reinforcement was termed interference. Interference between tensile reinforcement has also been studied by Guilloux et al. (1979) for the pull-out resistance from soil. However interference between reinforcement has yet to be introduced into a limit equilibrium design method.
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ALEIXO, MARCONI SOARES. "STRESS - STRAIN BEHAVIOR OF A GNEISS RESIDUAL SOIL USING THE CUBIC TRIAXIAL CELL". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1998. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=1526@1.
Testo completoAbstract (sommario):
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORO conhecimento do comportamento de solos residuais é de grande importância para projetos geotécnicos no Brasil e, em particular, na região do Rio de Janeiro, tendo em vista que o clima tropical e as características geológicas favorecem a ocorrência de mantos residuais de grande espessura. O presente trabalho trata do estudo do comportamento tensão-deformação de um solo residual proveniente de um perfil de alteração de rocha gnáissica do maciço da Tijuca, Rio de Janeiro. Como os solos residuais gnáissicos preservam as foliações herdadas da rocha matriz, investigou-se em particular a relevância de se considerar a ocorrência de anisotropia nas características de resistência e deformabilidade destes solos. No estudo foi utilizado o equipamento triaxial cúbico desenvolvido na PUC-Rio. Este equipamento possibilita o controle independente das três tensões principais, sendo mais adequado para a reprodução das trajetórias de tensões tridimensionais, usualmente associadas com obras geotécnicas no campo, e em particular, para estudos sobre as características de anisotropia de solos. O programa experimental constou de ensaios de compressão axial e hidrostática, sob condições drenadas de carregamento, utilizando o equipamento triaxial cúbico. Foram realizados também ensaios oedométricos convencionais, de modo a se obter as características de compressibilidade do solo. Foram moldados corpos de prova a partir de blocos indeformados, paralelos e perpendiculares à foliação observada no solo, o que possibilitou a análise dos resultados para direções distintas de carregamento. Para efeito de comparação sobre a relevância do arranjo estrutural dos grãos do solo, foram ensaiados também corpos de prova compactados dos mesmos materiais. A análise dos resultados permitiu a obtenção dos módulos de deformabilidade e dos parâmetros de resistência do solo residual. Em particular, foram verificados os efeitos da direção de carregamento dos corpos de prova, do nível das tensões de confinamento, do grau de intemperismo, do arranjo estrutural dos grãos e dos efeitos do grau de saturação. Pode-se concluir que os solos estudados não apresentaram efeitos marcantes de anisotropia nas características de resistência. No entanto, quanto à deformabilidade, pode-se considerar que o solo residual jovem apresentou características anisotrópicas.
The knowledge of the mechanical behaviour of residual soils is of great importance in geotechnical projects, because of its abundance in tropical regions, such as Brazil and particularly in the area of Rio de Janeiro. The present work presents a study on the fundamental stress-strain behaviour of a residual soil resulting from a profile of a gneiss rock in Rio de Janeiro. As the gneiss residual soils preservethe bedding planes from the parent rock, the relevance of considering anisotropy in the stress- strain characteristics of these soils was investigated. The cubic triaxial equipment developed at PUC-Rio was used in this research. This equipment allows the independent control of the three principal stresses, allowing the reprodution of three-dimensional stress paths, usually associated with geotechnical works in the field. The experimental program consisted of axial and hidrostatic tests, under drained loading conditions, using the cubic triaxial equipment. One- dimensional oedometer tests were also performed, in order to obtain the compressibility characteristics of the residual soil. Undisturbed specimens were prepared with the bedding planes parallel or perpendicular to the loading direction. Analysis of the test results showed the effects of load direction, confining stress level, weathering degree, structural soil fabric and saturation degree. It may be concluded that the gneiss residual soils which were selected for this research do not present significant effects of anisotropy in the strength characteristics. In the stress- strain characteristics, however, it may be concluded that the young residual soil showed effects of anisotropy.
EL conocimiento sobre el comportamiento de suelos residuales resulta de gran importancia para los proyectos geotécnicos en Brasil y, en particular, en la región de Rio de Janeiro, considerando que el clima tropical y las características geológicas favorecen la existencia de mantos residuales de gran espesor. El presente trabajo estudia el comportamiento tensión-deformación de un suelo residual proveniente de un perfil de alteración de roca gnáisica del macizo de la Tijuca, Rio de Janeiro. Como los suelos residuales gnáisicos preservan las foliaciones heredadas de la roca matriz, fue necesario estudiar si resultaba relevante considerar la aparición de anisotropía en las características de resistencia y deformabilidad de estos suelos. En el estudio se utilizó el equipo triaxial cúbico desarrollado en la PUC-Rio. Este equipo permite el control independente de las tres tensiones principales, siendo más adecuado para la reproducción de las trayectorias de tensiones tridimensionales, usualmente asociadas a obras geotécnicas en el campo, y en particular, para estudios sobre las características de anisotropía de suelos. El programa experimental incluyó ensayos de compresión axial e hidrostática, sobre condiciones drenadas de carga, utilizando el equipo triaxial cúbico. Fueron realizados también ensayos oedométricos convencionales, con el objetivo de obtener las características de compresibilidad del suelo. Fueron moldados cuerpos de prueba a partir de bloques no deformados, paralelos y perpendiculares a la foliación observada en el suelo, lo que permitió el análisis de los resultados para distintas direcciones de carga. Para efecto de comparación sobre la relevancia del arreglo extructural de los granos del suelo, se realizaron ensayos con cuerpos de prueba compactados de los mismos materiales. El análisis de los resultados permitió la obtención de los módulos de deformabilidad y de los parámetros de resistencia del suelo residual. En particular, se verificaron los efectos de la dirección de carga de los cuerpos de prueba, del nível de las tensiones de contensión, del grado de intemperización, de la disposición extructural de los granos y de los efectos del grado de saturación. Se puede concluir que los suelos estudiados no presentaran efectos marcantes de anisotropía en las características de resistencia. Sin embargo, con respecto a la deformabilidad, se puede considerar que el suelo residual joven presentó características anisotrópicas.
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Corral, Jofré Gonzalo Andrés. "Re-analysis of deep excavation collapse using a generalized effective stress soil model". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/60759.
Testo completoAbstract (sommario):
Thesis (Civ. E.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 137-138).
This thesis re-analyzes the well-documented failure of a 30m deep braced excavation underconsolidated marine clay. Prior analyses of the collapse of the Nicoll Highway have relied on simplified soil models with undrained strength parameters based on empirical correlations and piezocone penetration data. In contrast, the current research simulates the engineering properties of the key Upper and Lower Marine Clay units using a generalized effective stress soil model, MIT-E3, with input parameters calibrated using laboratory test data obtained as part of the post-failure site investigation. The model predictions are evaluated through comparisons with monitoring data and through comparisons with results of prior analyses using the Mohr-Coulomb (MC) model. The MIT-E3 analyses provide a modest improvement in predictions of the measured wall deflections compared to prior MC calculations and give a consistent explanation of the bending failure in the south diaphragm wall and the overloading of the strut-waler connection at the 9th level of strutting. The current analyses do not resolve uncertainties associated with performance of the JGP rafts, movements at the toe of the north-side diaphragm wall or discrepancies with the measured strut loads at level 9. However, they represent a significant advance in predicting excavation performance based directly on results of laboratory tests compared to prior analyses that used generic (i.e., non site-specific) design isotropic strength profiles.
by Gonzalo Andrés Corral Jofré.
Civ.E.
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Panwar, Anurag. "Determining the Effectiveness of Soil Treatment on Plant Stress using Smart-phone Cameras". Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6346.
Testo completoAbstract (sommario):
Plants are vital to the health of our biosphere, and effectively sustaining their growth is fundamental to the existence of life on this planet. A critical aspect, which decides the sustainability of plant growth is the quality of soil. All other things being fixed, the quality of soil greatly impacts the plant stress, which in turn impacts overall health. Although plant stress manifests in many ways, one of the clearest indicators are colors of the leaves. In this thesis, we conducted an experimental study in a greenhouse for detecting plant stress caused by nutrient deficienceies in soil using smartphone cameras, coupled with image processing and machine learning algorithms. The greenhouse experiment was conducted by growing two plant species; willows (Salix Pentandra) and poplars (Populus deltoides x nigra, DN34), in two treatments. These treatments included: unamended tailings (collected from a lead mine tailings pond and characterized by nutrient deficiency), and biosolids amended tailings. Biosolids are very rich in nutrients and were added to the tailings in one of the two treatments to supply plants with nutrients. Subsequently, we captured various images of plant leaves grown in both soils. Each image taken was pre-processed via filteration to remove associated noise, and was segmented into pixels to facilitate scalability of analysis. Subsequently, we designed random forests based algorithms to detect the stress of leaves as indicated by their coloring. In a dataset consisting of 34 leaves, our technique yields classifications with a high degree of prediction, recall and F1 score. Our work in this thesis, while restricted to two types of plants and soils, can be generalized. We see applications in the emerging area of urban farming in terms of empowering citizens with tools and technologies for enhancing quality of farming practices.
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Mahaman, Sabiou 1957. "Nitrogen requirements of grain sorghum (Sorghum bicolor (L.) Moench) under soil moisture stress". Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277251.
Testo completoAbstract (sommario):
Water and fertilizers are the two major agricultural inputs limiting yields in the arid and semi-arid regions of the world. Proper knowledge of their influence on crops should be obtained for appreciable returns. Therefore, a field study was conducted to evaluate the effects of four nitrogen (N) treatments (0, 56, 112, and 168 kg N/ha), two water (M) levels (39 and 58 cm), and two varieties (V) (Funks G-522DR and Conlee Rusler) on dry matter production, total N concentration, and yield of grain sorghum (Sorghum bicolor (L.) Moench). Total N concentration, dry matter, and grain yield were increased by N treatments. Generally, the highest N rate gave the most significant effects; the other rates had statistically the same responses. Varieties were different in their dry matter and grain yields, but had the same total nitrogen contents, as was suggested by the ANOVA and means analysis. There were no detectable interactions among the factors. Moisture had minimal effect on dry matter and grain yields, but influenced total N concentration significantly. Nitrogen contents increased with the higher moisture level.
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Wongareonwanakij, Sathaporn. "Effects of water stress and partial soil-drying on senescence of sunflower plants". Title page, contents and summary only, 1995. http://web4.library.adelaide.edu.au/theses/09A/09aw872.pdf.
Testo completoAbstract (sommario):
Bibliography: leaves 98-123. This thesis investigates the symptoms of leaf senescence in response to plant shoot water stress and demonstrates the effect of a non-hydraulic root signal in the senescence response of mature leaves of sunflower. The alleviation of the leaf soluble protein loss rate by excision of the root system in drying soil indicates that this signal originates in roots in dry soil and acts to promote protein loss.
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Jessett, Clifford Alan. "Investigation of the liquefaction of a soil profile using in situ tests". Thesis, City University London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316399.
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Menkiti, Ogugua Christopher. "Behaviour of clay and clayey-sand, with particular reference to principal stress rotation". Thesis, Imperial College London, 1995. http://hdl.handle.net/10044/1/8035.
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