Thèses : « Spatial variability of soils »

1

Young, Fred J. « Spatial variability of soil properties within a loess-covered, upland landscape / ». free to MU campus, to others for purchase, 1996. http://wwwlib.umi.com/cr/mo/fullcit?p9823319.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

2

Kim, Hyunki. « Spatial variability in soils stiffness and strength / ». Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-07132005-194445/.

Texte intégral

Résumé :

Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006.
Mayne, Paul, Committee Member ; Frost, David, Committee Member ; Santamarina, Carlos, Committee Chair ; Rix, Glenn, Committee Member ; Ruppel, Carolyn, Committee Member.

Styles APA, Harvard, Vancouver, ISO, etc.

3

Hendrayanto. « Analyses on Spatial Variability in Hydraulic Properties of Forest Soils ». Kyoto University, 1999. http://hdl.handle.net/2433/181882.

Texte intégral

Résumé :

Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第7873号
農博第1031号
新制||農||775(附属図書館)
学位論文||H11||N3236(農学部図書室)
UT51-99-G467
京都大学大学院農学研究科森林科学専攻
(主査)教授水山高久, 教授三野徹, 教授吉田博宣
学位規則第4条第1項該当

Styles APA, Harvard, Vancouver, ISO, etc.

4

El-Haris, Mamdouh Khamis. « Soil spatial variability : Areal interpolations of physical and chemical parameters ». Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184290.

Texte intégral

Résumé :

Four fields of 117 ha area located at the University of Arizona's Maricopa Agricultural Center were selected for this study. Two soil series, the Casa Grande sandy clay loam and Trix clay loam occur. Surface samples (0-25 cm) were collected on a 98 m interval and 3 rows providing 47 sites per field. Sites were classified either as surveying (32) or testing (15) in each of the four fields. Additional samples at 25-50, 50-75, 75-100, and 100-125 cm were obtained with duplicate surface undisturbed cores at 5 sites per field. Soil parameters include bulk density, saturated hydraulic conductivity, moisture retention, particle size analysis, pH, EC, soluble cations, SAR, and ESP. A quantification of the spatial interdependence of samples was developed based on the variogram of soil parameters. A linear model was best fitted to the clay, EC, Ca²⁺, Mg²⁺, Na⁺, SAR and ESP, and a spherical model to the sand, silt, pH, and K⁺ observed variograms. A comparison of variograms obtained conventionally and with the robust estimation of Cressie and Hawkins (1980) for sand and Ca²⁺ were performed with a fixed couples number per class and with a fixed class size. Additionally, a negative log-likelihood function along with cross-validation criteria were used with the jackknifing method to validate and determine variogram parameters. Three interpolation techniques have been compared for estimating 11 soil properties at the test sites. The techniques include Arithmetic Mean, Inversely Weighted Average, and Kriging with various numbers of neighbor estimates. Using 4 point estimates resulted in nearly identical results, but the 8 point estimates gave more contrast for results among the alternative techniques. Jackknifing was used with 4, 8, 15, 25 neighbors for estimating 188 points of sand and Ca²⁺ with the three techniques. Sand showed a definite advantage of Kriging by lowering the Mean Square Error with increasing neighbor number. The simple interpolator Arithmetic Mean was comparable and sometimes even better than the other techniques. Kriging, the most complex technique, was not the absolute best interpolator over all situations as perhaps expected. The spatial dependence for the 11 soil variables was studied by preparing contour maps by punctual Kriging. Sand and Ca²⁺ were also mapped by block Kriging estimates.

Styles APA, Harvard, Vancouver, ISO, etc.

5

Okae-Anti, Daniel Theophilus Akwa. « Spatial variability studies in relation to pedogenic processes in alluvial soils ». Thesis, University of Reading, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239027.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

6

Saez, Carolin Cordova. « Spatial variability of soil organic matter fractions in arable and grassland soils - implications for soil N supply ». Thesis, University of Reading, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542058.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

7

Huang, Xuewen. « Analysis of effects of soil properties, topographical variables and management practices on spatial-temporal variability of crop yields ». Diss., Connect to online resource - MSU authorized users, 2008.

Trouver le texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

8

Parker, Ronald Dean 1948. « The effect of spatial variability on output from the water erosion prediction project soil erosion computer model ». Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/191165.

Texte intégral

Résumé :

Spatial variability is all that stands between hydrology and science, forcing us to deal in probabilities and averages. Because of scale, we can not consider forces on individual soil particles, water molecules and solute ions when addressing human size problems. We must therefore look at aggregate properties and mean values for parameters and inputs in computer modeling of hydrologic phenomena. This research explores the impact of spatially variable inputs on the Water Erosion Prediction Project soil erosion computer program. Distributions of input variables are generated and assigned randomly to a grid of homogeneous rangeland hillslope elements. Values for runoff volume and sediment loss from each flow path are recorded and averaged to provide a distribution of outputs in the form of a sensitivity analysis. Variabilities of slope, slope length, soil textures, soil characteristics, terrain, convex and concave slopes, soil saturation, rainfall amount and vegetation were examined. Results show that use of mean inputs values in the WEPP representative hillslope model yields very similar outputs to the spatially variable research model using a distribution of inputs in all simulations in the case of totally random bare rangeland soils. When a decreasing trend in soil clay content is introduced in the variable model, the hillslope model using average values as inputs no longer provides a good estimate of the sediment loss. When random vegetation is generated and added to the simulation, runoff volume continues to be similar between the two models, but the sediment loss is much higher in the spatially variable model. In addition, the results of the standard hillslope model are much less responsive to changes in slope than those of the spatially variable model. It is concluded that spatial variability of soils must be considered when there is a linear change in input values with slope position. Likewise spatial variability of vegetation needs to be addressed in order to accurately estimate erosion on the rangeland watersheds considered in this dissertation. It is also found that this type of simulation provides a model for sensitivity analysis of a complex computer programs. Physically related inputs can be generated in such a way as to preserve the desired interrationships and distributions of inputs can be directly compared to generated distributions of outputs.

Styles APA, Harvard, Vancouver, ISO, etc.

9

Schöning, Ingo. « Organic matter stocks in temperate forest soils composition, radiocarbon age and spatial variability / ». [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=978952839.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

10

Suliman, Ahmed Saeid Ahmed. « Spectral and spatial variability of the soils on the Maricopa Agricultural Center, Arizona ». Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184678.

Texte intégral

Résumé :

Dry and wet fine earth spectral measurements were made on the Ap soil surface horizons on the Maricopa Agricultural Center by using a Barnes Modular Multiband Radiometer. Three subsets were used in the analyses 552, 101 and 11. There were three soil series, Casa Grande, Shontik and Trix, four soil mapping units, and three texture classes identified on the farm. The wet soil condition reduced the amplitude of the spectral curves over the entire spectrum range (0.45 to 2.35 μm). The spectral curves were statistically related to the soil mapping units to determine if the soil mapping units and texture classes could be separated. The wet soil condition and the smaller sample size increased the correct classification percentages for soil mapping units and texture classes. LSD tests showed there were significant differences between these groups. Simple- and Multiple-linear regression analysis were used to relate some soil physical (sand, silt and clay contents and color components) and chemical (iron oxide, organic carbon and calcium carbonate contents) to soil spectral responses in the seven bands under dry and wet conditions. There were high correlations levels among the spectral bands showing an overlap of spectral information. Generally, the red (MMR3) and near-infrared (MMR4) bands had the highest correlations with the studied soil properties under dry and wet conditions. Usually, the wet soil condition resulted in higher correlations than that for the dry soil condition over the total spectrum range. The predictive equations for sand, silt and clay and iron oxide contents were satisfactory. For organic carbon and color components, the greatest success was achieved when variation in spectral response within individual samples are smaller than that between soil mapping unit group averages. There was a poor relation between calcium carbonate and spectral response. A comparison of multi-level remotely sensed data collected by SPOT, aircraft, and ground instruments showed a strong agreement among the data sets, which correlated well to fine earth data, except for the SPOT data. Rough soil surfaces showed a reduction in reflectance altitude compared to laser level, and it appears to be directly proportional to the percent shadow in the viewing area measured by SPOT satellite and aircraft.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Amajuoyi, Ifeanyichukwu Larry. « Spatial variability of some selected chemical soil properties in forest soils under shifting cultivation in southeast Nigeria ». Thesis, University of Reading, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270420.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

12

Manyevere, Alen. « Evaluation and mapping of the spatial variability of soil fertility at Zanyokwe Irrigation Scheme in the Eastern Cape, South Africa ». Thesis, University of Fort Hare, 2010. http://hdl.handle.net/10353/d1001019.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

13

Ryan, Andrea L. « Assessment of spatial variability of silage corn quality and biomass using remote sensing and GIS techniques ». Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/30294.

Texte intégral

Résumé :

The Matsqui area of the Lower Fraser Valley exhibits extreme soil heterogeneity, as the alluvial soils in the area have been deposited by the Fraser River as a series of coarse-textured ridges and finer-textured depressional areas. This variability poses some obvious problems with respect to agricultural management. The main aim of this study was to evaluate soil spatial variability in four fields, and to relate this soil variability to corn production and quality. Site conditions, topography, and soil chemical and physical variables were related to corn biomass and nutrient concentrations using conventional correlation/regression analyses, and more spatially representative techniques such as those provided by remote sensing and geographic information systems. Variations in such biophysical variables as soil moisture, elevation, and bulk density had consistent impacts on corn productivity, although these effects varied from field to field, being influenced by inherent soil properties and individual field management. Good relationships were found between pixel brightness values extracted from digitized colour infra-red photos and corn quality variables. In three out of four fields, near infra-red pixel values gave good estimates of total corn crude protein content. Significant relationships were also found between pixel brightness values and corn phosphorus and calcium contents in certain fields. The spatial variability of corn quality and biomass could be quantified using image analysis classification techniques. The resulting classified images indicate to the farm operator where high vs low quality corn is being produced, and thereby provide a tool for selectively managing and harvesting the fields. The relationships and quantification of corn productivity and quality in the fields can further be improved through incorporation of the image data with the biophysical data base using GIS techniques. A multiple regression equation showing a significant relationship between elevation and pixel brightness values, and total corn phosphorus concentration was incorporated within the GIS to produce a quantitative corn quality map for the field exhibiting this relationship. The GIS overlay capability facilitates the classification of several corn variables, and allows the results to be displayed in a spatial manner. For example, corn biomass and quality maps were overlain using GIS techniques, to produce a combination map which then reflected both the quality and quantity of corn found in the field. Through integration of remote sensing and GIS techniques, soil and crop variability can be displayed in a spatial manner. The output from such procedures can aid farm operators in making selective field management and harvesting decisions.
Land and Food Systems, Faculty of
Graduate

Styles APA, Harvard, Vancouver, ISO, etc.

14

Fletcher, Cheryl Florence. « Spatial variability of weeds, soils and crops in fields of the south Peace River region, Alberta ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ40049.pdf.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

15

Zhang, Xi. « SPATIAL ESTIMATION OF HYDRAULIC PROPERTIES IN STRUCTURED SOILS AT THE FIELD SCALE ». UKnowledge, 2019. https://uknowledge.uky.edu/pss_etds/117.

Texte intégral

Résumé :

Improving agricultural water management is important for conserving water during dry seasons, using limited water resources in the most efficient way, and minimizing environmental risks (e.g., leaching, surface runoff). The understanding of water movement in different zones of agricultural production fields is crucial to developing an effective irrigation strategy. This work centered on optimizing field water management by characterizing the spatial patterns of soil hydraulic properties. Soil hydraulic conductivity was measured across different zones in a farmer’s field, and its spatial variability was investigated by using geostatistical techniques. Since direct measurement of hydraulic conductivity is time-consuming and arduous, pedo-transfer functions (PTFs) have been developed to estimate hydraulic conductivity indirectly through more easily measurable soil properties. Due to ignoring soil structural information and spatial covariance between soil variables, PTFs often perform unsatisfactorily when field-scale estimations of hydraulic conductivity are needed. The performance of PTFs in estimating hydraulic conductivity in the field was therefore critically evaluated. Due to the presence of structural macro-pores, saturated hydraulic conductivity (Ks) showed high spatial heterogeneity, and this variability was not captured by texture-dominated PTF estimates. However, the general spatial pattern of near-saturated hydraulic conductivity can still be reasonably generated by PTF estimates. Therefore, the hydraulic conductivity maps based on PTF estimates should be evaluated carefully and handled with caution. Recognizing the significant contribution of macro-pores to saturated water flow, PTFs were further improved by including soil macro-porosity and were proven to perform much better in estimating Ks compared with established PTFs tested in this study. Additionally, the spatial relationship between hydraulic conductivity and its potential influencing factors were further quantified by the state-space approach. State-space models outperformed current PTFs and effectively described the spatial characteristics of hydraulic conductivity in the studied field. These findings provided a basis for modeling water/solute transport in the vadose zone, and sitespecific water management.

Styles APA, Harvard, Vancouver, ISO, etc.

16

van, Haren Joost Lambertus Maria. « Spatial and Temporal Variability of Soil CO2 and N2O Fluxes in Tropical Forest Soils : the Influence of Tree Species, Precipitation, and Soil Texture ». Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145108.

Texte intégral

Résumé :

The tropics are the largest natural source of CO2 and N2O to the atmosphere and many tropical forests are changing due to climate change and forest fragmentation. To understand how these changes are affecting ecosystem feedbacks to climate change we need to investigate the plant-soil interactions in tropical forests on both local and regional scale. Locally, tree species do influence soil N2O fluxes and biogeochemistry in diverse forests. I found N2O fluxes close to four out of fifteen tree species consistently elevated above the overall mean and consistently low near two other species. However, only large (20%) changes in species composition would cause an appreciable effect on the landscape-scale forest flux. Experimental sugar additions elevated, whereas root abscission by permanently installed chambers reduced N2O fluxes, suggesting that N2O cycling is mostly driven by heterotrophic (carbon-limited) denitrifiers, and that carbon transport into the soil by trees may present a mechanism for the observed differences. To isolate species effects on soil processes, I investigated tropical monoculture plantation soil gas fluxes. As in the natural forest, flux differences were associated with tree species identity, though species N2O flux rank order on the plantation was unlike the forest, indicating that monoculture plantation plots are not generally informative for species influence on soil processes in diverse forests. Fast tree growth rates and overall lower fluxes of CO2 and N2O from plantation vs. natural forest or agricultural soils suggest that plantations initiated on abandoned farmland may reduce tropical ecosystem greenhouse gas fluxes. Motivated by the finding that tree carbon export may influence soil N2O fluxes, I investigated the effect of stand level growth rates on regional N2O flux variation and found that spatial and temporal N2O flux variability in the Amazon basin is significantly and positively correlated with forest growth rates. Extrapolating this correlation across the Amazon basin yields a mean soil N2O flux of 2.6 kg-N ha-1 -1 , higher than previously estimated. My work, through accounting for the processes that link vegetation carbon dynamics to soil biogeochemistry, indicates that tropical forests may be a bigger contributor to global N2O budget than previously thought.

Styles APA, Harvard, Vancouver, ISO, etc.

17

Narsilio, Guillermo Andres. « Spatial Variability and Terminal Density -Implications in Soil Behavior- ». Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10462.

Texte intégral

Résumé :

Geotechnical engineers often face important discrepancies between the observed and the predicted behavior of geosystems. Two conceptual frameworks are hypothesized as possible causes: the ubiquitous spatial variability in soil properties and process-dependent terminal densities inherent to granular materials. The effects of spatial variability are explored within conduction and diffusion processes. Mixtures, layered systems, inclusions and random fields are considered, using numerical, experimental and analytical methods. Results include effective medium parameters and convenient design and analysis tools for various common engineering cases. In addition, the implications of spatial variability on inverse problems in diffusion are numerically explored for the common case of layered media. The second hypothesis states that there exists a unique terminal density for every granular material and every process. Common geotechnical properties are readily cast in this framework, and new experimental data are presented to further explore its implications. Finally, an unprecedented field study of blast densification is documented. It involves comprehensive laboratory and site characterization programs and an extensive field monitoring component. This full scale test lasts one year and includes four blasting events.

Styles APA, Harvard, Vancouver, ISO, etc.

18

Li, Yixiang Li. « Numerical modeling of supported excavations considering soil spatial variability ». University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1510322541966921.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

19

Greenholtz, Deborah Esther 1958. « Spatial variability of hydrologic properties in an irrigated soil ». Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/278505.

Texte intégral

Résumé :

The spatial and temporal variability of water content, soil water tension, and derived hydraulic conductivity parameters are analyzed using geostatistical methods. The measured data sets were obtained from a 1985 experiment near Las Cruces, New Mexico. Post-irrigation water content and tension measurements had been recorded over 44 days at 455 sampling locations along a 91 x 1.5-meter transect. Unsaturated hydraulic conductivity values are derived using the instantaneous profile formula, and an exponential model is used to obtain values of saturated hydraulic conductivity and pore-size distribution parameters. The exponential model is found to inadequately describe the conductivity data for tensions near saturation, because excessively large saturated hydraulic conductivity values are derived. Semivariogram analysis shows ranges of dependence of three to 32 meters for water content and six to 34 meters for tension. As water content decreases, the coefficient of variation and variance are found to increase.

Styles APA, Harvard, Vancouver, ISO, etc.

20

Phefadu, Kopano Conferance. « Physico-chemical characterization and spatial variability of soils in the research block at University of Limpopo Experimental Farm ». Thesis, University of Limpopo, 2015. http://hdl.handle.net/10386/1686.

Texte intégral

Résumé :

Thesis (MSc. (Soil Science)) -- University of Limpopo, 2015
There exists a considerable level of spatial variability in soil physical and chemical properties within the research block; and the soils are generally shallow. Of all the measured parameters, electrical conductivity, Bray-1 P, exchangeable potassium, calcium and sodium as well as extractable iron and zinc showed a huge percent of variation across the field. Soil variability maps indicated the degree of variability within the research block. The spatial variability of the characterized parameters was significant across the research block. A correlation study was conducted to investigate the relationship between the measured soil physical and chemical properties. Regular soil analyses should be conducted to avoid failure/delay of experiments. It is recommended that inputs such as irrigation and fertilizer application must be varied based on varying soil conditions across the research block.
VLIR project 6 leaders

Styles APA, Harvard, Vancouver, ISO, etc.

21

Smith, Richard D. « Desertification, overgrazing and soil spatial variability in an arid savanna ». Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327643.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

22

FLORES, EMERSON ALEX FIGUEROA. « PROBABILISTIC ANALYSIS OF SLOPE STABILITY CONSIDERING SPATIAL VARIABILITY OF SOIL ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2008. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=12093@1.

Texte intégral

Résumé :

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
Freqüentemente as análises de estabilidade de taludes são feitas por métodos determinísticos, nos quais é obtido um Fator de Segurança (FS). Estes métodos não quantificam as incertezas existentes nas variáveis de entrada (parâmetros de resistência) na análise. Tampouco mostram detalhes sobre qual variável afeta mais o resultado. Os métodos probabilísticos permitem superar estes problemas. A presente pesquisa tem como objetivo comparar dois métodos probabilísticos geralmente utilizados (Estimativas Pontuais e Segundo Momento). Três projetos utilizados comumente na geotecnia são analisados: barragem de rejeitos, talude de solo e aterro sobre argila mole.Um aspecto importante na análise probabilística é a quantificação adequada do desvio padrão. É sabido que as propriedades dos solos mostram uma correlação no espaço, pelo que o desvio padrão calculado por métodos clássicos da estatística é superestimado em comparação ao valor real no campo. El-Ramly (2001) desenvolveu uma metodologia para o cálculo da probabilidade de ruptura considerando a correlação espacial das propriedades do solo. Esta metodologia é de difícil aplicação prática. Serão, portanto, avaliadas na presente pesquisa as técnicas geralmente usadas de probabilidade e estabilidade de taludes, juntamente com um fator de correção proposto por Vanmarcke (1977a). Estas técnicas de probabilidade de estabilidade de taludes são factíveis de serem utilizadas junto com este fator de correção. Verificou-se que o Método de Segundo Momento é de mais fácil utilização, e portanto adequado para emprego em projetos geotécnicos.
The analysis of slope stability is often determined by deterministic methods, in which a Factor of Security (FS) is obtained. These methods do not quantify the uncertainty in the input variables (strength parameters). Neither these methods show details which variable affects mostly the outcome results. The probabilistic methods allow overcoming these restrictions. This study aims at comparing two probabilistic methods of general use (Point Estimates and First Order Second Moment). Three projects commonly used in geotechnical engineering are analyzed: tailings dam, slope soil and embankment on soft clay. An important aspect of the probabilistic analysis is the proper quantification of the standard deviation. It is known that the soil properties show a correlation in space, so the standard deviation, calculated by traditional methods of statistics, is overestimated when compared to the real field value. El-Ramly (2001) developed a methodology for calculating the probability of failure considering the spatial correlation of the soil properties. This methodology is difficult to apply in practice. The present study will therefore evaluate the techniques generally used in probability of failure of slopes. These probability techniques applied to slope stability can be used together with a correction factor proposed by Vanmarcke (1977b). The Second Moment Method was found to be easier to use, and therefore more suitable for geotechnical projects.

Styles APA, Harvard, Vancouver, ISO, etc.

23

Blumenthal, Kinsey Megan. « Predicting Spatial Variability of Soil Organic Carbon in Delmarva Bays ». Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/73692.

Texte intégral

Résumé :

Agricultural productivity, ecosystem health, and wetland restoration rely on soil organic carbon (SOC) as vital for microbial activity and plant health. This study assessed: (1) accuracy of topographic-based non-linear models for predicting SOC; and (2) the effect of analytic strategies and soil condition on performance of spectral-based models for predicting SOC. SOC data came from 28 agriculturally converted Delmarva Bays sampled down to 1 meter. R2 was used as an indicator of model performance. For topographic-based modeling, correlation coefficients and condition indices reduced 50 terrain-related values to three datasets of 16, 11, and 7 variables. Five types of non-linear models were examined: Generalized Linear Mondel (GLM) ridge, GLM LASSO, Generalized Additive Model (GAM) non-penalized, GAM cubic splice, and partial least-squares regression. Carbon stocks varied widely, 50 to 219 Mg/ha, with the average around 93 Mg/ha. Topography shared a weak relationship to SOC with most attributes showing a correlation coefficient less than 0.3. GLM ridge and both GAMs achieved moderate accuracy at least once, usually using the 16 or 11 variable datasets. GAMs consistently performed the best. Prior to carbon analysis, hyperspectral signatures were recorded for the topmost soil horizons under different conditions: moist unground, dry unground, and dry ground. Twenty-four math treatment and smoothing technique combinations were run on each hyperspectral dataset. R2 varied greatly within datasets depending on analytic strategy, but all datasets returned an R2 greater than 0.9 at least twice. Moist unground soil models outperformed the others when comparing the best models among datasets.
Master of Science

Styles APA, Harvard, Vancouver, ISO, etc.

24

Wagstaffe, Daniel Raymond. « Spatial Variability of Soil Velocity using Passive Surface Wave Testing ». DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1526.

Texte intégral

Résumé :

Lifelines such as highways, pipelines, telecommunication lines, and powerlines provide communities with vital services, and their functionality is dependent upon the foundation soil that supports them. However, when designing the infrastructure, it can be difficult to know where to test the soil in order to give spatially representative sampling, particularly for long, lifeline structures. Finding this distance requires knowledge of the spatial correlation and/or the spatial variability of the soil parameter (stiffness, cohesion, etc.). But this correlation distance is not typically found in practice because it requires large amounts of data and the costs of retrieving that data can be high. Lack of representative sampling can lead to an overly conservative design and too much sampling can create an overly expensive sampling program. In this study, multiple tests using the geophysical method of spatial autocorrelation (SPAC) were conducted to find the soil stiffness along a 310 meter long profile. SPAC records passive surface waves which sample the underlying soil, and these surface waves can be used to create a shear wave velocity profile of the site. The spatial continuity of the stiffness (the soil velocity values) was then found using geostatistics. The geostastical tool primarily used in this study was the (semi-)variogram, but the covariance function and the correlogram are also shown. By using these tools, the spatial correlation/variability can give an estimate of the how far apart to test the foundation soil so that the data is spatially representative. In other words, finding the distance that the soil parameter is minimally correlated with itself. This study found the distance (the range of the semi-variogram) to be 70 meters for 5 meters depth, 100 meters for 10 to 15 meters depth, and 90 meters for 30 meters depth.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Paterson, Stacey. « Soil Spatial Scaling : Modelling variability of soil properties across scales using legacy data ». Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/19895.

Texte intégral

Résumé :

Understanding how soil variability changes with spatial scale is critical to our ability to understand and model soil processes at scales relevant to decision makers. This thesis uses legacy data to address the ongoing challenge of understanding soil spatial variability in a number of complementary ways. We use a range of information: precision agriculture studies; compiled point datasets; and remotely observed raster datasets. We use classical geostatistics, but introduce a new framework for comparing variability of spatial properties across scales. My thesis considers soil spatial variability from a number of geostatistical angles. We find the following: • Field scale variograms show differing variance across several magnitudes. Further work is required to ensure consistency between survey design, experimental methodology and statistical methodology if these results are to become useful for comparison. • Declustering is a useful tool to deal with the patchy design of legacy data. It is not a replacement for an evenly distributed dataset, but it does allow the use of legacy data which would otherwise have limited utility. • A framework which allows ‘roughness’ to be expressed as a continuous variable appears to fit the data better than the mono-fractal or multi-fractal framework generally associated with multi–scale modelling of soil spatial variability. • Soil appears to have a similar degree of stochasticity to short range topographic variability, and a higher degree of stochasticity at short ranges (less than 10km and 100km) than vegetation and Radiometrics respectively. • At longer ranges of variability (i.e. around 100km) only rainfall and height above sea level show distinctly different stochasticity. • Global variograms show strong isotropy, unlike the variograms for the Australian continent.

Styles APA, Harvard, Vancouver, ISO, etc.

26

Dong, Jingnuo. « Evaluating new approaches to measure and map soil moisture spatial variability ». Thesis, Oklahoma State University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1542171.

Texte intégral

Résumé :

Knowledge of soil moisture spatial patterns provides basic but important information in studies of hydrological processes. At the field to subwatershed scale, soil moisture spatial variability is critical to aid in hydrologic modeling, but has not been adequately studied. Two new approaches were taken to contribute to the study of soil moisture spatial variability at this scale. The Bayesian Maximum Entropy (BME) framework is a more general method than classical geostatistics and has not yet been applied to soil moisture spatial estimation. The recently developed mobile Cosmic-ray Soil Moisture Observing System (COSMOS), i.e. COSMOS rover, has a ∼660 m diameter footprint which can potentially be used in field to subwatershed scale soil moisture mapping. The objectives of this research are to compare the effectiveness of BME versus ordinary kriging (OK) for spatial prediction of soil moisture at the field scale, and to calibrate and validate a COSMOS rover for mapping 0 – 5 cm soil moisture at spatial scales suitable for evaluating satellite-based soil moisture estimates. High resolution aerial photography was incorporated into the soil moisture spatial prediction using the BME method. Soil moisture maps based on the BME and the OK frameworks were cross-validated and compared. The BME method showed only slight improvement in the soil moisture mapping accuracy compared to the OK method. The COSMOS rover was calibrated to field average soil moisture measured with impedance probes which were themselves calibrated to 0-5 cm soil moisture measured by soil sampling. The resulting rover calibration was then applied to map soil moisture around the Marena, Oklahoma In Situ Sensor Testbed (MOISST) in north central Oklahoma, USA and in the Little Washita River watershed in southwest, Oklahoma. The maps showed reasonable soil moisture patterns and a clear response to soil wetting by an intervening rainfall. The rover measured field averaged soil moisture with an RMSD of 0.039 cm³ cm^-3 relative to the impedance probes which themselves had an RMSE of 0.031 cm³ cm^-3 relative to soil moisture measured by soil moisture sampling. The results provide evidence that a COSMOS rover can be used effectively for near surface soil moisture mapping with acceptable accuracy.

Styles APA, Harvard, Vancouver, ISO, etc.

27

FERRE', CHIARA. « Monitoring of greenhouse gas emissions from agricultural and forest soils ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2009. http://hdl.handle.net/10281/7483.

Texte intégral

Résumé :

Global climate change is becoming a central issue in contemporary science as well as politics. There is a long-lasting debate about the cause of the climate change: anthropogenic activity versus the natural cycle. However, a scientific consensus is coming a conclusion that the contemporary climate change is mainly caused by anthropogenic emissions of the greenhouse gases (GHG), including carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). The main objective of the thesis is the monitoring of such GHG emissions from two ecosystem types: a forest and a rice paddy ecosystem. The forest site is a EMEP experimental station, taking part of the activity of GHG-AGOLU of FP7-JRC project, while the agricultural ecosystem was included in the CarboEurope project and represents also a Level 3 site in the frame of NitroEurope project. The gas monitoring was carried out in 2008. The thesis is composed by 4 chapters, corresponding to specific objectives. The first chapter is relative to the study of the spatial variability of the main soil chemical and physical properties on the basis of which the gas monitoring points were selected. The second and the third chapters are relative to a cropland site. In particular, the second chapter includes monitoring data of CH4, N2O and CO2 fluxes from the paddy field, both during the crop growth season and the fallow period, and the validation results of the DeNitrification DeComposition (DNDC) model, a process-oriented biogeochemical model used for simulating soil gas emissions from the paddy field, are reported. The third chapter contains the study of characterization of microbial community composition using phospholipid fatty acid analysis (PLFA), at eight sampling dates representative of different soil conditions and crop stages and consequently characterized by distinct soil greenhouse emission rates. The fourth and last chapter includes the monitoring study of soil respiration in a forest site and its partitioning into autotrophic and heterotrophic components, applying the indirect linear regression method.

Styles APA, Harvard, Vancouver, ISO, etc.

28

Reyes, Javier. « EXPLORING SPATIAL AND TEMPORAL VARIABILITY OF SOIL AND CROP PROCESSES FOR IRRIGATION MANAGEMENT ». UKnowledge, 2018. https://uknowledge.uky.edu/pss_etds/107.

Texte intégral

Résumé :

Irrigation needs to be applied to soils in relatively humid regions such as western Kentucky to supply water for crop uptake to optimize and stabilize yields. Characterization of soil and crop variability at the field scale is needed to apply site specific management and to optimize water application. The objective of this work is to propose a characterization and modeling of soil and crop processes to improve irrigation management. Through an analysis of spatial and temporal behavior of soil and crop variables the variability in the field was identified. Integrative analysis of soil, crop, proximal and remote sensing data was utilized. A set of direct and indirect measurements that included soil texture, electrical conductivity (EC), soil chemical properties (pH, organic matter, N, P, K, Ca, Mg and Zn), NDVI, topographic variables, were measured in a silty loam soil near Princeton, Kentucky. Maps of measured properties were developed using kriging, and cokriging. Different approaches and two cluster methods (FANNY and CLARA) with selected variables were applied to identify management zones. Optimal scenarios were achieved with dividing the entire field into 2 or 3 areas. Spatial variability in the field is strongly influenced by topography and clay content. Using Root Zone Water Quality Model 2.0 (RZWQM), soil water tension was modeled and predicted at different zones based on the previous delineated zones. Soil water tension was measured at three depths (20, 40 and 60 cm) during different seasons (20016 and 2017) under wheat and corn. Temporal variations in soil water were driven mainly by precipitation but the behavior is different among management zones. The zone with higher clay content tends to dry out faster between rainfall events and reveals higher fluctuations in water tension even at greater depth. The other zones are more stable at the lower depth and share more similarities in their cyclic patterns. The model predictions were satisfactory in the surface layer but the accuracy decreased in deeper layers. A study of clay mineralogy was performed to explore field spatial differences based on the map classification. kaolinite, vermiculite, HIV and smectite are among the identified minerals. The clayey area presents higher quantity of some of the clay minerals. All these results show the ability to identify and characterize the field spatial variability, combining easily obtainable data under realistic farm conditions. This information can be utilized to manage resources more effectively through site specific application.

Styles APA, Harvard, Vancouver, ISO, etc.

29

MARRONE, VITTORIO ALESSANDRO. « Rilevamento e rappresentazione cartografica della variabilità spaziale dei suoli a differenti scale d'indagine : i casi studio di Monastir e del Foglio 549 Muravera ». Doctoral thesis, Università degli Studi di Cagliari, 2007. http://hdl.handle.net/11584/265946.

Texte intégral

Résumé :

The considerable spatial variability of soils makes the possibility of making teoric models of survey and representation difficult. Nowadays, traditional surveys and others using the application of new technologies are still the best way to mark soils in a specific area. One main difference is that with the first methods, (openings of profiles, drillings, chemical analysis) is very expansive to do measurements in all the points of a particular site, and these expenditures are not sustainable by normal research centres and in general by public spending while, with the second methods there is a considerable reduction in prices. In the thesis's work the two different applied methodologies have been faced with different survey scale. In particular: with a very detailed scale the EMI (Induced ElectroMagnetism) technology has been used. This technology has the prerogative of being a forwarding method in mapping pedological variations, without any inconveniences neither to the structure nor to the dynamic character of the soil (Godwin and Miller, 2003; McBratney et al., 2003; Sommer et al., 2003). For the semi-detailed scale the area of Foglio Geologico Italia 549 - Muravera�is been chosen with a scale 1:50.000 Geopedological indications are from many executed profiles (66), and they have been used to value the spatial variability to a little scale and to represent with the Pedolandscape chart, with a scale of 1:50.000. The purpose is the management and visualization of obtained data in a synthetic way, and a geographic information system (GIS) is been predisposed to this.

Styles APA, Harvard, Vancouver, ISO, etc.

30

Quick, Tyler James. « Temporal and Spatial Variability in Base Materials Treated with Asphalt Emulsion ». BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2715.

Texte intégral

Résumé :

The first objective of this research was to investigate temporal trends in the mechanical properties of base materials stabilized with asphalt emulsion and to assess the rate at which emulsion-treated base (ETB) design properties are achieved. The second objective of this research was to identify construction and environmental factors most correlated to specific mechanical properties of ETB layers and to determine which construction factors exhibit the greatest variability. Additional statistical analysis was performed to determine if significant differences existed between different test sections on a given project. In this research, three experimental sections were established along a pavement reconstruction project near Saratoga Springs, Utah. Field tests were performed to assess the structural properties of the ETB immediately following construction and at 2, 3, 7, and 14 days; 4 months; and 1 year. Measured values were plotted against time to determine trends in ETB strength development. Several statistical analyses were then performed on the collected data. Modulus values were consistently low in all three sections during the first two weeks of testing, increased dramatically by 4 months, and then decreased considerably by 1 year. During the first two weeks following construction, the average ETB structural coefficient was 0.04. Only two of the three sections reached the design structural coefficient of 0.25, which occurred after approximately 3 months; however, the average structural coefficient measured for all three sections after 1 year of curing, which included a winter, was only 47 percent of the design strength. The results of this research show that, while pavement capacity is sufficient at 4 months, it is severely reduced during the first two weeks and at 1 year. Trafficking under these reduced capacities is not recommended. Statistical analysis showed that gradation, binder change during emulsion treatment, and moisture content have the most significant impact on ETB structural properties. Gradation and binder change during emulsion treatment also exhibited significant variability; tighter specifications on material gradations and improved uniformity in emulsion distribution should therefore be considered. Because of the negative impacts of moisture on ETB strength development, construction should not be performed in conditions of excess moisture.

Styles APA, Harvard, Vancouver, ISO, etc.

31

Neumann, William John III. « The use of ground penetrating radar to determine the presence, extent, and spatial variability of fire related hydrophobic soils in fire impacted watersheds in southern California ». Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2251.

Texte intégral

Résumé :

Ground Penetrating Radar (GPR) methods have been used to evaluate the presence, extent, and spatial variability of hydrophobic soils in Southern California Watersheds. It has been shown that high frequency ground penetrating radar equipment, under certain conditions, has the ability to determine the presence, depth, and persistence of post fire hydrophobic soils. As part of this study an extensive investigation was undertaken to not only evaluate the capability of this approach but also to understand under what conditions the method can be applied successfully and what are the limitations of the approach. The investigation includes use of computer simulations and modeling, laboratory investigations in sand boxes with native soils, and multiple field trials spanning a five year time period. Of particular significance is the finding that using GPR it is possible to: locate the interface between the uppermost burnt soil layer, and soil horizons below; quantify the depth at which the hydrophobic layer forms; and quantify the spatial extent of the layer. As part of this study best practice methods for both field and lab experimentation have also been developed and are presented in the body of the thesis. Based on this study it is concluded that the use of GPR can provide a much more accurate and comprehensive method of evaluating the nature of hydrophobic layers in such environments than the current point specific manual methods. As a result the use of GPR has significantly advanced our capacity to assess the potential for increased erosion and the generation of debris flows in such environments after rainfall events.

Styles APA, Harvard, Vancouver, ISO, etc.

32

Thomazini, André. « Spatial and temporal variability of CO2 dynamic and soil attributes in Maritime Antarctica ». Universidade Federal de Viçosa, 2016. http://www.locus.ufv.br/handle/123456789/10391.

Texte intégral

Résumé :

Submitted by Marco Antônio de Ramos Chagas (mchagas@ufv.br) on 2017-05-19T13:47:10Z No. of bitstreams: 1 texto completo.pdf: 1800381 bytes, checksum: 348713e32fe650d04684641d1f30d461 (MD5)
Made available in DSpace on 2017-05-19T13:47:10Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1800381 bytes, checksum: 348713e32fe650d04684641d1f30d461 (MD5) Previous issue date: 2016-04-25
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
A Antártica Marítima apresenta alta sensibilidade às mudanças climáticas, especialmente pelas alterações na temperatura do ar, que modificam a dinâmica do carbono e atributos do solo nos ecossistemas terrestres. Sendo assim, variáveis relacionadas ao solo (ou seja, carbono orgânico, temperatura do solo e umidade do solo), e o padrão de distribuição da vegetação, podem ser indicadores das mudanças climáticas. O objetivo deste trabalho foi investigar a relação espacial e temporal entre as trocas de carbono, o status de nutrientes do solo e seu desenvolvimento nos principais ecossistemas terrestres da Antártica Marítima. O estudo foi realizado na Península Keller e Coppermine, Ilha Rei George e Robert, respectivamente. Grids regulares foram instalados para avaliar a variabilidade espacial de atributos gerais do solo e troca de carbono em campos de liquens, musgos, liquens/musgos e locais de solo exposto, ao longo das áreas livres de gelo. Usando técnicas de geoestatística, a dependência espacial foi acessada através da modelagem do semivariograma e dimensão fractal. Amostras de solo foram coletadas em diferentes camadas para determinar alguns atributos gerais do solo. A respiração total do ecossistema, troca líquida do ecossistema e produção primária bruta foram determinadas medindo fluxos de CO 2 in situ, com um sistema automático de fechamento da câmara de medição (LI-COR Biosciences, Lincoln, NE, EUA), baseado em medições de curto e longo prazo. Os resultados indicam uma alta capacidade dos tapetes de musgos (principalmente por Sanionia uncinata), para atuar como dreno de carbono, em locais onde a umidade do solo é elevada. Por outro lado, onde o guano é depositado, a temperatura do solo é elevada, levando a um aumento da mineralização da matéria orgânica, respiração do ecossistema, atuando como fonte de carbono para a atmosfera. A dependência espacial variou entre os locais, sendo que a deposição do guano e a cobertura vegetal governam a extensão da estrutura espacial. Os valores de dimensão fractal mostraram que há uma forte relação espacial entre o carbono orgânico e o alumínio. Os solos são caracterizados principalmente pelas altas quantidades de bases e incipiente formação de argila. Em zonas com influência ornitogênica fraca, o solo é ácido e os valores de alumínio trocável são elevados, associados a uma acidez potencial elevada. A proximidade do permafrost está reduzindo a temperatura do solo, e consequentemente o número de dias de degelo. No entanto, sob o aquecimento atual, este local tende a agir progressivamente como uma fonte de CO 2 para a atmosfera. Por outro lado, mais turfeiras podem ser formadas devido derretimento de neve/gelo, armazenamento grandes quantidades de carbono. O balanço entre o ganho e perda de CO 2 precisa ser mais pesquisado na Antártica Marítima, a fim de elucidar a dinâmica atual considerando outras áreas livres de gelo.
Maritime Antarctica presents high sensitivity to climate change, especially by the alterations in air temperature, which modifies carbon dynamics and soil attributes in terrestrial ecosystems. Thus, variables related to soil (i.e. organic carbon, soil temperature and soil moisture), and vegetation distribution patterns, can represent climate change indicators. The objective of this work was to investigate the spatial and temporal relationship among carbon exchange, soil nutrient status and development in the main terrestrial ecosystems of Maritime Antarctica. The study was carried out at Keller and Coppermine Peninsula, in King George Island and Robert Island, respectively. Regular grids were installed to evaluate the spatial variability of general soil attributes and carbon exchange in lichens, mosses, lichens/mosses and bare soil sites along the ice- free areas. By using geostatistical techniques, spatial dependence was accessed through semivariogram and fractal dimension modeling. Soil was sampled at different soil layers to determine general soil attributes. Ecosystem respiration, net ecosystem exchange and gross primary production were determined by measuring CO 2 fluxes in situ with a closed automatic chamber system (LI-COR Biosciences, Lincoln, NE, USA), based on short and long-term measurements. Results indicate a high capacity of mosses carpets (especially by Sanionia uncinata) to act as a sink of carbon, where soil moisture is elevated. On the other hand, where guano is deposited, soil temperature is enhanced, leading to increase soil organic matter mineralization, ecosystem respiration, acting as a source of carbon to the atmosphere. Spatial dependence strongly varied among sites, where guano deposition and vegetation coverage are reported to drive the extension of spatial structure. Fractal dimension values showed great spatial relationship between organic carbon and aluminum. Soils are mainly characterized by the high amounts of bases and weak clay formation. In zones with weak ornithogenic influence, soil is acid and values of exchangeable aluminum are high, associated with elevated potential acidity. The proximity of permafrost is leading to lower soil temperatures, reducing the number of thaw days. However, under current climate warming, this site will progressively act as a source of CO 2 to the atmosphere. On the other hand, peatlands could be formed due snow/ice melting, storing large amounts of carbon. The balance of uptake and release of CO 2 needs to be further researched in Maritime Antarctica, to elucidate the current dynamic for other different ice-free areas.

Styles APA, Harvard, Vancouver, ISO, etc.

33

Siewert, Matthias Benjamin. « High-resolution mapping and spatial variability of soil organic carbon storage in permafrost environments ». Doctoral thesis, Stockholms universitet, Institutionen för naturgeografi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-134986.

Texte intégral

Résumé :

Large amounts of carbon are stored in soils of the northern circumpolar permafrost region. High-resolution mapping of this soil organic carbon (SOC) is important to better understand and predict local to global scale carbon dynamics. In this thesis, studies from five different areas across the permafrost region indicate a pattern of generally higher SOC storage in Arctic tundra soils compared to forested sub-Arctic or Boreal taiga soils. However, much of the SOC stored in the top meter of tundra soils is permanently frozen, while the annually thawing active layer is deeper in taiga soils and more SOC may be available for turnover to ecosystem processes. The results show that significantly more carbon is stored in soils compared to vegetation, even in fully forested taiga ecosystems. This indicates that over longer timescales, the SOC potentially released from thawing permafrost cannot be offset by a greening of the Arctic. For all study areas, the SOC distribution is strongly influenced by the geomorphology, i.e. periglacial landforms and processes, at different spatial scales. These span from the cryoturbation of soil horizons, to the formation of palsas, peat plateaus and different generations of ice-wedges, to thermokarst creating kilometer scale macro environments. In study areas that have not been affected by Pleistocene glaciation, SOC distribution is highly influenced by the occurrence of ice-rich and relief-forming Yedoma deposits. This thesis investigates the use of thematic maps from highly resolved satellite imagery (<6.5 m resolution). These maps reveal important information on the local distribution and variability of SOC, but their creation requires advanced classification methods including an object-based approach, modern classifiers and data-fusion. The results of statistical analyses show a clear link of land cover and geomorphology with SOC storage. Peat-formation and cryoturbation are identified as two major mechanisms to accumulate SOC. As an alternative to thematic maps, this thesis demonstrates the advantages of digital soil mapping of SOC in permafrost areas using machine-learning methods, such as support vector machines, artificial neural networks and random forests. Overall, high-resolution satellite imagery and robust spatial prediction methods allow detailed maps of SOC. This thesis significantly increases the amount of soil pedons available for the individual study areas. Yet, this information is still the limiting factor to better understand the SOC distribution in permafrost environments at local and circumpolar scale. Soil pedon information for SOC quantification should at least distinguish the surface organic layer, the mineral subsoil in the active layer compared to the permafrost and further into organic rich cryoturbated and buried soil horizons.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Lucian, Charles. « Geotechnical Aspects of Buildings on Expansive Soils in Kibaha, Tanzania ». Doctoral thesis, KTH, Jord- och bergmekanik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9244.

Texte intégral

Résumé :

The focus of this study is on potential damages to buildings resulting from expansive soils in Tanzania, particularly clay soils in Kibaha. For the fact that most of the affected structures are founded on expansive soils, a clear understanding of the behaviour of soils and their interaction with structures has been of interest to the study in order to evaluate properly the source of the problem.The geotechnical behaviour of expansive clay soils is investigated by looking into the geomorphologic, geological and climatic conditions and mineralogical composition of the soils in the study area.Two sites, representative of known problem-areas in Kibaha were selected for geotechnical tests. Geotechnical site investigation consisted of open trial pits, profile description and the collection of both disturbed and undisturbed samples. To extend and amplify the findings, supplementary samples were collected from the environs of the two sites.The collected samples were submitted to soil laboratories at KTH, ARU, SEAMIC and DIT for mineralogical composition tests, natural water content, density, Atterberg limits and swell tests. The results of this investigation indicate that soils in Kibaha contains clay (31%), have high liquid limit (59%) and plastic limit (37%) which indicate high potential swell.Since swell pressure, free swell and swell percent are key properties of expansive soils, the swell properties were measured by free swell tests and one-dimensional oedometer swell tests. The free swell ranged from 100% to 150% and the swell pressure was in the region of 45 kPa. The coefficient of linear extensibility (COLE) was determined for characterizing expansive clays. For all tested samples, COLE ranged from 0.09 to 0.14 indicating that soils fall in the region of high to very high expansion potential rating. The properties of expansive soils were confirmed by the x-ray diffraction test which showed the presence of smectite in the soil. Furthermore, total suction measurement technique using filter paper method indicated that the soils have high suction values, signifying that they have a tendency to swell upon wetting depending on plasticity of particular soil.The depth of the active zone was measured as a function of moisture variations in the profiles during two extreme weather conditions. The active zone depth was found to be between 1.0 and 2.0 m deep. Procedures to assess models to predict swell in the case study were outlined together with their validity.Vertical and horizontal spatial variability in selected soil properties was defined using geostatistical techniques through the fitting of variogram. The indicator semivariograms of both clay contents and free swell gave a range of 20 m horizontally and 1.0 m vertically, with the horizontal variograms exhibiting greater ranges than the dipping variograms.Physical conditions of the surveyed properties in the area confirmed that building damages are associated with poor building materials triggered by expansive soils. In support of the obtained data, the actual behaviour of the foundations was supplemented with prototypes of strip foundations whose performances were monitored over a period of four months. Finally, suggested are the ways forward to solve the problem of foundation on expansive soil
QC 20100824

Styles APA, Harvard, Vancouver, ISO, etc.

35

Pan, Luan. « Means to optimize soil water management through monitoring spatial and temporal variability of geophysical soil attributes ». Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=117181.

Texte intégral

Résumé :

To optimize irrigation water use, temporal and spatial sensor-based data related to soil water content were integrated. Nine locations in a 37-ha agricultural field were selected using field elevation and soil ECa maps for monitoring the soil matric potential and temperature at four depths (18, 48, 79 and 109 cm) with a wireless sensor network. Using a linear regression approach, a series of time-specific equations were developed to quantify both the temporal and spatial soil water stress status through a Water Stress Index (WSI). The WSI was estimated using soil matric potential measurements along with supplemental soil characteristics, such as site-specific soil matric potential corresponding to 25% soil water depletion that was derived based on soil physical properties. Further analysis was performed to quantify the percentage of the field that undergoes a potential shortage in water supply. These results could be used to optimize irrigation scheduling and to assess the potential for variable-rate irrigation. The second study investigated the way in which the WSI prediction quality is affected by the number and placement of temporal soil water content monitoring sites. The concept, potentially, could be used to investigate a variety of site-specific crop management strategies. It was developed to assess WSI predictability in context that the modeled relationship between WSI and spatial field data (ECa and elevation) is not perfect at any given point of time. The established regression model between ECa, field topography maps and WSI from the first study was applied to construct WSI maps representing a specific point in time in six experimental fields with different crop growing conditions located in Nebraska, USA. Artificial regression error models with different degrees of spatial structure were superimposed onto these maps to simulate actual WSI distribution across the fields. Both random and optimized monitoring site placement strategies were evaluated in terms of the ability to predict the simulated WSI maps. The results showed that it was necessary to optimize the selection when the number of monitoring sites was low. However, a random placement method was equally efficient when the number of monitoring sites was high. Careful selection of representative field areas representing significant field areas with extreme conditions should allow only 2 or 3 monitoring sites to produce results with relatively low WSI prediction error.Through the process of water management optimization, it was noted that the ability to detect site-specific water storage capacity is an important task. Since it is related to the change of soil physical properties with depth, a third study was conducted to develop a dynamic scanning of soil profile tools using a galvanic contact resistivity approach. Transmitting and receiving electrodes were configured in an equatorial dipole array. An automated scanner system has been developed and tested in the agricultural field environment with different soil profiles. While operating in the field, the distance between the current injecting and measuring pairs of rolling electrodes was varied continuously from 40 to 190 cm. The resulting scans were evaluated against 1-m deep soil profiles and that of an electromagnetic induction instrument at various depths, up to 3 m.
Pour atteindre l'utilisation optimale de l'eau d'irrigation, des données spatio-temporelles provenant de sondes et reliées au contenu en eau du sol ont été intégrées. Ainsi, dans un champ agricole de 37 hectares, neuf sites ont été sélectionnés en utilisant les cartes d'élévation et de CEa du sol afin d'assurer le suivi du potentiel matriciel et de la température du sol à quatre profondeurs (18, 48, 79 et 109 cm) avec un réseau de capteurs sans fil. Utilisant une approche de régression linéaire, une série d'équations spécifiques au temps a été développée pour quantifier l'état de stress hydrique du sol dans le temps et l'espace à l'aide d'un Indice de Stress Hydrique (ISH). L'ISH a été estimé en utilisant des mesures de potentiel matriciel du sol combiné à ses caractéristiques supplémentaires, telles que celles calculées à partir de ses propriétés physiques et du potentiel matriciel spécifique au site correspondant à un appauvrissement de 25% des eaux du sol. Une analyse additionnelle a permis de quantifier la fraction du site ayant un potentiel d'approvisionnement en eau déficitaire. Ces résultats pourraient être utilisés afin d'optimiser la planification de l'irrigation et d'évaluer le potentiel d'irrigation à débits variables.La seconde étude a permis un examen plus approfondi de la qualité de prédiction de l'ISH influencé par le nombre et l'emplacement de sites chronologiques de surveillance du contenu hydrique du sol. Le concept pouvant potentiellement être utilisé pour étudier une diversité de stratégies de gestion de cultures a été développé afin d'évaluer la prévisibilité de l'ISH en tenant compte de la relation imparfaite entre cet indice et les données spatiales à tout temps donné. Le modèle de régression établi entre la CEa, les cartes topographiques du champ et l'ISH de la première étude a été appliqué afin de construire des cartes d'ISH représentant un moment spécifique pour six champs expérimentaux sous différentes conditions de croissance au Nebraska, USA. Des modèles artificiels d'erreur de régression avec différents degrés de structure spatiale ont été superposés sur ces cartes pour simuler la distribution réelle de l'ISH à travers ces champs. Autant de stratégies aléatoires et optimisées de placement de sites de surveillance ont été évaluées en termes de leur habilité à prédire les cartes d'ISH simulées. Les résultats démontrent qu'il était nécessaire d'optimiser la sélection de sites de surveillance lorsque leur nombre était bas. Cependant, la méthode de placement aléatoire était tout aussi efficace lorsque le nombre de sites était élevé. Une sélection rigoureuse des régions du champ permettant de représenter ses aires significatives avec des conditions extrêmes devrait permettre la production de résultats ayant une erreur de prédiction de l'ISH très basse à partir de seulement deux ou trois sites de surveillance.À travers le processus d'optimisation de la gestion de l'eau, il a été noté que l'aptitude à détecter la capacité d'emmagasinement d'eau spécifique au site est une tâche importante. Puisqu'elle est liée au changement de propriétés physiques du sol avec la profondeur, la troisième étude a été menée afin de développer un outil de balayage (scan) dynamique des profils du sol en utilisant une approche de résistance du contact galvanique. Les électrodes émettrices et réceptrices ont été configurées suivant un dispositif dipôle équatorial. Un système de scanner automatisé a été développé et testé dans un environnement de terre agricole avec différents profils de sol. Lors de l'utilisation sur le terrain, la distance entre les pairs d'électrodes roulantes d'injection et de mesure variait continuellement de 40 à 190 cm. Les balayages résultants ont été évalués avec des profils de sols de 1m de profondeur, alors que ceux fait à partir d'un appareil d'induction électromagnétique ont été évalués à des profondeurs variées allant jusqu'à 3m.

Styles APA, Harvard, Vancouver, ISO, etc.

36

Zimmermann, Beate. « Spatial and temporal variability of the soil saturated hydraulic conductivity in gradients of disturbance ». Phd thesis, Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1640/.

Texte intégral

Résumé :

As land-cover conversion continues to expand into ever more remote areas in the humid tropics, montane rainforests are increasingly threatened. In the south Ecuadorian Andes, they are not only subject to man-made disturbances but also to naturally occurring landslides. I was interested in the impact of this ecosystem dynamics on a key parameter of the hydrologic cycle, the soil saturated hydraulic conductivity (synonym: permeability; Ks from here on), because it is a sensitive indicator for soil disturbances. My general objective was to quantify the effects of the regional natural and human disturbances on the saturated hydraulic conductivity and to describe the resulting spatial-temporal patterns. The main hypotheses were: 1) disturbances cause an apparent displacement of the less permeable soil layer towards the surface, either due to a loss of the permeable surface soil after land-sliding, or as a consequence of the surface soil compaction under cattle pastures; 2) ‘recovery’ from disturbance, either because of landslide re-vegetation or because of secondary succession after pasture abandonment, involves an apparent displacement of the less permeable layer back towards the original depth an 3) disturbances cause a simplification of the Ks spatial structure, i.e. the spatially dependent random variation diminishes; the subsequent recovery entails the re-establishment of the original structure. In my first study, I developed a synthesis of recent geostatistical research regarding its applicability to soil hydraulic data, including exploratory data analysis and variogram estimation techniques; I subsequently evaluated the results in terms of spatial prediction uncertainty. Concerning the exploratory data analysis, my main results were: 1) Gaussian uni- and bivariate distributions of the log-transformed data; 2) the existence of significant local trends; 3) no need for robust estimation; 4) no anisotropic variation. I found partly considerable differences in covariance parameters resulting from different variogram estimation techniques, which, in the framework of spatial prediction, were mainly reflected in the spatial connectivity of the Ks-field. Ignoring the trend component and an arbitrary use of robust estimators, however, would have the most severe consequences in this respect. Regarding variogram modeling, I encouraged restricted maximum likelihood estimation because of its accuracy and independence on the selected lags needed for experimental variograms. The second study dealt with the Ks spatial-temporal pattern in the sequences of natural and man-made disturbances characteristic for the montane rainforest study area. To investigate the disturbance effects both on global means and the spatial structure of Ks, a combined design-and model-based sampling approach was used for field-measurements at soil depths of 12.5, 20, and 50 cm (n=30-150/depth) under landslides of different ages (2 and 8 years), under actively grazed pasture, fallows following pasture abandonment (2 to 25 years of age), and under natural forest. Concerning global means, our main findings were 1) global means of the soil permeability generally decrease with increasing soil depth; 2) no significant Ks differences can be observed among landslides and compared to the natural forest; 3) a distinct permeability decrease of two orders of magnitude occurs after forest conversion to pasture at shallow soil depths, and 4) the slow regeneration process after pasture abandonment requires at least one decade. Regarding the Ks spatial structure, we found that 1) disturbances affect the Ks spatial structure in the topsoil, and 2) the largest differences in spatial patterns are associated with the subsoil permeability. In summary, the regional landslide activity seems to affect soil hydrology to a marginal extend only, which is in contrast to the pronounced drop of Ks after forest conversion. We used this spatial-temporal information combined with local rain intensities to assess the partitioning of rainfall into vertical and lateral flowpaths under undisturbed, disturbed, and regenerating land-cover types in the third study. It turned out that 1) the montane rainforest is characterized by prevailing vertical flowpaths in the topsoil, which can switch to lateral directions below 20 cm depth for a small number of rain events, which may, however, transport a high portion of the annual runoff; 2) similar hydrological flowpaths occur under the landslides except for a somewhat higher probability of impermeable layer formation in the topsoil of a young landslide, and 3) pronounced differences in runoff components can be observed for the human disturbance sequence involving the development of near-surface impeding layers for 24, 44, and 8 % of rain events for pasture, a two-year-old fallow, and a ten-year-old fallow, respectively.
Der tropische Bergregenwald in den Südecuadorianischen Anden unterliegt sowohl anthropogenen Eingriffen, d.h. der Umwandlung von Naturwald in Rinderweiden, als auch natürlichen Störungen in der Form von Hangrutschen. Ziel meiner Arbeit war es, die Auswirkungen dieser regionalen Störungsdynamik auf einen Schlüsselparameter des hydrologischen Kreislaufs, die gesättigte hydraulische Wasserleitfähigkeit (Ks), zu untersuchen und die resultierenden raum-zeitlichen Muster zu beschreiben. In der ersten Studie habe ich eine Synthese aktueller geostatistischer Forschung hinsichtlich ihrer Eignung für die Analyse bodenhydrologischer Daten entwickelt. Diese beinhaltet explorative Datenanalyse und verschiedene Techniken zur Schätzung der Kovarianzparameter; die Ergebnisse habe ich in Bezug auf die Ungenauigkeit räumlicher Vorhersagen bewertet. Es hat sich dabei herausgestellt, dass die Schätztechniken teilweise beachtliche Unterschiede in den Parametern hervorrufen, welche sich hauptsächlich in der räumlichen Konnektivität widergespiegeln. Die wichtigste Rolle im Zusammenhang mit der räumlichen Vorhersage kommt jedoch den vorgeordneten explorativen Analyseschritten zu. In der zweiten Studie habe ich mich mit der Beschreibung des raum-zeitlichen Muster der Wasserleitfähigkeit in den anthropogenen und natürlichen Störungsgradienten beschäftigt. Wichtigste Ergebnisse waren, dass es keine signifikanten Unterschiede der Wasserleitfähigkeit zwischen den verschieden alten Hangrutschen und dem Naturwald gibt. Daraus lässt sich schließen, dass die natürlichen Störungen im Untersuchungsgebiet lediglich marginale Auswirkungen auf die Bodenhydrology haben. Das steht in starkem Kontrast zum anthropogenen Störungskreislauf: die Wasserleitfähigkeit im Weideboden hat gegenüber dem Naturwald um zwei Größenordnungen abgenommen; eine „Erholung“ nach Nutzungsaufgabe scheint mindestens ein Jahrzehnt in Anspruch zu nehmen. Die räumlichen Abhängigkeit von Ks in den Oberböden von Wald und einer alten Brache ist stärker als in jenen der gestörten Flächen, was auf eine störungsbedingte Beeinträchtigung der räumlichen Struktur in geringer Bodentiefe schließen lässt. In der dritten Studie habe ich diese raum-zeitlichen Informationen mit dem örtlichen Niederschlagsregime in Verbindung gebracht, um Rückschlüsse auf die Auswirkungen der störungsbedingten Änderungen von Ks auf hydrologische Fließwege zu ziehen. Es hat sich gezeigt, dass im tropischen Bergregenwald und unter Hangrutschen ubiquitäre Tiefenversickerung dominiert, es allerdings zu einer Verschiebung in laterale Fließrichtungen für die seltenen intensiven Regenereignisse kommen kann. Anthropogene Störungen gehen mit einer um bis zu 50 Prozent erhöheren Wahrscheinlichkeit des Auftretens oberflächennaher Stauschichten einher, was die Bedeutung lateraler Fließwege erhöht. Dies trifft in vergleichbarer Größenordnung auch auf ein Vergleichsökosystem im Tieflandregenwald zu.

Styles APA, Harvard, Vancouver, ISO, etc.

37

Nijbroek, Ravic. « Understanding and simulating spatial soil water and yield variability in an irrigated soybean field ». [Florida] : State University System of Florida, 1999. http://etd.fcla.edu/etd/uf/1999/amp7403/nijbroek.pdf.

Texte intégral

Résumé :

Thesis (M.E.)--University of Florida, 1999.
Title from first page of PDF file. Document formatted into pages; contains xvi, 151 p.; also contains graphics. Vita. Includes bibliographical references (p. 148-150).

Styles APA, Harvard, Vancouver, ISO, etc.

38

Fan, Haijian. « Performance Based Design of Deep Foundations in Spatially Varying Soils ». University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1384959587.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

39

Whitaker, Martha Patricia Lee 1965. « Small-scale spatial variability of soil moisture and hydraulic conductivity in a semi-arid rangeland soil in Arizona ». Thesis, The University of Arizona, 1993. http://hdl.handle.net/10150/192081.

Texte intégral

Résumé :

The correlation scales of soil moisture and hydraulic conductivity were investigated within a 4.4 hectare semi-arid rangeland watershed using measurements obtained from time domain reflectometry and disc permeameters, respectively. Soil moisture measurements were collected at four different times in 1991 to yield a varied set of natural soil moisture conditions. Soil moisture was sampled over a 30 meter grid, two perpendicular transects at 5 meter intervals, once at 1 meter intervals, and once at intervals of — 0.10 m within a 1 xl meter plot. Variogram functions showed evidence of spatial correlation only when the grid and perpendicular transect data were combined. A total of 30 measurements each of saturated and unsaturated hydraulic conductivity were collected along a 300 meter curvilinear transect at approximately 10 meter intervals. Although spatial correlation was evident, variogram resolution may possibly be improved by obtaining more measurements.

Styles APA, Harvard, Vancouver, ISO, etc.

40

Hirobe, Muneto. « Spatial Variability of Soil Nitrogen Dynamics along a Forest Slope in a Cryptomeria japonica D.Don Plantation ». Kyoto University, 1999. http://hdl.handle.net/2433/181395.

Texte intégral

Résumé :

Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第8030号
農博第1080号
新制||農||789(附属図書館)
学位論文||H11||N3325(農学部図書室)
UT51-99-T741
京都大学大学院農学研究科地域環境科学専攻
(主査)教授武田博清, 教授谷誠, 教授小﨑隆
学位規則第4条第1項該当

Styles APA, Harvard, Vancouver, ISO, etc.

41

Uribeetxebarria, Alonso de Armiño Asier. « Assessing soil and canopy spatial variability in fruit orchards to improve management and sampling by using auxiliary information provided by proximal and remote sensors ». Doctoral thesis, Universitat de Lleida, 2019. http://hdl.handle.net/10803/666921.

Texte intégral

Résumé :

Aquesta Tesi doctoral s’ha centrat en l’estudi de la variabilitat espacial present en parcel•les fructícoles de la zona central de la Vall de l’Ebre. En una primera part, i amb l’objectiu d’obtenir zones de maneig diferenciat, la variabilitat del sòl i el vigor dels presseguers (Prunus pèrsica (L.) Stokes) foren analitzats. En una segona part, la informació auxiliar aportada per diferents sensors fou utilitzada per estimar paràmetres quantitatius (kg/arbre) i qualitatius (fermesa i índex refractomètric) mitjançant tècniques de mostreig avançades (mostreig estratificat (StRS) i el ranked set sampling (RSS)). Les dades utilitzades durant la Tesi foren recopilades en2 parcel•les agrícoles en el decurs de 2 campanyes, 2015 i 2016 en dos. A més dels mostreigs de camp, ambdues parcel•les van ser caracteritzades mitjançant diferents sensors (propers i remots) emprats en Agricultura de Precisió. El nou procediment desenvolupat possibilita delimitar zones de maneig basades en el NDVI i CEA que permeten realitzar la gestió diferenciada dels cultius. A més, s'ha demostrat que tant el STRS com l'RSS són més eficients que el mostreig aleatori simple (SRS).
Esta Tesis doctoral se centra en el estudio de la variabilidad espacial presente en parcelas frutícolas de la zona central del Valle del Ebro. En un primera parte, y con el fin de obtener zonas de manejo diferenciado, la variabilidad del suelo y el vigor de los melocotoneros (Prunus pérsica (L.) Stokes) fueron analizados. En una segunda parte, la información auxiliar aportada por diferentes sensores fue utilizada para estimar parámetros cuantitativos (kg/árbol) y cualitativos) de los melocotoneros mediante técnicas de muestreo avanzadas (muestreo estratificado (StRS) y ranked set sampling (RRS)). Los datos utilizados durante la tesis fueron recopilados en 2 parcelas agrícolas durante el transcurso de 2 campañas, 2015 y 2016. Además de los muestreos de campo, ambas parcelas fueron caracterizadas mediante sensores (próximos y remotos) empleados en Agricultura de Precisión. El nuevo procedimiento desarrollado posibilita delimitar zonas de manejo basadas en el NDVI y CEa que permiten realizar la gestión diferenciada de los cultivos. Además, se ha demostrado que tanto el StRS como el RSS son más eficientes que el muestreo aleatorio simple (SRS)
The aim of the present Thesis is the analysis of spatial variability in fruit orchards of the central area of the Ebro Valley. In the first part, soil variability and peach trees (Prunus pérsica (L.) vigour were analysed with the objective to obtain differentiated management areas. In the second part, auxiliary information provided by different type of sensors was used to estimate quantitative (kg/tree) and qualitative parameters (fruit firmness and refractometric index) by using advanced sampling techniques (stratified sampling (StRS) and ranked set sampling (RSS)). During this Thesis, data corresponding to two agricultural campaigns (2015, 2016) were collected in two peach orchards. Moreover, to field sampling, both plots were characterized by different sensors (contact and remote) employed in Precision Agriculture. The information provides by NDVI and ECa, together with the new procedure developed makes it possible to delimit management areas that allow site-specific crop management. In addition, it has been shown that both StRS and RSS are more efficient than simple random sampling (SRS).

Styles APA, Harvard, Vancouver, ISO, etc.

42

Lachérade, Lucas. « Apports de la modélisation de la variabilité spatiale géotechnique appuyée par la géologie dans un projet de creusement de tunnel : application au Grand Paris Express ». Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0063.

Texte intégral

Résumé :

L’urbanisation croissante du monde et la densification des aires urbaines entraînent une multiplication des projets d’aménagement souterrains. Dans ce cadre, la connaissance du sous-sol urbain constitue l’un des grands enjeux actuels et futurs. Cependant, cette connaissance est souvent partielle et incertaine, induisant des risques élevés lors de la phase de construction des ouvrages. C'est dans ce contexte que s'inscrit cette thèse. Elle contribue à valoriser la caractérisation et l'intégration de la variabilité spatiale géotechnique des sous-sols dans la construction d’ouvrages souterrains de grands linéaires, avec une application spécifique à la ligne 15 Ouest du Grand Paris Express.êEn raison de la diversité des thématiques interagissant avec la variabilité spatiale géotechnique, plusieurs défis se manifestent, incitant à adopter une approche pluridisciplinaire pour les surmonter. Dans un premier temps, les données géotechniques, notamment celles provenant des essais pressiométriques, sont conditionnées en vue de la modélisation de leur variabilité spatiale. Des contrôles de qualité et un traitement des essais dont les valeurs de pression limite nette ne sont pas atteintes sont mis en place. Ce processus conduit au développement d’une approche de modélisation géostatistique qui intègre les hétérogénéités géotechniques tant latérales que verticales, par l’identification de secteurs géotechniques homogènes. La variabilité spatiale des paramètres de l’essai pressiométrique est ensuite modélisée sur l’entièreté de la ligne 15 Ouest au moyen de méthodes géostatistiques déterministes et d’algorithmes de simulation. Les performances des deux techniques sont évaluées et des recommandations sont formulées quant à leur utilisation dans le cadre d’un projet de creusement de tunnel.êConsécutivement, une transposition de la variabilité spatiale géotechnique est réalisée vers d’autres thématiques. La corrélation linéaire entre le phénomène d’altération météorique des formations géologiques et leurs propriétés pressiométriques est étudiée. Cela conduit à la quantification de la dégradation des valeurs d’essais des terrains altérés et à l’intégration de l’altération en tant qu’information auxiliaire dans la modélisation de variabilité spatiale de la pression limite nette. Par la suite, la fiabilité des données d'essai pressiométrique est évaluée par le développement d'un système de notation basé sur les courbes d'essai. Une classification de la fiabilité du module pressiométrique est proposée en utilisant des algorithmes d'apprentissage automatique. Cette classification est employée pour identifier les essais peu fiables, permettant ainsi d’évaluer l’impact de l’incertitude de mesure du module pressiométrique sur la modélisation géostatistique. La dernière thématique abordée concerne l’intégration de la variabilité spatiale du module pressiométrique dans le calcul et l’analyse des tassements de surface induits par le creusement de tunnel. Soulignant les différences d’estimation par rapport à une approche traditionnelle utilisant un module d’élasticité homogène, elle met en lumière l’impact des hétérogénéités du sous-sol sur les courbes de tassement
The increasing urbanisation of the world and the densification of urban areas are leading to a multiplication of underground development projects. In this context, knowledge of the urban underground is one of the major current and future challenges. However, this knowledge is often partial and uncertain, leading to major risks during the construction phase. This is the background to this thesis. It contributes to the characterisation and integration of the geotechnical spatial variability of subsoils in the construction of large linear underground structures, with a specific application to the Grand Paris Express West 15 line.êDue to the diversity of the themes interacting with geotechnical spatial variability, a number of challenges arise, prompting the adoption of a multidisciplinary approach to deal with them. Firstly, geotechnical data, particularly from pressuremeter tests, are adapted to model their spatial variability. Quality controls and processing of tests with unachieved net pressure limit values are implemented. This process leads to the development of a geostatistical modeling approach that incorporates both lateral and vertical geotechnical heterogeneities, by identifying homogeneous geotechnical sectors. The spatial variability of the pressuremeter test parameters is then modelled over the entire West 15 line using deterministic geostatistical methods and simulation algorithms. The performance of the two techniques is evaluated and recommendations are provided regarding their application in a tunnelling project.êGeotechnical spatial variability is then transposed to other themes. The linear correlation between the weathering of geological formations and their pressuremeter properties is studied. This leads to the quantification of the degradation of the test values of weathered soils and the integration of weathering as auxiliary information in the modeling of the spatial variability of the net limit pressure. The reliability of the pressuremeter test data is then assessed by developing a scoring system based on the test curves. A classification of the reliability of the pressuremeter modulus, using machine learning algorithms, is proposed. This classification is used to identify unreliable tests, thus making it possible to assess the impact of pressuremeter modulus measurement uncertainty on geostatistical modeling. The last theme addressed concerns the integration of the spatial variability of the pressuremeter modulus in the calculation and analysis of surface settlements induced by tunnel excavation. Highlighting the differences in estimation compared to a conventional approach using a homogeneous modulus of elasticity, it underscores the influence of subsoil heterogeneities on settlement curves

Styles APA, Harvard, Vancouver, ISO, etc.

43

Peterson, Shelley. « Spatial variability of soil nitrogen, crop yields and delta yield in relation to variable rate nitrogen fertilization ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ35922.pdf.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

44

Angstmann, Julia L. « Spatial and temporal variability of tree transpiration and its drivers along a soil drainage gradient in the boreal black spruce forest ». Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1990985251&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

45

Sow, Djibril. « Variabilité spatiale de la résistance au cisaillement des discontinuités des fondations rocheuses de barrages ». Thèse, Université de Sherbrooke, 2015. http://hdl.handle.net/11143/6707.

Texte intégral

Résumé :

Résumé : Les barrages induisent un impact potentiellement important sur l'environnement et la société par la modification des écosystèmes, le déplacement des populations en amont et surtout par la présence d'un risque imposé aux populations situées à l'aval. Même si les ruptures de ces ouvrages ont une probabilité d'occurrence faible, la cause principale des accidents, à côté des submersions par des crues imprévues, a toujours été la rupture des fondations (ICOLD 1993) suite à des problèmes d'érosion, ou d'insuffisance de résistance au cisaillement le long des discontinuités rocheuses, des joints de levées ou de l'interface barrage-fondation. La fréquence de ruptures par défaut de résistance au cisaillement des discontinuités des fondations des barrages en béton est estimée à 21 % (ICOLD 1995). Les fondations rocheuses présentent souvent une variabilité verticale et horizontale des propriétés de résistance au cisaillement des discontinuités. Une variabilité verticale peut être matérialisée par une moyenne de la propriété de résistance qui varie en profondeur et dont la prise en compte réduit la variance de cette propriété de résistance. Aussi, la rupture des fondations rocheuses par défaut de résistance au cisaillement des discontinuités est un mécanisme qui mobilise les propriétés ponctuelles de résistance au cisaillement présentes sur cette discontinuité. La résistance au cisaillement mobilisée le long de cette discontinuité présente parfois une variance moins élevée que celle de la résistance ponctuelle au cisaillement (échelle de laboratoire). Ces phénomènes de variabilité spatiale ne sont pas pris en compte dans la justification du comportement en cisaillement des fondations ni dans les travaux de recherches publiées dans la littérature. L'objectif de la thèse est d'élaborer une démarche d'analyse de la variabilité spatiale de la résistance au cisaillement qui prend en compte cette réduction de la dispersion. Cette démarche a été élaborée dans le contexte de l'état de l'art actuel, avec la combinaison des impératifs suivants : • La démarche est basée sur une méthodologie expérimentale i)-alternative à l'essai de cisaillement direct (coûteux en temps et en argent) pouvant être relativement simple à mettre en œuvre ii)- qui permet de générer des données quantitatives de cisaillement suffisamment abondantes pour analyser la variabilité spatiale de la résistance au cisaillement. • Cette démarche a été mise en œuvre au contexte des outils numériques et des méthodes de justification de la résistance à l'effort tranchant d'une fondation rocheuse de barrage-poids. La méthodologie expérimentale définie dans la thèse a fait l'objet d'une validation par étude comparative avec 35 essais de cisaillement direct sur des joints à différents degrés de rugosité et d’altération, prélevés d'une fondation de barrage-poids en béton. Il a été développé une démarche d'analyse de la variabilité spatiale de la résistance au cisaillement des joints. Cette démarche repose sur l'utilisation des données géo référencées de paramètres de cisaillement caractérisant la même famille de discontinuité le long d'un forage vertical. Afin de valider la pertinence et l’applicabilité de cette démarche, nous l’avons implémentée dans un cas d'étude de fondation rocheuse de barrage. A l'aide d'un code de calcul numérique basé sur la méthode des éléments finis, une étude a permis d'illustrer la pertinence de l'analyse de la variabilité spatiale de la résistance au cisaillement des joints dans une étude de stabilité au glissement des fondations rocheuses de barrage. Les résultats montrent que la prise en compte de la variabilité spatiale des paramètres de cisaillement permet d'augmenter la marge de sécurité mesurée à travers une hausse du coefficient de sécurité et une baisse significative de la probabilité de défaillance. // Abstract : Dams induce a potentially significant impact on the environment and society by changing ecosystems, by populations’ relocation upstream and especially by the presence of an imposed risk on populations located downstream. Although dam failures have a low probability, the main cause of accidents, near submersions by unexpected flood has been foundations failures (ICOLD 1993) due to problems of erosion, or insufficient shear strength along the rock discontinuities or the interface between dam and foundation. Among dam failures, 21% are related to lack of shear strength along the discontinuities of the foundations (ICOLD 1995). It is well known that rock, as soil, is a complex engineering material formed y natural process, which induces vertical and horizontal variability. Plus, the sliding process of a rock foundation discontinuity is a mechanism that mobilizes points shear properties of this discontinuity. The variability of shear properties averaged over the sheared discontinuities is less than that of their point shear properties. This is known as the average effect in spatial variability. These phenomena of spatial variability are not taken into account in the standards of stability analysis of dam foundations sliding or research work published in the literature. The aim of the thesis is to develop an analysis of the spatial variability of shear strength that takes into account the reduction of the variability by scaling up effect. This approach was developed in the context of the current state of the art. An experimental method, which aimed to investigate in a simple way the shear strength of joints, was suggested in the thesis and has been validated by comparative study with more than thirty direct shear tests on joints taken from a foundation of concrete gravity dam. It was developed a process to analyze the spatial variability of the shear strength of the joints using the input parameters of the model of Barton and Choubey (1977). This approach is based on the use of geo -referenced data on these parameters characterizing the family of discontinuity along a vertical borehole. To validate the relevance and applicability of this approach, we have implemented it in a case study of a rock dam foundation. Using finite element software, a study illustrates the relevance of the analysis of the spatial variability of the shear strength of the joints in the assessment of stability against rock dam foundations sliding. The results show that taking into account the spatial variability of shear parameters can increase the margin of safety measured through an increase in the safety factor and a significant decrease in the probability of failure.

Styles APA, Harvard, Vancouver, ISO, etc.

46

Manning, Grant Russell. « Relations between spatial variability of soil properties and grain yield response to nitrogen fertilizer in a variable Manitoba soil-landscape ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ45091.pdf.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

47

Durrett, Melody S. « Spatial variability in plant and soil properties on New Zealand seabird islands, and the effects of introduced rats ». Thesis, University of Alaska Fairbanks, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3624440.

Texte intégral

Résumé :

Seabirds are ecosystem engineers with two major impacts on island ecosystems: they bring large quantities of marine nutrients to the terrestrial environment in the form of guano, carcasses, feathers, eggs, and spilled food, and they disturb the soil surface. Burrowing seabirds can denude the soil surface of all seedlings and leaf litter, plowing them under and loosening the soil. However, seabirds are colonial, and burrows are not even spaced over the surface of an island, producing spatial variability within a single island that might reveal how seabird activities control island ecosystem function.

In this dissertation I review seabird island ecology in general, focusing on how introduced predators have reduced seabird populations, interrupting seabird activities and altering island ecology. I then describe three studies designed to quantify the effects of seabirds on soil and plant properties within individual islands and compare these patterns across islands varying in seabird density, especially where seabirds have declined because of invasive rats (Rattus spp.).

I used geostatistics to quantify the spatial variance in seabird burrows and various soil and plant properties (including soil and leaf N) within six islands of low, intermediate, and high burrow density. I found that burrow density was not a good predictor at within-island scales, and though the variance of some soil properties (pH, soil δ¹⁵N, and soil compaction) peaked on intermediate islands as expected, variables reflecting the soil N cycle (net ammonification and net nitrification potential, NH₄⁺ and NO₃^-) continued to increase in variability on very high-density seabird islands. Ecosystem properties clearly responded to seabirds at different spatial scales, possibly because seabirds deposit guano at different spatial scales than they dig.

Using data within three rat-invaded and three rat-free islands, I used structural equation models to examine seabird influences on N cycling. I found some mechanisms that were constant across islands, such seabird-related decreases in soil water and pH, but other mechanisms differed between invaded and uninvaded islands, suggesting that rats manifest an alternative state for island N cycles, which may or may not be reversible.

Finally, I investigated whether plants can use ammonia (NH₃ gas) volatilized from seabird islands, measuring NH₃ concentrations across 10 islands and within a single island where I also experimentally manipulated plant N demand. Both rat-invaded and rat-free islands produced meaningful concentrations of NH₃ gas, and multiple plant species including Melicytus ramiflorus and Coprosma macrocarpa used it for up to 20% and 30% (respectively) of their total leaf N. Plant N demand modified NH₃ uptake, suggesting that plants located not on seabird colonies, but downwind, may benefit the most from this gaseous N source.

I suggest that future studies attempt to estimate thresholds of burrow density at which seabird-controlled ecosystem properties can recover from rat invasion.

Styles APA, Harvard, Vancouver, ISO, etc.

48

Holleran, Molly E. « Quantifying catchment scale soil variability in Marshall Gulch, Santa Catalina Mountains Critical Zone Observatory ». Thesis, The University of Arizona, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1538334.

Texte intégral

Résumé :

The quantification and prediction of soil properties is fundamental to further understanding the Critical Zone (CZ). In this study we aim to quantify and predict soil properties within a forested catchment, Marshall Gulch, AZ. Input layers of soil depth (modeled), slope, Saga wetness index, remotely sensed normalized difference vegetation index (NDVI) and national agriculture imagery program (NAIP) bands 3/2 were determined to account for 95% of landscape variance and used as model predictors. Target variables including soil depth (cm), carbon (kg/m²), clay (%), Na flux (kg/m²), pH, and strain are predicted using multivariate linear step-wise regression models. Our results show strong correlations of soil properties with the drainage systems in the MG catchment. We observe deeper soils, higher clay content, higher carbon content, and more Na loss within the drainages of the catchment in contrast to the adjacent slopes and ridgelines.

Styles APA, Harvard, Vancouver, ISO, etc.

49

Junior, José Geraldo de Abreu Sousa. « Sensoriamento remoto e sistema de informações geográficas na caracterização de solos e quantificação de seus atributos ». Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/11/11140/tde-02032006-170350/.

Texte intégral

Résumé :

Com a crescente adoção da agricultura de precisão, há uma busca por informações mais detalhadas da variabilidade espacial dos solos em escalas que viabilizem um manejo diferenciado da área de produção. Entretanto, o custo das análises de solo é sem dúvida um dos principais entraves para obtenção dessas informações. A adoção do geoprocessamento, utilizando-se o sensoriamento remoto, GPS e sistemas de informações geográficas para caracterização de solos e quantificação de seus atributos, é um desafio que vem sendo buscado por vários pesquisadores por ser uma tecnologia alternativa de avaliação do solo, podendo ser mais barata, rápida e com menor impacto ambiental. Contudo, como qualquer tecnologia de ponta, ela deve ser devidamente testada e ajustada para os mais diversos tipos de solos e regiões. Para tanto, foram escolhidas áreas localizadas na região de São Carlos e Ibaté, São Paulo, tendo os seguintes objetivos: (i) caracterizar o comportamento espectral de solos por sensores terrestre (FieldSpec) e orbital (ASTER); (ii) determinar alterações no comportamento espectral dos solos ao longo de diferentes toposseqüências; (iii) gerar modelos de quantificação de atributos químicos e granulométricos dos solos a partir de sua radiação eletromagnética e (iv) caracterizar os solos da região conforme a altitude e declividade do terreno utilizando-se técnicas de sistema de informações geográficas. Para isso foram coletadas amostras no campo e realizado o mapeamento da área. As amostras foram avaliadas por diferentes sensores e correlacionou-se seus atributos com a reflectância. Desta forma, modelos espectrais de atributos dos solos foram elaborados. O mapa de solos elaborado foi cruzado com informações de declive e altitude para sua caracterização. Verificou-se que os atributos granulométricos e a matéria orgânica possuem uma grande influência no comportamento espectral dos solos. Verificou-se também, que solos localizados em cotas mais elevadas do relevo apresentam maior intensidade de reflectância do que os situados em posições inferiores, devido à variação do material de origem da referida região. As correlações entre os atributos e os dados espectrais do solo indicam uma tendência de aumentar o coeficiente de correlação em maiores comprimentos de onda. Os modelos elaborados para quantificação dos atributos granulométricos resultaram em valores estimados muito próximos dos determinados pelas análises convencionais (argila: R² = 0,69). Em escalas regionais há uma tendência de ocorrência de determinadas classes de solo em altitudes e declividades similares. Na área estudada, por exemplo, o Latossolo Amarelo foi encontrado predominantemente nas cotas mais altas (815-835 m) e em relevo plano (1-3 %). Conclui-se que a partir de informações de declividade e elevação da área, a extrapolação pedológica em locais sem apoio de campo deve ser feita com cautela.
With the increasing in adoption of precision agriculture, there is a need more detailed information about soil spatial variability in order to make possible a better management of crop fields. However, the cost of soil chemical analysis is the most important obstacle to obtain this information. The use of geoprocessing techniques, such as remote sensing, GPS and geographic information system, for soil characterization and quantification of their attributes is a challenge pursued for several researchers because it is an alternative technology for soil evaluation that can be cheaper, faster, and with lower environmental impact. Nevertheless, like any new technology, it must be tested and adjusted with different soil types located in different areas. For this research, two areas were chosen: São Carlos and Ibaté, São Paulo region, with the following objectives: (i) characterize the soil spectral response using terrestrial (FieldSpec) and orbital (ASTER) sensors; (ii) determine the changes on soil spectral response across different toposequences; (iii) generated models to quantify soil chemical and granulometric attributes based on its electromagnetic radiation and (iv) characterize the soil in conformity with altitude and slope using geographic information system techniques. Soil samples were collected and a soil map was developed. Soil samples were analyzed by both sensors and their attributes was correlated with spectral reflectance. Then spectral models were developed to quantify soil attributes. Soil map was crossed with declivity and elevation information for characterization. It was verified that the granulometric and organic matter attributes have a great influence on soil spectral response. It was verified that soils located in higher altitudes presented higher reflectance intensity than those located in lower positions due to the variation on parent material. The correlations between soil attributes and spectral data showed a tendency to increase the correlation coefficient at higher wavelengths. The models elaborated to quantify the granulometric attributes resulted in estimated values very close to the determined by conventional laboratory analysis (clay content: R² = 0.69). In regional scale there is a tendency of some soil classes occur at similar altitudes and slope. For example, the Typic Haplustox was found predominant at higher altitudes (815-835 m) and plan relief (1-3%). It was possible to conclude that based on information about slope and altitudes for this area, the pedologic extrapolation in new areas without field work should be done with caution.

Styles APA, Harvard, Vancouver, ISO, etc.

50

Kreba, Sleem. « LAND USE IMPACT ON SOIL GAS AND SOIL WATER TRANSPORT PROPERTIES ». UKnowledge, 2013. http://uknowledge.uky.edu/pss_etds/31.

Texte intégral

Résumé :

The consequences of land use choices on soil water and gas transport properties are significant for gas and water flux in agricultural environments. Spatial and temporal patterns and associations of soil water and soil gas characteristics and processes in different land uses are not well understood. The objectives of this study were to 1) characterize soil structure under crop and grass systems, 2) quantify spatial patterns and associations of soil physical characteristics in crop and grass systems, and 3) quantify spatial and temporal patterns and associations of CO2 and N2O fluxes. The research was conducted in a 60 by 80 m field divided into grass and crop systems. Sixty sampling points were distributed in four transects with 5- and 1-m spatial intervals between measurement points. Gas fluxes were measured, at two-week time intervals, 22 times during a year. Pore size distribution was more homogeneous and more continuous pores were found in the grass than in the crop system. The spatial variability of most selected soil physical characteristics was more structured in the crop than in the grass system, which reflected the impact of land use and soil structure on their spatial patterns. CO2 flux was dependent for a longer distance in the grass than in the crop system, however, the two land-use systems exhibited similar spatial ranges of N2O flux. Gas fluxes were temporally dependent for a longer period in the grass than in the crop system. The spatial associations between CO2 and N2O fluxes and selected biochemical and physical factors depended on the flux sampling season and land use. Soil temperature was the dominant controlling factor on the temporal variability of CO2 and N2O fluxes but not on the spatial behavior. Considering the spatial and temporal ranges and dependency strength of soil variables helps identify efficient sampling designs that can result in better time and resource management. Spatial and temporal relationships between the selected soil variables also improve understanding soil management and sampling soil variables. This study provides the baseline and recommendations for future investigations specifically for sampling designs, soil management, and predictions of different soil processes related to gas fluxes.

Styles APA, Harvard, Vancouver, ISO, etc.

Thèses sur le sujet « Spatial variability of soils »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres