Soil Parameter Modeling

The effects of cyclic loading are extremely dependent upon the soil and nature of cyclic deformation as shown in the previous section. The potential for pore water pressure generation either in clays, silts, or sands governs their behavior under cyclic loading. Two analytical approaches have been developed to model this behavior. 

Total stress-strain approaches in which the cyclic strain or stress conditions of interest are simulated on laboratory specimens and behavior inferred directly 

Effective stress-strain approaches in which one attempts to determine analytically the pore water pressures generated and their influence on the soil behavior. Laboratory tests on the sediments are utilized at a more fimdamental level to determine pore pressure generation characteristics 

The effective stress approaches are more intuitively satisfactory from a fundamental standpoint. However, in present offshore practice it is not common that enough information is known about either the in-situ stress condition or the stress-strain pore water pressure characteristics of the material imder cyclic loading conditions to enable effective implementation of this approach. 

The total stress-strain approaches for cyclic loading problems have largely evolved from work on earthquake response related problems. In general, two methodologies have evolved using the total stress-strain approach. The first method involves the development of parameters for input into a stress-strain matrix such as employed in a typical finite-element simulation. 

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M. van Noordwijk and S. C. van de Geijn, Root, shoot and soil parameters required for proeess-oriented models of crop growth limited by water or nutrients. Plant Soil I8S (1996). 

UNSAT-H simulates plant transpiration with a PET concept. The model partitions plants removal of soil-water between soil layers based on (1) distribution of plant roots within the soil profile for cheatgrass (an invading and weedy grass species found in dry regions of Washington State) or (2) the user may supply other functions. The user must enter soil-water parameters that describe the limits for plant extraction of water from each layer of soil. The model also uses the same daily value pattern for the LAI for each year. 

UNSAT-H does not address the effects of soil density on plant growth and water balance. Disadvantages caused by the computational methods used to estimate soil water flow include the following (1) the model requires the user to choose from several submodels to solve the Richards equation this choice should be made by a person with training in advanced soil physics and (2) the model requires the input of several soil parameters that are difficult to estimate for the completed cover soil. 

Soil parameter inputs, their use within the model, and appropriateness of estimates that affect plant growth, and water use and storage. 

Parameters subject to calibration within SWAT were selected after a preliminary sensitivity analysis and literature review, to partially compensate for the inadequacy of the initial values assumed for some of them (especially those related to soil type), model structure and other sources of uncertainty. A detailed description about the SWAT parameters can be found in [5, 6], while a brief description of the selected parameters is provided next ... 

The objective of this study was to demonstrate the physical transport of TCE by EO through cores of undisturbed soil. While research approaches have been performed on packed columns of pure clay (e.g. kaolinite), few have used native soils, and only in the form of slurries. At this time, no information is available for transport of TCE by EO through intact cores of natural soil. Therefore, the results of EO experiments using undisturbed soil are more applicable to actual site conditions than using single mineral soil. Parameters governing TCE transport in the soil are used in a one dimension advective model to describe TCE transport during the experiment. 

When soil parameters influencing the availability of a substance are known and models are available to predict the available fraction, SQSs can be expressed as a function of these soil properties. This approach reduces the variability of the data and increases the ecological relevance of the SQS. 

Again, this approach can be applied to substances that are either rich or poor in ecotoxicity data. The prerequisites are knowledge of the soil parameter values influencing bioavailability of the substance in the individual ecotoxicity tests and applicability of the model for the species that is tested. This approach further reduces uncertainty and increases the ecological relevance of the SQS. 

Frolking and Grill (1994) developed a peat soil climate model driven by daily weather and used correlations of CH4 flux with environmental parameters to investigate how climate and weather control the observed temporal variability... 

Cosby B. J., HombergerG. M., Galloway J. N., and Wright R. F. (1985a) ModeUing the effects of acid deposition assessment of a lumped-parameter model of soil water and streamwater chemistry. Water Resour. Res. 21, 51-63. 

Barrow [772] derived a kinetic model for sorption of ions on soils. This model considers two steps adsorption on heterogeneous surface and diffusive penetration. Eight parameters were used to model sorption kinetics at constant temperature and another parameter (activation energy of diffusion) was necessary to model kinetics at variable T. Normal distribution of initial surface potential was used with its mean value and standard deviation as adjustable parameters. This surface potential was assumed to decrease linearly with the amount adsorbed and amount transferred to the interior (diffusion), and the proportionality factors were two other adjustable parameters. The other model parameters were sorption capacity, binding constant and one rate constant of reaction representing the adsorption, and diffusion coefficient of the adsorbate in tire solid. The results used to test the model cover a broad range of T (3-80°C) and reaction times (1-75 days with uptake steadily increasing). The pH was not recorded or controlled. 

Blackburn et al. [4] provided the first ENM-based geographic predictions for the potential distribution of B. anthracis for the lower 48 states. That modeling scenario was based on a six-variable niche definition and included two soil parameters (soil moisture content and soil pH). These parameters are not available for Mexico, so to project the geographic distribution of an unknown data set, it is necessary to construct models for both countries with the same ecological parameters. This required the development of a modified coverage set that included variables available for both countries. 

Results from the first modeling effort for B. anthracis [4] indicated that mean NDVI was the most limiting variable in the rule set. For this chapter, I provide a five-variable coverage set to define the ecological niche for B. anthracis. Soil parameters were removed from the coverage set and replaced with an additional NDVI variable -annual amplitude [68]. 

The review is organized as follows first, we discuss aspects of the unitary approach for combining adsorptive and capillary contributions, and present the new pore scale model of Tuller et al. (1999). The upscaling scheme of Or and Tuller (1999) for representing sample scale retention properties will be presented, followed by illustrative examples with measured characteristic data and a discussion of critical soil parameters. The role of liquid-vapor interfacial area will be highlighted by comparisons of model predictions with limited measurements. Finally, we introduce hydrodynamic considerations of unsaturated flow in films and comers leading to prediction of hydraulic conductivity of rough rock surfaces and unsaturated porous media. 

For other metals, such as Cd, Zn, Cu, and Ni, no simple sohd with properties simulating metal solubility in soils exists. Lindsay (1979) previously advocated the concept of a fictitious sohd phase called soil-Cu. There are a number of theoretical and semi-theoretical models that have been used to describe (ad)sorpfion of transition metals onto reactive surfaces (Fe, Mn or Al oxides soil organic matter). While probably more correct in a mechanistic sense than the solubility relations discussed below, these models have not proven to be particularly useful with intact soils because they contain a very complex assemblage of colloidal surfaces. Moreover, they do not seem to adequately predict increases in metal solubility with increases in total soil metal burden. This has led an increasing number of researchers to develop purely empirical models that describe trace-metal solubility as a function of simple soil parameters such as pH, organic matter content, and total metal content (e.g. McBride et al., 1997 Gray et al.,... 

T. goesingense. The required input parameters were partly measured for the experimental conditions of the rhizobox experiment and partly obtained from literature data. The curves that matched best measured labile Ni were those obtained by the most simple initial model, the model including release from a fixed Ni phase and the two-stage sorption model. The simulation results for each of the three models were quite similar, indicating that the influence of the additionally included processes was relatively small under the assumptions of equilibrium between fixed phase and solution in the bulk soil. The models including both root hairs and exudation overestimated depletion of labile Ni close to... 

We apply the presented maximiun entropy concept within this example for the modeling of the soil parameters and evaluate the influence of the parameter imcertainties on the failure probability. The limit state function of the bearing failure of a simple strip foimdation with pure vertical loading can be derived based on Terzaghi (1943) and Meyerhof (1953) as... 

Parameters of van Genuchten equation Or, 0s, a, n were predicted from 80 soil basic properties (such as soil bulk density, particle size distribution, OM) using the enter linear regression model (namely, linear regression parameter model, LRP) with bootstrap methods based on the relationship between SWRC and basic properties. 

In reality the soil-parameters, such as those describing the Kanai-Tajiml model, cannot be determined deterministically. Analytically these uncertainties can be taken into account by treating each parameter as a random variable. The fact that the values of the parameters may be predicted within a particular range leads to the assumption of a parabolically shaped probability density function (p.d.f.) for the parameters Cg and oo. The p.d.f. for the parameter Gq may be assumed of an exponential shape. 

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