Academic literature on the topic 'Soil hydraulic stress'
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Journal articles on the topic "Soil hydraulic stress"
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Nguyen, Thuy Huu, Matthias Langensiepen, Jan Vanderborght, Hubert Hüging, Cho Miltin Mboh, and Frank Ewert. "Comparison of root water uptake models in simulating CO<sub>2</sub> and H<sub>2</sub>O fluxes and growth of wheat." Hydrology and Earth System Sciences 24, no. 10 (October 23, 2020): 4943–69. http://dx.doi.org/10.5194/hess-24-4943-2020.
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Abstract. Stomatal regulation and whole plant hydraulic signaling affect water fluxes and stress in plants. Land surface models and crop models use a coupled photosynthesis–stomatal conductance modeling approach. Those models estimate the effect of soil water stress on stomatal conductance directly from soil water content or soil hydraulic potential without explicit representation of hydraulic signals between the soil and stomata. In order to explicitly represent stomatal regulation by soil water status as a function of the hydraulic signal and its relation to the whole plant hydraulic conductance, we coupled the crop model LINTULCC2 and the root growth model SLIMROOT with Couvreur's root water uptake model (RWU) and the HILLFLOW soil water balance model. Since plant hydraulic conductance depends on the plant development, this model coupling represents a two-way coupling between growth and plant hydraulics. To evaluate the advantage of considering plant hydraulic conductance and hydraulic signaling, we compared the performance of this newly coupled model with another commonly used approach that relates root water uptake and plant stress directly to the root zone water hydraulic potential (HILLFLOW with Feddes' RWU model). Simulations were compared with gas flux measurements and crop growth data from a wheat crop grown under three water supply regimes (sheltered, rainfed, and irrigated) and two soil types (stony and silty) in western Germany in 2016. The two models showed a relatively similar performance in the simulation of dry matter, leaf area index (LAI), root growth, RWU, gross assimilation rate, and soil water content. The Feddes model predicts more stress and less growth in the silty soil than in the stony soil, which is opposite to the observed growth. The Couvreur model better represents the difference in growth between the two soils and the different treatments. The newly coupled model (HILLFLOW–Couvreur's RWU–SLIMROOT–LINTULCC2) was also able to simulate the dynamics and magnitude of whole plant hydraulic conductance over the growing season. This demonstrates the importance of two-way feedbacks between growth and root water uptake for predicting the crop response to different soil water conditions in different soils. Our results suggest that a better representation of the effects of soil characteristics on root growth is needed for reliable estimations of root hydraulic conductance and gas fluxes, particularly in heterogeneous fields. The newly coupled soil–plant model marks a promising approach but requires further testing for other scenarios regarding crops, soil, and climate.
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Windisch, Étienne J. "The hydraulics problem in slope stability analysis." Canadian Geotechnical Journal 28, no. 6 (December 1, 1991): 903–9. http://dx.doi.org/10.1139/t91-107.
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Hydraulic pressures and forces are obtained on a typical slice, as used in current methods of slope stability analysis, under hydrostatic and flowing groundwater conditions. It is shown that current methods do not satisfy some basic hydraulics and soil mechanics principles. The effective normal stress on the lower boundary of a slice is shown to be underestimated, and the resultant hydraulic force is not accounted for adequately. Key words: effective stress, hydraulic pressure, hydraulic gradient, hydraulic force, slope stability.
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Yang, N., and S. L. Barbour. "The impact of soil structure and confining stress on the hydraulic conductivity of clays in brine environments." Canadian Geotechnical Journal 29, no. 5 (October 1, 1992): 730–39. http://dx.doi.org/10.1139/t92-081.
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Numerous studies have been completed in recent years on the alteration of the hydraulic conductivity of clayey soils as a result of exposure to concentrated organic or inorganic permeants. These hydraulic conductivity changes have been attributed to either changes in microstructure, due to contraction of the diffuse double layer, or to the alteration of the macrostructure, as a result of volume changes leading to shrinkage fractures or fissures. In this paper, the change in hydraulic conductivity of a highly plastic natural clay during exposure to a concentrated sodium chloride (NaCl) solution is described. The performance of samples with three different initial soil structures, prepared by slurry, static compaction, and kneading compaction, were investigated under various levels of confining stress. Hydraulic conductivity tests were carried out before and after the samples were exposed to the NaCl solutions. Scanning electron microscope photography was used to compare the soil structures before and after brine permeation. The test results show that the alteration of hydraulic conductivity is strongly related to the initial soil structure and the level of confining stress. No significant change in the microfabric of the clay was observed; however, the size of the interaggregate pores appeared to increase as a result of the physicochemical volume change that occurred during brine permeation. The increase in hydraulic conductivity that occurred during brine permeation could be prevented by increasing the level of confining stress. The stress levels at which significant increases in hydraulic conductivity occurred appeared to be coincident with low levels of vertical stress which allowed the sample to undergo lateral shrinkage and a subsequent loss of confinement. Key words : hydraulic conductivity, clay soils, osmotic consolidation, sodium chloride brine, soil structure, scanning electron microscope.
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Chen, Meng Qiao, Jian Kun Liu, and Jun Hua Xiao. "Soil Stress of Shield Tunnel Face in Sands under High Hydraulic Pressure." Advanced Materials Research 588-589 (November 2012): 1983–87. http://dx.doi.org/10.4028/www.scientific.net/amr.588-589.1983.
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Based on the under river tunneling project of Nanjing Metro Puzhulu-Binjianglu interval, a numerical model was built to simulate the process of losing stability, variation of soil stress and the soil arching effect caused by soil stress redistribution under high hydraulic pressure were studied. The results show that, compared to no hydraulic pressure, the limit supporting pressure is reached when smaller soil deformation has occurred and it is much greater under high hydraulic pressure. Along the depth from the bottom, soil vertical stress first decreases and then remains unchanged with increasing face displacement; Soil horizontal stress first decreases and then increases slightly. Soil lateral pressure coefficient first increases and then decreases along the depth from the bottom. Soil vertical and horizontal stress decrease in front of the tunnel face, where the failure region forms. Soil vertical stress decreases and horizontal stress increases above the failure region, where the vault region forms. Soil vertical stress increases and horizontal stress decreases around the failure region, where the skewback region forms. The results are conductive to better reveal the failure mechanism and determine the limit supporting pressure under high hydraulic pressure.
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Brom, Jakub, Renata Duffková, Jan Haberle, Antonín Zajíček, Václav Nedbal, Tereza Bernasová, and Kateřina Křováková. "Identification of Infiltration Features and Hydraulic Properties of Soils Based on Crop Water Stress Derived from Remotely Sensed Data." Remote Sensing 13, no. 20 (October 15, 2021): 4127. http://dx.doi.org/10.3390/rs13204127.
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Knowledge of the spatial variability of soil hydraulic properties is important for many reasons, e.g., for soil erosion protection, or the assessment of surface and subsurface runoff. Nowadays, precision agriculture is gaining importance for which knowledge of soil hydraulic properties is essential, especially when it comes to the optimization of nitrogen fertilization. The present work aimed to exploit the ability of vegetation cover to identify the spatial variability of soil hydraulic properties through the expression of water stress. The assessment of the spatial distribution of saturated soil hydraulic conductivity (Ks) and field water capacity (FWC) was based on a combination of ground-based measurements and thermal and hyperspectral airborne imaging data. The crop water stress index (CWSI) was used as an indicator of crop water stress to assess the hydraulic properties of the soil. Supplementary vegetation indices were used. The support vector regression (SVR) method was used to estimate soil hydraulic properties from aerial data. Data analysis showed that the approach estimated Ks with good results (R2 = 0.77) for stands with developed crop water stress. The regression coefficient values for estimation of FWC for topsoil (0–0.3 m) ranged from R2 = 0.38 to R2 = 0.99. The differences within the study sites of the FWC estimations were higher for the subsoil layer (0.3–0.6 m). R2 values ranged from 0.12 to 0.99. Several factors affect the quality of the soil hydraulic features estimation, such as crop water stress development, condition of the crops, period and time of imaging, etc. The above approach is useful for practical applications for its relative simplicity, especially in precision agriculture.
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Andersen, Knut H., Colin G. Rawlings, Tom A. Lunne, and Trond H. By. "Estimation of hydraulic fracture pressure in clay." Canadian Geotechnical Journal 31, no. 6 (December 1, 1994): 817–28. http://dx.doi.org/10.1139/t94-099.
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For offshore drilling, and in particular when drilling from fixed platforms in deep waters, the mud pressure will be high compared with the hydraulic fracture pressure (i.e., the formation strength) close to the sea floor. The first casing (the conductor) should therefore be installed to a depth where the formation strength is sufficient to prevent hydraulic fracturing of the soil. The consequences of hydraulic fracture could be mud flowing into the formation and loss of mud circulation. This slows down the drilling and, in cases where large quantities of mud flow into the formations beneath the platform, may even threaten the integrity of the foundation soils and create a safety problem. A conservative approach with too deep conductor setting depths will, on the other hand, lead to high unnecessary costs. This paper presents a new approach for calculating hydraulic fracture pressures. The new calculation approach considers two important factors that are generally not covered by theories found in the literature: nonlinearity of the stress–strain properties of the soil, and pore-pressure changes in the soil due to changes in total normal stress and shearing of the soil. The stress–strain properties and the shear-induced pore pressure are determined from laboratory tests. The proposed calculation approach has been verified against a series of laboratory model hydraulic fracture tests and in situ hydraulic fracture tests carried out at numerous offshore sites. The paper also presents a rational approach to establish the maximum allowable drilling mud pressure in clay formations and recommends partial safety coefficients that depend upon the consequences of hydraulic fracture and the quality of the soil data. Key words : hydraulic fracture, boreholes, clay, conductor setting depth, model tests, in situ tests, calculations.
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Guérin, Marceau, Georg von Arx, Dario Martin-Benito, Laia Andreu-Hayles, Kevin L. Griffin, Nate G. McDowell, William Pockman, and Pierre Gentine. "Distinct xylem responses to acute vs prolonged drought in pine trees." Tree Physiology 40, no. 5 (January 24, 2020): 605–20. http://dx.doi.org/10.1093/treephys/tpz144.
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Abstract Increasing dryness challenges trees’ ability to maintain water transport to the leaves. Most plant hydraulics models use a static xylem response to water stress. Yet, in reality, lower soil moisture and warmer temperatures during growing seasons feed back onto xylem development. In turn, adjustments to water stress in the newly built xylem influence future physiological responses to droughts. In this study, we investigate the annual variation of anatomical traits in branch xylem in response to different soil and atmospheric moisture conditions and tree stress levels, as indicated by seasonal predawn leaf water potential (ΨL,pd). We used a 6-year field experiment in southwestern USA with three soil water treatments applied to Pinus edulis Engelm trees—ambient, drought (45% rain reduction) and irrigation (15–35% annual water addition). All trees were also subject to a natural 1-year acute drought (soil and atmospheric) that occurred during the experiment. The irrigated trees showed only moderate changes in anatomy-derived hydraulic traits compared with the ambient trees, suggesting a generally stable, well-balanced xylem structure under unstressed conditions. The artificial prolonged soil drought increased hydraulic efficiency but lowered xylem construction costs and decreased tracheid implosion safety ((t/b)2), suggesting that annual adjustments of xylem structure follow a safety–efficiency trade-off. The acute drought plunged hydraulic efficiency across all treatments. The combination of acute and prolonged drought resulted in vulnerable and inefficient new xylem, disrupting the stability of the anatomical trade-off observed in the rest of the years. The xylem hydraulic traits showed no consistent direct link to ΨL,pd. In the future, changes in seasonality of soil and atmospheric moisture are likely to have a critical impact on the ability of P. edulis to acclimate its xylem to warmer climate. Furthermore, the increasing frequency of acute droughts might reduce hydraulic resilience of P. edulis by repeatedly creating vulnerable and less efficient anatomical structure.
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Han, Bowen, Guoqing Cai, Lin Xie, Jian Li, and Chenggang Zhao. "Bounding surface constitutive model for unsaturated soils considering microscopic pore structure and bonding effect." E3S Web of Conferences 195 (2020): 02007. http://dx.doi.org/10.1051/e3sconf/202019502007.
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This article presents a bounding surface model for unsaturated soils by using skeleton stress and bonding variable based on microcosmic pore structure as constitutive variables. A Hydraulic hysteresis soil-water characteristic curve model considering deformation and hydraulic hysteresis is combined to achieve hydraulic coupling. The proposed model can capture the change of the inter-particles bonding effect in the deformation process of unsaturated soils and accurately predict the hydraulic mechanical behavior of unsaturated soils under complicated loading paths and wetting-drying cycles. The validity of the proposed model is confirmed by the results of unsaturated isotropic compression tests, wetting-drying cycles tests and unsaturated triaxial shear tests reported in the literature.
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Ma, Tiantian, Changfu Wei, Pan Chen, Huihui Tian, and De'an Sun. "A Unified Elastoplastic Model of Unsaturated Soils Considering Capillary Hysteresis." Journal of Applied Mathematics 2013 (2013): 1–15. http://dx.doi.org/10.1155/2013/537185.
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Unlike its saturated counterparts, the mechanical behavior of an unsaturated soil depends not only upon its stress history but also upon its hydraulic history. In this paper, a soil-water characteristic relationship which is capable of describing the effect of capillary hysteresis is introduced to characterize the influence of hydraulic history on the skeletal deformation. The capillary hysteresis is viewed as a phenomenon associated with the internal structural rearrangements in unsaturated soils, which can be characterized by using a set of internal state variables. It is shown that both capillary hysteresis and plastic deformation can be consistently addressed in a unified theoretical framework. Within this context, a constitutive model of unsaturated soils is developed by generalizing the modified Cam-Clay model. A hardening function is introduced, in which both the matric suction and the degree of saturation are explicitly included as hardening variables, so that the effect of hydraulic history on the mechanical response can be properly addressed. The proposed model is capable of capturing the main features of the unsaturated soil behavior. The new model has a hierarchical structure, and, depending upon application, it can describe the stress-strain relation and the soil-water characteristics in a coupled or uncoupled manner.
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Nalbantoglu, Zalihe, and Erdil Riza Tuncer. "Compressibility and hydraulic conductivity of a chemically treated expansive clay." Canadian Geotechnical Journal 38, no. 1 (February 1, 2001): 154–60. http://dx.doi.org/10.1139/t00-076.
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The paper presents a series of laboratory tests and evaluates the effect of lime and fly ash on the compressibility and hydraulic characteristics of an expansive soil in Cyprus. The tests were performed at different percentages of lime (07%) and fly ash (15 and 25%) by dry weight of soil, and additional tests were also performed on soils treated with 15% fly ash plus 3% lime. Previously published research reveals that few data are available concerning the compressibility and hydraulic conductivity of lime-treated soils. The results of this study indicate an increase in the vertical effective yield stress (apparent preconsolidation pressure) and a decrease in the compressibility characteristics of the treated soils. Moreover, unlike some of the findings in the literature, higher hydraulic conductivity values were obtained with time. This finding has been substantiated by the reduced cation exchange capacity (CEC) values, which indicate that the pozzolanic reaction causes the soils to become more granular in nature, resulting in higher hydraulic conductivity.Key words: cementation, compressibility, fly ash, hydraulic conductivity, lime.
Dissertations / Theses on the topic "Soil hydraulic stress"
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Chen, Rui. "Experimental study and constitutive modelling of stress-dependent coupled hydraulic hysteresis and mechanical behaviour of an unsaturated soil /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202007%20CHEN.
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Roshankhah, Shahrzad. "Physical properties of geomaterials with relevance to thermal energy geo-systems." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54893.
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Energy related geo-systems involve a wide range of engineering solutions from energy piles to energy geo-storage facilities and waste repositories (CO₂, nuclear). The analysis and design of these systems require proper understanding of geo-materials, their properties and their response to extreme temperature and high stress excitations, the implications of mixed-fluid conditions when contrasting fluid viscosities and densities are involved, the effect of static and cyclic coupled hydro-thermo-chemo-mechanical excitations, and rate effects on the response of long design-life facilities.
This study places emphasis on thermal geo-systems and associated physical properties. Uncemented soils and rocks are considered. The research approach involves data compilation, experimental studies and analytical methods. Emphasis is also placed to engineer geomaterials in order to attain enhanced performance in energy geo-systems. The thermal conductivity and stiffness of most geomaterials decrease as temperature increases but increase with effective stress. This macroscale response is intimately related to contact-scale conduction and deformation processes at interparticle contacts. Pore-filling liquids play a critical role in heat conduction as liquids provide efficient conduction paths that can diminish the effects of thermal contact resistance. Conversely, grains and fluids can be selected to attain very low thermal conductivity in order to create mechanically sound thermal barriers. In the case of rock masses, heat (and gas) recovery can be enhanced by injecting fluids at high pressure to cause hydraulic fractures. Scaled experiments reveal the physical meaning of hydraulic fractures in pre-structured rocks (e.g., shale) and highlight the extensive self-propped dilational distortion the medium experiences. This result explains the higher production rate from shale gas and fractured geothermal reservoirs that is observed in the field, contrary to theoretical predictions.
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Tse, Man Kit. "Influence of stress states on soil-water characteristics, conjunctive surface-subsurface flow modelling and stability analysis /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202007%20TSE.
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Guhr, Alexander [Verfasser], and Egbert [Akademischer Betreuer] Matzner. "Adaptions of saprotrophic filamentous fungi to drought stress in soils : Hydraulic redistribution through mycelia networks and transcriptional responses / Alexander Guhr ; Betreuer: Egbert Matzner." Bayreuth : Universität Bayreuth, 2016. http://d-nb.info/1133167276/34.
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McEwen, Amiana Marie. "Abundance, Distribution, and Geometry of Naturally Occurring Macropores in Stream Banks." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/95948.
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Preferential flow paths are areas of substantially higher permeability than surrounding media. Macropores and soil pipes are a type of preferential flow path where conduit-like voids in the subsurface are typically greater than three millimeters in diameter. They are known to occur in agricultural and forest soils, often as a result of biological and physical processes. Macropores also exist in stream banks and have the potential to enhance the exchange of water and solutes between the channel and riparian groundwater, yet the geographic distribution of bank macropores is unknown. Here we determined the abundance, distribution, and geometry of naturally occurring surface-connected macropores in the banks of 20 streams across five physiographic provinces in the Eastern United States. We identified a total of 1,748 macropores, which were present in all 20 streams, with 3.8 cm average width, 3.3 cm average height, 11.5 cm average depth, and 27.9 cm average height above water surface elevation. Macropore abundance, distribution and geometry were statistically different between physiographic provinces, stream orders, and soil textures, with the latter being the most important. Macropores tended to be larger and more abundant in soils with a high cohesiveness and a low hydraulic conductivity compared to soils with a low cohesiveness and high hydraulic conductivity. As a result, streams with greater longitudinal heterogeneity of soil texture also had greater heterogeneity of macropore density. However, macropore size and height above baseflow water surface elevation also increased with stream order and therefore stream size. This work represents the first attempt to characterize macropores across a variety of riverine systems and presents evidence that macropores may play an important role in hyporheic exchange within stream banks. These results may have water quality implications, where macropores may enhance hyporheic exchange yet reduce the filtering capacity of riparian buffer zones.MS
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Frimpong, Justice Okona. "Soil hydraulic and salinity restrictions to water availability in very sandy soils." Thesis, 2017. http://hdl.handle.net/2440/106798.
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This study tried to evaluate the veracity of Grant and Groenevelt (2015) assertion that the inflection point on the water retention curve (WRC), plotted on semi-log scale, marks the onset of hydraulic stress in plants grown in sandy soils. That is, as the soil dries during drainage and evapotranspiration, there comes a point (argued to be the inflection point) when the unsaturated hydraulic conductivity cannot keep up with plant demand for water; thus, plants begin to suffer. Interest in the inflection point stemmed from the need to find unbiased criteria to weight the water capacity downward in the integral water capacity (IWC) model of Groenevelt et al. (2001) to account for soil hydraulic restrictions. If the inflection point was truly a good indicator of the onset of plant stress, then the matric suction at this point can easily be found from the fitting parameter, kₒ (m), in Grant and Groenevelt (2015) water retention model; by coincidence it can also be found from the fitting parameter, 1/α (m) in the water retention model of (Van Genuchten 1980).
The experimental components of this study consisted of two main parts: In the first part, water retention curves for a range of different sands and sandy soils were prepared, their inflection points identified, and two points on either side of the inflection point (wetter and drier) identified (Chapters 3 and 4). In the second part, wheat plants were grown in a glasshouse to Zadoks et al. (1974) growth stage 21 in pots of the different sands held, constant, at three different soil water suctions: at, above and below the inflection point (Chapter 5).
Detailed water retention curves were prepared using multiple replicates (up to 20) of four sands and two sandy soils (Very coarse sand, Coarse sand, Medium sand, Fine sand, Very fine sand, and Sandy loam) placed in small rings on ceramic pressure plates at different matric suctions ranging from saturation to 25 kPa or greater. Each of the individual sets of water retention data (up to 20) were fitted to the water retention models of Groenevelt and Grant (GG), and Van Genuchten (VG), and the inflection points identified from the appropriate fitting parameters. As might be expected, the different models produced slightly different inflection points, but these indeed corresponded pretty well (but not precisely) with kₒ and 1/α respectively. There was a strong inverse correlation between the mean particle size of the sands and sandy soils, and the values of kₒ and 1/α; that is, the inflections points shifted to greater matric suctions as mean particle size decreased, such that the Very coarse sand had the smallest values of kₒ and 1/α while the Sandy loam had the largest values of kₒ and 1/α.
Because the VG model fitted the measured water retention data slightly better than did the GG model, the parameters from the VG model were chosen to identify the soil water conditions for the plant experiments. The matric suction at the inflection point, hᵢ (m), was identified from 1/α, and this corresponded with the maximum differential water capacity, C(hᵢ). The wetter, hw, and drier, hd, matric suctions were chosen to correspond with the matric suctions at 90 % of the maximum differential water capacity (on either side of the inflection point). The value 90 % was chosen as being close to the inflection point yet falling outside its 95 % confidence interval. The (up to) 20 estimates of hw, hi and hd were used to identify the corresponding volumetric water contents directly from the water retention curves, and these were averaged and converted to gravimetric water contents that could be used to set up the soil water conditions in the pot study.
Following a 6 x 2 x 3 completely randomised factorial design, litre-sized pots of each sand or sandy soil (5 replicates) were set up at the three different water contents corresponding to hw, hi and hd, (covered in plastic beads to minimise evaporation) and wheat seeds (2 different genotypes) planted and grown in them to growth stage 21. To keep soil water contents constant, daily pot weights were recorded and then water added (calibrated for increasing plant mass over time) to replace water evapo-transpired. The measure of plant response to the soil water conditions was the mass (fresh and dry) of shoots and roots.
Although one of the wheat genotypes performed significantly better than the other (consistent with the literature), the F-test or analysis of variance (ANOVA) indicated that the wheat genotypes never responded to the soil moisture conditions or matric suction effects at or surrounding the inflection point. Possible reasons for the lack of response to the soil moisture conditions may be related to the choice of the wet and dry-side matric heads, particularly on the dry side; that is, the matric suction on the dry side of the inflection point, which corresponded to 90 % of the maximum water capacity, may not be sufficiently dry to induce a hydraulic stress. Contrast to this, was the source of variation that arose from the three and two factor interaction effects on the dry weights of shoot and root respectively, which showed significant differences. However, this was not convincing enough for one to accept the null hypothesis of the study due to the inconsistent nature of trends observed in the dry weights obtained at or surrounding the inflection point matric suction. On this basis, the importance of the inflection point as a marker of hydraulic stress in plants is not rejected at this stage – further research is needed.Thesis (M.Phil.) -- University of Adelaide, School of Agriculture, Food and Wine, 2017
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Goharrokhi, Masoud. "Effect of hydraulic shear stress on the banks of the Red River." 2015. http://hdl.handle.net/1993/30968.
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This study focuses on flow-induced bank erosion on the Red River. The study includes field measurements, experimental testing, and numerical simulation. Soil samples from the riverbank were collected at seven sites and their erodibility parameters were estimated through laboratory testing. The hydraulic shear stresses applied to the river reach were obtained by developing a 2D numerical model. Erosion rates for these sites were modeled using a linear excess shear stress equation.
A bank monitoring and total suspended sediment investigation were also conducted to assess the erosion and deposition rates and patterns. The locations susceptible to erosion were determined and the periods during which these processes are likely to occur were estimated.
The numerical modeling and soil testing results show that most of the time, the magnitude of flow shear stresses exerted on the bank are less than the soil sample critical shear stresses. Therefore, without considering other bank widening mechanisms as well as their interactions, the fluvial bank erosion (in isolation) should not be a significant process. However, bank monitoring shows significant bank erosion.
It is recommended that the effect of subaerial processes (especially freeze-thaw) be investigated further to determine their effects on flow-induced erosion. The monitoring results convincingly show that climate-related phenomena influences cohesive soil structures and consequently, a soil’s cohesive resistance forces are significantly reduced. Therefore it can be concluded that subaerial mechanisms play a significant role in widening the banks of the Red River.February 2016
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Wang, Wu-Liang, and 王屋樑. "The effection of effective stress and hydraulic gradient on soil/geotextile system." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/20645039687638979919.
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Vandeleur, Rebecca. "Grapevine root hydraulics: the role of aquaporins." 2008. http://hdl.handle.net/2440/57505.
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Hydraulic conductance of roots of the grapevine cultivar, Chardonnay, varies diurnally, peaking at 1400 h. The diurnal amplitude of hydraulic conductance between 600 and 1400 h was not altered when potted grapevines were water-stressed by withholding water for 8 days. However, the diurnal change was greatly reduced for water-stressed Grenache. If the diurnal change in root hydraulic conductance is a result of changes in aquaporin gene expression or activity, it suggests that aquaporins respond differently in water-stressed Chardonnay and Grenache roots. Both Chardonnay and Grenache demonstrated a reduction in hydraulic conductance in response to water stress, with Grenache exhibiting a larger reduction. Suberisation of the roots increased in response to water stress, with complete suberisation of the endodermis occurring closer to the root tip of Grenache compared to the more drought sensitive Chardonnay. The drought sensitive rootstock, 101-14 (V. riparia × V. rupestris) demonstrated a similar reduction in hydraulic conductance to Chardonnay, while drought tolerant 1103 Paulsen (V. berlandieri × V. rupestris) had a non-significant reduction when water-stressed compared to the large reduction observed for drought tolerant Grenache. Therefore, in this study the degree of reduction in hydraulic conductance did not relate to the drought tolerance of the four varieties examined. The impact of partial drying (watering only half the root system) on hydraulic conductance also differed between Chardonnay and Grenache. There was no change in the conductance of the whole root system of Chardonnay due to an increase in conductance of the roots in the wet half which compensated for the reduction on the dry side. In contrast, Grenache did suffer a reduction measured over the whole root system due to a much larger reduction on the dry side compared to Chardonnay. There was an increase in hydraulic conductance on the wet side but this could not compensate for the large reduction on the dry side. Two aquaporins (VvPIP1;1 and VvPIP2;2) were cloned from the roots of grapevine cultivar Chardonnay. The genes were expressed in Xenopus oocytes to determine their osmotic permeability. As has been shown in a number of plant species, VvPIP1;1 was only slightly permeable to water, whereas VvPIP2;2 did transport water. However, when VvPIP1;1 was injected into the oocytes with VvPIP2;2, there was a substantial increase in the osmotic permeability. There was no significant variation in the diurnal expression of VvPIP2;2, whereas VvPIP1;1 showed a peak in expression at 1000 h prior to the peak in hydraulic conductance and peaked again at 1800 h. VvPIP2;2 did not vary in transcript level in response to water stress or rewatering in Chardonnay or Grenache roots. The level of VvPIP1;1 doubled in water stressed Chardonnay roots and declined again when the vines were rewatered 24 h previously. This response to water stress did not occur in Grenache roots. The roots used were from the apical 5 cm. Similar roots were used to measure the water permeability of the cortical cell membranes using the cell pressure probe. Changes in cell membrane permeability in response to water stress corresponded to changes in VvPIP1;1 expression. An experiment to determine if shoot topping had an effect on root hydraulic conductance revealed a significant 50% decline. This response was also observed in soybean (Glycine max L.) and maize (Zea mays L.). A range of experiments have been performed to determine the reason for the decline. Possibilities included a response to final leaf area and reduced transpirational demand; loss of a carbohydrate sink; or hormonal signals such as abscisic acid, auxin and ethylene. At this stage the nature of the positive or negative signal that causes the change in root hydraulic conductance remains elusive. However, the signal did cause a reduction in the transcript level of VvPIP1;1, indicating the involvement of aquaporins in the response. The root hydraulic conductance of grapevines is variable and dependent on factors such as time of day, water-stress, transpiration rate and unknown signals from the shoot. A proportion of this variability is due to changes in aquaporin number or activity. There are also genotypic differences which may be beneficial for future breeding efforts to improve water use efficiency of grapevines.http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1311202
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Vandeleur, Rebecca. "Grapevine root hydraulics: the role of aquaporins." Thesis, 2008. http://hdl.handle.net/2440/57505.
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Hydraulic conductance of roots of the grapevine cultivar, Chardonnay, varies diurnally, peaking at 1400 h. The diurnal amplitude of hydraulic conductance between 600 and 1400 h was not altered when potted grapevines were water-stressed by withholding water for 8 days. However, the diurnal change was greatly reduced for water-stressed Grenache. If the diurnal change in root hydraulic conductance is a result of changes in aquaporin gene expression or activity, it suggests that aquaporins respond differently in water-stressed Chardonnay and Grenache roots. Both Chardonnay and Grenache demonstrated a reduction in hydraulic conductance in response to water stress, with Grenache exhibiting a larger reduction. Suberisation of the roots increased in response to water stress, with complete suberisation of the endodermis occurring closer to the root tip of Grenache compared to the more drought sensitive Chardonnay. The drought sensitive rootstock, 101-14 (V. riparia × V. rupestris) demonstrated a similar reduction in hydraulic conductance to Chardonnay, while drought tolerant 1103 Paulsen (V. berlandieri × V. rupestris) had a non-significant reduction when water-stressed compared to the large reduction observed for drought tolerant Grenache. Therefore, in this study the degree of reduction in hydraulic conductance did not relate to the drought tolerance of the four varieties examined.
The impact of partial drying (watering only half the root system) on hydraulic conductance also differed between Chardonnay and Grenache. There was no change in the conductance of the whole root system of Chardonnay due to an increase in
conductance of the roots in the wet half which compensated for the reduction on the dry side. In contrast, Grenache did suffer a reduction measured over the whole root system due to a much larger reduction on the dry side compared to Chardonnay. There was an increase in hydraulic conductance on the wet side but this could not compensate for the large reduction on the dry side.
Two aquaporins (VvPIP1;1 and VvPIP2;2) were cloned from the roots of grapevine cultivar Chardonnay. The genes were expressed in Xenopus oocytes to determine their osmotic permeability. As has been shown in a number of plant species, VvPIP1;1 was only slightly permeable to water, whereas VvPIP2;2 did transport
water. However, when VvPIP1;1 was injected into the oocytes with VvPIP2;2, there was a substantial increase in the osmotic permeability. There was no significant variation in the diurnal expression of VvPIP2;2, whereas VvPIP1;1 showed a peak in expression at 1000 h prior to the peak in hydraulic conductance and peaked again at 1800 h. VvPIP2;2 did not vary in transcript level in response to water stress or rewatering in Chardonnay or Grenache roots. The level of VvPIP1;1 doubled in water stressed Chardonnay roots and declined again when the vines were rewatered 24 h previously. This response to water stress did not occur in Grenache roots. The roots used were from the apical 5 cm. Similar roots were used to measure the water permeability of the cortical cell membranes using the cell pressure probe. Changes in cell membrane permeability in response to water stress corresponded to changes in VvPIP1;1 expression.
An experiment to determine if shoot topping had an effect on root hydraulic conductance revealed a significant 50% decline. This response was also observed in soybean (Glycine max L.) and maize (Zea mays L.). A range of experiments have been performed to determine the reason for the decline. Possibilities included a response to final leaf area and reduced transpirational demand; loss of a carbohydrate sink; or hormonal signals such as abscisic acid, auxin and ethylene. At this stage the nature of the positive or negative signal that causes the change in root hydraulic conductance remains elusive. However, the signal did cause a reduction in the transcript level of VvPIP1;1, indicating the involvement of aquaporins in the response.
The root hydraulic conductance of grapevines is variable and dependent on factors such as time of day, water-stress, transpiration rate and unknown signals from the shoot. A proportion of this variability is due to changes in aquaporin number or activity. There are also genotypic differences which may be beneficial for future breeding efforts to improve water use efficiency of grapevines.
Books on the topic "Soil hydraulic stress"
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service), SpringerLink (Online, ed. Water Resources in Mexico: Scarcity, Degradation, Stress, Conflicts, Management, and Policy. Berlin, Heidelberg: Springer-Verlag Berlin Heidelberg, 2011.
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Carmelo, Consesa Garcia, and Lenzi Mario A, eds. Check dams, morphological adjustments, and erosion control in torrential streams. Hauppauge, N.Y: Nova Science, 2009.
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Hannula, Steven R. Temporal and spatial variations of hydraulic conductivity in a stream bed in Golden, Colorado. Fort Collins, Colo: Colorado Water Resources Research Institute, Colorado State University, 1995.
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Check dams, morphological adjustments, and erosion control in torrential streams. Hauppauge, N.Y: Nova Science, 2009.
Find full textBook chapters on the topic "Soil hydraulic stress"
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Rosa da Costa, A., J. Metcalfe, T. A. Lodge, and W. J. Davies. "Soil drying and the resulting chemical and hydraulic effects on leaf growth." In Plant Response to Stress, 267–75. Berlin, Heidelberg: Springer Berlin Heidelberg, 1987. http://dx.doi.org/10.1007/978-3-642-70868-8_16.
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Rojas, Eduardo. "Expansive Soils." In Towards a Unified Soil Mechanics Theory: The Use of Effective Stresses in Unsaturated Soils (Third Edition), 171–202. BENTHAM SCIENCE PUBLISHERS, 2022. http://dx.doi.org/10.2174/9789815050356122010013.
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In this chapter, the elastoplastic framework for the volumetric behavior of soils developed in Chapters 8 and 9 is extended to account for the case of expansive soils. The hydraulic behavior of the soil is simulated using the porous-solid model developed in Chapter 4. The result is an elastoplastic framework where the value and sign of the expansion index depend on the density of the soil as well as the state of stresses and the direction of the increment of the effective stress with respect to the yield surfaces in the plane of effective mean stress against suction. Experimental and numerical comparisons show the ability of the model to simulate the behavior of expansive soils under different stress paths.
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Wang, Manyu, Yong Liu, Lu Yang, Jing Wu, and Guilin Niu. "Coupled Hydro-Mechanical Analysis of Rainfall-Induced Instability of Non-Uniform Soil Slopes." In Advances in Transdisciplinary Engineering. IOS Press, 2021. http://dx.doi.org/10.3233/atde210191.
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In recent years, more considerable attentions are paying on the hazards of large-scale landslides induced by heavy rainfall. However, the heterogeneity in hydraulic properties of soils may affect the seepage pattern of water infiltrated into soil slopes. Inspired by this fact, this paper aimed to evaluate the effect of the spatial variability in hydraulic conductivity on failure mechanism of an unsaturated soil slope subjected to rainfall infiltration, being implemented in the framework of a transient coupled hydro-mechanical analysis. The concept of random field was adopted to model the spatial randomness of saturated hydraulic conductivity ks following a uniform distribution. The finite element method was then incorporated to conduct Monte Carlo simulations. The resultant findings show that the mode of shallow slope failure is more likely to occur than the deep one due mainly to the highly variable distribution of ks near slope surface. Note that the decrease in the effective stress of soils resulting from the increase of pore water pressure is the most critical reason for the occurrence of slope failure. In addition, from the random element analyses results, it indicates that the value of Qari calculated by performing a deterministic analysis based on arithmetic average value kari gives a prediction of flow rate on average, but the calculated Qmax based on maximum value kmax provides a more conservative assessment on total flow rate across soil slope, which can offer useful suggestions for practitioners to take available measures to drain in advance.
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Rojas, Eduardo. "Undrained Tests." In Towards a Unified Soil Mechanics Theory: The Use of Effective Stresses in Unsaturated Soils (Third Edition), 270–83. BENTHAM SCIENCE PUBLISHERS, 2022. http://dx.doi.org/10.2174/9789815050356122010017.
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When undrained triaxial tests are performed, two main phenomena occur. First, the compression of the sample produces an increase in the degree of saturation and therefore, a reduction in the value of suction. Second, with the reduction in the sizes of pores, the retention curves shift on the axis of suction. Thereafter, the simulation of undrained triaxial tests requires the correct simulation of the hydromechanical coupling phenomenon. A fully coupled constitutive model for unsaturated soils is used herein to simulate the behavior of unsaturated soils subjected to undrained conditions. The mechanical model is based on the modified Critical State model and the effective stress concept. The hydraulic model uses the grain and pore size distributions to approximately reproduce the structure of soils. This model is able to simulate the soil-water retention curves during wetting-drying cycles. Plastic volumetric strains modify the pore size distribution of the soil, which in turn affects the retention curves and, therefore, the current effective stress. Some comparisons between numerical and experimental results of undrained triaxial tests show the adequacy of the model.
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Keefer, Robert F. "Engineering Aspects of Soils." In Handbook of Soils for Landscape Architects. Oxford University Press, 1999. http://dx.doi.org/10.1093/oso/9780195121025.003.0020.
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Although most landscape architects use soils primarily for growing plants, sometimes they need to know how engineers look at soils. Engineers are not concerned about soil properties that relate to growing plants. Engineers consider soil as a support for building foundations, use in earthworks, a place for burying pipes that carry electricity, water, gas or oil, and as a tool for disposing of hazardous, municipal, industrial, and household wastes. Soil properties that engineers consider important are hydraulic conductivity (permeability), compressive strength, shear strength, and lateral pressures. Soil mechanics deals with stress/strain/time relationships. Some engineering properties of a soil that describe the relation of clays to water content were studied by a Swedish scientist, Atterberg, in 1911. Soil clays based on water content were categorized into solid, semi-solid, plastic, and liquid. The dividing lines between each of these four states are known as the “Atterberg limits,” that is, shrinkage limit (from solid to semisolid), plastic limit (from semi-solid to plastic), and liquid limit (from plastic to liquid). These points can be measured for individual clays. The Atterberg limits are used by engineers to classify soils based on their moisture properties. These limits are particularly useful for evaluating soil compressibility, permeability, and strength. The plasticity of a clay soil depends on the type and amount of clay mineral and organic materials present. Plasticity is the reaction a soil has to being deformed without cracking or crumbling. The “liquid limit” is a term indicating the amount of water in a soil between the liquid state and the plastic state. Soils are first divided into two categories of coarse-grained and fine-grained. Coarse-grained soils are those in which more than half of the material is larger than a no. 200 sieve. Fine-grained soils are those in which more than half of the material is smaller than a no. 200 sieve. Coarse-grained soils are further divided into two categories of gravels and sands. Gravels are those with more than half of the coarse material larger than a no. 4 sieve. Sands are those with more than half of the coarse material smaller than a no. 4 sieve.
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Rojas, Eduardo. "Hydraulic Conductivity." In Towards a Unified Soil Mechanics Theory: The Use of Effective Stresses in Unsaturated Soils (Third Edition), 312–28. BENTHAM SCIENCE PUBLISHERS, 2022. http://dx.doi.org/10.2174/9789815050356122010019.
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In this chapter, the probabilistic porous network model is employed to establish a fully analytical equation for the relative hydraulic conductivity of soils. From this approach, a parameter accounting for the proportion of pores of different sizes forming continuous paths of saturated elements between the boundaries is used to compute the hydraulic conductivity. This approach avoids the effect of the size of the network on the results and the necessity of the pore-scale model approach required by computational networks to obtain the hydraulic conductivity of soils. Similarly, constraints related to computing time and memory size are avoided. In addition, single, double, or triple structured soil can be considered for the network. The theoretical and experimental comparisons indicate that capillary flow can account for the hydraulic conductivity of soils for the full range of suction of sandy and silty soils. Finally, all parameters required in the relative conductivity equation can be obtained by fitting the numerical with the experimental retention curves.
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Shmakova, Marina. "Sediment Transport in River Flows: New Approaches and Formulas." In Sediment Transport [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.103942.
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A new method for estimating the total sediment discharge, as built on balance of power acting to moving sediment particle in “water stream-bottom sediments—sediments” system, enables consideration of interrelated influence of hydraulic variables state of flow and sediment. At the same time, the basic sticking point of river hydraulics, that is, interaction of fluid and bottom, is specified not from the part of fluid boundary, but from that of bottom sediments and their properties, well studied in soil science. Setting the size of bottom sediments by means of their qualitative characteristics allows avoiding calculation errors that occur when using specific values of quantiles of bottom sediments in calculations. Consideration of the critical velocities and the phase hydraulic space of the flow allowed obtaining the equations for transporting capacity of the flow, suspended, and bed load discharges.
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White, Robert E. "Soil–Water–Vine Relationships and Water Management." In Soils for Fine Wines. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195141023.003.0008.
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Water is a prerequisite for vine growth. It is essential for photosynthesis and to maintain the hydrated conditions and cell turgor necessary for a host of other biochemical processes in the plant. As we saw in chapter 4, diffusion of nutrient ions to the root, and their movement by mass flow into the vine’s “transpiration stream,” both depend on water. The volumetric water content θ, defined as the volume of water per unit volume of soil (section 3.3.2), indicates how much water the soil can hold. However, to understand what drives water movement in the soil, we must understand the forces acting on the water because they affect its potential energy. The energy status of soil water also influences its availability to plants. There is no absolute scale of potential energy. But we can measure changes in potential energy when useful work is done on a measured quantity of water or when the water itself does useful work. These changes are observed as changes in the free energy of water, which gives rise to the concept of soil water potential. The derivation of the soil water potential ψ (psi) is given in appendix 7. Historically, the energy status of soil water has been described by a number of terms related to soil water potential, such as pressure, suction, or hydraulic head. These terms ψ and their units are explained in box 6.1. The terms and head will be used in this book. Several forces act on soil water to decrease its free energy and give rise to component potentials. These are adsorption forces, capillary forces, osmotic forces, and gravity. Adsorption Forces. In very dry soils (relative humidity, RH, of the soil air <20%), water is adsorbed onto the clay and silt particles as a monolayer in which the molecules are hydrogen bonded to each other and the surface. With an increase in RH, more water molecules are adsorbed by hydrogen bonding to those on the surface. The charged surfaces of clay minerals also attract cations, and the electric field of the cation orients the polar water molecules around the ion to form a hydration shell, containing 6–12 water molecules.
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Liu, K., R. Mackay, J. Xue, and A. Tolooiyan. "Experimental study of brown coal hydraulic behavior at low confining stress." In Unsaturated Soils: Research & Applications, 1125–30. CRC Press, 2014. http://dx.doi.org/10.1201/b17034-164.
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Liu, K., R. Mackay, J. Xue, and A. Tolooiyan. "Experimental study of brown coal hydraulic behavior at low confining stress." In Unsaturated Soils: Research & Applications, 1125–30. CRC Press, 2020. http://dx.doi.org/10.1201/9781003070580-29.
Full textConference papers on the topic "Soil hydraulic stress"
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Stone, Mark C., John O. Goreham, Li Chen, and Asako B. Stone. "Impacts of Shear Stress on Saturated Hydraulic Conductivity of a Polyacrylamide Treated Soil." In World Environmental and Water Resources Congress 2008. Reston, VA: American Society of Civil Engineers, 2008. http://dx.doi.org/10.1061/40976(316)102.
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Moncadaa, R., Y. Nakajimab, T. Moric, T. Kawaid, and M. Kazamae. "Effects Of Stress State And Hydraulic Conditions On Soil Erodibility For Cohesionless Soils In Contact With Damaged Pipes." In 18th Southeast Asian Geotechnical Conference (18SEAGC) & Inaugural AGSSEA Conference (1AGSSEA). Singapore: Research Publishing Services, 2013. http://dx.doi.org/10.3850/978-981-07-4948-4_037.
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Krishnamurthy, Ravi M., Barry Martens, David Feser, Peter Marreck, and Reg MacDonald. "Liquid Pipeline Stress Corrosion Cracking." In 2000 3rd International Pipeline Conference. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/ipc2000-187.
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The integrity management of a pipeline with stress corrosion cracking was accomplished in two distinct phases. The initial phase, from 1993 to 1996, consisted of excavations that quantified damage (stress corrosion cracking & corrosion), fracture mechanics modeling and hydrostatic testing, with a short-term objective of restoring Maximum Operating Pressure (MOP). Limited testing was conducted to evaluate the hydrostatic line on the 610 mm (24″) diameter line. The second phase, from 1996 until present, included running a shear wave ultrasonic tool, a zero degree ultrasonic tool, fracture mechanics modeling and rehabilitation digs. The extensive data collection during rehabilitation was utilized to evaluate the relationships between cracking susceptibility and degree of Stress Corrosion Cracking (SCC) with parameters such as soil type, drainage, topography and magnitude of pressure fluctuations. Corrosion products predominantly consisted of iron carbonate, very much characteristic of the low pH SCC mechanism. Following the shear wave ultrasonic tool, a zero-degree compression wave ultrasonic tool was utilized to characterize the long axial corrosion locations with potential shallow cracking. A re-inspection plan was developed using crack growth rates, hydraulic simulations of pressure fluctuations and excavation data. The reliability of the pipeline was increased and the overall integrity management costs were reduced. Presently, hydrotesting is not being used to manage integrity of Rainbow’s system.
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Kang, Jidong, Darren Bibby, Romain Blanchard, and Wenyue Zheng. "Full-Scale Stress Corrosion Crack Growth Testing of an X70 Spiral-Welded Pipe in Near-Neutral pH Soil Environment." In 2016 11th International Pipeline Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/ipc2016-64443.
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Stress corrosion cracking (SCC) in near-neutral pH environment remains a major concern for high pressure pipelines transporting oil and gas in Canada since its first discovery in 1980s. A variety of laboratory experiments and models have been developed to address different aspects of this complex problem. Full-scale pipe SCC testing using soil box that mimics the condition in the field can directly assess crack growth in terms of pressure level, range of pressure fluctuation, soil conditions, etc. This type of test also offers the most direct validation of SCC models. A state-of-the-art full-scale SCC pipe testing facility has been established at CanmetMATERIALS Hamilton Laboratory. The facility includes a new hydraulic power unit (HPU), an upgraded 500 kN fatigue frame, and a new 2000 psi (14MPa) pressurization system. In addition, a 24-channel direct current potential drop (DCPD) unit has been refurnished for in-situ monitoring of crack growth. The full-scale pipe SCC testing facility has been successfully used to measure crack growth in an X-70 (Grade 483) large diameter (914 mm or 36” OD) spiral seam-welded pipe. Six axial cracks were made using saw cutting and fatigue pre-cracking in the base metal and across the spiral-weld metal. All cracks were buried under two types of soil boxes with soil obtained from a near-neutral pH SCC pipeline failure site mixed with distilled water or NS4 solution. The pH of the solution was maintained between 6.9 and 7.2 throughout the testing. Several loading conditions were tested and DCPD was used to monitor SCC growth rate during all the tests. No detectable growth was observed in the cracks of weld area during all the tests mainly due to over-matching strength. Crack growth was also not detected for the base metal until the maximum pressure was raised up to 95% SMYS with R = 0.7. The threshold of the range of stress intensity factor, (ΔK)th for SCC is thus estimated to be between 11.53 to 13.52 MPa m1/2. The measured average crack growth rate was 5.98×10−7 mm/s.
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Biswas, Dipankar, Steven A. Lottes, Pradip Majumdar, and Milivoje Kostic. "Development of an Analysis Methodology for Pressure Flow Scour Under Flooded Bridge Decks Using Commercial CFD Software." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-37198.
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Bridges are a significant component of the ground transportation infrastructure in the United States. With about sixty percent of bridge failures due to hydraulic causes, primarily scour, application of computational fluid dynamics (CFD) analysis techniques to the assessment of risk of bridge failure under flood conditions can provide increased accuracy in scour risk assessment at a relatively low cost. The analysis can be used to make optimum use of limited federal and state funds available to maintain and replace bridges and ensure public safety while traveling on the nation’s roads and highways during and after floods. Scour is the erosion of riverbed material during high flow conditions, such as floods. When scouring of the supporting soil around the piers and abutments of bridges takes place, risk of bridge failure increases. A simulation methodology to conservatively predict equilibrium shape and size of the scour hole under pressure flow conditions for flooded bridge decks using commercial CFD software was developed. The computational methodology has been developed using C++ to compute changes in the bed contour outside of the CFD software and generate a re-meshing script to change the bed boundary contour. STAR-CD was used to run the hydrodynamic analysis to obtain bed shear stress, and a BASH script was developed to automate cycling between computing bed shear stress with the CFD software and computing changes in the bed contour due to scour predicted using the computed shear stress for the current bed contour. A single-phase moving boundary formulation has been developed to compute the equilibrium scour hole contour that proceeds through a series of quasi-steady CFD computations. It is based on CFD analysis of the flow fields around the flooded bridge deck and shear stress computed at the bed modeled as a rough wall. A high Reynolds number k-ε turbulence model with standard wall functions, based on a Reynolds-Averaged Navier-Stokes (RANS) turbulence model, was used to compute bed shear stress. The scour sites on the bed were identified as those sites where the computed shear stress exceeded the critical shear stress computed from a published correlation for flat bed conditions. Comparison with experimental data obtained from the Turner-Fairbank Highway Research Center (TFHRC), McLean, VA, USA, revealed larger discrepancies than anticipated between the bridge inundation ratio and the scour hole depth. Although scour hole slopes were small for the cases tested, a correction to critical shear stress to account for bed slope was also tested. It did not significantly improve the correlation between CFD prediction and experimental observations. These results may be a consequence of using only excess shear stress above critical as a criteria for scour when other physical mechanisms also contribute to the initiation of scour. Prediction of scour depth using federal guidelines over predicts scour depth by as much as an order of magnitude in some cases. Over prediction is acceptable for purposes of ensuring bridge safety. CFD methods for scour prediction can be a significant improvement of current methods as long as under prediction of scour depth is avoided. Conservative scour prediction using CFD methods can be achieved by using conservative values of parameters such as critical shear stress and effective bed roughness.
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Kebede, Yulian A., Mohammed A. Gabr, and Mohammad F. Kayser. "Scour Zone Characterization by Deep Impinging Jet." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-24257.
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Scour downstream of many hydraulic structures such as culverts and spillways may be treated as analogues to jet scour. This study presents the characterization of a fluidized zone by an impinging jet using a recently developed In Situ Erosion Evaluation Probe (ISEEP). Jet embedment was varied from 0.61 m (2 ft) to 2.43 m (8 ft) in the laboratory with a jet velocity ranging from 3 m/s to 6 m/s using an external pump. A number of piezometers were installed radially and with depth around the probe to characterize the extent of the fluidized zone (zone where effective stress reaches zero). Results indicated that the shape of the embedded fluidized zone changes from spherical to elliptical with increasing impinging distance. The nature of the zone expansion was categorized into three phases: initial, transition, and steady state. A jet velocity of 3.8 m/s resulted in a lateral distance of the fluidization zone that extended 0.3 m from the probe. At jet velocities of 4.2 m/s and 4.5 m/s, the lateral distance of the fluidization zone reached about 0.40 m and 0.45 m, respectively. Vertically, a jet velocity of 4.2 m/s fluidized the soil up to 0.3 m above the jet (probe tip) at 2.4 m embedment depth. At an embedment depth of 2.4 m, this maximum fluidization zone occurs as a closed fluidization. The dimensions of this zone are a function of the applied jet velocity (considering the values used in this study).
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Rainer Horn and Christian Albrechts. "STRESS STRAIN EFFECTS IN STRUCTURED UNSATURATED SOILS ON COUPLED MECHANICAL AND HYDRAULIC PROCESSES." In 2002 Chicago, IL July 28-31, 2002. St. Joseph, MI: American Society of Agricultural and Biological Engineers, 2002. http://dx.doi.org/10.13031/2013.10376.
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Sêco e Pinto, Pedro, Ricardo Oliveira, and Alexandre Portugal. "The Case of the New Tagus River Leziria Bridge." In The 13th Baltic Sea Region Geotechnical Conference. Vilnius Gediminas Technical University, 2016. http://dx.doi.org/10.3846/13bsgc.2016.007.
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A brief description of the New Tagus River Leziria Bridge composed by 1695 m North Viaduct, by 970 m Main Bridge and by South Viaduct with a length of 9200 m is presented. The observed thickness of the foundation alluvia material varies between 35 m and 55 m with a maximum value of 62 m. Hundred eighteen boreholes were performed with a depth between 21 m and 71 m and eight boreholes were performed from a maritime platform. Standard penetration tests (SPT) were carried out in all boreholes 1.5 m apart. In addition CPTu tests, seismic cone tests, crosshole and downhole tests were performed. In three boreholes continuous undisturbed sampling with a triple sampler Geogor S was performed. Related with static laboratory tests namely identification tests, triaxial tests, direct shear tests and oedometer tests were performed. In addition for the dynamic characterization reasonant columns tests and torsional cyclic tests were performed. One of the most important considerations for the designers is the risk of earthquakes since Lisbon was wiped out by an 8.5 Ritcher magnitude earthquake in 1755. The seismic studies related to the design spectra were performed. The liquefaction potential evaluation was performed only by field tests taking into account the disturbance that occurs during sampling of sandy materials. In this analysis attention was drawn for SPT and CPT tests as seismic tests have only been used when soil contains gravel particles. The shear stress values were computed from a total stresses model, that gave results on the conservative side using the code “SHAKE 2000”. For the North and South Viaducts 1.5 m diameter piles were used and for the Main Bridge 2.2 m diameter piles were used. For the construction of the piles metallic casings were driven by a vibrofonceur or a hydraulic hammer and the piles length varies between 20 m to 56 m. Static pile load tests (both vertical and horizontal tests) were carried out on trial piles. In addition pile dynamic tests were performed. The construction aspects related with piles and bridge construction are addressed. To assess the integrity of the piles reception tests by sonic diagraphies (crosshole tests) were performed. Some problems that have occurred during piles construction in the Main Bridge, due to the gravel and cobbles dimensions, are described. The bridge was monitored with the purposes of: (i) Validation of design criteria and calibration of mental model; (ii) Analysis of bridge behavior during his life; and (iii) Corrective measures for the rehabilitation of the structure.
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Ajmera, Beena, Binod Tiwari, and Lafa Taher Nassruldin. "Effect of Plasticity and Effective Normal Stress on Coefficient of Consolidation and Hydraulic Conductivity of Fine-Grained Soils having Different Pore Fluid Salinities." In IFCEE 2018. Reston, VA: American Society of Civil Engineers, 2018. http://dx.doi.org/10.1061/9780784481585.009.
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Bohan, Paul, and Donogh Lang. "Advancements in Deepwater Drilling Riser Modelling." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-24108.
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Experience with modern ultra-deepwater capable drilling vessels and their associated marine riser tensioner systems has led to increased concerns over tensioner load variations in extreme environments. Modern drilling riser tensioners are complex hydro-pneumatic systems whereby the tension applied at the slip-ring can vary significantly with tensioner stroke in response to vessel heave. The aforementioned tensioner load variations that occur with modern tensioner systems can have a significant effect on the loads transferred to the wellhead and conductor/casing. This can lead to fatigue concerns at critical locations. The connectors along the conductor and surface casing can be highly susceptible to fatigue if they are located in regions of high bending loads below the mudline. This paper will give a detailed overview of recent technology advancements that have been incorporated into the latest version of an industry-standard tool for global analysis of drilling risers [1] and that allow these concerns to be addressed. It will focus on two main areas where significant enhancements have been made in tensioner and wellhead & casing modelling. (Note that the version of the software incorporating these capabilities will be made commercially available during 2014.) The advanced tensioner modelling capability consists of a detailed tensioner model that includes individual hydraulic and pneumatic components of the tensioner system that are fully integrated with a non-linear 3D structural finite element model. This tensioner model is capable of fully capturing all transient behaviour and load variations of real world tensioner systems. This paper will describe in detail this unique modelling capability and its application, including riser recoil analysis. Additionally, accurate modelling of the wellhead, conductor/casing and the surrounding soil structure is crucial in order to accurately predict bending loads experienced in this region. This includes modelling individual wellhead sections (high pressure housing, low pressure housing and tapered sections) and multi-pipe structures for conductor/casing sections (including cement layers). The advanced soil modelling includes the capability to specify different soil types at different depths. This paper will describe in detail these advanced modelling capabilities. The detailed tensioner modelling capability represents a highly advanced technical and innovative development and is fundamental to providing a realistic recoil analysis capability. The advanced wellhead and casing modelling allows for accurate prediction of the stresses experienced in this critical region and accurate determination of the fatigue lives of these components. This paper will demonstrate how all of these advanced modelling capabilities can be used to accurately model deepwater drilling risers and provide increased confidence in conducting drilling operations in the harshest of environments.
Reports on the topic "Soil hydraulic stress"
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Shani, Uri, Lynn Dudley, Alon Ben-Gal, Menachem Moshelion, and Yajun Wu. Root Conductance, Root-soil Interface Water Potential, Water and Ion Channel Function, and Tissue Expression Profile as Affected by Environmental Conditions. United States Department of Agriculture, October 2007. http://dx.doi.org/10.32747/2007.7592119.bard.
Full textAbstract:
Constraints on water resources and the environment necessitate more efficient use of water. The key to efficient management is an understanding of the physical and physiological processes occurring in the soil-root hydraulic continuum.While both soil and plant leaf water potentials are well understood, modeled and measured, the root-soil interface where actual uptake processes occur has not been sufficiently studied. The water potential at the root-soil interface (yᵣₒₒₜ), determined by environmental conditions and by soil and plant hydraulic properties, serves as a boundary value in soil and plant uptake equations. In this work, we propose to 1) refine and implement a method for measuring yᵣₒₒₜ; 2) measure yᵣₒₒₜ, water uptake and root hydraulic conductivity for wild type tomato and Arabidopsis under varied q, K⁺, Na⁺ and Cl⁻ levels in the root zone; 3) verify the role of MIPs and ion channels response to q, K⁺ and Na⁺ levels in Arabidopsis and tomato; 4) study the relationships between yᵣₒₒₜ and root hydraulic conductivity for various crops representing important botanical and agricultural species, under conditions of varying soil types, water contents and salinity; and 5) integrate the above to water uptake term(s) to be implemented in models. We have made significant progress toward establishing the efficacy of the emittensiometer and on the molecular biology studies. We have added an additional method for measuring ψᵣₒₒₜ. High-frequency water application through the water source while the plant emerges and becomes established encourages roots to develop towards and into the water source itself. The yᵣₒₒₜ and yₛₒᵢₗ values reflected wetting and drying processes in the rhizosphere and in the bulk soil. Thus, yᵣₒₒₜ can be manipulated by changing irrigation level and frequency. An important and surprising finding resulting from the current research is the obtained yᵣₒₒₜ value. The yᵣₒₒₜ measured using the three different methods: emittensiometer, micro-tensiometer and MRI imaging in both sunflower, tomato and corn plants fell in the same range and were higher by one to three orders of magnitude from the values of -600 to -15,000 cm suggested in the literature. We have added additional information on the regulation of aquaporins and transporters at the transcript and protein levels, particularly under stress. Our preliminary results show that overexpression of one aquaporin gene in tomato dramatically increases its transpiration level (unpublished results). Based on this information, we started screening mutants for other aquaporin genes. During the feasibility testing year, we identified homozygous mutants for eight aquaporin genes, including six mutants for five of the PIP2 genes. Including the homozygous mutants directly available at the ABRC seed stock center, we now have mutants for 11 of the 19 aquaporin genes of interest. Currently, we are screening mutants for other aquaporin genes and ion transporter genes. Understanding plant water uptake under stress is essential for the further advancement of molecular plant stress tolerance work as well as for efficient use of water in agriculture. Virtually all of Israel’s agriculture and about 40% of US agriculture is made possible by irrigation. Both countries face increasing risk of water shortages as urban requirements grow. Both countries will have to find methods of protecting the soil resource while conserving water resources—goals that appear to be in direct conflict. The climate-plant-soil-water system is nonlinear with many feedback mechanisms. Conceptual plant uptake and growth models and mechanism-based computer-simulation models will be valuable tools in developing irrigation regimes and methods that maximize the efficiency of agricultural water. This proposal will contribute to the development of these models by providing critical information on water extraction by the plant that will result in improved predictions of both water requirements and crop yields. Plant water use and plant response to environmental conditions cannot possibly be understood by using the tools and language of a single scientific discipline. This proposal links the disciplines of soil physics and soil physical chemistry with plant physiology and molecular biology in order to correctly treat and understand the soil-plant interface in terms of integrated comprehension. Results from the project will contribute to a mechanistic understanding of the SPAC and will inspire continued multidisciplinary research.
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Wibowo, Johannes, and Jamie López-Soto. Field Jet Erosion Tests on Benbrook Dam, Texas. Engineer Research and Development Center (U.S.), December 2021. http://dx.doi.org/10.21079/11681/42545.
Full textAbstract:
This report summarizes the results of eight field Jet Erosion Tests (JETs) performed on Benbrook Dam, TX. The results from these tests will be used by the U.S. Army Corps of Engineers, Fort Worth District, in assessments of the erosion resistance of the Benbrook Dam with regards to possible overtopping by extreme flooding. The JETs were performed at four different locations, i.e., two locations at the lowest crest elevation and two locations at the mid-slope face of the downstream embankment. Variations in estimated critical hydraulic shear stress and erosion rate values may have been caused by differences in soil composition, i.e., when the material changed from silt/sand to clay. The resulting values of the Erodibility Coefficient, Kd, and Critical Stress, τc, are very useful information in assessing the stability of Benbrook Dam during an overtopping event. Because of the observed natural variability of the materials, combining the erosion parameters presented in this report with the drilling logs and local geology will be imperative for assessing erosion-related failure modes of Benbrook Dam.
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Snyder, Victor A., Dani Or, Amos Hadas, and S. Assouline. Characterization of Post-Tillage Soil Fragmentation and Rejoining Affecting Soil Pore Space Evolution and Transport Properties. United States Department of Agriculture, April 2002. http://dx.doi.org/10.32747/2002.7580670.bard.
Full textAbstract:
Tillage modifies soil structure, altering conditions for plant growth and transport processes through the soil. However, the resulting loose structure is unstable and susceptible to collapse due to aggregate fragmentation during wetting and drying cycles, and coalescense of moist aggregates by internal capillary forces and external compactive stresses. Presently, limited understanding of these complex processes often leads to consideration of the soil plow layer as a static porous medium. With the purpose of filling some of this knowledge gap, the objectives of this Project were to: 1) Identify and quantify the major factors causing breakdown of primary soil fragments produced by tillage into smaller secondary fragments; 2) Identify and quantify the. physical processes involved in the coalescence of primary and secondary fragments and surfaces of weakness; 3) Measure temporal changes in pore-size distributions and hydraulic properties of reconstructed aggregate beds as a function of specified initial conditions and wetting/drying events; and 4) Construct a process-based model of post-tillage changes in soil structural and hydraulic properties of the plow layer and validate it against field experiments. A dynamic theory of capillary-driven plastic deformation of adjoining aggregates was developed, where instantaneous rate of change in geometry of aggregates and inter-aggregate pores was related to current geometry of the solid-gas-liquid system and measured soil rheological functions. The theory and supporting data showed that consolidation of aggregate beds is largely an event-driven process, restricted to a fairly narrow range of soil water contents where capillary suction is great enough to generate coalescence but where soil mechanical strength is still low enough to allow plastic deforn1ation of aggregates. The theory was also used to explain effects of transient external loading on compaction of aggregate beds. A stochastic forInalism was developed for modeling soil pore space evolution, based on the Fokker Planck equation (FPE). Analytical solutions for the FPE were developed, with parameters which can be measured empirically or related to the mechanistic aggregate deformation model. Pre-existing results from field experiments were used to illustrate how the FPE formalism can be applied to field data. Fragmentation of soil clods after tillage was observed to be an event-driven (as opposed to continuous) process that occurred only during wetting, and only as clods approached the saturation point. The major mechanism of fragmentation of large aggregates seemed to be differential soil swelling behind the wetting front. Aggregate "explosion" due to air entrapment seemed limited to small aggregates wetted simultaneously over their entire surface. Breakdown of large aggregates from 11 clay soils during successive wetting and drying cycles produced fragment size distributions which differed primarily by a scale factor l (essentially equivalent to the Van Bavel mean weight diameter), so that evolution of fragment size distributions could be modeled in terms of changes in l. For a given number of wetting and drying cycles, l decreased systematically with increasing plasticity index. When air-dry soil clods were slightly weakened by a single wetting event, and then allowed to "age" for six weeks at constant high water content, drop-shatter resistance in aged relative to non-aged clods was found to increase in proportion to plasticity index. This seemed consistent with the rheological model, which predicts faster plastic coalescence around small voids and sharp cracks (with resulting soil strengthening) in soils with low resistance to plastic yield and flow. A new theory of crack growth in "idealized" elastoplastic materials was formulated, with potential application to soil fracture phenomena. The theory was preliminarily (and successfully) tested using carbon steel, a ductile material which closely approximates ideal elastoplastic behavior, and for which the necessary fracture data existed in the literature.
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Tuller, Markus, Asher Bar-Tal, Hadar Heller, and Michal Amichai. Optimization of advanced greenhouse substrates based on physicochemical characterization, numerical simulations, and tomato growth experiments. United States Department of Agriculture, January 2014. http://dx.doi.org/10.32747/2014.7600009.bard.
Full textAbstract:
Over the last decade there has been a dramatic shift in global agricultural practice. The increase in human population, especially in underdeveloped arid and semiarid regions of the world, poses unprecedented challenges to production of an adequate and economically feasible food supply to undernourished populations. Furthermore, the increased living standard in many industrial countries has created a strong demand for high-quality, out-of-season vegetables and fruits as well as for ornamentals such as cut and potted flowers and bedding plants. As a response to these imminent challenges and demands and because of a ban on methyl bromide fumigation of horticultural field soils, soilless greenhouse production systems are regaining increased worldwide attention. Though there is considerable recent empirical and theoretical research devoted to specific issues related to control and management of soilless culture production systems, a comprehensive approach that quantitatively considers all relevant physicochemical processes within the growth substrates is lacking. Moreover, it is common practice to treat soilless growth systems as static, ignoring dynamic changes of important physicochemical and hydraulic properties due to root and microbial growth that require adaptation of management practices throughout the growth period. To overcome these shortcomings, the objectives of this project were to apply thorough physicochemical characterization of commonly used greenhouse substrates in conjunction with state-of-the-art numerical modeling (HYDRUS-3D, PARSWMS) to not only optimize management practices (i.e., irrigation frequency and rates, fertigation, container size and geometry, etc.), but to also “engineer” optimal substrates by mixing organic (e.g., coconut coir) and inorganic (e.g., perlite, pumice, etc.) base substrates and modifying relevant parameters such as the particle (aggregate) size distribution. To evaluate the proposed approach under commercial production conditions, characterization and modeling efforts were accompanied by greenhouse experiments with tomatoes. The project not only yielded novel insights regarding favorable physicochemical properties of advanced greenhouse substrates, but also provided critically needed tools for control and management of containerized soilless production systems to provide a stress-free rhizosphere environment for optimal yields, while conserving valuable production resources. Numerical modeling results provided a more scientifically sound basis for the design of commercial greenhouse production trials and selection of adequate plant-specific substrates, thereby alleviating the risk of costly mistrials.