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• 1. [Article] Exploring mechanisms that drive the development of reversible soil hydrophobicity

  This study focuses on one widespread characteristic of poor soil quality: hydrophobic soil. Previous research has produced conclusive evidence to show that soil hydrophobicity is affected by soil organic ...

  Citation × Citation Citation Abstract Copy Title: Exploring mechanisms that drive the development of reversible soil hydrophobicity Author: Woolverton, Priscilla B. This study focuses on one widespread characteristic of poor soil quality: hydrophobic soil. Previous research has produced conclusive evidence to show that soil hydrophobicity is affected by soil organic matter (SOM) and soil water content (WC). Hydrophobicity that responds to changes in WC is a unique form of surface hydrophobicity and is termed "reversible hydrophobicity" (RHP). Recent experimental results support an amphiphilic model for SOM, which contains mechanisms for the occurrence of RHP. What has not been directly demonstrated, however, are conformational changes in the orientation of amphiphilic moieties as an effect of WC that would be associated with RHP. Quincy soils, which exhibit RHP, were investigated at varying WC using Photoacoustic Fourier transform infrared spectroscopy (Pas-FTIR), chemical analysis of carbon:nitrogen, and physical measurement of hydrophobicity, using the Capillary Rise Method and the Sessile Drop Method, in order to reveal how SOM and water interact to drive the creation of hydrophobic surfaces. This investigation suggests that SOM and water interact at the molecular scale to drive hydrophobic phenomena at the field-scale. Title: Exploring mechanisms that drive the development of reversible soil hydrophobicity Author: Woolverton, Priscilla B. This study focuses on one widespread characteristic of poor soil quality: hydrophobic soil. Previous research has produced conclusive evidence to show that soil hydrophobicity is affected by soil organic matter (SOM) and soil water content (WC). Hydrophobicity that responds to changes in WC is a unique form of surface hydrophobicity and is termed "reversible hydrophobicity" (RHP). Recent experimental results support an amphiphilic model for SOM, which contains mechanisms for the occurrence of RHP. What has not been directly demonstrated, however, are conformational changes in the orientation of amphiphilic moieties as an effect of WC that would be associated with RHP. Quincy soils, which exhibit RHP, were investigated at varying WC using Photoacoustic Fourier transform infrared spectroscopy (Pas-FTIR), chemical analysis of carbon:nitrogen, and physical measurement of hydrophobicity, using the Capillary Rise Method and the Sessile Drop Method, in order to reveal how SOM and water interact to drive the creation of hydrophobic surfaces. This investigation suggests that SOM and water interact at the molecular scale to drive hydrophobic phenomena at the field-scale. Close

• 2. [Article] Effects of soil moisture-tension on rubidium uptake by sunflowers

  There is considerable evidence that the growth and elongation of plant roots increases linearly or almost linearly with increasing water contents or decreasing moisture-tension of soil. If this is true ...

  Citation × Citation Citation Abstract Copy Title: Effects of soil moisture-tension on rubidium uptake by sunflowers Author: Stevenson, David Stuart There is considerable evidence that the growth and elongation of plant roots increases linearly or almost linearly with increasing water contents or decreasing moisture-tension of soil. If this is true it is difficult to distinguish the effects of different water contents on absorption phenomena such as water or ion uptake from the effects of the water contents on the root growth itself. Any absorption process which directly correlates with the amount of root growth is subject to misinterpretation as to the ultimate effect of changing water contents on the particular process. One useful alternative is to measure the root growth precisely and account for, through covariance, the differences in root growth as a result of differences in water contents or moisture-tensions in the soil. Samples of soil at various water contents and containing rubidium ions, were placed around the stems of six-week old sunflower plants and adventitious roots allowed to grow into the soil samples. The period of adventitious root growth was six days. Root growth water lost from the soil samples and the rubidium taken up into the above-ground parts of the plants were measured. All experiments were conducted in a controlled-environment growth room. Root growth was found to be closely related to the initial water contents of the soil samples. The relationship was slightly curvilinear. Water taken up by the adventitious roots was found to be dependent upon the amount of root growth and therefore closely related to the initial water contents. In all cases where the adventitious root systems were exposed to soil that was drier than that containing the main root systems of the plants the amounts of water which moved into the plants appeared to be small, much of the water remained in the adventitious roots themselves. When the water content of the soil for the adventitious roots was at a higher water content than that containing the main root systems, considerably more water appeared to move into the plants through the adventitious root systems. Rubidium uptake was not consistently affected by the different water contents, nor was the uptake correlated with the amount of root growth. There was, however, at least as much rubidium accumulated in the plants in 28 hours, when the adventitious roots were wetter than the main root systems, as was accumulated in the plants in six days when the adventitious roots were drier than the main root systems. It appears that the transport of water from the roots to the plants may be an important factor in ion accumulation and it may be that the uptake of ions will not correlate with water conditions at the root surface unless and until rapid transport of water takes place. Since water uptake appears to be closely related to the amount of root growth, the effects of water contents on the absorption process itself must be interpreted with caution or the root growth measured and accounted for. It is not known if the same holds true for ion uptake. In these experiments the rubidium uptake was not closely related to root growth but it is not possible to say if this holds true for ion absorption in general. Title: Effects of soil moisture-tension on rubidium uptake by sunflowers Author: Stevenson, David Stuart There is considerable evidence that the growth and elongation of plant roots increases linearly or almost linearly with increasing water contents or decreasing moisture-tension of soil. If this is true it is difficult to distinguish the effects of different water contents on absorption phenomena such as water or ion uptake from the effects of the water contents on the root growth itself. Any absorption process which directly correlates with the amount of root growth is subject to misinterpretation as to the ultimate effect of changing water contents on the particular process. One useful alternative is to measure the root growth precisely and account for, through covariance, the differences in root growth as a result of differences in water contents or moisture-tensions in the soil. Samples of soil at various water contents and containing rubidium ions, were placed around the stems of six-week old sunflower plants and adventitious roots allowed to grow into the soil samples. The period of adventitious root growth was six days. Root growth water lost from the soil samples and the rubidium taken up into the above-ground parts of the plants were measured. All experiments were conducted in a controlled-environment growth room. Root growth was found to be closely related to the initial water contents of the soil samples. The relationship was slightly curvilinear. Water taken up by the adventitious roots was found to be dependent upon the amount of root growth and therefore closely related to the initial water contents. In all cases where the adventitious root systems were exposed to soil that was drier than that containing the main root systems of the plants the amounts of water which moved into the plants appeared to be small, much of the water remained in the adventitious roots themselves. When the water content of the soil for the adventitious roots was at a higher water content than that containing the main root systems, considerably more water appeared to move into the plants through the adventitious root systems. Rubidium uptake was not consistently affected by the different water contents, nor was the uptake correlated with the amount of root growth. There was, however, at least as much rubidium accumulated in the plants in 28 hours, when the adventitious roots were wetter than the main root systems, as was accumulated in the plants in six days when the adventitious roots were drier than the main root systems. It appears that the transport of water from the roots to the plants may be an important factor in ion accumulation and it may be that the uptake of ions will not correlate with water conditions at the root surface unless and until rapid transport of water takes place. Since water uptake appears to be closely related to the amount of root growth, the effects of water contents on the absorption process itself must be interpreted with caution or the root growth measured and accounted for. It is not known if the same holds true for ion uptake. In these experiments the rubidium uptake was not closely related to root growth but it is not possible to say if this holds true for ion absorption in general. Close

• 3. [Article] Characterization of hydrologic parameters and processes in shrink-swell clay soils

  Vertisols and other vertic-intergrade soils are found all over the globe, including many agricultural and urban areas. These soils are characterized by their cyclical shrinking and swelling behaviors, ...

  Citation × Citation Citation Abstract Copy Title: Characterization of hydrologic parameters and processes in shrink-swell clay soils Author: Stewart, Ryan D. Vertisols and other vertic-intergrade soils are found all over the globe, including many agricultural and urban areas. These soils are characterized by their cyclical shrinking and swelling behaviors, where bulk density and porosity distribution both vary as functions of time and/or soil moisture. In turn, alterations in physical soil parameters become manifest as crack networks, which open during the shrinkage phase and re-seal as the soil swells. As a consequence, when present these soils can significantly impact agriculture and infrastructure, and can act as a dominant control on the local hydrology. Therefore, understanding how water moves through and interacts with these soils is of utmost importance to ensure their proper utilization and management. This study had three objectives: 1) to identify the role of initial soil moisture on infiltration in a rigid (non-swelling) soil; 2) to quantify variation in the soil's hydraulic properties, using single-ring infiltration measurements taken in a vertic soil over a 1.5 year period; and 3) to build on these concepts to examine data from a set of instrumented field plots in a vertic soil located in the Secano Interior region of Chile. Significant findings of the study include 1) the development of a new formulation to describe a soil's wetting front potential (a measure of capillary pull) in terms of initial degree of saturation; 2) the creation of a simple correction to approximate the decrease of wetting front potential in wetter soils, thereby improving the accuracy of the traditional Green and Ampt sorptivity model in such conditions; 3) an equation to accurately estimate hydraulic parameters from short-duration infiltration tests, when steady-state conditions have not been realized; 4) a new theoretical model to estimate crack porosity as a function of soil moisture, which was developed based on the soil shrinkage curve; and 5) modification of the traditional two-term Philip infiltration model for use in vertic soils. The field study also showed that crack networks cause highly complex and non-linear wetting of the soil profile, with water simultaneously infiltrating from the soil surface and from the soil-crack interfaces; that cracks can seal at the surface while remaining open and hydraulically active below the surface, which indicates that surface-based monitoring alone may not be sufficient to predict water movement and soil response in vertic soils; and that the transition between infiltration and runoff may be strongly correlated with the cumulative amount of net precipitation that had reached the soil surface, so that cumulative amount of precipitation has the potential to be a simple yet accurate metric to predict runoff in vertic soils. These findings offer improved understanding of soil-water interactions in vertic soils, and reveal that very simple concepts underlie seemingly complex systems. As a result, the concepts and formulations developed in this study should allow for straightforward integration into other studies and models. Title: Characterization of hydrologic parameters and processes in shrink-swell clay soils Author: Stewart, Ryan D. Vertisols and other vertic-intergrade soils are found all over the globe, including many agricultural and urban areas. These soils are characterized by their cyclical shrinking and swelling behaviors, where bulk density and porosity distribution both vary as functions of time and/or soil moisture. In turn, alterations in physical soil parameters become manifest as crack networks, which open during the shrinkage phase and re-seal as the soil swells. As a consequence, when present these soils can significantly impact agriculture and infrastructure, and can act as a dominant control on the local hydrology. Therefore, understanding how water moves through and interacts with these soils is of utmost importance to ensure their proper utilization and management. This study had three objectives: 1) to identify the role of initial soil moisture on infiltration in a rigid (non-swelling) soil; 2) to quantify variation in the soil's hydraulic properties, using single-ring infiltration measurements taken in a vertic soil over a 1.5 year period; and 3) to build on these concepts to examine data from a set of instrumented field plots in a vertic soil located in the Secano Interior region of Chile. Significant findings of the study include 1) the development of a new formulation to describe a soil's wetting front potential (a measure of capillary pull) in terms of initial degree of saturation; 2) the creation of a simple correction to approximate the decrease of wetting front potential in wetter soils, thereby improving the accuracy of the traditional Green and Ampt sorptivity model in such conditions; 3) an equation to accurately estimate hydraulic parameters from short-duration infiltration tests, when steady-state conditions have not been realized; 4) a new theoretical model to estimate crack porosity as a function of soil moisture, which was developed based on the soil shrinkage curve; and 5) modification of the traditional two-term Philip infiltration model for use in vertic soils. The field study also showed that crack networks cause highly complex and non-linear wetting of the soil profile, with water simultaneously infiltrating from the soil surface and from the soil-crack interfaces; that cracks can seal at the surface while remaining open and hydraulically active below the surface, which indicates that surface-based monitoring alone may not be sufficient to predict water movement and soil response in vertic soils; and that the transition between infiltration and runoff may be strongly correlated with the cumulative amount of net precipitation that had reached the soil surface, so that cumulative amount of precipitation has the potential to be a simple yet accurate metric to predict runoff in vertic soils. These findings offer improved understanding of soil-water interactions in vertic soils, and reveal that very simple concepts underlie seemingly complex systems. As a result, the concepts and formulations developed in this study should allow for straightforward integration into other studies and models. Close

• 4. [Article] Climate Warming, Soil Moisture Dynamics, and Water Budget Partitioning: Experimental Results from a Willamette Valley Ecosystem

  Presented at The Oregon Water Conference, May 24-25, 2011, Corvallis, OR.

  Citation × Citation Citation Abstract Copy Title: Climate Warming, Soil Moisture Dynamics, and Water Budget Partitioning: Experimental Results from a Willamette Valley Ecosystem Author: McDonnell, Jeffrey, Gregg, Jillian, Pangle, Luke Presented at The Oregon Water Conference, May 24-25, 2011, Corvallis, OR. Title: Climate Warming, Soil Moisture Dynamics, and Water Budget Partitioning: Experimental Results from a Willamette Valley Ecosystem Author: McDonnell, Jeffrey, Gregg, Jillian, Pangle, Luke Presented at The Oregon Water Conference, May 24-25, 2011, Corvallis, OR. Close

• 5. [Article] Mapping variability of soil water content and flux across 1-1000 m scales using the Actively Heated Fiber Optic method

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://agupubs.onlinelibrary.wiley.com/agu/journal/10.1002/%28ISSN%291944-...

  Citation × Citation Citation Abstract Copy Title: Mapping variability of soil water content and flux across 1-1000 m scales using the Actively Heated Fiber Optic method Author: English, Marshall, Rodriguez-Sinobas, Leonor, van de Giesen, Nick, El Khoury, Laureine, Selker, John S., Benitez Buelga, Javier, Sayde, Chadi This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://agupubs.onlinelibrary.wiley.com/agu/journal/10.1002/%28ISSN%291944-7973/. Title: Mapping variability of soil water content and flux across 1-1000 m scales using the Actively Heated Fiber Optic method Author: English, Marshall, Rodriguez-Sinobas, Leonor, van de Giesen, Nick, El Khoury, Laureine, Selker, John S., Benitez Buelga, Javier, Sayde, Chadi This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://agupubs.onlinelibrary.wiley.com/agu/journal/10.1002/%28ISSN%291944-7973/. Close

• 6. [Article] Ecohydrological mediation of water budget partitioning and time scales of subsurface flow in a seasonally semi-arid grassland

  Understanding how the interactions and feedbacks between plant function, climate, and soils ultimately affects the terrestrial water balance and subsurface flow processes is major challenge in scientific ...

  Citation × Citation Citation Abstract Copy Title: Ecohydrological mediation of water budget partitioning and time scales of subsurface flow in a seasonally semi-arid grassland Author: Pangle, Luke A., 1981- Understanding how the interactions and feedbacks between plant function, climate, and soils ultimately affects the terrestrial water balance and subsurface flow processes is major challenge in scientific hydrology. This dissertation summarizes the findings of a manipulative climate warming experiment, an observational field study that utilized stable-isotope tracers, and associated modeling analyses that I used to examine the physiological and physical mechanisms by which grassland ecosystems mediate water-balance partitioning and transit times of water flowing through the subsurface. Utilizing the climate-controlled mesocosm experiment, I examined the responses of evapotranspiration, soil moisture, and potential groundwater recharge to a 3.5˚C temperature increase in a grassland ecosystem experiencing a Mediterranean climate. I hypothesized that a warmer climate would cause a shift in the soil-water balance toward greater evapotranspiration, and less recharge. The results showed that warming treatments enhanced evapotranspiration during the spring. However, this reduced soil moisture more rapidly, resulting in less evapotranspiration during the summer than occurred under ambient temperatures, and no difference when considered over the entire year. Groundwater recharge was reduced during late-spring storms relative to the ambient temperature treatment, but these reductions were a small fraction of the annual total, and were offset by slightly greater recharge in the fall under warming treatments. The results highlighted the potential for interactions between climate, vegetation, and soils to moderate the hydrological response to climate warming, particularly in environments where precipitation is seasonal and out of phase with the vegetation growing season. I conducted additional field studies that utilized three lysimeters with surface conditions ranging from bare soil through two stages of aggrading grassland vegetation. Using hydrometric data, stable-isotopes as conservative tracer, and two hydrograph-separation techniques I evaluated whether aggrading grassland vegetation and root systems alter time scales of subsurface flow, and how this alteration may influence potential groundwater recharge. I tested the hypothesis that soil structural change under aggrading vegetation would enhance the rapid infiltration of precipitation-event water, resulting in greater potential recharge during individual storms. Contrary to this expectation, results from both hydrograph-separation techniques showed that precipitation-event water comprised 0 - 6% of potential recharge among all the storm events I analyzed, being greatest under bare soil, and always zero in grasslands ranging in age from 3.8 - 5.9 years. These results contradicted my original hypothesis, and were attributed to the low intensity of local precipitation, large soil-water storage potential, and the predominantly shallow rooting tendency of the grassland vegetation. In a final analysis I used stable-isotope measurements and a linear-time-invariant convolution approach to model mean-transit times and transit-time distributions of subsurface flow under each surface condition, and over the entire water year. The results showed that mean-transit times were not significantly different in the presence of aggrading vegetation. From these analyses I concluded that physical alteration of the soil by aggrading plant root systems was not an ecohydrologically significant mechanism in this system. Ex post facto analyses showed that, at the time scale of individual storm events, the reduction of effective precipitation by interception and evaporative loss from the grassland canopies was of much greater importance--even with very low leaf area indices. At the annual time scale, root expansion enabled much greater exploitation of soil water during the summer drought, causing a shift from a recharge-dominated to an evapotranspiration-dominated soil-water balance within the first year of growth. Title: Ecohydrological mediation of water budget partitioning and time scales of subsurface flow in a seasonally semi-arid grassland Author: Pangle, Luke A., 1981- Understanding how the interactions and feedbacks between plant function, climate, and soils ultimately affects the terrestrial water balance and subsurface flow processes is major challenge in scientific hydrology. This dissertation summarizes the findings of a manipulative climate warming experiment, an observational field study that utilized stable-isotope tracers, and associated modeling analyses that I used to examine the physiological and physical mechanisms by which grassland ecosystems mediate water-balance partitioning and transit times of water flowing through the subsurface. Utilizing the climate-controlled mesocosm experiment, I examined the responses of evapotranspiration, soil moisture, and potential groundwater recharge to a 3.5˚C temperature increase in a grassland ecosystem experiencing a Mediterranean climate. I hypothesized that a warmer climate would cause a shift in the soil-water balance toward greater evapotranspiration, and less recharge. The results showed that warming treatments enhanced evapotranspiration during the spring. However, this reduced soil moisture more rapidly, resulting in less evapotranspiration during the summer than occurred under ambient temperatures, and no difference when considered over the entire year. Groundwater recharge was reduced during late-spring storms relative to the ambient temperature treatment, but these reductions were a small fraction of the annual total, and were offset by slightly greater recharge in the fall under warming treatments. The results highlighted the potential for interactions between climate, vegetation, and soils to moderate the hydrological response to climate warming, particularly in environments where precipitation is seasonal and out of phase with the vegetation growing season. I conducted additional field studies that utilized three lysimeters with surface conditions ranging from bare soil through two stages of aggrading grassland vegetation. Using hydrometric data, stable-isotopes as conservative tracer, and two hydrograph-separation techniques I evaluated whether aggrading grassland vegetation and root systems alter time scales of subsurface flow, and how this alteration may influence potential groundwater recharge. I tested the hypothesis that soil structural change under aggrading vegetation would enhance the rapid infiltration of precipitation-event water, resulting in greater potential recharge during individual storms. Contrary to this expectation, results from both hydrograph-separation techniques showed that precipitation-event water comprised 0 - 6% of potential recharge among all the storm events I analyzed, being greatest under bare soil, and always zero in grasslands ranging in age from 3.8 - 5.9 years. These results contradicted my original hypothesis, and were attributed to the low intensity of local precipitation, large soil-water storage potential, and the predominantly shallow rooting tendency of the grassland vegetation. In a final analysis I used stable-isotope measurements and a linear-time-invariant convolution approach to model mean-transit times and transit-time distributions of subsurface flow under each surface condition, and over the entire water year. The results showed that mean-transit times were not significantly different in the presence of aggrading vegetation. From these analyses I concluded that physical alteration of the soil by aggrading plant root systems was not an ecohydrologically significant mechanism in this system. Ex post facto analyses showed that, at the time scale of individual storm events, the reduction of effective precipitation by interception and evaporative loss from the grassland canopies was of much greater importance--even with very low leaf area indices. At the annual time scale, root expansion enabled much greater exploitation of soil water during the summer drought, causing a shift from a recharge-dominated to an evapotranspiration-dominated soil-water balance within the first year of growth. Close

• 7. [Article] Relationships between degree of ponding and uniformity of soil moisture distribution under irrigation sprinklers

  Often low intake rate soils need special consideration when applying water during an irrigation. Surface flooding for extended periods may cause adverse crop growth conditions. Properly designed sprinkler ...

  Citation × Citation Citation Abstract Copy Title: Relationships between degree of ponding and uniformity of soil moisture distribution under irrigation sprinklers Author: Dehlinger, Charles Robert Often low intake rate soils need special consideration when applying water during an irrigation. Surface flooding for extended periods may cause adverse crop growth conditions. Properly designed sprinkler systems often eliminate irrigation problems, because the application rate and quantity of water applied can be readily controlled. Research workers who have studied sprinkler irrigation disagree on many things. Differences are found in the literature concerning the procedures used to determine sprinkler distribution uniformity and the optimum rate of application of water to the soil. Several authors suggest that moisture movement within the soil occurs after an irrigation. If trans location of moisture occurs, it may be possible to use sprinkler system design specifications that are less critical than those now in use. In order to determine the effect of sprinkler application rate on the resulting soil moisture distribution it is necessary to have criteria relating degree of ponding, crop cover, and slope of the land to the uniformity of soil moisture. Experimental plots were designed and prepared to study and relate these factors to each other. Sprinkler distribution measurements were made to be used in computing sprinkler uniformity. Using neutron equipment, soil moisture determinations were made before the irrigation, one day after irrigation, and three days after irrigation to determine the effect of the irrigation. Final analysis of the data from the experiment indicated that there was not an optimum degree of ponding. In fact, ponding, application rate, grade of plots, and crop cover did not appear to appreciably affect the distribution of soil moisture after an irrigation. Title: Relationships between degree of ponding and uniformity of soil moisture distribution under irrigation sprinklers Author: Dehlinger, Charles Robert Often low intake rate soils need special consideration when applying water during an irrigation. Surface flooding for extended periods may cause adverse crop growth conditions. Properly designed sprinkler systems often eliminate irrigation problems, because the application rate and quantity of water applied can be readily controlled. Research workers who have studied sprinkler irrigation disagree on many things. Differences are found in the literature concerning the procedures used to determine sprinkler distribution uniformity and the optimum rate of application of water to the soil. Several authors suggest that moisture movement within the soil occurs after an irrigation. If trans location of moisture occurs, it may be possible to use sprinkler system design specifications that are less critical than those now in use. In order to determine the effect of sprinkler application rate on the resulting soil moisture distribution it is necessary to have criteria relating degree of ponding, crop cover, and slope of the land to the uniformity of soil moisture. Experimental plots were designed and prepared to study and relate these factors to each other. Sprinkler distribution measurements were made to be used in computing sprinkler uniformity. Using neutron equipment, soil moisture determinations were made before the irrigation, one day after irrigation, and three days after irrigation to determine the effect of the irrigation. Final analysis of the data from the experiment indicated that there was not an optimum degree of ponding. In fact, ponding, application rate, grade of plots, and crop cover did not appear to appreciably affect the distribution of soil moisture after an irrigation. Close

• 8. [Article] Unsaturated Soils and Foundation Design : Theoretical Considerations for an Effective Stress Framework

  This study presents the theoretical background necessary to model the bearing capacity of shallow and deep foundations in partially saturated soils. The conventional bearing capacity equations for shallow ...

  Citation × Citation Citation Abstract Copy Title: Unsaturated Soils and Foundation Design : Theoretical Considerations for an Effective Stress Framework Author: Baker, Josiah D. This study presents the theoretical background necessary to model the bearing capacity of shallow and deep foundations in partially saturated soils. The conventional bearing capacity equations for shallow and deep foundations and the ?-method for deep foundation side resistance have been modified to include the effects of matric suction and varying water contents according to the effective stress framework. A closed-form solution has been proposed for the bearing capacity equation that modifies the overburden, unit weight, and cohesion terms in the conventional equation. The ?-method has been modified to consider suction stresses along the deep foundation and a reduction in K₀ due to tension cracking near the surface. The modified bearing capacity equation for shallow foundations shows good agreement to load-tests performed in partially saturated soils. Monte Carlo simulations were performed on silt loams, sands, and clays to characterize variance and distribution of bearing capacity. The results show that silts have the largest variance while clays have the smallest variance in predicted bearing capacity. Title: Unsaturated Soils and Foundation Design : Theoretical Considerations for an Effective Stress Framework Author: Baker, Josiah D. This study presents the theoretical background necessary to model the bearing capacity of shallow and deep foundations in partially saturated soils. The conventional bearing capacity equations for shallow and deep foundations and the ?-method for deep foundation side resistance have been modified to include the effects of matric suction and varying water contents according to the effective stress framework. A closed-form solution has been proposed for the bearing capacity equation that modifies the overburden, unit weight, and cohesion terms in the conventional equation. The ?-method has been modified to consider suction stresses along the deep foundation and a reduction in K₀ due to tension cracking near the surface. The modified bearing capacity equation for shallow foundations shows good agreement to load-tests performed in partially saturated soils. Monte Carlo simulations were performed on silt loams, sands, and clays to characterize variance and distribution of bearing capacity. The results show that silts have the largest variance while clays have the smallest variance in predicted bearing capacity. Close

• 9. [Article] Water loss and uptake in clayey subsoil materials

  B and C horizon samples from twenty four selected profiles along a north-south transect in the Willamette Valley were examined for possible correlation between shrinkage properties and kind of clay minerals ...

  Citation × Citation Citation Abstract Copy Title: Water loss and uptake in clayey subsoil materials Author: Stannard, Davis Robertson B and C horizon samples from twenty four selected profiles along a north-south transect in the Willamette Valley were examined for possible correlation between shrinkage properties and kind of clay minerals present. Observations of linear shrinkage, weight loss from a condition of maximum plasticity, and changing character of X-ray diffraction patterns were made on 'tablets' of the untreated soil material during drying and subsequent heating at various temperatures to 950°C. Differential-thermal analysis of undried 'whole soil' samples was also made. On the basis of the X-ray diffraction patterns, soil samples were placed in five groups and a pair of B and C horizon samples from a profile representative of each group was selected for characterization of clay mineral suites by conventional X-ray diffraction analysis and differential thermal analysis. Differences found in clay mineral suites of the five profiles justified the initial grouping and provided a basis for the attempt to observe correlations between shrinkage behavior and the kind of clay minerals present. Clays of the two-layer lattice type (kandites) were found dominant in most samples from the Salem Hills. A more detailed distinction of these was made between the red, acid, over-deepened colluvium dominated by kaolinite (with iron and aluminum hydrates associated), and those relatively shallow soils lying on profoundly weathered tuffaceous sediments which were characterized by dominance of poorly crystalline clays of both two-layer and three-layer lattice type (probably hydrated halloysite and smectite of the beidel-Iite-nontronite sequence) . Clays of the three-layer lattice type (micaceous, or showing expansion properties) were dominant in soils on the valley floor. A further distinction of these was made between the silty soils showing micaceous material as well as other material of varying degrees of expansion, and those soils on alluvial clay which appeared to contain most or all of which was smectite (probably of the beidellite-nontronite sequence ). Detailed examination of shrinkage curves for two soil samples containing the same amount of clay, but of different mineralogy (kaolinite vis a vis smectite), failed to reveal differences in shrinkage due to differing lattice type. In general, a difference in shrinkage was not observed between those samples on the transect with dominantly three-layer lattice clays and those with dominantly two-layer lattice clays. Most of the variation in shrinkage could be attributed to variations in particle size and surface area, as measured by clay content and water distinctions in clay mineralogy on field under other circumstances was loss. The possibility of making the basis of shrinkage in the not excluded. Title: Water loss and uptake in clayey subsoil materials Author: Stannard, Davis Robertson B and C horizon samples from twenty four selected profiles along a north-south transect in the Willamette Valley were examined for possible correlation between shrinkage properties and kind of clay minerals present. Observations of linear shrinkage, weight loss from a condition of maximum plasticity, and changing character of X-ray diffraction patterns were made on 'tablets' of the untreated soil material during drying and subsequent heating at various temperatures to 950°C. Differential-thermal analysis of undried 'whole soil' samples was also made. On the basis of the X-ray diffraction patterns, soil samples were placed in five groups and a pair of B and C horizon samples from a profile representative of each group was selected for characterization of clay mineral suites by conventional X-ray diffraction analysis and differential thermal analysis. Differences found in clay mineral suites of the five profiles justified the initial grouping and provided a basis for the attempt to observe correlations between shrinkage behavior and the kind of clay minerals present. Clays of the two-layer lattice type (kandites) were found dominant in most samples from the Salem Hills. A more detailed distinction of these was made between the red, acid, over-deepened colluvium dominated by kaolinite (with iron and aluminum hydrates associated), and those relatively shallow soils lying on profoundly weathered tuffaceous sediments which were characterized by dominance of poorly crystalline clays of both two-layer and three-layer lattice type (probably hydrated halloysite and smectite of the beidel-Iite-nontronite sequence) . Clays of the three-layer lattice type (micaceous, or showing expansion properties) were dominant in soils on the valley floor. A further distinction of these was made between the silty soils showing micaceous material as well as other material of varying degrees of expansion, and those soils on alluvial clay which appeared to contain most or all of which was smectite (probably of the beidellite-nontronite sequence ). Detailed examination of shrinkage curves for two soil samples containing the same amount of clay, but of different mineralogy (kaolinite vis a vis smectite), failed to reveal differences in shrinkage due to differing lattice type. In general, a difference in shrinkage was not observed between those samples on the transect with dominantly three-layer lattice clays and those with dominantly two-layer lattice clays. Most of the variation in shrinkage could be attributed to variations in particle size and surface area, as measured by clay content and water distinctions in clay mineralogy on field under other circumstances was loss. The possibility of making the basis of shrinkage in the not excluded. Close