Drained shear strength of fine-grained soil-solid surface interfaces

Herein are reported the results of an investigation on the effective angle of interfacial friction between fine-grained soils and solid surfaces as influenced by the roughness of the material surface, the soil type and the overconsolidation ratio. The ratio of interfacial friction angle to the angle of internal friction (evaluated at constant overconsolidation ratio) of the soil is independent of the overconsolidation ratio. An empirical correlation between this ratio and the roughness of the interface has been proposed.

Urban ecosystem services at the plant-soil interface

Continuing urbanization is a crucial driver of land transformation, having widespread impacts on virtually all ecosystems. Terrestrial ecosystems, including disturbed ones, are dependent on soils, which provide a multitude of ecosystem services. As soils are always directly and/or indirectly impacted through land transformation, land cover change causes soil change. Knowledge of ecosystem properties and functions in soils is increasing in importance as humans continue to concentrate into already densely-populated areas. Urban soils often have hampered functioning due to various disturbances resulting from human activity. Innovative solutions are needed to bring the lacking ecosystem services and quality of life to these urban environments. For instance, the ecosystem services of the urban green infrastructure may be substantially improved through knowledge of their functional properties. In the research forming this thesis, the impacts of four plant species (Picea abies, Calluna vulgaris, Lotus corniculatus and Holcus lanatus) on belowground biota and regulatory ecosystem services were investigated in two different urban soil types. The retention of inorganic nitrogen and phosphorus in the plant-soil system, decomposition of plant litter, primary production, and the degradation of polycyclic aromatic hydrocarbons (PAHs) were examined in the field and under laboratory conditions. The main objective of the research was to determine whether the different plant species (representing traits with varying litter decomposability) will give rise to dissimilar urban belowground communities with differing ecological functions. Microbial activity as well as the abundance of nematodes and enchytraeid worm biomass was highest below the legume L. corniculatus. L. corniculatus and the grass H. lanatus, producing labile or intermediate quality litter, enhanced the proportion of bacteria in the soil rhizosphere, while the recalcitrant litter-producing shrub C. vulgaris and the conifer P. abies stimulated the growth of fungi. The loss of nitrogen from the plant-soil system was small for H. lanatus and the combination of C. vulgaris + P. abies, irrespective of their energy channel composition. These presumably nitrogen-conservative plant species effectively diminished the leaching losses from the plant-soil systems with all the plant traits present. The laboratory experiment revealed a difference in N allocation between the plant traits: C. vulgaris and P. abies sequestered significantly more N in aboveground shoots in comparison to L. corniculatus and H. Lanatus. Plant rhizosphere effects were less clear for phosphorus retention, litter decomposition and the degradation of PAH compounds. This may be due to the relatively short experimental durations, as the maturation of the plant-soil system is likely to take a considerably longer time. The empirical studies of this thesis demonstrated that the soil communities rapidly reflect changes in plant coverage, and this has consequences for the functionality of soils. The energy channel composition of soils can be manipulated through plants, which was also supported by the results of the separate meta-analysis conducted in this thesis. However, further research is needed to understand the linkages between the biological community properties and ecosystem services in strongly human-modified systems.

Effect of soil preparation of boreal spruce forest on air and soil temperature conditions in forest regeneration areas.

The effect of scarification, ploughing and cross-directional plouhing on temperature conditions in the soil and adjacent air layer have been studied during 11 consecutive growth periods by using an unprepared clear-cut area as a control site. The maximum and minimum temperatures were measured daily in the summer months, and other temperature observations were made at four-hour intervals by means of a Grant measuring instrument. The development of the seedling stand was also followed in order to determine its shading effect on the soil surface. Soil preparation decreased the daily temperature amplitude of the air at the height of 10 cm. The maximum temperatures on sunny days were lower in the tilts of the ploughed and in the humps of the cross-directional ploughed sites compared with the unprepared area. Correspondingly, the night temperatures were higher and so the soil preparation considerably reduced the risk of night frost. In the soil at the depth of 5 cm, soil preparation increased daytime temperatures and reduced night temperatures compared with unprepared area. The maximum increase in monthly mean temperatures was almost 5 °C, and the daily variation in the surface parts of the tilts and humps increased so that excessively high temperatures for the optimal growth of the root system were measured from time to time. The temperature also rose at the depths of 50 and 100 cm. Soil preparation also increased the cumulative temperature sum. The highest sums accumulated during the summer months were recorded at the depth of 5 cm in the humps of cross-directional ploughed area (1127 dd.) and in the tilts of the ploughed area (1106 dd.), while the corresponding figure in the unprepared soil was 718 dd. At the height of 10 cm the highest temperature sum was 1020 dd. in the hump, the corresponding figure in the unprepared area being 925 dd. The incidence of high temperature amplitudes and percentage of high temperatures at the depth of 5 cm decreased most rapidly in the humps of cross-directional ploughed area and in the ploughing tilts towards the end of the measurement period. The decrease was attributed principally to the compressing of tilts, the ground vegetation succession and the growth of seedlings. The mean summer temperature in the unprepared area was lower than in the prepared area and the difference did not diminish during the period studied. The increase in temperature brought about by soil preparation thus lasts at least more than 10 years.

Analysis of forest soil chemistry and hydrology with a dynamic model ACIDIC.

In this study we analyze how the ion concentrations in forest soil solution are determined by hydrological and biogeochemical processes. A dynamic model ACIDIC was developed, including processes common to dynamic soil acidification models. The model treats up to eight interacting layers and simulates soil hydrology, transpiration, root water and nutrient uptake, cation exchange, dissolution and reactions of Al hydroxides in solution, and the formation of carbonic acid and its dissociation products. It includes also a possibility to a simultaneous use of preferential and matrix flow paths, enabling the throughfall water to enter the deeper soil layers in macropores without first reacting with the upper layers. Three different combinations of routing the throughfall water via macro- and micropores through the soil profile is presented. The large vertical gradient in the observed total charge was simulated succesfully. According to the simulations, gradient is mostly caused by differences in the intensity of water uptake, sulfate adsorption and organic anion retention at the various depths. The temporal variations in Ca and Mg concentrations were simulated fairly well in all soil layers. For H+, Al and K there were much more variation in the observed than in the simulated concentrations. Flow in macropores is a possible explanation for the apparent disequilibrium of the cation exchange for H+ and K, as the solution H+ and K concentrations have great vertical gradients in soil. The amount of exchangeable H+ increased in the O and E horizons and decreased in the Bs1 and Bs2 horizons, the net change in whole soil profile being a decrease. A large part of the decrease of the exchangeable H+ in the illuvial B horizon was caused by sulfate adsorption. The model produces soil water amounts and solution ion concentrations which are comparable to the measured values, and it can be used in both hydrological and chemical studies of soils.

Frame Soil Interaction And Winkler Model

The Winkler spring model is the most convenient representation of soil support in the domain of linear elasticity for framed structure-soil interaction analyses. The closeness of the analytical results obtained using this model with those corresponding to the elastic half-space continuum has been investigated in the past for foundation beams. The findings, however, are not applicable to framed structures founded on beam or strip footings. Moreover, the past investigations employ the concept of characteristic length which does not adequately account for the stiffness contribution of the superstructure. A framed structure on beam foundation can be described parametrically by the ratios of stiffnesses of superstructure and foundation beams to that of soil. For a practical range of soil allowable pressures, the ranges of these relative stiffness ratios have been established. The present study examines the variation between interactive analyses based on Winkler springs with those using the half-space continuum over these ranges of relative stiffness ratios. The findings enable the analyst to undertake a Winkler spring-based-interaction analysis with knowledge of the likely variation of values with those derived for the more computation-intensive half-space continuum.

Bioremediation of diesel oil contaminated soil and water

Diesel spills contaminate aquatic and terrestrial environments. To prevent the environmental and health risks, the remediation needs to be advanced. Bioremediation, i.e., degradation by microbes, is one of the suitable methods for cleaning diesel contamination. In monitored natural attenuation technique are natural processes in situ combined, including bioremediation, volatilization, sorption, dilution and dispersion. Soil bacteria are capable of adapting to degrade environmental pollutants, but in addition, some soil types may have indigenous bacteria that are naturally suitable for degradation. The objectives for this work were (1) to find a feasible and economical technique to remediate oil spilled into Baltic Sea water and (2) to bioremediate soil contaminated by diesel oil. Moreover, the aim was (3) to study the potential for natural attenuation and the indigenous bacteria in soil, and possible adaptation to degrade diesel hydrocarbons. In the aquatic environment, the study concentrated on diesel oil sorption to cotton grass fiber, a natural by-product of peat harvesting. The impact of diesel pollution was followed in bacteria, phytoplankton and mussels. In a terrestrial environment, the focus was to compare the methods of enhanced biodegradation (biostimulation and bioaugmentation), and to study natural attenuation of oil hydrocarbons in different soil types and the effect that a history of previous contamination may have on the bioremediation potential. (1) In the aquatic environment, rapid removal of diesel oil was significant for survival of tested species and thereby diversity maintained. Cotton grass not only absorbed the diesel but also benefited the bacterial growth by providing a large colonizable surface area and hence oil-microbe contact area. Therefore use of this method would enhance bioremediation of diesel spills. (2) Biostimulation enhances bioremediation, and (3) indigenous diesel-degrading bacteria are present in boreal environments, so microbial inocula are not always needed. In the terrestrial environment experiments, the combination of aeration and addition of slowly released nitrogen advanced the oil hydrocarbon degradation. Previous contamination of soil gives the bacterial community the potential for rapid adaptation and efficient degradation of the same type of contaminant. When the freshly contaminated site needs addition of diesel degraders, previously contaminated and remediated soil could be used as a bacterial inoculum. Another choice of inoculum could be conifer forest soil, which provides a plentiful population of degraders, and based on the present results, could be considered as a safe non-polluted inoculum. According to the findings in this thesis, bioremediation (microbial degradation) and monitored natural attenuation (microbial, physical and chemical degradation) are both suitable techniques for remediation of diesel-contaminated sites in Finland.

Mechanistic evaluation of mitigation of petroleum hydrocarbon contamination by soil medium

Present in situ chemical treatment technologies for mitigation of petroleum hydrocarbon contamination are in the developmental stage or being tested. To devise efficient strategies for restricting the movement of petroleum hydrocarbon (PHC) molecules in the contaminated soil, it is proposed to utilize the sorption–interaction relationships between the petroleum contaminants and the soil substrate. The basic questions addressed in this paper are as follows (i) What are the prominent chemical constituents of the various petroleum fractions that interact with the soil substrate? (ii) What are the functional groups of a soil that interact with the contaminants? (iii) What are the bonding mechanisms possible between the soil functional groups and the PHC contaminants? (iv) What are the consequent changes brought about the soil physical properties on interaction with PHC's? (v) What are the factors influencing the interactions between PHC molecules and clay particles of the soil substrate? (vi) What is the possibility of improving the soil's attenuation ability for PHC's? The development of answers to the basic questions reveal that petroleum hydrocarbons comprise a mixture of nonpolar alkanes and aromatic and polycyclic hydrocarbons, that have limited solubility in water. The bonding mechanism between the nonpolar PHC's and the clay surface is by way of van der Waals attraction. The adsorption of the nonpolar hydrocarbons by the clay surface occurs only when their (i.e., the hydrocarbon molecules) solubility in water is exceeded and the hydrocarbons exist in the micellar form. Dilute solutions of hydrocarbons in water, i.e., concentrations of hydrocarbons at or below the solubility limit, have no effect on the hydraulic conductivity of clay soils. Permeation with pure hydrocarbons invariably influences the clay hydraulic conductivity. To improve the attenuation ability of soils towards PHC's, it is proposed to coat the soil surface with "ultra" heavy organic polymers. Adsorption of organic polymers by the clay surface may change the surface properties of the soil from highly hydrophilic (having affinity for water molecules) to organophilic (having affinity for organic molecules). The organic polymers attached to the clay surface are expected to attenuate the PHC molecules by van der Waals attraction, by hydrogen bonding, and also by adsorption into interlayer space in the case of soils containing swelling clays.

Technique for Using Fine-Grained Soil in Reinforced Earth

The performance of reinforced earth structures depends on the mobilization of interfacial shearing resistance between soil and reinforcement. This criterion typically eliminates the use of fine-grained soil as a backfill material in reinforced earth structures. Considering the distribution of induced interfacial shear stress in soil around the surface of the reinforcement, it has been shown that only a thin zone of frictional material around the reinforcement is required to mobilize almost full interfacial shearing resistance of sand. Six series of pullout tests have been conducted, with different types of reinforcement, to study the effect of thickness of sand (frictional material) around the reinforcement on the pullout resistance. Sawdust and kaolin clay have been used as bulk backfill material, providing the soil with negligible friction. With low-friction-strength soil as bulk material, a 15-mm thickness of sand around the reinforcement is required to increase the interfacial shearing resistance to that with sand as the bulk material. With this new technique, low-frictional fine-grained soils can be used as bulk backfill material in reinforced earth constructions.

Estimation of soil hydraulic properties and their uncertainty: comparison between laboratory and field experiment

Often the soil hydraulic parameters are obtained by the inversion of measured data (e.g. soil moisture, pressure head, and cumulative infiltration, etc.). However, the inverse problem in unsaturated zone is ill-posed due to various reasons, and hence the parameters become non-unique. The presence of multiple soil layers brings the additional complexities in the inverse modelling. The generalized likelihood uncertainty estimate (GLUE) is a useful approach to estimate the parameters and their uncertainty when dealing with soil moisture dynamics which is a highly non-linear problem. Because the estimated parameters depend on the modelling scale, inverse modelling carried out on laboratory data and field data may provide independent estimates. The objective of this paper is to compare the parameters and their uncertainty estimated through experiments in the laboratory and in the field and to assess which of the soil hydraulic parameters are independent of the experiment. The first two layers in the field site are characterized by Loamy sand and Loamy. The mean soil moisture and pressure head at three depths are measured with an interval of half hour for a period of 1 week using the evaporation method for the laboratory experiment, whereas soil moisture at three different depths (60, 110, and 200 cm) is measured with an interval of 1 h for 2 years for the field experiment. A one-dimensional soil moisture model on the basis of the finite difference method was used. The calibration and validation are approximately for 1 year each. The model performance was found to be good with root mean square error (RMSE) varying from 2 to 4 cm(3) cm(-3). It is found from the two experiments that mean and uncertainty in the saturated soil moisture (theta(s)) and shape parameter (n) of van Genuchten equations are similar for both the soil types. Copyright (C) 2010 John Wiley & Sons, Ltd.

Influence of Osmotic Suction on the Soil-Water Characteristic Curves of Compacted Expansive Clay

Unsaturated clays are subject to osmotic suction gradients in geoenvironmental engineering applications and it therefore becomes important to understand the effect of these chemical concentration gradients on soil-water characteristic curves (SWCCs). This paper brings out the influence of induced osmotic suction gradient on the wetting SWCCs of compacted clay specimens inundated with sodium chloride solutions/distilled water at vertical stress of 6.25 kPa in oedometer cells. The experimental results illustrate that variations in initial osmotic suction difference induce different magnitudes of osmotic induced consolidation and osmotic consolidation strains thereby impacting the wetting SWCCs and equilibrium water contents of identically compacted clay specimens. Osmotic suction induced by chemical concentration gradients between reservoir salt solution and soil-water can be treated as an equivalent net stress component, (p(pi)) that decreases the swelling strains of unsaturated specimens from reduction in microstructural and macrostructural swelling components. The direction of osmotic flow affects the matric SWCCs. Unsaturated specimens experiencing osmotic induced consolidation and osmotic consolidation develop lower equilibrium water content than specimens experiencing osmotic swelling during the wetting path. The findings of the study illustrate the need to incorporate the influence of osmotic suction in determination of the matric SWCCs.

Physical properties of a boreal clay soil under differently managed perennial vegetation

The physical properties of surface soil horizons, essentially pore size, shape, continuity and affinity for water, regulate water entry into the soil. These properties are prone to changes caused by natural forces and human activity. The hydraulic properties of the surface soil greatly impact the generation of surface runoff and accompanied erosion, the major concern of agricultural water protection. The general target of this thesis was to improve our understanding of the structural and hydraulic properties of boreal clay soils. Physical properties of a clayey surface soil (0 - 10 cm, clay content 51%), with a micaceous/illitic mineralogy subjected to three different management practices of perennial vegetation, were studied. The study sites were vegetated buffer zones located side by side in SW Finland: 1) natural vegetation with no management, 2) harvested once a year, and 3) grazed by cattle. The soil structure, hydraulic properties, shrinkage properties and soil water repellency were determined at all sites. Two distinct flow domains were evident. The surface soil was characterized by subangular blocky, angular blocky and platy aggregates. Hence, large, partially accommodated, irregular elongated pores dominated the macropore domain at all sites. The intra-aggregate pore system was mostly comprised of pores smaller than 30 μm, which are responsible for water storage. Macropores at the grazed site, compacted by hoof pressure, were horizontally oriented and pore connectivity was poorest, which decreased water and air flux compared with other sites. Drying of the soil greatly altered its structure. The decrease in soil volume between wet and dry soil was 7 - 10%, most of which occurred in the moisture range of field conditions. Structural changes, including irreversible collapse of interaggregate pores, began at matric potentials around -6 kPa indicating, instability of soil structure against increasing hydraulic stress. Water saturation and several freezethaw cycles between autumn and spring likely weakened the soil structure. Soil water repellency was observed at all sites at the time of sampling and when soil was dryer than about 40 vol.%. (matric potential < -6 kPa). Therefore, water repellency contributes to water flow over a wide moisture range. Water repellency was also observed in soils with low organic carbon content (< 2%), which suggests that this phenomenon is common in agricultural soils of Finland due to their relatively high organic carbon content. Aggregate-related pedofeatures of dense infillings described as clay intrusions were found at all sites. The formation of these intrusions was attributed to clay dispersion and/or translocation during spring thaw and drying of the suspension in situ. These processes generate very new aggregates whose physical properties are most probably different from those of the bulk soil aggregates. Formation of the clay infillings suggested that prolonged wetness in autumn and spring impairs soil structure due to clay dispersion, while on the other hand it contributes to the pedogenesis of the soil. The results emphasize the dynamic nature of the physical properties of clay soils, essentially driven by their moisture state. In a dry soil, fast preferential flow is favoured by abundant macropores including shrinkage cracks and is further enhanced by water repellency. Increase in soil moisture reduces water repellency, and swelling of accommodated pores lowers the saturated hydraulic conductivity. Moisture- and temperature-related processes significantly alter soil structure over a time span of 1 yr. Thus, the pore characteristics as well as the hydraulic properties of soil are time-dependent.

Stiffness Coefficients of Layered Soil Systems

One of the most important dynamic properties required in the design of machine foundations is the stiffness or spring constant of the supporting soil. For a layered soil system, the stiffness obtained from an idealization of soils underneath as springs in series gives the same value of stiffness regardless of the location and extent of individual soil layers with respect to the base of the foundation. This paper aims to develop the importance of the relative positioning of soil layers and their thickness beneath the foundation. A simple and approximate procedure called the weighted average method has been proposed to obtain the equivalent stiffness of a layered soil system knowing the individual values of the layers, their relative position with respect to foundation base, and their thicknesses. The theoretically estimated values from the weighted average method are compared with those obtained by conducting field vibration tests using a square footing over different two- and three-layered systems and are found to be very good. The tests were conducted over a range of static and dynamic loads using three different materials. The results are also compared with the existing methods available in the literature.

Sediment Volume Tests for Expansive Soil Identification and Classification

Equilibrium sediment volume tests are conducted on field soils to classify them based on their degree of expansivity and/or to predict the liquid limit of soils. The present technical paper examines different equilibrium sediment volume tests, critically evaluating each of them. It discusses the settling behavior of fine-grained soils during the soil sediment formation to evolve a rationale for conducting the latest version of equilibrium sediment volume test. Probable limitations of equilibrium sediment volume test and the possible solution to overcome the same have also been indicated.

A photoelastic approach to framed structure-foundation beam-soil interaction

The interaction of a framed structure with a foundation beam resting on an elastic medium, representing the soil, has been studied using the photoelastic method. The contact pressure distribution, the fibre stress in the foundation beam and frame structure, as well as the stresses in the elastic medium, have been obtained. These have been compared with theoretical results obtained by idealizing the soil as (a) elastic half plane, and (b) elastic half space. It is shown that the photoelastic method can provide an easy solution to this type of problem if the soil can be idealized as an elastic continuum.