Influence Of Soil Heterogeneity Research Articles

Influence of Soil Heterogeneity on Water Flow and Solute Transport Characterized by Dye Tracer Experiments

Soil heterogeneity is a key factor affecting horizontal water flow and solute transport in unsaturated soil, in which particle distribution, pore structure, and pore connectivity in the soil all present fractal characteristics. The initial water content of soil has significant influence in the resulting heterogeneity of the soil structure, which can affect the water flow and solute transport. In this study, through a series of horizontal transport laboratory simulation experiments in soil columns, the initial water content dependency of transport was elucidated using the fractal Richards’ equation (FRE) model. We first observed that water flows faster in soil columns with higher initial water content, but the law is opposite in the initial process of water flow. By analyzing the variation of parameter values in the FRE model, we speculated that the abnormal phenomenon of early diffusion is caused by the heterogeneity of the soil structure. To elucidate the mechanisms of the water content’s dependency of the solute transport process and to identify the circumstance of altering of flow regime, a series of dye tracer experiments were conducted. Results show that in soil columns with low water content, the inflow of external fluid leads to the agglomeration of soil particles. Combined with matric suction, the heterogeneity of the soil structure is enhanced, which affects the formation of water flow and solute transport paths. It even leads to preferential flow in unsaturated soil columns with low water content.

Stability Analysis of Shield Inclined Tunnel Faces under the Change Effect of Soil Heterogeneity and Pore Water with Buried Depth

The purpose of this work is to look at how soil heterogeneity and pore water pressure impact shield inclined tunnel excavation face stability as burial depth varies. The calculation model of excavation face stability was established, and the supporting pressure of maintain the excavation face stability was solved via the upper bound method. The results showed that the soil heterogeneity coefficient and pore water pressure coefficient had substantial effects on the supporting pressure. The location of failure face and failure range of shield inclined tunnel under varied heterogeneity coefficient and pore water pressure coefficient were presented. In addition, the boundary depth of shallow tunnel under the influence of soil heterogeneity and pore water was obtained, which supplemented the relevant tunnel code.

Dynamic responses of graded nonhomogeneous unsaturated soils under a strip load

Abstract Based on the three-phase porous media mixed theory, the dynamic governing equations of unsaturated soils is established and the dynamic response of graded nonhomogeneous unsaturated soils subjected to a strip load is studied. Combined with the reverberation-ray matrix method (RRMM) and the boundary condition, the calculation formula of the displacement, stress and pore pressure of graded nonhomogeneous unsaturated soils is derived. Assuming that the continuous variation of physical and mechanical properties of unsaturated soils along the thickness-coordinate by exponential law distribution, the numerical solution of the displacement, stress, and pore pressure then obtained by using numerical inverse Fourier transformation, and the influence of soil heterogeneity and saturation on the dynamic response of unsaturated soils is discussed. The results show that the displacement decreased with increasing gradient factor, and the stress first increased then decreased with the gradient factor increased, and the pore pressure first decreased then increased with increasing gradient factor. The displacement and pore pressure under different gradient factors all increase with increasing saturation.

Influence of Soil Heterogeneity on the Contact Problems in Geotechnical Engineering

Contact problems are widely encountered in geotechnical engineering, such as the contact between soils and concrete used in earth and rockfill dams, tunnels and coastal levees. Due to the unknown contact region and contact forces, the contact problems have strong boundary nonlinearity. In addition, soils have been recognized as heterogeneous materials in geotechnical engineering. The existence of the soil heterogeneity increases the nonlinearity of the contact problems. Currently, the contact problems are mostly analysed without considering the soil heterogeneity, which may not reflect the contact behavior well. In order to investigate the influence of soil heterogeneity on the contact problems, in this paper, a simple plane-strain contact problem is analysed as an example. In this example, Young’s modulus is taken to be a spatially variable. The local average subdivision (LAS) is used to model the heterogeneity of Young’s modulus. The penalty method is utilised to determine the contact behavior. By the first use of linking the penalty method with the LAS, the proposed approach can be used to analyse the contact problems considering soil heterogeneity. The results show that the influence of soil heterogeneity on the elastic contact problems is significant. The contact forces of the heterogeneous case present apparent variation compared to the results of the homogeneous case. The distribution of the contact force at a specific point is also normal when Young’s modulus is normally distributed, moreover, the coefficient of variation (COV) and the horizontal scale of fluctuation of Young’s modulus affect the extent of variation of the normal contact forces. The standard deviation of the normal contact force increases with the increase of the COV and decreases with the increase of the horizontal scale of fluctuation of Young’s modulus. From the analyses, to better predict the deformation/stress in the contact problems, heterogeneity needs to be considered.

Influence of soil heterogeneity on soybean plant development and crop yield evaluated using time-series of UAV and ground-based geophysical imagery

Understanding the interactions among agricultural processes, soil, and plants is necessary for optimizing crop yield and productivity. This study focuses on developing effective monitoring and analysis methodologies that estimate key soil and plant properties. These methodologies include data acquisition and processing approaches that use unmanned aerial vehicles (UAVs) and surface geophysical techniques. In particular, we applied these approaches to a soybean farm in Arkansas to characterize the soil–plant coupled spatial and temporal heterogeneity, as well as to identify key environmental factors that influence plant growth and yield. UAV-based multitemporal acquisition of high-resolution RGB (red–green–blue) imagery and direct measurements were used to monitor plant height and photosynthetic activity. We present an algorithm that efficiently exploits the high-resolution UAV images to estimate plant spatial abundance and plant vigor throughout the growing season. Such plant characterization is extremely important for the identification of anomalous areas, providing easily interpretable information that can be used to guide near-real-time farming decisions. Additionally, high-resolution multitemporal surface geophysical measurements of apparent soil electrical conductivity were used to estimate the spatial heterogeneity of soil texture. By integrating the multiscale multitype soil and plant datasets, we identified the spatiotemporal co-variance between soil properties and plant development and yield. Our novel approach for early season monitoring of plant spatial abundance identified areas of low productivity controlled by soil clay content, while temporal analysis of geophysical data showed the impact of soil moisture and irrigation practice (controlled by topography) on plant dynamics. Our study demonstrates the effective coupling of UAV data products with geophysical data to extract critical information for farm management.

Bending Analysis of Circular Thin Plates Resting on Elastic Foundations Using Two Modified Vlasov Models

The influence of soil heterogeneity is studied on the bending of circular thin plates using two modified Vlasov foundation models. The model parameters are determined reasonably using an iterative technique. According to the principle of minimum potential energy and considering transversely isotropic soils and Gibson soils, the governing differential equations and boundary conditions for circular thin plates on two modified Vlasov foundations are derived using a variational approach, respectively. The determination of attenuation parameters is a difficult problem, which has hindered the further application of the Vlasov foundation model. The equation that must be satisfied by the attenuation parameter is determined, and an iterative method is used to solve the problem. A comparative analysis is conducted between two modified Vlasov models and the traditional Vlasov model. The results show that the governing equations and boundary conditions for circular thin plates resting on two modified foundations are consistent with those for a circular thin plate on traditional two-parameter foundation after degradation. The accuracy and reliability of the proposed solutions are demonstrated by comparing the obtained results with those reported in the literature. The heterogeneity of soils, including the transversely isotropic soils and Gibson soils, has a certain effect on characteristic parameters of the foundation models as well as the deformations and internal forces of circular thin plates. The present study could be employed as a reference for future engineering designs.

Soil heterogeneity and plant species diversity in experimental grassland communities: contrasting effects of soil nutrients and pH at different spatial scales

Background and aimsCurrent knowledge of soil heterogeneity-diversity relationships (HDR) is largely based on studies manipulating single factor, but the advancements in HDR may require a comprehensive experiment incorporating multiple factors.MethodsWe conducted a three-year field experiment in which a seed mixture of 16 common grassland species was sown in plots with heterogeneous soils consisting of small (10 cm × 10 cm) or large patches (30 cm × 30 cm) of low and high nutrients or low and high pH, and homogeneous soils with an even mixture of low and high nutrient/pH soils. Soil nutrients and pH were manipulated in separate treatments. We determined plant species richness and diversity at two focal scales (40 cm × 40 cm plot-scale and 10 cm × 10 cm patch-scale).ResultsPlot-scale richness and diversity were not influenced by soil heterogeneity, but patch-scale richness was lower in plots with heterogeneous nutrients than in plots where nutrients were distributed homogeneously. There was no difference between the two heterogeneous nutrient soils with different grain sizes. Patch-scale diversity was higher in heterogeneous pH soils of large patch size than in heterogeneous pH soils of small patch size or the homogeneous pH soil at the final harvest. Species richness and diversity quantified at both plot and patch scales declined in all soils over time.ConclusionsThe influence of soil heterogeneity on plant species diversity depends on whether the soil varies in nutrients or pH, and on the temporal-spatial scale at which species diversity and soil heterogeneity are measured. These results indicate that soil heterogeneity has the potential to promote plant coexistence and future HDR studies should consider multiple soil factors at various temporal-spatial scales.

Heterogeneous soil conditions influence fungal alkaline phosphatase activity in roots of Lotus corniculatus

Extremes in soil water, temperature, pH and inorganic nutrient availability can highly influence mycorrhizal formation and nutrient acquisition. However, the influence of soil heterogeneity and seasonal soil changes on fungal alkaline phosphatase (ALP) activity in mycorrhizal roots is unknown. Whether the activity of intraradical fungal ALP is influenced by soil texture heterogeneity, soil depth, nutrient concentrations and root density during the growing season were addressed in this research. The root system of Lotus corniculatus grown on a reclamation site was analyzed for intraradical mycorrhizal ALP activity in 0–10, 10–20 and 20–30cm depth increments of sandy soil and in clay–silt fragments (mostly localized in 10–20cm) from May to September. Root length density and water soluble nutrient contents in sandy soil and clay–silt fragments were determined for each sample. Soil water content and soil temperature data of a nearby site were used for climate conditions on sampling dates. Fungal ALP activity in roots growing in clay–silt fragments was higher than in those growing in sandy soil, independent of sampling date. Fungal ALP activity in sandy soil increased with soil depth which is related to decreasing root densities and lower nutrient concentrations. However, nutrient dense clay–silt fragments significantly positively influenced local mycorrhizal ALP activity in L. corniculatus roots, suggesting that the ability of mycorrhizae to selectively take up phosphorus and other nutrients from those nutrient hot spots is enhanced and could play a significant role in successful establishment of pioneer plant species on infertile reclamation sites.

Factors Affecting Sampling Error of Nutrient Element Contents of Arable Fields

A sampling proficiency test is evaluated to analyze the influence of soil heterogeneity and sampling parameters on sampling error of nutrient contents. The influence of parameters on sampling error was assessed by multiple linear regression, regression tree analysis, and variance component analysis (VCA). Error was governed mainly by heterogeneity. Among sampling parameters, the number of increment samples had the largest influence. VCA revealed that the component between sampling repetitions was larger than the component between samplers. This suggests a predominance of heterogeneity for the influence on sampling error, increasing with field-scale heterogeneity. Sampling patterns of low complexity seemed sufficient for the homogeneous field, whereas sampling performance was enhanced by more complex sampling pattern on fields of intermediate and high heterogeneity. Overall, the results suggest that sampling error on arable fields sampled with simplified sampling schemes is often determined by soil heterogeneity and to a lesser degree by sampling parameters.

Influence of Soil Heterogeneity and Spatial Discretization on Catchment Water Balance Modeling

This study investigated the impacts of the spatial variability of soil hydraulic properties and the effects of spatial discretization on the water balance in a fully coupled system. The integrated surface–subsurface, three‐dimensional, finite element model HydroGeoSphere was applied to the forested Wüstebach basin (27 ha) to simulate water fluxes. The fully coupled flow simulation model was applied to the headwater catchment at two different spatial resolutions (25 and 100 m). The change in spatial resolution required an aggregation of the soil map, which influenced the water fluxes and the spatial patterns of soil moisture. The nonlinear relationship between soil moisture and transpiration caused the spatial aggregation of soil moisture to have a larger effect on the water balance than did aggregating the soil hydraulic properties. In addition to the total discharge, the effects on the spatial patterns of the simulated soil moisture were also investigated. The results show that aggregating soil hydraulic properties results in lower uncertainties than does using a coarser discretization. This can be explained by the nonlinearity of the relationship between soil moisture and evapotranspiration.

Discussion of “Pile Behavior—Consequences of Geological and Construction Imperfections” by Harry G. Poulos

The author must be commended for giving another remarkable contribution to foundation engineering. Designs are almost always made assuming ideal situations, but geological and construction imperfections do exist. Especially in the case of bored piles, one must recognize that construction effects have a major influence on their stiffness. A very competent designer, using very reliable soil information and an extraordinarily precise method for predicting the bearing capacity of a pile, may, in some cases, make a not-so-reliable prediction. In other words, these very favorable conditions alone do not guarantee a successful design. The reason is that in the design phase no one knows how the pile is going to be built. The author has shown very clearly the influence of a “soft base” in the stiffness of a pile. Fig. 25 shows that for a given load, the pile with “unclean” base settles about three times more than a similar pile with a “clean” base. And it is not a 20 or 30% difference, but a 200% difference. The discusser would like to add new information on this matter. The case of a foundation for a large industrial plant will be analyzed. The foundation consisted of about 4,000 mechanically drilled bored piles, 70 cm in diameter. The soil was a compacted fill. The design specification required that after finishing the drilling procedure, the walls of the shaft should have to be cleaned by a foreman using steel brittle brushes. After that, the bases had to be cleaned and then, the pile concreted. To evaluate the influence of the “cleaning” procedure on the bearing capacity of the pile, two load tests were carried out. Although the two test piles were close to each other and within the same compacted layer, it was decided to carry out two SPTTs. The SPT-T is the traditional SPT complemented with torque measurements, Decourt and Quaresma Filho 1994 . In order to reduce the influence of soil heterogeneity on the results, the discusser required the axes of the piles to coincide exactly with the axes of the borings SPT-T . The results of the two SPT-Ts were very close to each other, so it was considered that direct comparison between the two load

Influence of soil heterogeneity on load redistribution and settlement of a hyperstatic three-support frame

Spatial and geometrical variability of mechanical soil properties can induce differential settlements and load redistribution in hyperstatic structures. Therefore damage prevention requires specific attention to be paid to the global mechanisms of soil–structure interaction. A reduced-scale model of a hyperstatic three-support frame (scale 1:100) is installed on the CEA-CESTA centrifuge, up to 100g. Various configurations are studied, with different loadings, different structural stiffnesses, and different geometries of the soil layer. Strain gauges are fixed at various points so as to enable the retro-analysis of all components of forces at free ends. Displacements are recorded at several points on the structure and on the free surface. A numerical model of the frame (based on beam theory with elastic supports) is calibrated, first to determine an equivalent support stiffness, and second to quantify the effect of variations of the structural stiffness/soil modulus ratio on the structural response. A probabilistic approach based on Monte Carlo simulation is thus developed. It mixes the soil description, based on random field theory and enabling the description of spatial correlation of properties and the frame model identified above. The influence of (a) scattering in soil properties and (b) spatial correlation of soil properties—through correlation length or scale of fluctuation—is quantified in terms of displacements and bending moments in the frame. The approach reveals the important weight/influence of soil variability on differential settlement and load redistribution, particularly when the scale of fluctuation of soil and length of span have the same magnitude. The analysis makes it possible to evaluate the risk that the bending moment in any critical section may be larger than predicted by the usual engineer's model. Some conclusions are drawn to better estimate ‘characteristic bending moments’ in the frame, accounting for both the soil variability and the soil–frame interaction.

Influence of soil heterogeneity on load redistribution and settlement of a hyperstatic three-support frame

Spatial and geometrical variability of mechanical soil properties can induce differential settlements and load redistribution in hyperstatic structures. Therefore damage prevention requires specific attention to be paid to the global mechanisms of soil–structure interaction. A reduced-scale model of a hyperstatic three-support frame (scale 1:100) is installed on the CEA-CESTA centrifuge, up to 100g. Various configurations are studied, with different loadings, different structural stiffnesses, and different geometries of the soil layer. Strain gauges are fixed at various points so as to enable the retro-analysis of all components of forces at free ends. Displacements are recorded at several points on the structure and on the free surface. A numerical model of the frame (based on beam theory with elastic supports) is calibrated, first to determine an equivalent support stiffness, and second to quantify the effect of variations of the structural stiffness/soil modulus ratio on the structural response. A probabilistic approach based on Monte Carlo simulation is thus developed. It mixes the soil description, based on random field theory and enabling the description of spatial correlation of properties and the frame model identified above. The influence of (a) scattering in soil properties and (b) spatial correlation of soil properties—through correlation length or scale of fluctuation—is quantified in terms of displacements and bending moments in the frame. The approach reveals the important weight/influence of soil variability on differential settlement and load redistribution, particularly when the scale of fluctuation of soil and length of span have the same magnitude. The analysis makes it possible to evaluate the risk that the bending moment in any critical section may be larger than predicted by the usual engineer's model. Some conclusions are drawn to better estimate ‘characteristic bending moments’ in the frame, accounting for both the soil variability and the soil–frame interaction.

Influence of soil heterogeneity and competition on growth features of three meadow species

The effect of competition and artificially created soil heterogeneity was studied in a pot experiment. A tussock grass, Holcus lanatus , and the rhizomatous sedge Carex hartmanii were grown alone and in combination with another tussock grass, Molinia caerulea , in homogeneous and heterogeneous soil treatments. The heterogeneous treatment consisted of four compartments, two nutrient rich and two nutrient poor. In the homogenous treatment total nutrient content was the same as in the heterogeneous treatment. Soil heterogeneity increased M. caerulea total production, and increased C. hartmanii root:shoot ratio; no effect on H. lanatus was observed. Both M. caerulea and C. hartmanii were able to place their underground organs preferentially into nutrient rich patches. M. caerulea and H. lanatus total biomass was lower in the presence of the competitor; C. hartmanii responded to competition only by increased allocation to rhizoms. M. caerulea was more affected by competition in the heterogeneous environment

Influence of Soil Heterogeneity on the Coexistence of Grassland Species

(1) In fifteen lowland grasslands, as the quotient of root density in the lower (5-10 cm) layer of soil to that in the upper (0-5 cm) layer increases so there is a decrease in number of species per unit area and in an index of dominance. (2) This quotient, a measure of the heterogeneity of root development, was not related to the difference in pH or concentration of extractable phosphate or potassium in the two soil layers. (3) In a pot experiment an infertile acid sand and a fertile calcareous loam, either mixed or in distinct upper and lower soil layers, were used to grow a standard mixture of five grassland plants. Dominance of one or two species was less marked where there was a distinct lower layer of soil, and this was true irrespective of the total above-ground biomass of all plants. (4) The amount of calcium in the shoots indicates that the species differed in rooting depth, although the spatial distribution of the root system was not analysed. (5) Soil heterogeneity can therefore be shown experimentally to influence the coexistence of species. The distribution of roots in the field may be of great importance in this respect.

Influence of soil heterogeneity on water regime and yields of lucerne, sugar beet and wheat

Lucerne plants in the first crop year as well as plants of spring wheat from different sites of the respective experimental plots showed differences in sap exudation from detopped roots or from stumps of the main shoots, reflecting differences in properties of the soil profile. The differences in sap exudation were observed at a time when the plants did not show any visible differences in water availability.

The influence of soil heterogeneity on the growth and yield of successive crops

1. The interaction of physical conditions of the soil and the establishment of plant together with its subsequent growth and yield have been studied for wheat and swedes on a variable piece of land, maintained as a uniformity trial.2. Ploughing draught was taken as a criterion of the physical condition of the soil and various simple measurements on the crop were made from time to time during growth.3. The establishment of wheat showed substantial negative correlations with ploughing draught but the correlations between ploughing draught and the performance of the plant diminished as growth progressed. This was shown to be the result of the overwhelming importance of the spacing factor operating beneficially on plots where the plant was abnormally poor. The effect of this factor is traced step by step.4. Swedes differing from wheat in almost every detail of cultivation and growth, cycle showed no correlation between soil conditions and germination or between the various growth stages and physical soil conditions. The highest significant correlation was between the number of roots per plot after singling and ploughing draught and an explanation of this is given.5. There was a significant but only moderate correlation between the yields of the two crops.