Uniform Soil Research Articles

Design grounding grid resistance of substation for two soil layer model

All Grounding planning of a substation is important and various design applications are available using calculation uniform soil resistivity, even though actual resistivity data measured is more than one layer. This is caused by limited availability of the application in processing data only for resistivity one layer. Substation grounding grid application (ASPG) 1.0 can be used for designing grid grounding. The ASPG was developed from Lab View software and has ability to data process for resistivity two-layer that to refer IEEE Std. 80-2013. Grid grounding resistance is considering a combination of grid conductor and ground conductor. This paper discusses the calculation of the magnitude of substation grid grounding using formulas developed by Schwarz, Sulivan and Sunde. The design result obtained is more accurate in substitute resistivity for resistivity two-layer model and calculation grounding resistance substation.

Determining Spatial Scales of Soil Moisture—Cloud Coupling Pathways Using Semi‐Idealized Simulations

AbstractThe spatial scales of land‐atmosphere interactions over heterogeneous, realistic soil moisture patterns are critical to improve our understanding of land‐atmosphere interactions. However, these scales are poorly quantified. We use high‐resolution numerical experiments to quantify the spatial scales for a selected day during the Holistic Interactions of Shallow Clouds, Aerosols, and Land‐Ecosystems (HI‐SCALE) campaign in Oklahoma. A semi‐idealized approach (removing background winds and surface topography while retaining the real‐world data for other boundary conditions) enables examination of the local influence from the surface. Simulations that apply uniform surface, variable land cover with uniform soil moisture, and variable land cover with variable soil moisture are then compared. Land cover variations, especially water and urban surfaces, create two variance peaks in the surface sensible heat flux in the scales >10 km (meso‐β) and <6 km (meso‐γ). Both peaks are enhanced by the observation‐based soil moisture distribution that has most of its variance in the meso‐β scale. Atmospheric response in the meso‐β scale is hydrostatic with weak vertical motion. The land cover variations induce secondary circulations in the scales of 2.5–6 km. The additional soil moisture variability intensifies extreme circulations over dry soil patches and sharp sensible heat flux gradients, slightly extending the characteristic scales to 2.5–9 km. While their areal coverage is small, soil moisture variations on such “hotspots” lead to substantially larger convective cloud structure and domain‐mean rainfall, calling for a consideration of their non‐linear effect in large‐scale models.

Undrained capacity of circular shallow foundations on two-layer clays under combined VHMT loading

Wind turbines are typically designed based on fatigue and serviceability limit states, but still require an accurate assessment of bearing capacity. Overconsolidated clay deposits in Canada often have a thin layer of crust with a relatively high undrained shear strength developed from weathering, desiccation, and geochemical processes. However, existing design methods only assess the bearing capacity using effective area and inclination factor without consideration of surficial crusts. This paper studies the undrained VHMT (vertical, horizontal, moment, and torsional) failure envelope of circular foundations founded on a surficial crust underlain by a uniform soil with a zero-tension interface condition using finite element analysis. An analytical expression for the VHMT failure envelope is derived.

Human vs. Machine, the Eyes Have It. Assessment of Stemphylium Leaf Blight on Onion Using Aerial Photographs from an NIR Camera

Aerial surveillance could be a useful tool for early detection and quantification of plant diseases, however, there are often confounding effects of other types of plant stress. Stemphylium leaf blight (SLB), caused by the fungus Stemphylium vesicarium, is a damaging foliar disease of onion. Studies were conducted to determine if near-infrared photographic images could be used to accurately assess SLB severity in onion research trials in the Holland Marsh in Ontario, Canada. The site was selected for its uniform soil and level topography. Aerial photographs were taken in 2015 and 2016 using an Xnite-Canon SX230NDVI with a near-infrared filter, mounted on a modified Cine Star—8 MK Heavy Lift RTF octocopter UAV. Images were taken at 15–20 m above the ground, providing an average of 0.5 cm/pixel and a field of view of 15 × 20 m. Photography and ground assessments of disease were carried out on the same day. NDVI (normalized difference vegetation index), green NDVI, chlorophyll index and plant senescence reflective index (PSRI) were calculated from the images. There were differences in SLB incidence and severity in the field plots and differences in the vegetative indices among the treatments, but there were no correlations between disease assessments and any of the indices.

The influence of layered soil on ice-seabed interaction: Soft over stiff clay

Ice gouging is one of the main threats for the structural integrity of the offshore pipelines in the territories that floating icebergs can reach. The safe and cost-effective burial depth of pipelines for protection against the iceberg attack depends on accurate assessment of the subgouge soil deformation and the ice keel-seabed contact forces. Layered seabed soil strata that are found in many geographical locations adds to the complexity of assessing the ice keel-seabed interaction process by signifying the effect of strain rate dependence and strainsoftening in the soil layers interaction areas and ice-seabed contact zone. The existing design codes simplify the seabed condition by assuming a uniform soil strata. This in turn affects the accuracy and cost-effectiveness of the design. In this paper, large deformation finite element (LDFE) analysis was conducted using Coupled Eulerian Lagrangian (CEL) approach to investigate the free-field ice gouging in layered (soft over stiff clay) cohesive seabed. A modified Tresca soil model was coded in a user subroutine to account for the effects of strain rate and strain-softening on the mobilised undrained shear strength. A comprehensive parametric study was conducted to examine the effect of gouging features and soil shear strength profiles on the subgouge soil deformation, developed plastic shear strains and the resultant ice keel reaction forces. The analysis results showed that the seabed response to ice gouging is heavily dependent on the soil strata, where the layers interaction effects can override the usual response expected from a uniform seabed. Practical solutions were proposed to improve the pipeline design in layered seabed soils.

Ameliorative role of potassium on water relations, antioxidative enzymes and yield of sweet corn genotypes under water deficit

Purpose: In recent years, it has been revealed that potassium delivers drought stress tolerance in many crops. This nutrient is not yet tested for sweetcorn. Therefore, this study investigated the impact of drought and soil applied potassium on water relations, antioxidant enzymes and yield attributes of two sweet corn genotypes in India. Research Method: The factorial experiment was set-up with 5 replications in complete randomized block design. Factor one comprised of two genotypes (Sugar-75 and NSC 901B), factor two had six different water treatments and factor three with two different potassium levels. This investigation was designed with two genotypes of sweet corn to study the interaction between various water deficit conditions and soil applied potassium. Findings: Drought stress significantly decreased the water potential, osmotic potentialand relative water content and caused osmotic stress in sweet corn plants. Antioxidant enzymes activities were found to be up-regulated under drought stress while yield attributes were adversely affected by water deficit. Application of potassium increased the adaptation to water deficit stress by positively modulating the tested parameters. Results procured from this study suggested that exogenously applied potassium mitigated the drought mediated constrains on sweet corn and enhanced drought tolerance. Research limitation: The experiments were carried out in polythene pots to provide a uniform soil condition which was the main limitation when compared to field trials. Originality/value: Results of this experiment revealed that exogenous application of potassium can alleviate the damaging effect of drought stress on sweet corn. However, more research on other crops is needed to ensure its long-term sustainability.

Numerical analysis of piled rafts with short bored piles

Abstract Numerical analysis of the behavior of piled rafts seated on uniform soil with low bearing capacity has been important to support the project design. The calibration of the numerical model with instrumented load test allows usage of the results, in given conditions, in the foundation design of small and medium-sized buildings built on soils with the same mechanical properties analyzed in this paper. In this context, this paper evaluates numerical models, which allow to consider the influence of short bored piles connected to the raft. The models are also assessed using piled rafts concepts. From the results obtained, the load supported by the total shaft resistance is significant for the case of bored piles, and this load is from 14% to 30% higher in the case more flexible or thinner raft. Inserting piles in the rafts reduces settlement and increases overall stiffness. Such effects are amplified in piles with higher slenderness ratios (L/d).

Performance of Grounding Electrodes Under Lightning Strokes in Uniform and Two-Layer Soils Considering Soil Ionization

This article presented the characteristics of the grounding electrodes in uniform and two layer soils when subjected to lightning including the impacts of soil ionization with frequency, soil resistivity, and permittivity variations. The critical breakdown field strength of two layer soils with different values of the reflection factors was presented. The transient probabilistic grounding potential rise and the transient impedances of the horizontal and vertical electrodes were investigated in uniform and two layer soils including the effect of soil ionization with frequency. Finally, the influences of resistivity and permittivity variations which have substantial impacts on the electric field at the occurrence of the soil ionization were considered. Moreover, transmission line approach (TL) with the aid of ATP has been used to compute the transient grounding voltages. The results indicated that the reflection factor has a significant impact on the equivalent radius of the grounding electrode. It is also observed that the peak values of the lightning induced voltages decreases sharply when the soil ionization phenomenon considering the variations in soil resistivity and permittivity with the stroke frequency changes. Furthermore, the impedances of the burial electrodes that have negative reflection factors were lower than that in case of positive reflection factors.

Probabilistic Risk Assessment of Slope Failure in 3‐D Spatially Variable Soils by Finite Element Method

Quantitative risk assessment of landslides induced by slope failure is an important precondition for formulating effective disaster prevention, mitigation measures, and establishing a landslide risk warning system. In general, the location of the critical slip surface and the failure mode is unlikely to be predicted due to the spatial variability in soil. It remains a challenging task to effectively identify the critical slip surface and conduct the efficient risk assessment based on a three‐dimensional (3‐D) slope with spatial variability. Based on Monte Carlo simulation and the random field method, a quantitative risk evaluation method for slope failure considering the spatial variability of soil parameters is proposed in the study. Compared with a uniform soil slope, the landslide volume, the critical slip surface, and the factor of safety considering the spatial variability of soil are all uncertain; thus, the soil spatial variability has a significant effect on the failure mode and stability of the slope. By using the random finite element method, the critical slip surface of the slope is accurately identified, the corresponding landslide volume and slide distance are calculated, and the modified risk index for a landslide is further enriched, which can provide the reference basis for predicting the landslide deformation, quantitatively evaluating the landslide risk, and mitigating the landslide disaster.

АНАЛИТИЧЕСКОЕ ИССЛЕДОВАНИЕ СОВМЕСТНОЙ ЗАДАЧИ ТЕПЛОВЛАГОПЕРЕНОСА В ПОЧВОГРУНТАХ

The paper shows the mechanism of the effect of moisture on thermal processes. On the basis of mathematical models of the motion of two equations of heat and moisture, the problems of their joint movement in the soil are theoretically solved. Mathematical models of heat and moisture propagation are developed, depending on the nature and with the internal features of the soil, the specifics of heat and moisture exchange in the soil. Heat and moisture exchange processes are intertwined, crossed with each other and represent a single energy act of heat and mass transfer. Such a generalized approach when covering the issues of heat and moisture exchange in soils seems to be the most promising, reflecting the real nature of natural processes that occur organically together for both substances of heat and moisture. A mathematical model of uniform soil moisture with the lowest losses is theoretically justified, a system of a mathematical model of heat and moisture transfer is developed, and its approximate analytical solutions for various physical and mechanical properties of the soil are obtained.

Liquefaction-induced lateral load on pile group of wharf system in a sloping stratum: A centrifuge shake-table investigation

In order to investigate the liquefied soil pressure inposed on an individual pile of pile group, a centrifugal shake table test on a pile-supported wharf on the sloping saturated sand stratum has been designed and implemented in this study. Final test results, including processing results of free-field soil responses as well as lateral displacements at the deck, are presented and discussed in detail. Analysis of pile bending moments of pile group shows that seaside pile bottom can come under more bending moment in contrast to landside piles, and the bending moment seems greater at pile top and bottom. A simplified finite element model has been constructed for an accurate analysis of liquefied soil pressure arising from lateral soil flow, where triangular soil pressure and uniform soil pressure need to be calibrated according to the measured monotonic bending moment of piles. Furthermore, comparisons with the current distribution law were made using the experimental outcomes. Finally, for investigating the effect of pile connection point rotational stiffness, parametric studies were carried out.

Experimental Investigation on the Mechanism of Piping in Different Two-Stratum Levee Foundations with Weak Spots

Abstract Earthen levees along rivers may break down because of piping; this is especially the case for levees built on two-stratum levee foundations with an impervious stratum and an underlying pervious substratum. However, the initial stage of this piping is difficult to recognize because finding the piping outlets along the whole levee is challenging. Practical experience confirms that weak spots, such as holes or thickness reductions in the blanket stratum, usually occur at the levee toe. Some of these are harmless, whereas others are not. This study takes weak spots into consideration and provides a detailed description and evaluation of the piping features. Experiments were conducted on three models with different pervious conditions in a flume. Weak spots caused by holes, a thickness reduction, or exposure of the substratum at the levee toe were tested. The results show that the thickness reduction influences the formation of continuous sand boiling once the confined water bursts the blanket stratum. The potential for piping is reduced when the pervious substratum is composed of thin and uniform soil. In the absence of a covering stratum, piping happens with sand boiling. Three typical phenomena, namely sand boiling near the levee toe, a pressure decrease of the confined water, and a rise in the hydraulic gradient in the pervious substratum, could be used as indicators of the occurrence of piping.

Numerical analysis and safety design of grounding systems in underground compact substations

This paper presents a mathematical and numerical formulation to design and analyze grounding systems in underground electrical substations. The developed approach is based on the well known Maxwell’s Equations. The proposed problem is solved by means of the Boundary Element Method (BEM). The utilization of BEM allows to introduce the geometry and electrical characteristics of the enclosure in a uniform soil. Therefore, a more realistic approximation of the soil structure is achieved. This formulation allows to obtain the main parameters of these protection systems (the grid resistance, the Ground Potential Rise, and the step and mesh voltage). It also allows to compute the surface and step voltage distributions. In addition, as a secondary result, the voltage and current density distributions over the enclosure are obtained. Finally, two grounding system analyses of real underground electrical substations are presented to demonstrate the industrial application and the modelization capabilities of the proposed formulation.

Interpretation of TRT data in the presence of natural convection and groundwater flow in saturated ground

Ground thermal properties play important roles in the design of geothermal heat exchangers (GHEs). Constant ground thermal properties, as often considered in analysis and design of GHEs, often do not account for the coupled effect of thermal and pore fluid flow in saturated ground. This paper presents a series of advanced finite element analyses (FEAs) of thermal response test (TRT) on a geothermal borehole heat exchanger (BHE) installed in uniform and multi-layered saturated soil deposits. Considering coupled thermo-hydro flow in saturated ground, FEAs explore the effects of ground hydraulic characteristics (e.g., groundwater flow, soil permeability), power injection rate, and duration of thermal response test on the value of effective ground thermal conductivity keff. Results show that the value of keff, in the presence of coupled thermo-hydro flow condition, can be multiple times of the thermal conductivity value estimated considering only conductive heat transport in coarse grained soil. Example calculations following two available BHE design standards confirm that consideration of soil permeability and selection of appropriate duration of TRT may lead to significant reduction in the design length of BHEs.

Stability analysis of shield tunnel face under complex ground conditions

Current underground space development features ever-increasing scales. More and more planned tunnel lines have alignments that are characterized by varying passing depths. Both conditions make it more frequent that the shield tunnel face is exposed to heterogeneous ground consisting of distinct soil layers and hydraulic loads, which makes it remarkably challenging to maintain a stable shield face. This work presents a limit equilibrium model to analyze the face stability of shield tunnel under complex ground conditions. The model is consistent with the existing method of slices for uniform soil profile in that the effect of horizontal arching is considered without the need of an a priori assumption on the distribution of horizontal stresses, but extends it to the stratified ground by allowing the variation of failure mechanism across soil layers. Three-dimensional coupled pore fluid flow and stress finite element analyses are performed to study the tunnel face stability in heterogeneous ground consisting of horizontal layers and subjected to hydraulic loads. The results show that the multilayer wedge model can compute limit support pressures that are reasonably close to finite element solutions. Lastly, the finite element method and the multilayer wedge model are employed to analyze the stability of tunnel face in aquifer-aquitard alternate layers with confined water.

Critical Level of Manganese in Soil and Leaves: It’s Relationship to Fruit Quality of Mangosteen (Garcinia mangostana L.)

Manganese (Mn) is one of the essential micronutrients that plays a crucial role in plants' growth and development and is also considered a limiting factor for crop production. This study aimed to determine the critical level of Mn in soil and leaves for improving the quality of mangosteen fruit. The research was conducted in 2015 in several mangosteen production centers, including West Sumatra (Simalanggang and Banja Laweh), West Java (Karacak and Barengkok), Bali (Belimbing and Selamadeg). A well-maintained of fifteen to twenty years old mangosteen plants were used with uniform soil fertility. Purposive random sampling is conducted in each location to select ten plants from each site. Soil samples are taken from under the plant canopy around 0-30 cm in depth at the four cardinal directions. The terminal leaves that collected from the middle part of the plant canopy are used as the leaf samples. Physiological ripe fruits are taken after ripening with index 3-4. The parameters observed consist of (1) soil pH of H2O, Ca, Mg, Mn-available, (2) levels of Mn, Ca, Mg, and K in the leaves, (3) fruit quality (fruit weight, fruit diameter, fruit skin thickness, aryl weight, seed weight). The results showed the Mn content in the soil ranged from 18.89 to 33.63 ppm. Available Mn is negatively affected by pH, Ca, and Mg exchangeability. Soil Mn is linearly related to leaf Mn with R2 0.76. The critical values of Mn in leaf and soil for mangosteen plants in Indonesia were 425 ppm and 22 to 24 ppm, respectively.

Estimating the limits of renewable energy from phytomass

The energy production from phytomass on agricultural and forest lands can be calculated on the basis of the annual production of hydrocarbons (cellulose, starch, sugar, etc.), without needing to take into account the type of phytomass and the mean-weighted specific power production per unit of land area. Land with a mostly uniform climate and soil class produces similar specific power per unit of land area. It was proved in the case of the Czech Republic, where the meanweighted value of specific power production has been calculated as 3.16 kW/ha. Biomass energy can be released in three ways in which conversion takes place. i) direct phytomass combustion, ii) conversion to methane (biogas), iii) conversion to bioethanol. Conclusions about the effectiveness of different conversion methods were obtained by executing the enthalpy balances of the individual transfer processes. The method using methane (raw gas) seems to be the most energetically advantageous. The close connection between the circulation of CO2, H2O, and O2 has been quantified. The same amount of water as CO2 is produced and remains int in the atmosphere, and it significantly reflects radiation away from the ground. Cooling heat flux can be lowered about 1.6 times, thus contributing to climate change.

Optimization of substation grounding grid design for horizontal and vertical multilayer and uniform soil condition using Simulated Annealing method.

Grounding systems are critical in safeguarding people and equipment from power system failures. A grounding system’s principal goal is to offer the lowest impedance path for undesired fault current. Optimization of the grounding grid designs is important in satisfying the minimum cost of the grounding system and safeguarding those people who work in the surrounding area of the grounded installations. Currently, there is no systematic guidance or standard for grounding grid designs that include two-layer soil and its effects on grounding grid systems, particularly vertically layered soil. Furthermore, while numerous studies have been conducted on optimization, relatively limited study has been done on the problem of optimizing the grounding grid in two-layer soil, particularly in vertical soil structures. This paper presents the results of optimization for substation grounding systems using the Simulated Annealing (SA) algorithm in different soil conditions which conforms to the safety requirements of the grounding system. Practical features of grounding grids in various soil conditions discussed in this paper (uniform soil, two-layer horizontal soil, and two-layer vertical soil) are considered during problem formulation and solution algorithm. The proposed algorithm’s results show that the number of grid conductors in the X and Y directions (Nx and Ny), as well as vertical rods (Nr), can be optimized from initial numbers of 35% for uniform soil, 57% for horizontal two-layer soil for ρ1> ρ2, and 33% for horizontal two-layer soil for ρ1< ρ2, and 29% for vertical two-layer soil structure. In other words, the proposed technique would be able to utilize square and rectangle-shaped grounding grids with a number of grid conductors and vertical rods to be implemented in uniform, two-layer horizontal and vertical soil structure, depending on the resistivity of the soil layer.

Investigation of soil–pile–structure interaction induced by vertical loads and tunnelling

The response of pile groups and piled structures to vertical and tunnelling-induced loads is studied. A two-stage model is adopted that can efficiently consider external actions, greenfield tunnelling movements, superstructure stiffness, ultimate pile shaft and base stresses, pile-soil interactions in uniform or layered soils, and local soil behaviour (as either linear elastic, elastic perfectly-plastic, or nonlinear). Several scenarios are analysed: namely, piles subjected to vertical loads; piles and piled structures that are affected by tunnelling induced ground movements. Model results for piles under vertical loads compare well with field and other analytical models, confirming the robustness of the model. For tunnelling adjacent to or beneath single piles and pile groups, the impact of layered soils, soil yielding, and hyperbolic transfer mechanisms are shown to be significant, indicating that these aspects should be considered in risk assessments when using simplified models. Analyses of tunnelling beneath free-head piles and piled equivalent beams (describing flexible slabs or stiff buildings) confirm that pile-foundation connections and superstructures decrease tunnelling-induced displacements and deformations at the surface level; however, their action can also worsen the foundation distress with respect to force-moment structural capacity. Considering that the envelopes of fully-flexible and perfectly rigid superstructures will not always be conservative, soil-pile-structure interaction models are recommended for design.

Evaluating the Effect of Embedment Depth on Collapse Failure Analysis of Strip Foundation

Bearing ultimate capacity of shallow footing on uniform soil can be evaluated experimentally. However, analytical and experimental methods are difficult to analyze and predict complicated behaviour of soil beneath the footing collapse failure on layered soil. A strip footing on dense sand overlying soft clay of bearing capacity is computed utilizing the three-dimensional (3D) geometry model by finite element method analysis. The soil model of the Mohr-Coulomb failure criterion is selected in the assessment. The effect of embedment depth with ratio foundation width (B) to the top layer thickness (H) exposed to vertical point loading is evaluated for different strength properties of soil layers. The present results were verified from established analytical formula. It shows the ultimate bearing capacity on layered soils on a strip footing increase in width of the footing. Local shear failure mechanism is observed in one of all cases with most cases indicate general shear failure mechanism occur for layered soil of dense overlying soft clay.