F. Pishro; M. Bakhtiari; N. Shahnikaramzadeh
Abstract
Introduction: Investigation of water passing through soil is one of the most important problems in soil mechanics and environmental engineering. It is an important parameter for predicting the movement of water and contaminants dissolved in the water through the soil and measured on soil samples in ...
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Introduction: Investigation of water passing through soil is one of the most important problems in soil mechanics and environmental engineering. It is an important parameter for predicting the movement of water and contaminants dissolved in the water through the soil and measured on soil samples in the lab and sometimes tests carried out in the field. Soil permeability generally depends on two factors, the first one is soil Specifications contains an empty space of soil, surface roughness of solid particles, saturation, and another one is characteristics of the fluid (water) that passes through soil. Already few efforts have been made to recognize the characteristics of anisotropy in the geotechnical designs therefore this study has been done. Physical and mechanical properties of soils and sedimentary rocks are generally heterogeneous and hydraulic conductivity (k) is not an exception. The anisotropy of hydraulic conductivity of soils has a great influence on the fluid flow and the transmission of contamination. Knowing the hydraulic conductivity in cases such as flow through dams and dikes, internal erosion in soil masses, settling of consolidated clay levels, optimal design of water and oil wells, and the design of drainage systems for roads, airports and agricultural land. Generally, the hydraulic conductivity is more in the horizontal direction than the hydraulic conductivity in the vertical direction, and the hydraulic conductivity anisotropy is shown with a non-dimensional parameter rk which is equal to the ratio of the horizontal hydraulic conductivity to the vertical hydraulic conductivity. According to Chapuis et al. (1989), on more than 100 measurements of hydraulic conductivity along with the results of the experiments of Chapuis et al. (1990), Rice et al. (1970) and Leroueil et al. (1990), the anisotropy of the hydraulic conductivity of clays, sands and sedimentary rocks are almost like each other. The degree of anisotropy may depend on the shape of the particles, their arrangement, or the orientation of the free space among the particles of the soil, which appears to be less than 4. Due to the impossibility of preparing intact samples from grain materials, as well as the lack of suitable measuring instruments for grain samples, there are few valid results for non-sticky materials. As Chapuis et al. (1989) and Sferlazza et al. (2009) in accordance with most of the experimental results, the anisotropy of hydraulic conductivity increases with density, and also the degree of anisotropy decreases with increasing porosity ratio.
Materials and Methods: In order to conduct the present research, measurement device was designed and built. This device is a cube with 150 mm ×150 mm × 173 mm dimensions. The components of the device are: bleeding valves, inlet and outlet valves, porous plates and the size of the sample respectively. In this study, four uniform soil samples were selected for test. Samples are prepared in falling manner, with three porosity and under three different hydraulic gradient were tested. In Table 1 The general pattern of research experiments is presented. In this study, 36 tests were performed.
Table 1-Pattern of research experiments
Parameter Diameter particle Void ratio Water head
The number of test cases 4 3 3
To measure vertical permeability, due to large grains samples, according to ASTM D-2434 standard fixed-load test method has been used. First, the porous plate is placed on the bottom of the measuring device to prevent the soil from entering and exiting the water penetration then The soil is inserted from the fixed height into the device and the porous plate is placed on the sample. Then place should be located at the top of the device and close the screws so there should be no water leak. Then the weight of the soil should be measured and connect the system to the water. Then the outlet tap should be opened and water should be passed through the soil sample until the sample would be completely saturated and no air bubbles come out of the outlet pipe and fix water level. Then the water head and weigh the empty container and the duration of the outflow of water for a given water volume should be measured. After performing the test at a specified head, the elevation of water should be changed by reservoir adjustment and the permeability coefficient would be measured in other loads.
Results and Discussion:
The effect of hydraulic loads on horizontal and vertical hydraulic conductivity coefficients for uniform samples
Horizontal and vertical hydraulic conductivity tests were performed on uniform samples including coarse aggregate materials with a diameter of 0.85, 2, 6.35, and 5.9 mm. In Figures (1) to (3), the effect of hydraulic load on horizontal and vertical hydraulic conductivity for uniform samples in minimum and maximum conditions is shown.
(B( (A(
(D( (C(
Figuer1- According hydraulic conductivity to hydraulic gradient for uniform samples with A) vertical hydraulic conductivity, minimal porosity B) Horizontal hydraulic conductivity, minimal porosity C) vertical hydraulic conductivity, maximum porosity D) horizontal hydraulic, maximum porosity
Investigations showed that in all cases, with increasing hydraulic load, the horizontal and vertical hydraulic conductivity decreased and then the process of change was almost constant.
Investigation of the effect of porosity on horizontal and vertical hydraulic conductivity of uniform samples
The results showed that the horizontal hydraulic conductivity coefficient for all samples was higher than the vertical hydraulic conductivity coefficient.
Also, the results showed that the minimum hydraulic conductivity (e = 0.46) and maximum porosity (e = 0.97) were about 34.33 and 0.35 percent higher than the hydraulic hydraulic conductivity, respectively.
Investigation of the effect of porosity on the anisotropy coefficient of hydraulic conductivity of uniform samples: The results showed that with increasing porosity, the coefficient of heterogeneity of hydraulic conductivity for uniform samples was reduced and this coefficient was for uniform samples in the range of 0.89 to 1.35.
Conclusions: The final results can be summarized as follow:
1. The permeability in the horizontal direction is often greater than the permeability in the vertical direction.
2. The anisotropy permeability for uniform sample is between 0.85-1.35.
3. The anisotropy permeability decreases with increasing porosity.
4. In the uniform samples, maximum permeability occurs at higher hydraulic conductivity.
5. With increasing the uniformity coefficient, the amount of hydraulic conductivity decreases.
Mehdi Zangiabadi; manoochehr gorji; Mehdi Shorafa; Saeed Khavari Khorasani; Saeed Saadat
Abstract
Introduction: Soil is the main source of water retention and availability for plant uptake. The supplement of water is completely dependent on soil physical properties. The soils with higher values of available water are generally more productive because they can supply adequate moisture to plants during ...
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Introduction: Soil is the main source of water retention and availability for plant uptake. The supplement of water is completely dependent on soil physical properties. The soils with higher values of available water are generally more productive because they can supply adequate moisture to plants during the intervals between irrigation or rainfall events. Generally according tothe spatial and temporal distribution of precipitation, Iran has an arid climate in which most of the relatively low annual precipitation falls from October through April. Thus, water deficiency along with the lack of organic carbon in the soil justifies the necessity of studying the soil, water and plant relationships that may improve the efficiency of water consumption in agricultural practices. For that reason, this research was conducted to investigate the relationship between some soil physical properties and Integral Water Capacity (IWC) index as one of the soil physical quality indices.
Materials and Methods: This study was conducted in Torogh Agricultural and Natural Resources Research Station in Khorasan-Razavi province, north-eastern Iran during 2013-2014. This station is located in south-east of Mashhad city with a semi-arid climate, annual precipitation of 260 mm and mean air temperature of 13.5 °C. The soil was classified in Entisols and Aridisols with a physiographic unit of alluvial plain that generally had medium to coarse textures in topsoil. Thirty points with different soil textures and organic carbon contents were selected as experimental plots. In order to measure different properties of the soil, two soil cores (8 cm diameter × 4 cm length cylinder for bulk density and 5 cm diameter × 5.3 cm length cylinder for sandbox measurements) and one disturbed soil sample (for other measurements) were collected from 0-30 cm depth of each plot. After conducting required laboratory analysis and field measurements using standard methods, the soil moisture curve parameters (RETC program), Porosity (POR), Air Capacity (AC), Relative Field Content (RFC) and Integral Water Capacity (IWC) index, were calculated. In this regard, integration calculations were done by Mathcad Prime 3 software. Finally, the relationship between the measured properties and IWC index were analyzed using Pearson correlation coefficient and stepwise multiple linear regression by SAS (9.1) statistical software.
Results and Discussion: Laboratory analysis results showed that the soil texture classes of samples were loam (40%), silt loam (23%), silty clay loam (17%), clay loam (13%), and sandy loam (7%). On average, very fine sand particles were dominant between five size classes of sand and the lowest values were devoted to very coarse sand particles. Soil porosity and air capacity calculation results indicated that on average bulk soil porosity (PORt) and bulk soil air capacity (ACt) were 0.46 and 0.20 (cm3cm-3), respectively. According to the results, RFC of 60% of studied soil samples were lower than 0.6, 7% were higher than 0.7 and only 33% were between 0.6-0.7 (optimal range). IWC index calculations were resulted in 0.13-0.25 (cm3cm-3) in different soil textures. The highest IWC were related to Loam and Clay Loam textures, respectively. Statistical analyses indicated that there were no significant relationship between soil particles (sand, silt and clay) and organic carbon content with IWC index. The factors of soil bulk density and RFC were negatively correlated with IWC index that means decreasing the soil bulk density and RFC would lead to the reduction of the effects of water uptake limitation factors by increasing the values of weighting functions (IWC calculations), and improvement of soil physical quality. High significant (P < 0.001) positive correlation coefficients were observed between IWC index and the factors of soil PORt, ACt and soil matrix air capacity (ACf) in this study. Multiple regression analysis results showed that IWC index could be estimated by the factors of ACt and PORt with the determination coefficient of 0.63. The partial determination coefficients indicated that ACt factor accounted for 50% and PORt accounted for 13% of IWC index variations.
Conclusion: The results indicated that in medium to coarse-textured soils, IWC index could be estimated using the bulk soil air capacity (ACt) and bulk soil porosity (PORt) factors that are derived from soil volumetric water content at saturation and field capacity points.
zahra dianat maharluei; ali akbar moosavi
Abstract
Introduction: In arid and semi-arid soils, low organic matter is one of the barriers to achieving optimal performance. The soils with more organic matter have a better structure and are more resistant to erosive factors such as water and wind. Soil organic matter has a particular importance and has significant ...
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Introduction: In arid and semi-arid soils, low organic matter is one of the barriers to achieving optimal performance. The soils with more organic matter have a better structure and are more resistant to erosive factors such as water and wind. Soil organic matter has a particular importance and has significant impact on the stability of soil aggregates, the extension of plant root system, carbon and water cycles and soil resistance to erosion. This substance acts as a cementing agent and plays an important role in soil flocculation and formation of resistant aggregates.Also, the addition of organic matter to the soil increases soil porosity and decreases soil bulk density.
Materials and Methods: In this research, the effect of the two types of organic matter (compost and the ripe fruit waste of fig) on some soil physical properties was studied. A factorial experiment based on completely randomized design, including the four levels of compost and the ripe fruit waste of fig (0, 1, 2 and 4 by weight %) and three soil types (loamy sand, loam and silty clay loam) with three replications was carried out. The soil samples were collected from the three territories of Fars Province: loamy sand soil from Shiraz, loamy soil from Maharlu and Silty clay loam soil from Zarghan area. The soil samples were air dried and passed through a 2 mm sieve. The physical properties including the bulk density, particle density, porosity, moisture content and soil crust strength was measured. In this research, the soil texture by hydrometer method, Electrical conductivity of the soil saturated paste extract by electrical conductivity meter, saturated paste pH by pH meter, seedling emergence test, soil crust strength by a pocket penetrometer (HUMBOLDT MFG.CO.) bulk density by cylindrical sample and particle density by pycnometer method were measured. The fig fruit treatments were prepared by thoroughly mixing the dried powder of ripe fig fruit passed through a 2 mm sieve (with the rates of 0, 1, 2, and 4 % by dry weight) with the air dried soils. Also, the compost treatments were prepared by thoroughly mixing the dried powder of compost passed through a 2 mm sieve (with the rates of 0, 1, 2, and 4 % by dry weight) with the air dried soils. The test measurement PVC cylinders with an inner diameter of 12.5 cm and a height of 20 cm were prepared. The bottom ends of the cylinders were closed with a screened PVC plate. These cylinders were uniformly filled with the treated soils and irrigated a few times to make a homogeneous soil column. About 3 cm of the top end of the cylinders were left empty.
Results and Discussion: The results showed that all the rates of the ripe fruit waste of fig and the compost treatments significantly decreased crust strength of all soils compared to control at 1% probability level. The results also showed nearly the greater effect of all the treatments on crust strength of loamy sand soil compared to the other soils. All the rates of the ripe fruit waste of fig and compost treatments significantly increased the moisture content of all the soils compared to control at 1% probability level. Moreover, the greater effect of all the treatments on the moisture content of silty clay loam soil compared to other soils was generally observed. All the rates of the ripe fruit waste of fig and compost treatments decreased the bulk density and particle density of all the soils compared to control. Tthe greatest impact was observed in the compost treatments at the level of 4% by dry weight and silty clay loam texture. Also, all the rates of the ripe fruit waste of fig and compost treatments increased the porosity of all the soils compared to control, and the greatest impact belonged to the compost treatments at the level of 4% by dry weight andsilty clay loam texture.
Conclusion: The results showed that the use of the ripe fruit waste of fig and compost in the soil increased moisture content and decreased crust strength significantly compared to the control. Also, the ripe fruit waste of fis and compost in the soil increased porosity and decreased bulk density and particle density compared to the control, but this increase and decrease were not significant.Reduction in crust strength caused by the ripe fruit waste of fig application was more than compost application. However, the effect of compost application on the soil bulk density, particle density, porosity and moisture content was more than the ripe fruit waste of fig application.
M. Moradi Tayyebi; E. Amiri Tokaldany
Abstract
Introduction: Study of flow characteristics in rock porous media is one the most interesting issues for scientists and engineering dealing with river engineering works. So, there is no surprise that many models to describe the relationship between the flow velocity of clear water with hydraulic gradient, ...
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Introduction: Study of flow characteristics in rock porous media is one the most interesting issues for scientists and engineering dealing with river engineering works. So, there is no surprise that many models to describe the relationship between the flow velocity of clear water with hydraulic gradient, rock size, porosity, Reynolds number, and kinematic viscosity, have been introduced. Due to the large spaces between the coarse materials, flow velocity passing through the materials is high which in turn results in higher amounts of Reynolds number of flow. This type of flow classified as turbulent flow. Although Darcy law rules the flow in porous media, it is used for laminar flow in fine porous media and its application is not recommended for turbulent flows. Moreover, as the flow parameters in turbulent flows vary against time, the state of the flow is not steady. The equations describing the turbulent flows are obtained using equations defining basic concepts of hydrodynamics and turbulence effects. Due to complexity of the turbulent flow, these equations are described in the form of the partial differential equations. In order to introduce the specifications of this type of flow, various relationships have been provided by many researchers. However, their applications are confined to the limited conditions of porosity and size materials. In this study, we aim to provide a relationship which can be applied for a wide range of porosity and material size of porous media.
Materials and Methods: To describe the relation between effective hydraulic parameters in coarse porous media, we used dimensional analysis theorem of Buckingham. In this regard six dimensionless parameters have been provided from which a relationship including four constant parameters has been obtained. We used a part of (70 percent) several available sets of data, provided from Soil Conservation and Watershed Management Research Institute, Irrigation and Reclamation Engineering Department of the University of Tehran, and mostly from published results, to find the magnitude of the constant parameters. So, we introduced a new equation which expresses a relationship between hydraulic gradient, porosity, and Froud number. Finally, using the remained part of (30 percent) available data, we compared the results of the new equation with those obtained from available models.
Results and Discussion: To evaluate the new introduced equation and comparing the results obtained from the new equation and those obtained from available equations, we computed the magnitude of relative errors as well as the mean relative errors of the hydraulic gradient estimated from all equations versus the hydraulic gradients provided from field and laboratory observations. It is found that the new equation has the least mean of relative error (15.3 percent) among all equations. Moreover, for various magnitudes of rock size as well as porosity, we computed the mean relative error of estimated hydraulic gradients according to observed data. We found that the new equation has the second largest accuracy (with the mean error of 11.64%) among all evaluated models in this research. Finally, we developed two relationships between hydraulic gradient and Froud number using actual as well as apparent velocities. Again, it is found that the new relationship has the least mean of relative error (14.03 percent) among all equations.
Conclusion: Since all available equations introduced to express the flow characteristics in coarse porous media, can be used in a defined limits of porosity, rock size, etc., in this research we aimed to provide a new relationship which can be used for a wider range of porous media specifications. So, based on dimensional analysis and using several sets of available field and laboratory data, a new equation has been introduced in this research which can be used for a wide range of rock size, Reynolds number, and porosity; i.e. rock diameter of 0.5 to 20 cm, Reynolds number greater than 100, and porosity of 0.35 to 0.55. Moreover, we introduced two equations to demonstrate the relationship between hydraulic gradient and actual velocity as well as apparent velocity. When we evaluated the results obtained from the new relationship with those obtained from some available equations, we found that the relative error of the new equation is 14 percent, which illustrates that the error of the results produced by the new equation is less than those produced by the available equations.
