Effect of wetting on pore structure of compacted fine-grained soils (original) (raw)
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International Journal of GEOMATE, 2021
Sanitary landfills (SLFs) are usually employed as final waste disposal facility to protect public health and the environment. As a result of rapid population growth and urbanization, there is currently a great demand to construct SLFs in the Philippines. The hydraulic conductivity characteristics of remolded samples of a locally abundant fine-grained soil compacted at different compaction energy level is investigated to determine the suitability of the soil as landfill liner material. The hydraulic conductivity of lining system is one very salient feature of the SLF to prevent contamination of nearby soil and water sources. The physical properties of the soil are determined through a series of laboratory tests which includes the grain-size distribution, specific gravity, Atterberg limits, soil classification, Cation Exchange Capacity (CEC), X-ray powder diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The falling head laboratory test was conducted to determine the saturated coefficient of hydraulic conductivity. A numerical model was formulated that can predict hydraulic conductivity as a function of the void ratio. The resulting coefficient of hydraulic conductivity ranges from 1.98 x 10-6 to 1.0 x 10-7 cm/sec meet the Philippine standard requirement. The soil being classified as clay loam can readily be used as top lining material. However, additional study on unconfined compressive strength and volumetric shrinkage among other parameters is recommended prior to use of the fine-grained soil as bottom lining material as soil amendment maybe necessary.
Hydraulic conductivity of remolded fine-grained soils versus index properties
Hydraulic conductivity is a dominant parameter in the design of engineered waste disposal facilities such as landfill liners and covers, lagoon liners and slurry walls. It is of interest to a geotechnical or geo-environmental engineer to develop a predictive method of determining the hydraulic conductivity of fine-grained soils, in order to assess its suitability as a liner material. To predict the hydraulic conductivity of soils, researchers and geotechnical engineers have attempted to correlate it with index properties of the soils, such as the liquid limit, void ratio and specific surface. Based on the present study a predictive method has been developed in this paper to predict the hydraulic conductivity in terms of void ratio and shrinkage index (Liquid limit – shrinkage limit) for remoulded fine-grained soils. Though the initial conditions for the soil will affect the hydraulic conductivity behaviour to some extent, both the void ratio and soil characteristics are primary factors in affecting the hydraulic conductivity. Therefore for predictive purpose, the study of hydraulic conductivity behaviour of remoulded fine-grained soils as presented in this paper can be found to be useful for compacted soils also.
Compaction Characteristics of B.C Soil through Pore Fluids
Journal of Architectural Engineering Technology, 2015
The industrial structure and their foundations are exposed to hazardous environments and hence behavior should be given a due consideration in the design and execution. Similarly are employed in design of the landfills as impermeable membranes due to their low permeability. Clay liners eliminate or limit the movement of leachate from the landfills. The landfills liners are exposed to various chemical, biological and physical events, due to movement of leachate through them. The effects of pollutants on clays are complex due primarily to exchange or nature of pore fluid. There are number of mechanisms through which individual contaminants affect the engineering properties. Including chemical reactions such as dissolution or precipitation and physic-chemical phenomena, affecting intermolecular forces of water solutions. The compressive effective stress in liners, when applied during permeation may play a key role in controlling the chemically induced changes in hydraulic conductivity and compressibility.
Hydraulic Conductivity of Thirteen Compacted Clays
Clays and Clay Minerals, 1995
Hydraulic conductivity tests were conducted on thirteen compacted clayey soils being used for compacted clay liners at landfills throughout the United States. The soils were prepared to various molding water contents and then compacted and permeated in the laboratory. Results of the tests show that for all of the soils, zones exist in the compaction plane (i.e., dry unit weight vs. water content) where the hydraulic conductivity is similar. These zones fall roughly parallel to contours of constant initial saturation (degree ofsaturation at compaction), with lower hydraulic conductivities generally occurring for conditions corresponding to higher initial saturation. Wet of the line of optimums, lower hydraulic conductivity is also attained for soils that are more plastic and have a greater quantity of fines. A regression equation was developed from the data to estimate hydraulic conductivity given the initial saturation, compactive effort, plasticity index, and clay content.
Effect of Shape, Size of Pores on Saturated Hydraulic Conductivity of Some Iraqi Soils
Journal of Zankoy Sulaimani, 2014
This study aims to find out the effect of shape, size of pores on saturated hydraulic conductivity. Ten pedons were selected from the north of Iraq; five pedons were selected from Sulamani province: Bakhteari forest, Bazian, Choesoor, Kanakow and Sarsank was from Duhok province. While in the middle sites, five pedons were selected from Baghdad, two from college of agriculture, Al-Tarmia, and Al-Raeed experimental station, the last pedon from Al-Anbar province-Al-Husaenia. Disturbed and undisturbed soil samples were taken from surface and subsurface horizons from each pedon. Some chemical and physical properties were determined, which include texture, carbonate minerals, free iron oxides, organic matter, bulk density, porosity and hydraulic conductivity. Also they were used for micro morphological characterization as thin section and scanning electron microscopy. The results indicated that the highest value of saturated hydraulic conductivity of the northern sites were 77.73cm.hr-1 at P 4 A 1 (north), the lowest value was 0.47 and 0.47 cm.hr-1 observed in surface and subsurface horizons of P3. The high value of middle sites was 9.89 cm.hr-1 in P 9 A 1 ; the lowest value was 0.89 cm.hr-1 in P 8 C 1. Micro morphological characterization showed variation in the shapes and size of pores for all studied horizons. Also, they showed coating and filling material affecting the pores. The dominant shapes were channels, chambers, voids. The results show that there are differences in shapes and size of pores between north and middle sites, where the dominant shapes of pores in middle sites were chamber and packing. The results showed the existence of free iron oxides which increased MWD and bulk density and decrease hydraulic conductivity and porosity; also it's forming type of shape as small chamber. Organic matter forms meta vughs which make the hydraulic conductivity high because this type of shape is more stable.
Evaluation of Soil-Water Characteristic Curve and Pore-Size Distribution of Fine-Grained Soils
Water
A soil’s physical properties, mineral types, and pore structure significantly influence the shape and properties of the soil-water characteristic curve (SWCC). This study investigated the effects of the soil’s physical properties and mineral types on the SWCC and pore-size distribution (PSD). Eight different soils from an alluvial deposit in Istanbul and Adapazarı/Türkiye were used in the study. The test samples were prepared by compaction at optimum water content (OWC) and wet side of optimum water content (wet of OWC). The samples were prepared by consolidation from the slurry. The PSDs of the samples were calculated using the SWCCs and evaluated with scanning electron microscope (SEM) analysis. In addition, the mineral types of all soils were determined by X-ray diffraction analysis. The soil which contains illite-type minerals has higher matric suction than containing kaolin-type. The effect of the clay percentage is more pronounced in silty soils than in plasticity and activity...
Hydraulic conductivity study of compacted clay soils used as landfill liners for an acidic waste
Three natural clayey soils from Tunisia were studied to assess their suitability for use as a liner for an acid waste disposal site. An investigation of the effect of the mineral composition and mechanical compaction on the hydraulic conductivity and fluoride and phosphate removal of three different soils is presented. The hydraulic conductivity of these three natural soils are 8.5 Â 10 À10 , 2.08 Â 10 À9 and 6.8 Â 10 À10 m/s for soil-1, soil-2 and soil-3, respectively. Soil specimens were compacted under various compaction strains in order to obtain three wet densities (1850, 1950 and 2050 kg/m 3). In this condition, the hydraulic conductivity (k) was reduced with increasing density of sample for all soils. The test results of hydraulic conductivity at long-term (>200 days) using acidic waste solution (pH = 2.7, charged with fluoride and phosphate ions) shows a decrease in k with time only for natural soil-1 and soil-2. However, the specimens of soil-2 compressed to the two highest densities (1950 and 2050 kg/m 3) are cracked after 60 and 20 days, respectively, of hydraulic conductivity testing. This damage is the result of a continued increase in the internal stress due to the swelling and to the effect of aggressive wastewater. The analysis of anions shows that the retention of fluoride is higher compared to phosphate and soil-1 has the highest sorption capacity. Crown
Influence of microstructure on drying- and wetting-characteristics of fine-grained soils
Geomechanics and Geoengineering, 2019
The importance of soil water retention characteristics (SWRCs) for understanding behaviour of soil in its unsaturated state has been acknowledged in recent years. However, the hysteresis associated with SWRCs poses difficulties in relating the water retention characteristics with unsaturated soil properties. During wetting and drying cycles, soil, depending on its properties, undergoes microstructural changes (namely mainly changes in pore sizes and their distribution) and these changes would affect the hysteresis. However, few studies have attempted to quantify or demonstrate this aspect. This study attempts to relate the soil microstructure changes (quantified by dominant pore diameter, d d) with the hysteresis associated with SWRCs (quantified by the slope of suction hysteresis, S ψh), by employing mercury intrusion porosimetry, MIP, for obtaining the pore size characteristics at initial slurried stage, end of drying cycle and end of wetting cycle for different soils. Efforts are also made to understand the influence of soil-specific parameters on pore size characteristics. The results indicate that S ψh and soil parameters such as clay content, specific surface area, cation exchange capacity and linear shrinkage are inversely proportional to d d in air dry state. Further, the study presents the quantification of differential volume changes during drying and wetting processes for different soils.
The hydraulic properties of unsaturated porous media very much depend on their pore structure as defined by the size, arrangement, and connectivity of pores. Several empirical and quasi-empirical approaches have been used over the years to derive pore structure information from the particle size distribution. In this study, we used the discrete element method to simulate the pore structure of various sands as affected by compaction and particle mixing processes. We used five sands with different mean grain sizes to investigate the effects of different sand mixing ratios and degrees of compaction on pore structure as well as on the intrinsic permeability and the soil water retention curve. Average pore body and pore throat sizes were found to be determined mostly by the smaller particles as represented by the effective diameter D 10 . The effects of compaction on the average pore body and pore throat radii were used to simulate expected decreases in the permeability. We obtained mostly linear relationships between permeability and the average pore body and throat radii when mixing different unimodal sands. The intrinsic permeability of the coarser sands was found to be far more sensitive to porosity than the finer sands. Simulations of unsaturated conditions showed that the van Genuchten hydraulic parameter a increased nonlinearly with increasing grain size and mean pore body size of the sand mixtures. Compaction caused a linear decrease in a with decreasing porosity and pore body size. However, no clear correlation between the van Genuchten parameter n and porosity or D 10 was found for the different compaction and mixing simulations.