Effect of hydraulic gradient on swell and hydraulic response of desiccated expansive soil–an experimental study
TL;DR: In this article, the authors investigated the effect of initial hydraulic response during the initial stage of wetting in compacted clay liners and found that the cracks in liners act as preferential flow paths and affect the hydraulic response.
Abstract: Desiccation cracks in compacted clay liners act as preferential flow paths and affect the hydraulic response during initial stage of wetting. This paper investigates the effect of initial hydraulic...
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01 Dec 2022
TL;DR: In this article , the effect of remoulding water content on the infiltration rates during swelling process and hydraulic conductivity at the end of swelling process of a compacted expansive soil was brought out.
Abstract: The microstructure of compacted expansive soils differs depending on the remoulding water content and compaction dry density. In particular, along the standard Proctor compaction curve, the expansive soil compacted at water content less than the optimum water content has relatively larger macropores in comparison to the expansive soil compacted at water contents greater than the optimum water content. These changes in microstructure not only influence the hydraulic conductivity but also the infiltration rates during the swelling process of compacted expansive soils. Therefore, this paper brings out the effect of remoulding water content on the infiltration rates during swelling process and hydraulic conductivity at the end of swelling process of a compacted expansive soil. The oedometric-infiltrometer test arrangement was used to determine the hydraulic response, in terms of infiltration rates and hydraulic conductivity, upon inundation of the compacted expansive soil specimens remoulded with water contents corresponding to dry and wet side of optimum water contents at the same standard Proctor compaction dry density. As expected at the end of swelling process, the swell magnitude and hydraulic conductivity were relatively higher for the clay specimen compacted at dry of optimum water content. In addition, the infiltration test results showed that the time needed for the outflow (i.e. permeation flow) to occur and attain a steady state condition was comparatively less for the compacted clay specimen compacted at dry of optimum water content than at wet side of optimum water content. The changes in dry density and water content during the swelling process of compacted clay specimens were also traced.
TL;DR: In order to study the influence of different clay contents on the fractality of red clay, specimens having four different water contents were prepared as discussed by the authors , and the cracking characteristics of the specimens were observed at 20 °C and 60 °C. Image J software was used to measure and calculate the crack area, crack ratio, crack length and width of each sample.
Abstract: In order to study the influence of different clay contents on the fractality of red clay, specimens having four different water contents were prepared. The cracking characteristics of the specimens were observed at 20 °C and 60 °C. Image J software was used to measure and calculate the crack area, crack ratio, crack length and width of each sample. The test results showed that the development of cracks in red clay could be divided into three stages: crack generation, crack development and crack stabilization. The clay particle content, temperature and water content have significant effects on crack development, and from the test analyses, it was determined that for construction in the Guilin area, it is necessary to pay attention to drainage protection.
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TL;DR: In this article, a simple statistical theory, based upon the calculation of the probability of occurrence of sequences of pairs of pores of all the possible sizes, and of the contribution to the permeability made by each such pair, leads to an expression of the porosity as the sum of a series of terms.
Abstract: The permeability of a porous material to water is a function of the geometry of the boundary between the solid component and the pore space. Expressions of the Kozeny type purporting to represent this function are based upon the particle size or specific surface of the solids, and whilst, for engineering practice, they have given satisfaction for saturated sands, they may fail badly in other cases. By developing a Kozeny type of expression for the particular structure of a bundle of capillary tubes of assorted radii, we demonstrate the cause of the failure. Such failure may be avoided by relating permeability to pore-size distribution, which is the factor of prime concern and which may be measured directly by even simpler means than are used to determine particle-size distribution. The pore-size distribution is arrived at by an interpretation of the moisture characteristic of the material, i.e. of the curve of moisture content plotted against pressure deficiency. A simple statistical theory, based upon the calculation of the probability of occurrence of sequences of pairs of pores of all the possible sizes, and of the contribution to the permeability made by each such pair, leads to an expression of the permeability as the sum of a series of terms. By stopping the summation at a selected upper limit of pore size one may calculate the permeability at any chosen moisture content and plot it as a function of that content. An example is presented, using a coarse graded sand specified by its moisture characteristic. To check these calculations, experimental determinations of the permeabilities of unsaturated materials are presented, using two different grades of sand and a sample of slate dust, the results being compared with computed values. The agreement seems good, and is certainly better than that provided by the Kozeny formula as developed, with difficulty, for the purpose. The limitations and possible improvements of our concept are very briefly discussed, and finally it is shown how a combined use of the moisture characteristic and the permeability (which is itself derivable from the moisture characteristic) leads to an expression for the coefficient of diffusion of water in the material as a function of moisture content. From this it should be possible, in principle, to calculate in suitable cases the course of water movement down a gradient of moisture content. Such a calculation awaits a satisfactory solution of the problem of non-linear diffusion.
794 citations
"Effect of hydraulic gradient on swe..." refers background in this paper
...Childs and Collis-George (1950) reported similar results on unsaturated sands under applied hydraulic gradients ranging from 0.5 to 1....
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TL;DR: In this article, the hydraulic conductivity of geosynthetic clay liners (GCLs) permeated with non-standard liquids (i.e., liquids other than water) is discussed and supported with test data.
453 citations
"Effect of hydraulic gradient on swe..." refers background in this paper
...…conductivity owing to the migration of fine soil particles and seepage-induced consolidation of soil which eventually alter the hydraulic conductivity of the soils (Olsen, Nichols, and Rice 1985; Fox 1996; Shackelford et al. 2000; Kodikara and Rahman 2002; ASTM D5856-15 2015; ASTM D5084-16a 2016)....
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...And hence for laboratory hydraulic conductivity testing, higher hydraulic gradients are preferred in order to reduce the time required for testing of soils with low hydraulic conductivity (e.g. Fox 1996; Shackelford et al. 2000; Kodikara and Rahman 2002; ASTM D5856-15 2015; ASTM D5084-16a 2016)....
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...However, very high hydraulic gradients are not recommended for the determination of hydraulic conductivity owing to the migration of fine soil particles and seepage-induced consolidation of soil which eventually alter the hydraulic conductivity of the soils (Olsen, Nichols, and Rice 1985; Fox 1996; Shackelford et al. 2000; Kodikara and Rahman 2002; ASTM D5856-15 2015; ASTM D5084-16a 2016)....
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...…not influence the hydraulic conductivity of compacted soils, unless the soil specimens consolidate during testing under large hydraulic gradients, and even much larger hydraulic gradients (i> 300) in case of the geosynthetic clay liners, e.g., Shackelford et al. (2000) and ASTM D5084-16a (2016)....
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TL;DR: In this paper, the effect of W-D cycles on the geometric characteristics of crack patterns was analyzed by image processing, and the results showed that the observed cracks were significantly influenced by the applied WD cycles, but this influence was reduced after the third cycle.
253 citations
"Effect of hydraulic gradient on swe..." refers background in this paper
...Tang et al. (2011) also showed that the cracks formed on desiccated slurries completely closed within 2.5 minutes of wetting under very low hydraulic gradient....
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TL;DR: In this article, hydraulic conductivity tests were conducted on thirteen compacted clay-ey 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 conductivities is similar These zones fall roughly parallel to contours of constant initial saturation (degree ofsaturation at compaction), with lower hydraulic conduct
Abstract: 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 (ie, 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
225 citations
"Effect of hydraulic gradient on swe..." refers background in this paper
...Extensive studies have been carried out to determine the saturated hydraulic conductivity of compacted soils under a hydraulic gradient of 10 and above (e.g. Dunn and Mitchell 1984; Albright et al. 2006; Benson and Trast 1995)....
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TL;DR: In this article, the authors investigated the effect of an underlying coarse lower soil layer on the performance of a capillary barrier in soil columns of silty sand over pea gravel.
Abstract: Infiltration tests were conducted on soil columns of silty sand over pea gravel, concrete sand over pea gravel, and silty sand over concrete sand to investigate the capillary barrier effect of an underlying coarser soil layer. Water movement across the interface occurred when the suction head at the interface reached the breakthrough head of the coarser lower soil layer, defined as the suction head at which the coarser layer first became conductive, regardless of infiltration rate or the properties of the overlying finer soil layer. Thus, the coarser lower soil layer controlled breakthrough in this study. After infiltration was terminated, the suction head near the interface increased above the breakthrough head and the barrier was restored. The breakthrough head did not change substantially after eight test cycles of breakthrough and restoration for a capillary barrier with a pea gravel as the coarser lower soil layer. The barrier formed with the concrete sand as the coarser layer permitted breakthrough at a greater suction head than did the barrier with the pea gravel, indicating that the more uniform and coarse the lower soil layer is, the more effective the capillary barrier.
191 citations
"Effect of hydraulic gradient on swe..." refers background in this paper
...Increasing the height of ponding (i.e. hydraulic gradient) results in quicker saturation (e.g. Johnson 1963; Stormont and Anderson 1999; Kodikara and Rahman 2002), and thus impacts the infiltration rates....
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