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Journal ArticleDOI

Effect of hydraulic gradient on swell and hydraulic response of desiccated expansive soil–an experimental study

01 Apr 2021-International Journal of Geotechnical Engineering (Taylor and Francis Ltd.)-pp 1-14

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...
Topics: Expansive clay (57%), Hydraulic conductivity (55%), Hydraulic head (53%)
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Journal ArticleDOI
E. C. Childs1, N. Collis-George1Institutions (1)
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.

771 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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Journal ArticleDOI
Abstract: Fundamental factors and testing considerations affecting the evaluation of the hydraulic conductivity of geosynthetic clay liners (GCLs) permeated with non-standard liquids (i.e., liquids other than water) are discussed and supported with test data. Both aggregate-size distribution and montmorillonite content of the bentonite portion of the GCL have a potential effect on the hydraulic conductivity of GCLs. Other factors affecting the hydraulic conductivity of GCLs permeated with non-standard liquids include thickness of the adsorbed layer, prehydration of the GCL, void ratio of the GCL, and test duration. Results show that non-standard liquids containing both high concentrations of monovalent cations (e.g., 0.6 M NaCl) as well as low concentrations of divalent cations (e.g. 0.0125 M CaCl2) can cause significant increases (⩾1 order of magnitude) in hydraulic conductivity provided the test is performed sufficiently long to allow for exchange of adsorbed cations. Results also indicate that termination of hydraulic conductivity tests involving prehydrated GCLs before chemical equilibrium is established may result in measured hydraulic conductivities that do not represent equilibrium and may be unconservatively low. Finally, control of average effective stress is more important than control of hydraulic gradient when evaluating the hydraulic conductivity of GCLs.

407 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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Journal ArticleDOI
Craig H. Benson1, John M. TrastInstitutions (1)
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

208 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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Journal ArticleDOI
Chao-Sheng Tang1, Yu-Jun Cui2, Bin Shi1, Anh Minh Tang2  +1 moreInstitutions (2)
30 Oct 2011-Geoderma
Abstract: Laboratory tests were conducted to investigate the effect of wetting-drying (W-D) cycles on the initiation and evolution of cracks in clay layer. Four identical slurry specimens were prepared and subjected to five subsequent W-D cycles. The water evaporation, surface cracks evolution and structure evolution during the W-D cycles were monitored. The effect of W-D cycles on the geometric characteristics of crack patterns was analyzed by image processing. The results show that the desiccation and cracking behaviour was significantly affected by the applied W-D cycles: the measured cracking water content c, surface crack ratio Rsc and final thickness hf of the specimen increased significantly in the first three W-D cycles and then tended to reach equilibrium; the formed crack patterns after the second W-D cycle were more irregular than that after the first W-D cycle; the increase of surface cracks was accompanied by the decrease of pore volume shrinkage during drying. In addition, it was found that the applied W-D cycles resulted in significant rearrangement of specimen structure: the initially homogeneous and non-aggregated structure was converted to a clear aggregated-structure with obvious inter-aggregate pores after the second W-D cycle; the specimen volume generally increased with increasing cycles due to the aggregation and increased porosity. The image analysis results show that the geometric characteristics of crack pattern were significantly influenced by the W-D cycles, but this influence was reduced after the third cycle. This is consistent with the observations over the experiment, and indicates that the image processing can be used for quantitatively analyzing the W-D cycle dependence of clay desiccation cracking behaviour.

190 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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Journal ArticleDOI
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.

164 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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