Effect of Induced Osmotic Suction and Bentonite Content on Swell Behaviour and Hydraulic Conductivity of Compacted Red Soil
01 Jan 2021-pp 75-84
TL;DR: In this paper, the red soil was modified by adding 10% and 20% bentonite by dry weight to meet the hydraulic conductivity requirement, and multiple identical compacted specimens were set up in oedometric assemblies under a surcharge pressure of 12.5 kPa and were inundated with distilled water, 0.4 M CaCl2 and 0. 4 M NaCl solutions to study the swelling behaviour of red soil and red soil modified with different bentonite contents.
Abstract: Clay liners are integral part of both hazardous and municipal waste landfills that prevent leachate from percolating into the soil beneath and polluting it. Hence, the compacted soils must have very low hydraulic conductivity (<10–7 cm/s) to act as effective clay liners. Locally available red soil may be used as a liner material as it satisfies the design criteria. To meet the hydraulic conductivity requirement, the locally available red soil was modified by adding 10% and 20% bentonite by dry weight. Multiple identical compacted specimens were set-up in oedometric assemblies under a surcharge pressure of 12.5 kPa and were inundated with distilled water, 0.4 M CaCl2 and 0.4 M NaCl solutions to study the swelling behaviour of red soil and red soil modified with different bentonite contents. The specimens were compacted at their respective optimum moisture content values to their maximum dry unit weights. Falling head permeability tests were conducted to measure hydraulic conductivity using the rigid wall permeameters at a hydraulic gradient of 20 and surcharge pressure of 12.5 kPa. The nature of the inundating fluid and the bentonite content is seen to greatly affect the swelling behaviour and the hydraulic conductivity of the compacted red soil.
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TL;DR: In this paper, a large number of water-saturated specimens of Ponza bentonite (mainly composed of Namontmorillonite) were exposed, alternately, to distilled water and to saturated NaCI, KCl or CaC12 solutions in the course of laboratory direct shear tests and oedometer tests.
Abstract: The mechanical behaviour of clays is strongly influenced by pore fluid composition. Moreover, exposure to fluids different from their pore fluid may produce a transient stage during which the clays undergo noticeable volume changes. The aim of this paper is to investigate these phenomena and their causes. To this end, a large number of water-saturated specimens of Ponza bentonite (mainly composed of Namontmorillonite) were exposed, alternately, to distilled water and to saturated NaCI, KCl or CaC12 solutions in the course of laboratory direct shear tests and oedometer tests. Exposure to any of the three electrolytes produced consolidation of the specimens, a large decrease in deformability and an equally large increase in residual shear strength. At equilibrium, the mechanical behaviour became very similar to that exhibited by specimens that had been directly prepared with the appropriate salt solution as pore fluid. For both types of specimen (i.e. those prepared with the electrolyte and those exposed to...
308 citations
TL;DR: In this paper, a range of water content near the optimum value measured with the highest compactive energy proved to be suitable in meeting the objective of low hydraulic conductivity and shrinkage potential.
Abstract: Tests were performed on a clayey soil from a site in Texas to define ranges of water content and dry unit weight at which compacted test specimens would have: (1) Low hydraulic conductivity; (2) minimal potential for shrinkage upon drying; and (3) adequate shear strength. Test specimens were compacted with three compactive energies over a range of water content. Low hydraulic conductivity could be achieved over a broad range of water content, but relatively wet specimens underwent large shrinkage upon drying. A range of water content near the optimum value measured with the highest compactive energy proved to be suitable in meeting the objective of low hydraulic conductivity and shrinkage potential. The dry unit weight had to be greater than 96–98% of the maximum value from modified compaction (ASTM method D1557) to meet hydraulic conductivity, shrinkage, and strength objectives. A similar approach is suggested for development of compaction criteria at other projects in which low‐hydraulic‐conductivity li...
289 citations
Journal Article•
TL;DR: A discussion of a paper with the aforementioned title by Daniel and Wu, published in this journal (Volume 119, Number 2, February 1993), is presented as mentioned in this paper, focusing on the applicability of this study on desiccation cracking of clay liners/covers to a more geographically extensive area.
Abstract: A discussion of a paper with the aforementioned title by Daniel and Wu, published in this journal (Volume 119, Number 2, February 1993), is presented. The discussion focuses on the applicability of this study on desiccation cracking of clay liners/covers to a more geographically extensive area. Horvath notes that the authors concentrate on arid sites; however, the study has wider applicability. Horvath also comments on one of the proposed strategies--a soil layer to protect clay liners--noting a more cost-effective alternative is expanded polystyrene. Discussion is followed by closure from the authors.
259 citations
TL;DR: In this article, the effect of inflow of sodium chloride solutions on the swell-compression behavior of compacted expansive clays under a range of external loads was examined, and the results showed that the inflow increased the swell compression behavior of clays.
Abstract: The present study examines the effect of inflow of sodium chloride solutions on the swell–compression behaviour of compacted expansive clays under a range of external loads. Inflow of sodium chlori...
89 citations
TL;DR: In this article, the authors studied the behavior of mixtures of bentonite clay and nonswelling coarser fractions of different sizes and shapes and found that observed swelling occurs only after the voids of the nonswelled particles are filled up with swollen clay particles.
Abstract: Studies on the swelling behaviour of mixtures of bentonite clay and nonswelling coarser fractions of different sizes and shapes reveal that observed swelling occurs only after the voids of the nonswelling particles are filled up with swollen clay particles. The magnitude of the swell within the voids, called intervoid swelling is large when the size and percentage of the nonswelling coarser fraction is large. The observable swell, after intervoid swelling, is called primary swelling and follows a rectangular hyperbolic relationship with time. The total swell per gram of the clay decreases with an increase in the size of the nonswelling fraction and with a decrease in the percentage of swelling clay. Time-swell relationships show that swelling continues to occur for a long time after the primary swelling, and this is called secondary swelling.
79 citations