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Abstract
Low permeability soil liners are hydraulic barriers that control
migration of water or any other fluids through the soil media. One of the most important applications of low permeability soil liners is in landfills to avoid the transportation of contaminants to the ground water and surface water. The selected liner system must achieve consistent performance and be compatible with the
expected leachate for the design life time of the facility.
In this research, a study of how to decrease soil permeability by
mixing soil with lime was conducted. Lime is a cheap material that is available in Egypt. The grain size distribution of lime particles is similar to the grain size distribution of fine grained soil, so it can act as a filling material decreasing the size of voids in soil which leads to a decrease in the permeability of soil-lime mixture. The lime-amended soil not only reduces the amount of liquid passing the liner (by reducing the permeability) but also reduces the contamination in the leachate that moved through the liner.
To be accepted as a liner material, soil-lime mixture must achieve a coefficient of permeability less than 1x10-7 m/sec. and it must be stable under the effect of different working conditions in landfills such as leachate permeation, mixing water contentvariation, wet-dry cycles … etc. The effect of adding lime to soil
on the shear strength of soil must also be studied.
In this research, a series of laboratory tests were conducted to
study the effect of lime addition on soil compactibility, permeability and shear strength. The main purpose of these tests was to determine the percentage of lime needs to be added to soil to achieve a coefficient of permeability less than 1x10-7 m/sec. It
was proved that pure sand with 32% of lime will achieve permeability less than 1x10-7 m/sec. which is the main
requirement for a material to be used as a landfill liner. With the
increase of the percentage of fines in soil the required percentage of lime needs to be added to achieve a coefficient of permeability
less than 1x10-7 m/sec. decreased. For soil-lime mixture containing 20% fines, the required percentage of lime in the
mixture was 12%.
The stability of the soil-lime mixture under the change of compaction water content, type of permeating fluid and wet-dry cycles have been studied. It was proved that these factors had no
significant effect on the value of shear strength and coefficient of
permeability of the soil-lime mixtures.