The main task in the design and construction of impermeable liners in landfills is to block the migration of pollutants to the groundwater
systems or to reduce its rate to a reasonable amount. That is why environmental regulations force governments to construct engineered
waste dumps for waste management purposes. These liners are exposed to various types of chemical, biological, and physical processes
and are affected by the leachate which is produced from decomposition of waste materials accompanying methane gas. The leachate
includes a lot of components such as water and different types of salts. For this reason, the geotechnical characteristics of clay liners
which are evaluated in laboratories using distilled water or tap water might be far different from the representative sample of the in-situ
conditions. There are some evidences regarding the effect of these salts on the physical and mechanical properties of clay barriers which
could affect the long-term performance of these liners. Since the main criterion for impermeable bottom liners in landfills is their
hydraulics conductivity, the increase of this parameter could have a considerable environmental impact. This paper embraces the results
of a recent study on the effect of three inorganic salts, NaCl, CaCl2 and MgCl2 on some geotechnical properties of a common used clay
soil in impermeable bottom barrier in Kahrizak landfill, the main waste disposal center of the Tehran Metropolitan. Also the effect of
bentonite content by adding different percentage of this special clay mineral, 10 and 20 percent, on these properties was investigated.
Laboratory tests like liquid limit, compaction, 1D consolidation and free swell tests were performed for this purpose. Results indicated
that all of these salts could have a considerable effect on the geotechnical properties of the mixtures. The main reason of such effects is
the changes which occur in diffuse double layer of clay particles.
