THE IMPACT OF A SALT BRINE ON THE BEHAVIOUR OF COMPACTED FINE GRAINED SOIL - A LABORATORY STUDY.

The physical and chemical interactions of a NaCl brine with six compacted fine grained soils was investigated in the laboratory. Specifically, the hydraulic conductivity (K), engineering properties, leaching properties and breakthrough phenomena were evaluated for these soils. The effect of elevating the soaking temperatures to 70(DEGREES)C on the engineering index properties and closed isobaric batch reactor tests was also investigated. The K of brine was found to be greater than that of water in soils where the dominant clay was montmorillonite; whereas, a soil rich in illite and chlorite was virtually insensitive to variations in permeant solution composition. Long-term K testing with brine revealed that some compacted soils were prone to large increases in K. However, short-term testing of the same soils indicated a stable K. Long-term testing of all soils using water also indicated a relatively stable K. The batch reactors indicated that a brine extracted more silicon from the soils than the standard acid ammonium oxalate extraction. Similarly, more calcium was extracted than accountable by cation exchange capacity. Lysimeter studies indicated that the mass of material leached by the brine from the compacted soils was much less than the available amount of extractable material as demonstrated from the batch reactors. This implied that short circuiting was occurring. The breakthrough curves verified that channelling was occurring. Fractionation caused by anion exclusion and adsorption by the soils resulted in an increase in the mass ratio of chloride to sodium ions at low brine volume throughput. The moisture-mass density and liquid limits of soils that contained montmorillonite were significantly affected when soaked in brine. A lower optimum moisture content was achieved producing a greater mass density. An elevated soaking temperature of 70(DEGREES)C enhanced this effect. A soil rich in illite and chlorite was not affected by brine soaking. The liquid limits of soils high in montmorillonite were greatly reduced, resulting in soil reclassification after soaking. A similar but less significant decrease was observed in soils in which illite and/or chlorite were present as the dominant clay minerals. The plastic limit was unaffected by soaking. Elevating the soaking temperature to 70(DEGREES)C had no effect on the liquid and plastic limits of all soils tested. Source: Dissertation Abstracts International, Volume: 47-05, Section: B, page: 2088. Thesis (Ph.D.)--University of Windsor (Canada), 1985