Hydraulic conductivity and compressibility characteristics of bentonite enriched soils as a barrier material for landfills

Abstract

An experimental program was undertaken for the index and engineering properties (compaction, hydraulic conductivity and consolidation) of various mix proportions of sand, silt and coal ash with bentonite as an admixture to act as a barrier material for landfills. Thirty-four mixes were tested in all with different categories of mixes comprising of bentonite–sand, bentonite–sand-coal ash, bentonite-coal ash, bentonite-silt and bentonite-silt-coal ash mixes with bentonite content varying from 0 to 40% and coal ash from 0 to 90%. A series of hydraulic and mechanical tests were conducted to assess the Atterberg’s limits, hydraulic conductivity, compressibility characteristics, etc. of the mixes. The influence of bentonite and coal ash content, effective consolidation pressure and void ratio on the hydraulic conductivity and consolidation indices (compression index, swell index, coefficient of consolidation) was studied. The hydraulic conductivities of the sand-bentonite mixtures decreased from 1.75 × 10−5 to 3.34 × 10−11 m/s, when the bentonite content increased from 0 to 40%. An optimum amount of admixture viz. bentonite to be added to the base materials i.e. sand, silt and coal ash to obtain different category of mixes was ascertained. Disregarding the 5% soil-bentonite mix in case of sand and coal ash, an optimum mix of 10% sand-bentonite, 10% coal ash bentonite and a range of 5–10% for silt-bentonite is recommended for use as a barrier material considering the present study. The addition of coal ash to bentonite had a favourable effect on the properties of the mix in terms of hydraulic conductivity, to act as a barrier material.