LOAD-SETTLEMENT CHARACTERISTICS OF EXPANSIVE SOILS TREATED WITH FLY ASH COLUMNS

Geotechnical Engineering

Expansive soils are problematic in nature due to its excessive swelling and shrinkage characteristics under varying moisture content. This behavior is attributed due to the presence of clay mineral montmorillonite. This volumetric changes leads to structural damage of various civil engineering structures and their cost of repair is very high. Various techniques like soil replacement, pre-wetting, under reamed piles, lime-soil columns, surcharge loading, thermal methods are generally used to stabilize expansive soils. Chemical stabilization using lime, cement and fly ash have also given satisfactory results. Fly ash is a product obtained from flue gases of furnace, collected by electrostatic precipitators. The composition of fly ash varies depending on the source and type of coal burnt. Disposal of fly ash is a problem because it is produced in abundant quantities. In this present experimental work, model plate load tests were performed on expansive clay beds in which fly ash was introduced as compacted columns. The fly ash columns were kept floating 100 mm above the base plate. The diameter (d) and length (l) of the columns was kept 40mm and 400mm respectively (L/D=10). A casing pipe was kept vertically at the center of the tank with diameter equal to that of fly ash column. Oven dried fly ash at OMC was poured in the casing pipe and was compacted at its dry unit weight in 8 layers of 50mm each. The casing pipe was gradually withdrawn during the process of compaction. In case of twin columns, the center-to-center spacing between the columns was kept 60mm (S=1.5D) as per JGJ 79-2012 Technical code for Ground treatment of buildings. Load-settlement characteristics of expansive clay improved when fly ash was introduced in the form of columns.

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