Summary: Stabilization of Organic Soils with Fly Ash
Erdem O. Tastan1
; Tuncer B. Edil, F.ASCE2
; Craig H. Benson, F.ASCE3
; and Ahmet H. Aydilek, M.ASCE4
Abstract: The effectiveness of fly ash use in the stabilization of organic soils and the factors that are likely to affect the degree of stabilization
were studied. Unconfined compression and resilient modulus tests were conducted on organic soilfly ash mixtures and untreated soil spec-
imens. The unconfined compressive strength of organic soils can be increased using fly ash, but the amount of increase depends on the type of
soil and characteristics of the fly ash. Resilient moduli of the slightly organic and organic soils can also be significantly improved. The
increases in strength and stiffness are attributed primarily to cementing caused by pozzolanic reactions, although the reduction in water
content resulting from the addition of dry fly ash solid also contributes to strength gain. The pozzolonic effect appears to diminish as
the water content decreases. The significant characteristics of fly ash that affect the increase in unconfined compressive strength and resilient
modulus include CaO content and CaO=SiO2 ratio [or CaO=šSiO2 ž Al2O3Ž ratio]. Soil organic content is a detrimental characteristic for
stabilization. Increase in organic content of soil indicates that strength of the soilfly ash mixture decreases exponentially. For most of the
soilfly ash mixtures tested, unconfined compressive strength and resilient modulus increased when fly ash percentage was increased. DOI:
10.1061/(ASCE)GT.1943-5606.0000502. © 2011 American Society of Civil Engineers.
CE Database subject headings: Fly ash; Soil stabilization; Stiffness; Organic matter.
Author keywords: Organic soil; Fly ash; Stabilization; Strength; Stiffness; Stabilization.
Construction of roadways on soft organic soils can be problematic