MOISTURE RETENTION AND HYDRAULIC CONDUCTIVITY OF COARSE- TEXTURED SOILS AMENDED WITH COAL COMBUSTION FLY ASH
J .C. Seaman*, S.A. Aburime**, B.P. Jackson*; and T. Punshon*
*Savannah River Ecology Laboratory, The University of Georgia, Drawer
E, Aiken, SC 29802, USA
**Dept. of Engineering, Clark Atlanta University, 223 James P. Brawley
Dr. Atlanta, GA 30314, USA
1. ABSTRACT
Previous studies have suggested that an increase in water holding capacity
or matric potential (\II) may result from the addition of coal combustion
fly ash (FA) to coarse-textured soils, but common laboratory techniques
for evaluating such characteristics can be time-consuming and difficult
to replicate. Therefore, centrifuge- based methods were used to assess
the matric potential (\jJ) and hydraulic conductivity (K) as a function
of the degree of saturation for a coarse-textured surface soil from the
Southeastern US that was amended with acidic FA at application rates ranging
from 0- 15% (wt/wt). In repacked columns, a low ionic strength rainwater
surrogate was used as the leaching solution. For comparison, similar amounts
of standard clays and sand (i.e., kaolinite (KA); montmorillonite (MONT);
and ottawa sand (OS)) were added to the test soil to demonstrate the sensitivity
of the centrifuge-based methods. The water dispersible clay (WDC) content,
an indicator of the susceptibility of the soil clay to dispersion was
also evaluated for the amended soils. A minor increase in matric potential
was observed only at the highest FA application rates, while saturated
K (Ksat) actually increased and then leveled off with increasing
FA addition. In contrast, the matric potential and K for the other tested
amendments was altered in the expected manner. KA and MONT decreased HC
and increased matric potential at a given moisture content, while OS addition
increased the soil HC and decreased the water holding capacity. Consistent
respective trends were also evident in the particle size analyses of the
amended soil. The seemingly inconsistent behavior observed for the FA
amended columns may reflect changes in pore-water composition resulting
from soluble FA components that increased the background ionic strength
of the soil solution for the readily dispersive surface soil, as column
effluents were generally less turbid with increasing FA addition. Changes
observed in WDC for the various amendments support such a mechanism as
the dispersible clay decreased and the ionic strength increased significantly
for the FA amended soils.
SREL Reprint #2755
Seaman, J., S. A. Aburime, B. P. Jackson and T. Punshon. 2003. Moisture retention and hydraulic conductivity of coarse-textured soils amended with coal combustion fly ash. p. 91-103. In Chemistry of Trace Elements in Fly Ash, edited by K. S. Sajwan, A. K. Alva and R. F. Keefer. Kluwer Academic/Plenum Publishers.
