Time effect on shear strength and permeability of fly ash

This paper investigates the effect of time on the shear strength and the pe rmeability of fly ash, a major solid by-product of thermoelectric power pla nts. Direct shear tests using Mikasa's apparatus, conventional permeability tests, and consolidation tests were conducted on two silt-size fly ashes, with low free lime contents, obtained from two different power plants. The results show that the immediate settling of both fly ashes takes place in a short period of time during consolidation and does not change with time. T he rate of increase in shear strength with time is different depending on t he pozzolanic reactions taking place for the two ashes. The permeability te sts under constant stresses of 49 and 98 kPa for 12 days show that the coef ficient of permeability for the tested ashes is between 10(-6) and 10(-7) m /s. During this period the coefficient of permeability either remains const ant (for the case of the ash with a lower free lime content) or is slightly reduced (for the ash with a higher free lime content). The practical impli cations and the limitations of using low lime silt-size fly ash in vertical drains in the stabilization of soft ground are also discussed.