This paper presents an investigation into the stabilization of a soft clay subgrade of a military zone in Izmir, Turkey with a very high lime fly ash. Zero%, 5%, 10%, 15% and 20% (m/m) of the soil was replaced with fly ash. In addition to the control specimen, four different stabilized soil samples were prepared mixing fly ash with soil at optimum water contents determined by standard proctor test. Experiments lasted for 3 months and the unconfined compressive strength and shear strength parameters, cohesion and internal friction angle, were determined after 1, 7, 28 and 90 days. It was found that, inclusion of fly ash improved the properties of the soil. The improvements, appearing with increasing fly-ash content, were attributed to the pozzolanic reaction and pore refinement effect of fly ash as well as its high free-lime content. (c) 2005 Elsevier Ltd. All rights reserved.