Abstract: A ndesitic volcanic rocks and their weathering products "clays" are highly widespread around İzmir. The materialproperties of andesites vary with their weathering grades. Smectite type clay minerals are formed in moderately andcompletely weathered andesites. The clays formed as a result of weathering are determired to have formed in two waysduring the field observations. First, the andesitic lava alters the previously flown and partially solidified andesitic lava and aresiduel clay is formed. Secondly, the andesite is weathered by groundwater circulation through the discontinuities and byatmospheric factors, produce clay and silt. The smectite type clays formed as a weathering product, swell by taking water in their structure and developed instabilities controlling by the discontinuities. This may cause slope failures even at gentleslopes along the clay-filled cooling joints.In this paper, the geomechanic test results of the clay s formed from weathering of the andesite taken from Susuzdede Park,Osmangazi, Asansör Quarry and the Nenehatun Shaft of the İzmir Metro, are presented and the influence of such soil types onthe stability of the abondoned quarries and road slopes, are discussed.