This paper presents the results of geotechnical and mineralogical investigations on lime treated clay soils from Hamedan City, Iran, and effects of pH variations on their shear strength parameters. Initially, lime was added in different percentages and laboratory experiments were conducted after curing times. The results indicate that these soils can be stabilized satisfactorily with the addition of about 7 % lime. Also, investigation of the relationship between lime-treated geotechnical properties and lime percentage and curing time demonstrates high regression coefficients for the proposed relationships. Several laboratory tests were performed on treated and untreated clay soils with lime mixed with pore fluids with different pH values including 3, 5, 7 and 9. The results of shear strength tests indicated that the undrained shear strength parameters for untreated clays increased considerably if the pore fluid had a high pH (pH = 9) or a low pH (pH = 3). It can also be found that for lime-treated soils, maximum cohesion and friction angle values are achieved at pH = 9.
