This paper presents an experimental investigation on strength and hydraulic conductivity of a fine grained soil mixed with cement, Pulverised Fly Ash and Ground Granulated Blast Slag. Strength and permeability are important properties that defines the engineering behaviour of deep mixing improved soils. Cement contents of 4%, 8%, 12% and 16% by weight of dry soil were added using wet soil mixing technique. The percentages of cement were reduced and replaced with PFA, GGBS and Bentonite at 33.3% and 50% reductions respectively. Unconfined compressive strength (UCS) and permeability tests were conducted on cement, PFA/GGBS and Cement/Bentonite mixtures prepared at their respective optimum moisture content (OMC) and maximum dry density (MDD) and cured for different periods. The results show that an increase in % of additives causes decrease in porosity and increase in density of cement and cement/PFA stabilised soil and hence, increase in UCS. Except at some optimum values of 12% and 16% of additives in C+PFA combinations where the density of the improved soil decreases at fairly constant porosity resulting to an increase in UCS. This implies that % of additive and the type of additive controls the UCS of improved soils more than the influence of porosity and density on UCS. Decrease in porosity of samples improved using C+PFA+GGBS and C+B with increase in % of additives, resulted to increase in UCS but however, the reduction in density and increase in UCS also shows dominance of % and type of additive on strength over porosity and density. Cement-Bentonite and combination of PFA /GGBS with reduced amount of cement were observed to better improved permeability of the soil. This study has also defined the functional relationships between hydraulic conductivity and additive type based on the investigated % of additives and combinations
