This experimentation explores the potential of alkali-activated slag-sugarcane bagasse ash and waste foundry sand combination for the stabilization of lateritic soil subgrades of coastal Karnataka region. The sodium hydroxide and sodium silicate were used to produce the activator solution for an equivalent activator modulus of 1.25, prepared at 4% dosage of Na2O content with respect to the total binder. From the earlier investigation, the optimal slag and bagasse ash dosage were, respectively, found to be equal to 10%. As a continuation of research, this study reveals the effect of waste foundry sand as an additional ingredient to the alkali-activated slag-sugarcane bagasse ash blend, and an attempt was made to obtain the optimal dosage of waste foundry sand. This sand was varied at a regular interval of 10% and the series of IS light compaction tests were carried out. The optimized dosage of waste foundry sand is demined to be 30% of the total weight of the soil. The UCS and CBR tests were also performed on all the trial soil mixes. The results indicate that the strength of subgrade lateritic soil augments in the presence of slag-ash-sand blend up to a certain limits, after which it lessens. The improvement is attributed to the combined effect of mechanical stabilization through gradation improvement in the presence of waste foundry sand with the chemical stabilization by optimal alkali-activated slag-ash combination on the pure lateritic soil. This study also proposes a pavement design, a simple scanning-electron-microstructural analysis and a linear co-relationship between the strength parameters (CBR and UCS) of stabilized lateritic soil.