This experimentation explores the potential of geopolymerised slag-sugarcane bagasse ash and waste-foundry sand combination for the stabilization of lithomargic (shedi) soil subgrades of coastal Karnataka region. The caustic soda and water glass 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 baggase ash dosage were respectively found to be 10% and 15%. As a continuation of research, this study reveals the effect of waste-foundry sand (WFS) as an additional ingredient to the geopolymerised slag-ash blend, and an attempt was made to obtain the optimal dosage of waste-foundry sand. This sand was varied at a regular intermission of 10% and the series of proctor tests were carried out. The optimized dosage of waste sand is demined to be 20% of the total weight of the soil. The UCS value and CBR value assessments were also performed on all the trial soil mixes. The results designate that the strength of shedi soil increases in the presence of slag-ash-WFS blend up to a certain limits, afar which it lessens. The improvement is endorsed to the combined effect of mechanical stabilization through gradation improvement in the presence of sand with the chemical stabilization by geopolymerised salg-ash combo on the pure shedi 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 shedi soil.