The geotechnical properties of soils vary depending on the regional and environmental diversity in which they are found. Therefore, remediation methods for troubled soils depend on the environmental conditions and material sources found in that area. However, the soil layer must have sufficient bearing capacity to be suitable to withstand the applied loads. The parameters of elasticity, cohesion, strength, and durability are part of soil optimization in this study. To do this, the soil is stabilized by treating it with a mixture of coffee husk ash and limestone powder in proportions of (3, 5, 7, and 10) % for three types of additives (coffee husk ash, limestone powder, and coffee husk ash mixed with limestone powder) and for periods of (1, 7, 14, and 28) days. The extent of improvement in geotechnical properties was determined using the unconfined compressive strength test and Atterberg limits. Two mathematical equations were predicted, one relating soil cohesion to plasticity index and the other relating plasticity index to unconfined compressive strength. The experimental results indicated that the soil cohesive strength improved from 30 to 52 kN/m², and it was also observed that the soil activity decreased from 0.9 to 0.25. At 28 curing days, the 7% of CHA+L mixture reduced PI from 30 to be 6.8 and increased UCS from 60 to be 94 kN/m². Nevertheless, predictive equalities were developed to re-count plasticity index with strength then cohesion, their applicability is limited to the type CH – soil and stabilizer contents within the range of 0–10%. The best improvement occurred at 7% coffee husk ash and limestone powder.
