The strength value of unweathered clay shale stacked beneath the soil surface is high. Clay shale will deform and lose its strength if exposed to the surface and changes in weather conditions due to brittleness caused by weathering. Thus, it would be dangerous if used as embankment material due to its sensitiveness. This study analyses the effect of adding propylene glycol and potassium chloride to weathered clay shale. Propylene glycol and potassium chloride are commonly used as a drilling fluid to prevent the degradation of the shale layer. They can increase the stability of clay shale by making it more durable when in contact with the wetting and drying process. The results from this study show that propylene glycol, added to clay shale, can increase the value of soaked CBR to twice the initial value and decrease the swelling percentage. Adding potassium chloride to the clay shale can also increase the value of soaked CBR to twice the initial value and reduce the swelling percentage. However, the combination of Propylene glycol and potassium chloride cannot increase the value of soaked CBR and could even shrink the sample and reduce the optimum water content. © 2022,International Journal of Technology. All Rights Reserved.