Condition of soil in Coastal of Riau tends to soft, therefore the stabilization needed for
repairing soil bearing capacity. Many waste materials like oil palm ash and fiber found in Riau
province.. These Materials basically can be used for stabilization. Examination with cement
mixture and synthetic fiber which many found in commercial, it also can be done to get the
strength value improvement of the clay. One research studied combination of 8 percent oil palm
ash and 0.8 percent oil palm fiber. Water content was variation nearly from optimum moisture
content (OMC). Another research studying combination of 4 percent cement and 0,1 percent
synthesis fiber with the same water content variation. Refer to testing result of Unconfined
Compressive Strength, standard Proctor, Atterberg Limit and CBR laboratory. The Result of UCS
and CBR test indicated that the optimum value of combination of oil palm ash and oil palm fiber at
OMC. Generally, reduction water content (dry side) and addition water content (wet side) form
OMC is degrading the compressive strength of soil. while from the result of UCS to combination
cement and synthetic fiber do not improvement of value for the dry side and wet side where
optimum strength got at addition water at OMC, while at examination of CBR do not
improvement of value for the dry side and wet side where optimum strength got at addition with at
OMC.