Preliminary investigation of CBR value utilizing crushed coconut shell as additive in silty sand

Road surface deformation is influenced by the strength of its subgrade material. The detonation is measured based on the California Bearing Ratio (CBR), the ratio of the tested load to the standard load at a specific penetration. The focus of the present study is to determine the un-soaked CB R value of subgrade soil mixed with 0%, 2%, 4%, 6%, 8%. 10%, and 20% crushed coconut shell (CCS). The CBR values of the samples added with 2%, 4%, 6% and 8% CCS showed less significant increment ranging from -0.9% to 19% compared to the control sample. Nevertheless, the CBR value was observed to increase with higher percentages of CCS. The sample with 10% CCS demonstrated a considerably larger CBR value with 125% improvement or 2.3 times higher than the control sample. The highest CBR value was recorded by 20% CCS at 19.98%, that is 2.4 times higher than the control sample. Nonetheless, the high percentage of CCS resulted in reduced sample workability. For 6% CCS proportion, an increment of 14% moisture content reduced CB R value by 14% compared to the control sample. An optimal un-soaked CBR value of 13.12% was achieved for the addition of 10% CCS.