Abstract
Peat soil is characterized by high water content and low bearing capacity, making it unsuitable for use as a road subgrade without stabilization treatment. This study aims to analyze the physical characteristics of natural peat soil from Kenan Sandan, East Kotawaringin, and evaluate the California Bearing Ratio (CBR) values after stabilization using lime and fly ash. Laboratory tests included physical properties, Modified Proctor compaction, and soaked CBR tests with lime variations of 10%, 15%, 20%, and combinations of lime (15% and 20%) with 10% fly ash at 1 and 3-day curing periods. The results showed that the peat soil has a moisture content of 97.54%, specific gravity (Gs) of 2.22, liquid limit (LL) of 69.25%, plasticity index (PI) of 38.61%, and pH of 5, classifying it into the A-8 group (organic soil) based on AASHTO M145. The 3-day soaked CBR of natural soil was only 2.26%, failing to meet the minimum 6% requirement of MDPJ 2024. The 10% lime addition was ineffective, yielding a CBR of only 2.44%. However, 15% and 20% lime additions significantly increased CBR values to 20.22% and 22.59%, respectively. The highest performance was achieved by the 20% lime + 10% fly ash combination with a CBR of 27.04% at 3-day curing. Pavement thickness analysis indicated that stabilization with 15% lime or more can reduce the required Class C Aggregate Base (LFA) thickness to 150 mm. In conclusion, the combination of 20% lime and 10% fly ash is the most effective mixture for improving the bearing capacity of peat soil for road subgrades.