Improvement of Soil Properties Using Cola Acuminata Sap

The study investigates the potential use of Cola acuminata sap (CAS) as a bio-stabilizer to enhance the engineering properties of expansive soils in the Niger Delta region of Nigeria. Soil samples were collected from two locations, Agudama Ekpetia and Mbiama, and characterized. The CAS was analyzed and found to be primarily composed of carbohydrates, particularly polysaccharides, which can effectively modify soil properties. Soil-CAS mixes were prepared with CAS content ranging from 2% to 20%. Standard tests were conducted to evaluate the effects on Atterberg limits, compaction, California Bearing Ratio (CBR), and Unconfined Compressive Strength (UCS). The results showed that the addition of CAS significantly improved the engineering properties of the expansive soils. The CBR increased from 7.6% to 16.7% for soaked samples and from 8.2% to 17.9% for unsoaked samples in Mbiama, with similar improvements observed in Agudama Ekpetia. The UCS values also increased from 32.6 KN/m2 to 316.1 KN/m2 and from 38.2 KN/m2 to 349.9 KN/m2 after CAS treatment. The study recommends a maximum of 10% CAS addition for stabilizing the active soils, as it provides the optimal balance between enhanced engineering properties and practical application. Keywords — Expansive soils, Bio-stabilization, Cola acuminata sap, California Bearing Ratio, Unconfined Compressive Strength.