Stabilization of Expansive Subgrade Soil Derived from Ameki Formation in Ozuitem, Southeastern Nigeria, Using Coconut Husk Ash

This research investigated the possibility of using Coconut husk ash (CHA) as an additive in the modification of the geotechnical properties of clay soil from Ameki formation in Ozuitem so as to increase their strength bearing capacity and reduce their swelling potentials. The clay soil samples were collected from Ozuitem LGA of Abia State. Chemical analysis of the CHA shows that it contains 36.04%, 13.19% and 20.89% of K2O, SiO2 and CaO respectively. Preliminary tests to determine the geotechnical properties of the natural soil including Particle size distribution, Atterberg limits, Maximum Dry Density and California Bearing Ratio were determined in the laboratory to classify the soil according to ASTM D2487-17, 2011 and Nigerian Standard FMWH, 2010 classification of soils. The soil samples were later stabilized with various percentages of CHA (2, 4, 6, 8 and 10). The geotechnical tests earlier performed on the soils were repeated (after stabilization) to evaluate the effects of CHA on the geotechnical properties of the clay soils. Results of the study indicate that CHA stabilization of clay soils in Ozuitem has the general effect of reducing the swelling indicators, thereby reducing the swelling potential of the soil. The liquid limit ranges between 34.08% to 50.03%, plastic limit ranges between 19.18% and 27.68%, and plasticity index is between 13.22% to 23.85%. Optimum stabilization were achieved with 8% CHA stabilization. MDD of the stabilized clay soil generally increased with an increase in percentage of CHA from 1.55 g/cm3 at 0% CHA to a maximum value of 2.40 g/cm3 at 10% CHA. This represents 54% increase in MDD of the soil. The CBR values increased from 7.15 kN/m2 to 81.25 kN/m2 (soaked) and 29.90 kN/m2 to 113.57 kN/m2 (unsoaked) respectively. The maximum strength was achieved at 10% CHA content. Stabilization with CHA acts like cement stabilization by increasing both the CBR and MDD. Therefore, coconut husk ash can be effectively used to reduce swelling indicators and to improve MDD and CBR values in clay soil and should be encouraged in the construction industry.