STABILIZATION OF SOFT CLAY WITH BIO-ENZYME FOR ROAD PAVEMENT APPLICATIONS

Abstract

This study evaluated the compaction characteristics and strength of selected clay soils using non-toxic, bio-degradable liquid concentrate bio-enzyme fermented from vegetable extracts. The soils were stabilized with 5, 10, 15 and 20% urease bio-enzymes. Index properties tests including, moisture content, specific gravity, sieve analysis, Atterberg limits, as well as compaction, California bearing ratio (CBR) and unconfined compressive strength (UCS) were conducted. The liquid limit values obtained are 41 and 50.5%, plastic limit values were 28.1 and 35.9%, while plasticity index values were in 12.9 and 14.6% for samples A and B, respectively. The moisture content and specific gravity values for samples A and B were 16.9 and 21.6% and 2.79 and 2.75, respectively. The percentage passing through sieve No. 200 for sample A was 61.8 and 84.0% for sample B. Sample A was classified as clay soil (CL) or A-7-6 while sample B classified as CL or A-7-5 soils according to unified soil classification system (USCS) and American association for state and transportation officials (AASHTO) systems, respectively. According to the classification, the soils belong to weak class of clay soil that require stabilization and/or enhancement in order to support structural loads. Analysis were carried out to evaluate the compaction characteristics and strength of the soil. The results revealed that the optimum moisture content (OMC) decreased from 12.6% to 9.6% with an increase in enzyme percentage from 0% to 20% for sample A, while the same decreases were observed for sample B from 17.2 to 14.5%. The decrease was accompanied by a corresponding increase in maximum dry density (MDD) from 1.91 to 1.99g/m3 for sample A and 1702 to 1880Kg/m3 for sample B, which indicates that the soil has achieved a greater compaction at minimum compactive effort as the voids decreased. In addition, the work revealed an improvement in the CBR value from 21 to 45% (88% increment) for A-7-6 clay and 10 to 41% (178% increment) for A-7-5 clay when both samples were cured for 28 days with 0 to 20% Urease bio-enzymes. Finally, there is improvement in UCS of enzyme-stabilized clay after 28 days curing, therefore urease bio-enzymes is recommended as suitable for the stabilization of soft clay soils for road pavement applications.