EFFECT OF BIO-CEMENTATION ON THE UNCONFINED COMPRESSIVE STRENGTH OF COMPACTED LATERITIC SOIL BIO-TREATED AND UNTREATED CONDITIONS

Obviously, not all available soils found on earth satisfied the requirement for engineering projects. Therefore, enhancement of soil engineering properties is one of the key concerns of a geotechnical engineers. This paper evaluates the unconfined compressive strength characteristics of compacted natural and bio-treated problematic lateritic soil classified as A-2- 6 [2] using the American Association of State Highway and Transportation Officials (AASHTO) classification system and SC using the Unified Soil Classification system (USCS) after upgraded, using microbial induced calcite precipitation (MICP) technique for 7days, 14 days and 28 days curing period respectively. The soil was bio-treated with 0, 1.50 x 108, 6.0 x 108, 12 x 108, 18 x 108, 240 x 108 cells/ml of Bacillus pumilus (B. pumilus) suspension densities, a non- infective microorganism extracted from the natural lateritic soil, and cultured. The bio-treated soil was compacted using the British Standard Light (BSL), West African Standard (WAS) and British Standard High (BSH) compactive efforts at the moulding water content range of -2 to +4% optimum moisture content (OMC). The trampled soil samples were then infused with a cementitious reagent containing 10 g of NH4Cl, 20 g of Urea, 2.8 g of CaCl2, 3 g of Nutrient broth and 2.12 g of NaHCO3 per litre of de ionized water that trigger the MICP process in three circles with 2/3rd pore volume. The Atterberg limits results and linear shrinkage showed a better enhancement in the bio-treated than the natural soil. Peak unconfined compressive strength (UCS) values of 2,414 N/m2, 3,072 N/m2 and 3,143 N/m2 were achieved for specimen’s bio-treated with 25 % Bp – 75 % Cr, 50 % Bp – 50 % Cr and 75 % Bp – 25 % Cr mix ratios respectively using 12 x 108 cells/ml, when compacted with BSH energy and cured for the three curing periods, respectively. Similarly, a considerable increase in strength was observed when the specimens were bio- treated with 75 % Bp – 25 % Cr mix ratio and cured for 28 days recorded UCS values of 2,897 N/m2, 3,572 N/m2 and 3,710 N/m2 for specimens compacted with BSH energy. The calcite formed binds the soil grains together and then improved the stiffness as well as reduce the soil compressibility.