Unconfined Compressive Strength of Lateritic Soil Treated with Bacillus Coagulans for use as Liner and Cover Material in Waste Containment System

Abstract

The innovative and environmentally friendly Microbial Induced Calcite Precipitation (MICP) technique involves the use of micro-organisms to facilitate soil improvement. Urease positive bacteria in the company of urea and calcium sources formed dissolved ammonium and inorganic carbon, carbon dioxide and subsequent formation of calcite which is a pore filling material that stiffens the soil and improve its strength. The study involved assessing the potential of Bacillus coagulans(B.coagulans) to improve the unconfined compressive strength (UCS) of lateritic soil. The soil samples were treated with 1/3 pore volume B. coagulans suspension densities of 0, 1.5×108, 6 × 108, 1.2 × 109, 1.8× 109 and 2.4 × 109 cells/ml, respectively. Soil specimens were prepared at moulding water content (MWC) of -2, 0, +2 and +4 % relative to optimum moisture content (OMC) and compacted with the British Standard light (BSL) energy. Cementation reagent was allowed to percolate the compacted specimens until partial saturation was achieved. Results show that UCS values increased with rise in B. coagulans suspension density. UCS of natural soil prepared at -2 % OMC decreased from 278.3 kN/m2 to 141.45 kN/m2 at +4 % OMC. Similar trend were recorded for specimens treated with varying B. coagulans suspension densities when prepared at MWC of -2, 0, +2 and +4 % relative to OMC. Also, UCS values improved with rise in dry density. The UCS values of specimens prepared with B. coagulans suspension densities and compacted at MWC of -2, 0 and +2 OMC, respectively, satisfied the minimum requirement of 200 kN/m2 and can be apply as liner and cover materials in municipal solid waste containment system.