Unconfined Compressive Strength Testing of Bio-cemented Weak Soils: A Comparative Upscale Laboratory Testing

Abstract

Bio-cementation of soils has gained a lot of attention on a global level owing of its ability to improve strength characteristics of weak or marginal soils. In this study, two urease producing bacteria namely Bacillus subtilis (B.S) and Bacillus pasteurii (B.P) along with a cementation media have been used to enhance the unconfined compressive strength (UCS) of dredged soils. Maintaining an optimum temperature of 18–23 °C, treatment was provided using cementation media molarity (CMM) of 0.5 and 1.0 in full contact moulds (FCM) having a diameter of 38, 76 and 114 mm respectively for 8 cycles (6 h each). The extruded samples were further tested for UCS with the test results indicating that as the sample size increased, the UCS value increased irrespective of the bacteria used. Maximum values of UCS for both the bacteria’s were observed at 0.5 CMM. An increase in UCS from 280 kN/m2 in the untreated state to 735 and 820 kN/m2 for B.S and B.P respectively was noticed. The enhancement in UCS is attributed to the formation of calcite crystals which was further supported by elemental and mineral analysis. The main goal of this study was to improve weak soils and to explore the potential of a green ground improvement technique in field applications.