There is growing interest in using microbially induced calcite precipitation (MICP) for ground improvement. As part of a study to assess the performance of ex-situ mixed bio-cemented sand columns, a series of triaxial tests has been conducted to quantify the effects of the bio-cementation. Bender elements mounted in the end platens of a triaxial cell have been used to monitor the shear wave velocity throughout the cementation process and then during application of stress in the triaxial shearing tests. The results of tests on the bio-cemented sand are compared with tests on gypsum cemented and uncemented specimens. To assess the bio-cemented specimens a series of standard drained triaxial tests with bender elements were performed on Sydney sand which was mixed with urea contents in the range of 5 to 20% by weight, urea to calcium chloride in a 1:1 molar ratio, and a bacterial broth containing Bacillus Megaterium. Bacillus Megaterium is a ureolytic bacterium which hydrolyses urea to precipitate calcium carbonate (calcite). After curing the samples were subjected to various levels of mean effective pressure. The results show a good correlation between the amounts of urea and calcite precipitated and between the calcite precipitated and the degree of cementation achieved. For a given amount of cementation higher moduli and strengths were measured for the bio-cemented specimens than when using gypsum. Creating the bio-cementation by mixing produces homogeneous specimens with similar strengths and stiffnesses to the commonly used flushing technique.
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