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    • Harnessing microbially induced calcite precipitates to use in improving the engineering properties of loose sandy soils


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      This study investigates harnessing of microbially induced calcite precipitation (MICP) to use in soil treatment to improve the engineering properties of loose sandy soils. Experiments were conducted in sand specimens using a channel, a pond, and four sand-columns. A bacterial treatment followed by a cementationreagent solution (CRS) was applied to trigger calcite (CaCO3) precipitates. The submerged and surface percolation treatment methods were carried out in sand using CRS as the treatment solution. The treatment solution was maintained in an alkaline range (pH >= 7). The alkaline condition ensures active microbial induced calcite precipitation in the sand. The calcite precipitates bind the sand particles to increase the strength and stiffness of the soil matrix. The calcite bridged the sand particles and formed a biocemented water-impermeable crust layer ( ~2 mm thick). The calcite act as pore-filling material through the bioclogging process to reduce porosity and permeability. Permeability tests evaluate the effect of seepage control. The permeability was reduced to threeorder-of-magnitude (~ 99%) on the 7th day with little variation (~ 100%) until the 14th day. The compressive strength of the biotreated columns was between 585 and 875 kPa. The calcite content in the upper 10 mm thick in different columns was in the range of 11–14% and was gradually reduced from 9.8 to 3.4% below 10 mm. Hence, the observed 5–15% calcite content in natural biocemented products is comparable to MICP treated specimens. The scanning electron microscopic images show the calcite distribution patterns in the sand matrix

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