Microbial induced carbonate precipitation（MICP）

an environmental-friendly foundation treatment technology

can effectively improve the engineering performance of soil.Different nutrient solution components have a significant impact on the stabilization effect.This paper showed the effect of calcium chloride and calcium nitrate

which were chosen as the calcium sources in nutrient solution

on physico-mechanical properties of bio-cemented sand by penetration test

dry density test

water absorption test

and unconfined compressive strength test

respectively.The morphological differences of calcium carbonate precipitates from the two calcium sources were compared by scanning electron microscopy.Results showed that the overall density of the stabilized sand columns with calcium nitrate was higher

and the fractures after failure were smaller than those in calcium chloride stabilized sand under either saturated or dry conditions.Calcium carbonate in the stabilized sand columns with calcium nitrate had lower permeability coefficient and water absorption

and higher dry density and unconfined compressive strength.Less calcium carbonate precipitates in columns cultured with calcium chloride

as globular grains scattering on the sand surface

while more globular and cube-shaped calcium carbonate precipitates in columns cultured with calcium nitrate

which wraps sand particles

showing more significant agglomeration.Consequently

calcium nitrate is more efficient in culturing microorganisms than calcium chloride in terms of calcium source.