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Despite the large number of studies concerned with microbially induced carbonate precipitation (MICP) on soils, little attention has been paid to the effect of the chemical concentration used in the treatment on the precipitation pattern of calcium carbonate and their influence on engineering properties of MICP cemented soils. In this study, unconfined compressive strength tests were conducted on sand samples treated using 0⋅1, 0⋅25, 0⋅5 and 1 M urea–calcium chloride solutions. It was found that, although the strength of tested samples all increased after MICP treatment, the magnitude of this increase depended on the concentration used in the treatment and that the use of a low-chemical-concentration (i.e. urea and calcium chloride) solution resulted in stronger samples. Permeability test results showed that the use of a high-urea–calcium chloride-concentration solution resulted in a rapid drop in permeability at …