Cementation anisotropy associated with microbially induced calcium-carbonate precipitation and its treatment effect on calcareous and quartz sands

•A novel method of Microbially Induced Calcium Carbonate Precipitation (MICP) was proposed to prepare sand specimens with cementation anisotropy.•An insight was gained into the MICP-produced anisotropic cementation induced by gravity and surface conditions.•A comparison was made between the distinct MICP treatment mechanisms in quartz and calcareous sands.•Cementation anisotropy was found to have a substantial impact on the mechanical properties of bio-cemented sands.